HomeMy WebLinkAbout02.10.1994 Proposed City Hall Building-Parking Areas-HTS Projects No. 93-S-189·II
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11 REPORT GEOTECHNICAL INVESTIGATION 11 PROPOSED CITY HALL BUILDING AND PARKING AREAS/ACCESS DRIVES AND PROPOSED PAVILION 11 CITY OF FRIENDSWOOD. TEXAS
11 PREPARED FOR: 11 City of Friendswood
11 1306 Deepwood Friendswood. Texas 77546
I l PREPARED BY:
I !HTS. Inc. Consultants 416 Pickering Street Houston. Texas 77091-3312 11 HTS Project No. 93-S-189
I l February 10. 1994
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TABLE OF CONTENTS
EXECUTIVE SUt-ttARY PAGE NO. i
1.0 INTRODUCTION AND SUtflARY 1 1.1 Introd uction 1 1.2 Description of Proposed Facilities 2 1.3 Summary of Findings 3 1.3.1 Subsurface Soil Stratigraphy -City Hall and Parking Areas/ 3 Access Drives Site 1.3.2 Subsurface Soil Stratigraphy -Pavilion Site 4 1.3.3 Ground Water -City Hall and Parking Areas/Access Drives Site 5 1.3.4 Ground Water -Pavilion Site 5 1.3.5 Shrink/Swell Potential 5 1.4 Summary of Reconrnendations 6 1.4.1 Site Prepa ration 6 1.4.1.1 Site Preparation at Proposed City Hall 6 Building Area 1.4.1.2 Site Preparation at Areas of Proposed Parking 8 Areas/Access Drives 1.4.1.3 Site Preparation at Proposed Pavilion Area 9 1.4.2 Reconvnended Foundation Types and Allowable 11 Loadings -City Hall Building 1.4.3 Rigid Pa vement Design For Pavements at Proposed Parking 12 Areas/Access Drives 1.4.4 Reconrnended Foundation Types and Allowable Loadings -12 Pavilion 1.4.5 Excavation Dewatering Requirements 13 1.4.6 Earth Pressure Design Parameters for Design of 13 Below Gro und Structures 1.4.7 Earth Pressure Design Parameters for Design of 14 Temporary Shoring/Bracing for Excavations 1.4.8 Temporary Shoring and Bracing Requirements for 14 Excavations 1.4.9 Sewer Bedding Requirements 15 1.4.10 Requirements for Backfilling Excavations 15
2.0 FIELD INVESTIGATION 2.1 Site Surface Conditions 2.2 Subsurface Investigation
3.0 LABORATORY TESTING
4.0 SUBSURFACE CONDITIONS 4.1 Subsoils 4.2 Ground Water
5.0 ENGINEERING ANALYSES 5.1 Potential Vertical Rise Analyses 5.2 Bearing Capacity and Settlement Analyses -Drilled Piers 5.3 Pavement Design Analyses 5.4 Pavement Subgrade Soil Stabilization Analyses 5.5 Earth Pressure Design Parameter Analyses
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TABLE OF CONTENTS (Continued)
6.0 CONSTRUCTION CONSIDERATIONS 6.1 Foundation Construction 6.2 Backfill Around Structures 6.3 Surface Drainage
7.0 CLOSING REMARKS
TABLES Table 1 Table 2 Laboratory Test Sunvnary Sunvnary of Soil Properties Used For Engineering Analyses
FIGURES Figure 1 Vicinity Map Figure 2 Boring Locations -Proposed City Hall Building and Parking Areas/Access Drives Figure 3 Boring Location -Proposed Pavilion
APPENDICES Appendix A Boring Logs - Boring Nos. 1 through 5
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EXECUTIVE SUfflARY REPORT GEOTECHNICAL INVESTIGATION PROPOSED CITY HALL BUILDING AND PARKING AAEAS/ACCESS DRIVES AND PROPOSED PAVILION CITY OF FRIENDSWOOO. TEXAS
This report presents the results of a geotechnical investigation performed for the City of Friendswood at the sites of a proposed city hall building, parking areas and access drives pavement. and pavilion. The city hall building and parking areas and access drives are to be constructed at a site located about 650 feet northwest of the intersection of FM 518 and Shadwell Lane in Friendswood, Texas. The proposed pavilion is to be constructed at a site located about 750 feet southwest of the intersection of FM 518 and Shadwell Lane in Friendswood. Texas. Preliminary plans indicate that the proposed city hall building consists of a two story building with a gross floor space of about 22.000 square feet and the proposed pavement consists of about 40,000 square feet of reinforced concrete parking area/access drive pavement. Preliminary plans indicate that the proposed pavilion will consist of a 50 foot wide by 79 foot long timber structure.
The primary findings, conclusions. and reconvnendations of this geotechnical investigation are summarized as follows:
•Subsurface Soil and Ground Water Conditions -Proposed City HallThe site subsurface soils at four geotechnical boring locations at the proposedcity hall and parking areas and access drives site were generally found to consistof:
-stiff to hard fat clay with sand fill from the ground surface to a depth ofabout three feet.
-firm to very stiff fat clay with sand and fat clay between depths of about threefeet and six feet. and
-firm to very stiff fat clay from a depth of about six feet to the maximum boringdepth of 25 feet.
The site surficial soils have a very high shrink/swell potential. The maximum potential vertical rise (PVR) of the upper eight feet of the site soils is approximately 4.5 inches under a 1.0 psi restraining load.
Ground water was not encountered during drilling and the borings were dry 24 hours after the completion of drilling.
•Subsurface Soil and Ground Water Conditions -Proposed PavilionThe site subsurface soils at one geotechnical boring location at the proposedpavilion site were generally found to consist of:
-soft to very stiff fat clay from the ground surface to a depth of about 3.5feet.
-stiff to very stiff fat clay between depths of about 3.5 feet and 13 feet.
-very stiff lean clay between depths of about 13 feet and 17.5 feet. and
-hard fat clay from a depth of about 17.5 feet to the maximum boring depth of 25feet.
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EXECUTIVE SUMMARY (Continued)
The site surficial soils have a very high shrink/swell potential. The maximum potential vertical rise (PVR) of the upper eight feet of the site soils is approximately four inches under a 1.0 psi restraining load.
Ground water was not encountered during drilling. Ground water was measured at a depth of 21.5 feet below the existing ground surface 24 hours after the completion of drilling.
•Excavation Dewatering ReguirementsIt is expected that sumps and sump pumps will be effective in removing groundwater entering site excavations which are less than 20 feet in depth.
•Site Preparation at Proposed City Hall Building AreaSite preparation at the proposed city hall building area will require establishingsite drainage. stripping vegetation and organic topsoils to a depth of at leastsix inches. performing excavation as necessary to provide for the desired finalgrade. and proofrolling/compacting the exposed subgrade soils. If a slab-on-gradefloor system is used for the proposed city hall building. it will be necessary toplace/compact select fill over the exposed subgrade soils to minimum thickness of4.5 feet.
•Foundation Design -Proposed City Hall BuildingIt is recommended that the city hall building columns be founded on belled drilledpiers which bear at a depth of 13 feet below the existing ground surface at thetime of this investigation. Walls for the proposed city hall building should befounded on grade beams which bear on drilled piers. The drilled piers should bedesigned for allowable net bearing pressures of 3.000 psf for axial compressiondead loads plus sustained live loads and 4.500 psf for axial compression deadloads plus sustained and transient live loads.
Grade beams should be founded on drilled piers and extend at least 1.5 feet belowfinished grade. Minimum four inch high carton forms should be provided beneaththe grade beams. The floor for the proposed building may consist of a slab-ongrade floor with site preparation perfor med as described above. or alternatively.a structural floor slab (suspended floor slab) may be used.
•Site Preparation at Proposed Parking Areas and Access DrivesSite preparation at the proposed parking areas and access drives will require thestripping of vegetation and organic topsoils to a depth of at least six inches.establishing site drainage. proofrolling/compacting the ex posed soils.placing/compacting suitable earth fill or select fill as required to achieve thedesired grade and lime-stabilizing the upper eight inches of pavement subgradesoil. Lime-stabilization should be performed by blending the pavement subgradesoils with eight percent hydrated lime by dry soil weight (48 pounds of lime persquare yard of surface area) and moisture conditioning/compacting the soil-limemixture.
•Rigid Pavement Design For Proposed PavementRigid pavement for the proposed parking areas and access drives should consist ofsix inch thick reinforced concrete pavement. Reinforced concrete pavement shouldbe seven inches thick at areas where heavy waste hauling equipment will be used toload refuse.
•Site Preparation at Proposed Pavilion AreaSite preparation at the proposed pavilion area will require establishing sitedrainage. stripping vegetation and organic topsoils to a depth of at least six
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EXECUTIVE SUMMARY (Continued)
inches. performing excavation as necessary to provide for the desired final grade. and proofrolling/compacting the exposed subgrade soils. If a slab-on-grade floor system is used for the proposed pavilion. it will be necessary to place/compact select fill over the exposed subgrade soils to a minimum thickness of four feet.
•Foundation Design -Proposed PavilionIt is recommended that the pavilion columns be founded on belled drilled pierswhich bear at a depth of eight feet below the existing ground surface at the timeof this investigation. Walls for the proposed pavilion should be founded on gradebeams which bear on drilled piers. The drilled piers should be designed forallowable net bearing pressures of 3,000 psf for axial compression dead loads plussustained live loads and 4,500 psf for axial compression dead loads plus sustainedand transient live loads.
Grade beams should be founded on drilled piers and extend at least 1.5 feet belowfinished grade. Minimum four inch high carton forms should be provided beneaththe grade beams. The floor for the proposed pavilion may consist of a slab-ongrade floor with site preparation performed as described above. or alternatively,a structural floor slab (suspended floor slab) may be used.
Detailed recommendations concerning the design and construction of the proposed facilities as well as earth pressure design parameters. sewer bedding requirements. and excavation backfill requirements are provided in the text of this report.
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1.1 Introduction
REPORT GEOTECHNICAL INVESTIGATION PROPOSED CITY HALL BUILDING AND PARKING AREA/ACCESS DRIVES AND PROPOSED PAVILION CITY OF FRIENDSWOOD. TEXAS
1.0 INTROOUCTION AND SU""1ARY
This report presents the results of a geotechnical investigation performed for the
City of Friendswood at the sites of a proposed city hall building. parking areas and
access drives. and a proposed pavilion. The proposed city hall building site is
located about 650 feet northwest of the intersection of FM 518 and Shadwell Lane in
Friendswood. Texas as shown in Figures 1 and 2. The proposed pavilion site is
located about 750 feet southwest of the intersection of FM 518 and Shadwell Lane in
Friendswood. Texas as shown in Figures 1 and 3. Preliminary pl ans indicate that the
proposed city hall building consists of a two story building with a gross floor
space of about 22.000 square feet and the proposed pavement consists of about 40.000
square feet of reinforced concrete parking area/access drive pavement. Preliminary
plans indicate that the proposed pavilion will consist of a 50 foot wide by 79 foot
long timber structure. Preliminary locations/configurations for the proposed city
hall building. pavement. and pavilion are shown in Figure 2 and 3.
The purposes of this geotechnical investigation were to:
•define the existing site subsurface soil and ground water conditions.
•provide recommended foundation types. depths. and bearing pressures for the proposed single story building and pavilion.
•provide recommended pavement designs for the proposed parking area and accessdrive pavements. and
•present reconvnendations pertaining to the design and construction of the city hallbuilding and pavilion foundations and pavements for the proposed city hall parkingareas and access drives.
This geotechnical investigation was performed by HTS. Inc. Consultants (HTS) for the
City of Friendswood in accordance with a December 13. 1993 HTS proposed work scope.
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budget. and schedule which was approved by the City of Friendswood on December 16.
1993.
The scope of work for this geotechnical investigation consisted of:
•the drilling of two. 25 foot deep geotechnical borings (Boring Nos. 2 and 3) atthe proposed city hall site,
•the drilling of two, five foot deep geotechnical borings (Boring Nos. 1 and 4) atthe proposed city hall parking areas and access drives site.
•the drilling of one. 25 foot deep geotechnical boring (Boring No. 5) at the pro-posed pavilion site.
•performing field tests and recovering relatively undisturbed soil samples.
1 measuring ground water level depths in the geotechnic al borings,
•visually classifying samples obtained and conducting laboratory tests to determinethe physical and mechanical properties of the soils.
1 analyzing the field and laboratory test data.
•performing potential vertical rise analyses. bearing capacity analyses. and settlement analyses for foundations which may be used to support the proposed cityhall building and pavilion.
•performing pavement design analyses pertaining to the proposed city hall parkingarea and access drive pavement.
•performing engineering analyses to define earth pressure design parameters for usein the design of below ground structures and excavation shoring/bracing,
•providing recommended sewer bedding and backfill requirements.
•developing conclusions and recommendations concerning the design and constructionof foundations for the proposed city hall building and pavilion.
•developing conclusions and reconvnendations concerning pavement design and pavementsubgrade soil preparation, and
1 submitting four copies of a report of the investigation.
1.2 Description of Proposed Facilities
The proposed facilities consist of a two story city hall building, parking areas and
access drives at the city hall site. and a pavilion. Locations and confi gurations
of the proposed city hall building and pavements are shown in Figure 2. The loca
tion of the proposed pavilion is shown in Figure 3. Preliminary building and pave
ment locations/configurations which were available at the time this report was
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prepared suggest that the city hall building "footprint" will have a total area of
about 11.000 square feet and the total square footage of the pavement will be about
40.000 square feet. The preliminary city hall dimensions provide for an 80 foot
wide by 140 foot long building with a gross floor space of about 22.000 square feet.
The proposed pavilion consists of a timber frame structure with a slab on grade
floor. The pavilion "footprint" will have a total area of about 4.000 square feet.
The preliminary pavilion dimensions provide of a 50 foot wide by 79 foot long pavil
ion.
It was assumed that the proposed city hall building will be a two story steel frame
structure. Maximum loads for the proposed city hall building were assu med to be as
follows:
•axial compression dead loads plus sustained live loads of 60 kips per column andaxial compression dead loads plus sustained and transient live loads of 120 kipsper column.
•wall loadings of approximately 1.000 pounds per linear foot. andI I • floor loadings of approximately 50 pounds per square foot (psf).
I I It was assumed that the pavilion will consist of a wood frame structure with maximum
loads as follows:
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•axial compression dead loads plus sustained live loads of 30 kips per column andaxial compression dead loads plus sustained and transient live loads of 45 kipsper column.
•wall loadings of approximately 1.000 pounds per linear foot. and
•floor loadings of approximately 50 pounds per square foot (psf).
1.3 Summary of Findings
The pertinent findings of this investigation are provided below.
1.3.1 Subsurface Soil Stratigraphy -City Hall and Parking Areas/Access Drives Site The subsurface soil stratigraphy at the city hall and parking areas and access drives site boring locations (Boring Nos. 1 through 4) are described:
•by the laboratory test summary presented in Table 1.
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•by the summary of soil properties used for engineering analysespresented in Table 2. and•on the boring logs provided in Appendix A.
Data from Boring Nos. 1 through 4 suggest that the upper 25 feet of overburden soils are composed of three separate soil layers. HTS has designated these three soil layers as Layers IC through IIIC. Descriptions of these individual soil layers are provided below:
Laver IC
IIC
IIIC
Depth Below Ground Surface (feet) From the ground surface to a depth of 3'
0.5' to 6'
6' to the maximum boring depth of 25'
Soil Description Fi 11 -consistfngof-dark gray and brown stfff-to hard fat clay with sand with shells and gravel. The Layer IC clays have an average liquid limit of 85 percent. an average plasticity index of 62 percent. and an average moisture content of about 29 percent.
Dark gray, gray. brown. and tan firm to very stiff fat clay with sand and fat clay with slickensides. The Layer IIC clays have an average undrained shear strength of 1.000 psf. an average unconfined compressive strength of 1.0 ton per square foot Ctsf). an average liquid limit of 78 percent. an average plasticity index of 57 percent. approximately 75 percent soil particles passing a No. 200 sieve. and an average moisture content of about 27 percent.
Dark tan. tan. and light gray firm to very stiff fat clay with slickensides. calcareous nodules. and ferrous nodules. The Layer IIIC clays have an average undrained shear strength of 1,550 psf. an average unconfined compressive strength of 1.55 tsf. and an average moisture content of about 24 percent.
Subsurface Soil Stratigraphy -Pavilion Site The subsurface soil stratigraphy at the pavilion site boring location (Boring No. 5) are described:
•by the laboratory test sunvnary presented in Table 1.•by the summary of soil properties used for engi neering analysespresented in Table 2. and •on the boring log provided in Appendix A.
Data from Boring No. 5 suggest that the upper 25 feet of overburden soils are composed of four separate soil layers. HTS has designated these four soil layers as Layers IP through IVP. Descriptions of these individual soil layers are provided below:
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Layer IP
IIP
Depth Below Ground Surface (feet) From the ground surface to a depth of 3'
3.5' to 13'
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Soil Description Dark gray soft to very stiff fat clay with roots and ferrous nodules. The Layer IP clays have an undrained shear strength of 1.250 psf. an unconfined compressive strength of 1.25 tsf. a liquid limit of 79 percent. a plasticity index of 56 percent. approximately 89 percent soil particles passing a No. 200 sieve. and an average moisture content of about 27 percent.
Dark tan. tan. gray, and light gray stiff to very stiff fat clay with slickensides. calcareous nodules. ferrous nodules. and silt seams . The Layer IIP clays have an undrained shear strength of 1,400 psf. an unconfined compressive strength of 1.4 tsf. a liquid limit of 69 percent. a plasticity index of 48 percent. and an average moisture content of about 25 percent.
IIIP 13' to 17.5' Dark tan. gray, and light gray very stiff lean clay with silt pockets. silt partings, silt layers. and sand seams. The Layer IIIP clays have an undrained
IVP
shear strength of 1,750 psf. an unconfined compressive strength of 1.75 tsf. a liquid limit of 37 percent. a plasticity index of 19 percent. and a moisture content of about 18 percent.
17.5' to Dark tan. tan. and gray hard fat clay with slicken-the sides and calcareous nodules. maximum boring depth of 25'
1.3.3 Ground Water -City Hall and Parking Areas/Access Drives Site Ground water was measured in the borings at depths below the existing ground surface as shown on the boring logs contained in Appendix A. Ground water was not encountered during the drilling of Boring Nos. 1 through 4.
Boring Nos. 1 through 4 were dry and open to depths of from 4.2 feet to 24.2 feet below the existing ground surface 72 hours after the completion of drilling.
1.3.4 Ground Water -Pavilion Site Ground water was measured in the boring at a depth below the existing ground surface as shown on the boring log contained in Appendix A. Ground water was not encountered during the drilling of Boring No. 5.
Ground water was measured in Boring No. 5 at a depth of 21.5 feet and the bo ring was open to a depth of 23 feet below the existing ground surface 24 hours after the co mpletion of drilling.
1.3.5 Shrink/Swell Potential The potential shrink/swell of the overburden soils is generally classified as very high. The results of Atterberg limits testing indicate the following:
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Plasticity Bo ring Depth Soil Type Index Shrink/Swell Potential (feet) (,\')
1 0 - 2 Fat clay with sand. 56 Very high fill 2 0 - 2 Fat clay with sand. 69 Very high fill 2 4 - 6 Fat clay with sand 68 Very high 3 2 - 4 Fat clay with sand 45 High to very high 4 0.5-2 Fat clay with sand 56 Very high 2 -4 Fat clay 56 Very high 4 - 6 Fat clay 48 Very high 5 13 -15 Lean clay 19 Low to medium
The potential vertical rise (PVR) of the upper eight feet of the city hall site overburden soils is about 4.5 inches under a 144 psf [one pound per square inch (psi)] restraining load.
The PVR of the upper eight feet of the pavilion site overburden soils is about four inches under a 144 psf restraining load.
1.4 Sunvnary of Recoimtendations
Building foundation and pavement design/construction recommendations for the pro
posed city hall building, parking areas. access drives. and pavilion.
1.4.1 Site Preparation
1.4.1.1 Site Preparation at Proposed City Hall Building Area These recommendations pertain to the area of the proposed city hall building. The shrink/swell potential of the site surficial active clays may be mitigated by the use of site preparation techniques as described below. or alternatively, a structural floor slab (suspended floor slab) may be used. Mitigation of the shrink/swell potential of the site soils by using site preparation techniques will require the placement/compaction of inactive select fill to a minimum thickness of 4.5 feet at the proposed city hall building area.
If the designer chooses to use site preparation techniques to mitigate the site soil very high shrink/swell potential. it is recommended that site preparation at the building area be performed by:
•establishing site drainage and installing storm water drainage structures if required.
•stripping vegetation and organic topsoil to a minimum depthof about six inches.
•removing site overburden soils to a depth as necessary toachieve the desired final grade.
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•proofrolling the exposed in situ soils with a 15 ton roller.observing the soils during proofrolling to detect any wet.soft. or pumping soils and treating wet. soft. or pumpingsoils with suitable drying or stabilizing agents or removingthe unsuitable soils and placing/compacting suitable earthfill or select fill.
•compacting the exposed subgrade soils to an in-place drydensity equal to at least 95 percent of the maximum standarddry density (ASTM D 698) at a moisture content within± 2percent of the optimum moisture content. and
•placing/compacting imported inactive select fill to a minimumthickness of 4.5 feet above the exposed natural in situ soilswithin the proposed building perimeter and for a distance ofat least five feet beyond the proposed building perimeter.
Use of the site preparation technique as described above. should limit the maximum PVR of the soils beneath the building slab-on-grade floor to about one inch.
As an alternate. a structural floor slab (suspended floor slab) may be used to mitigate the site soil potential shrink/swell. If a structural floor slab is used, site preparation at the building area should be performed by:
•establishing site drainage and installing storm drainagestructures if required. and
•removing the upper six inches of site soils at the proposedbuilding area.
Suitable earth fill should consist of the on-site clays which are free of deleterious substances. Select fill should consist of a clayey sand or inactive lean clay with a maximum liquid limit of 35 percent and a plasticity index range of eight to 20 percent. The suitable earth fill or select fill should be placed in eight inch thick loose lifts and compacted to an inplace dry density equal to at least 95 percent of the maximum standard dry density (ASTM D 698) at a moisture content within ± 2 percent of the optimum moisture content.
The surficial clays excavated at the site will not be suitable for use as select fill at the proposed building area.
The construction contractor may encounter difficulty in densifying/preparing the surficial soils depending upon weather conditions. If inclement weather causes the surficial soils to become unsuitably wet. the construction contractor should:
•adequately dry the surficial soils by discing these materials.
•adequately dry the surficial soils by blending a stabilizingagent Clime) with the unsuitably wet soils. or
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•remove the unsuitably wet soils and replace the wet soil withsuitable earth fill or select fill having an acceptablemoisture content.
Site Preparation at Areas of Proposed Parking Areas/Access Drives Recommendations for subgrade soil preparation at all proposed paved areas (access drives and parking areas) have been developed so as to increase the shear strength and reduce the potential shrink/swell of the site surficial clays. It is recommended that pavement subgrade soils for the above described pavements be prepared as des cribed below.
•Vegetation and organic topsoil should be stripped to a depthof at least six inches.
•Site drainage should be established and storm drainagestructures installed if required .
•The exposed subgrade soil should be proofrolled with a 15 tonroller and the subgrade soil observed during proofrolling soas to detect any wet. soft. or pumping soils. Wet. soft. orpumping soils should be treated with suitable drying orstabilizing agents or the unsuitable soils should be removedand replaced with compacted suitable earth fill or selectfill material.
•The exposed subgrade soil should be compacted to an in-placedry density equal to at least 95 percent of the maximumstandard dry density CASTM D 698) at a moisture contentwithin± 2 percent of the optimum moisture content.
•If it is necessary to place fill to bring the pavementsubgrade soil to the desired grade elevation. suitable earthfill or select fill should be utilized. Suitable earth fillshould consist of the on-site clays which are free of deleterious substances. Select fill should consist of a clayeysand or inactive lean clay with a maximum liquid limit of 35percent and a plasticity index range of eight to 20 percent.The suitable earth fill or select fill should be placed ineight inch thick loose lifts and compacted to an in-placedry density equal to at least 95 percent of the maximumstandard dry density (ASTM D 698) at a moisture contentwithin± 2 percent of the optimum moisture content.
•After the exposed natural in situ subgrade soils have beencompacted to an in-place dry density equal to at least 95percent of the maximum standard dry density (ASTM D 698) andany required fill material placed/compacted. the upper eightinches of the pavement subgrade soils should be lime stabilized. Lime stabilization should be performed by blendingeight percent hydrated lime by dry soil weight (48 pounds ofhydrated lime per square yard of surface area) into thepavement subgrade soils. The blended soil-lime mixtureshould be compacted to an in-place dry density equal to atleast 95 percent of the maximum standard dry density CASTM D698)at a moisture content from one percent below to three
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percent above the optimum moisture content. Construction methods and materials should be similar to those specified in Item 220 entitled "Lime Stabilized Subgrade". of the most recent revision of the Harris County Engineering Department Specifications entitled "Specifications for the Construction of Roads and Bridges Within Harris County. Texas".
Lime stabilization should extend a minimum of three feet beyond the edge of the pavement in order to preclude edge failure of the pavement.
The surficial clay excavated at the site will not be suitable for use as select fill at the pavement areas.
The construction contractor may encounter difficulty in densifying and preparing the surficial soils depending upon weather conditions. If inclement weather causes the surficial soils to become unsuitably wet. the construction contractor should:
•adequately dry the surficial soils by discing these materials.
•adequately dry the surficial soils by blending a stabilizingagent Clime) with the unsuitably wet soils. or
•remove the unsuitably wet soils and replace the wet soil withsuitable earth fill or select fill having an acceptablemoisture content.
1.4.1.3 Site Preparation at Proposed Pavilion Area These recommendations pertain to the area of the proposed pavilion. The shrink/swell potential of the site surficial active clays may be mitigated by the use of site preparation techniques as described below. or alternatively, a structural floor slab (suspended floor slab) may be used. Mitigation of the shrink/swell potential of the site soils by using site preparation techniques will require the placement/compaction of inactive select fill to a minimum thick ness of four feet at the proposed pavilion area.
If the designer chooses to use site preparation techniques to mitigate the site soil very high shrink/swell potential. it is recommended that site prepar ation at the pavilion area be performed by:
•establishing site drainage and installing storm water drainage structures if required.
•stripping vegetation and organic topsoil to a minimum depthof about six inches.
•removing site overburden soils to a depth as necessary toachieve the desired final grade,
•proofrolling the exposed in situ soils with a 15 ton roller.observing the soils during proofrolling to detect any wet.soft. or pumping soils and treating wet. soft. or pumping
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soils with suitable drying or stabilizing agents or removing the unsuitable soils and placing/compacting suitable earth fill or select fill.
•compacting the exposed subgrade soils to an in-place drydensity equal to at least 95 percent of the maximum standarddry density (ASTM D 698) at a moisture content within± 2percent of the optimum moisture content. and
•placing/compacting imported inactive select fill to a minimumthickness of four feet above the exposed natural in situsoils within the proposed pavilion perimeter and for a distance of at least five feet beyond the proposed pavilionperimeter.
Use of the site preparation technique as des cribed above. should limit the maximum PVR of the soils beneath the pavilion slab-on-grade floor to about one inch.
As an alternate. a structural floor slab (suspended floor slab) may be used to mitigate the site soil potential shrink/swell. If a structural floor slab is used. site preparation at the pavilion area should be performed by:
•establishing site drainage and installing storm drainagestructures if required. and
•removing the upper six inches of site soils at the proposedbuilding area.
Suitable earth fill should consist of the on-site clays which are free of deleterious substances. Select fill should consist of a clayey sand or inactive lean clay with a maximum liquid limit of 35 percent and a plasticity index range of eight to 20 percent. The suitable earth fill or select fill should be placed in eight inch thick loose lifts and compacted to an inplace dry density equal to at least 95 percent of the maximum standard dry density (ASlM D 698) at a moisture content within ± 2 percent of the optimum moisture content.
The surficial clays excavated at the site will not be suitable for use as select fill at the proposed building area.
The construction contractor may encounter difficulty in densifying/preparing the surficial soils depending upon weather conditions. If inclement weather causes the surficial soils to become unsuitably wet. the construction contractor should:
•adequately dry the surficial soils by discing these materials.
•adequately dry the surficial soils by blending a stabilizingagent (lime) with the unsuitably wet soils. or
•remove the unsuitably wet soils and replace the wet soil withsuitable earth fill or select fill having an acceptable
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moisture content.
Recommended Foundation Types and Allowable Loadin gs -City Hall Building Belled drilled piers and grade beams should be used for support of the proposed city hall building columns and walls. The building floor may consist of a slab-on-grade floor with site preparation completed as described in Section 1.4.1.1 above, or alternatively, a structural floor slab (suspended floor slab) may be used. Foundation recommendations pertaining to the proposed city hall building columns. walls. grade beams. and the building floor are as follow:
•Building Columns and WallsThe city hall building columns should be founded on belled drilledpiers which bear at a depth of 13 feet below the ground surface at thetime of this investigation. Walls should be supp orted by grade beamswhich are founded on drilled piers. The drilled piers should bedesigned for allowable net bearing pressures of 3,000 psf for axialcompression dead loads plus sustained live loads and 4,500 psf foraxial compression dead loads plus sustained and transient live loads.The center to center spacing of the drilled piers should be equal to aa minimum of three times the drilled pier bell diameter. The maximum bell-to-shaft diameter ratio for drilled piers should be three.
Allowable shaft friction in compression and tension for the portionsof the drilled pier shafts below a depth of five feet beneath thefinished grade surface is 200 psf. The ultimate shaft friction whichcould be exerted against the drilled pier shafts as a result of swelling soils is 400 psf.
Use of the above recommended allowable net foundation bearing pressures provides for:
-a safety factor of at least 3.0 against a drilled pier bearing failure under axial compression dead loads plus sustained live loads,
-a safety factor of at least 2.0 against a drilled pier bearing failure under axial compression dead loads plus sustained and transientlive loads. and
-drilled pier maximum total settlements of about one inch.
Drilled piers should be belled in order to provide resistance against pullout forces which may be exerted on the drilled pier shafts by swelling soils. Because of the presence of slickensides in the overburden soils. severe caving of pier bells may occur during construction. The adverse effects of pier bell caving can be limited by:
-the designer using a maximum bell-to-shaft diameter ratio of three.
-the designer minimizing pier bell diameters. and
•the construction contractor minimizing the time between the completion of pier bell underreaming and concrete placement.
•Grade BeamsGrade beams should be founded on drilled piers and extend at least 1.5
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feet below finished grade. Minimum four inch high carton forms (void boxes) should be provided beneath the grade beams.
•Ground Level Floor SlabThe floor for the proposed city hall building may consist of aslab-on-grade floor with site preparation performed as described inSection 1.4.1.1 above. or alternatively, a structural floor slab(suspended floor slab) may be used. If a slab-on-grade is used. it issuggested that cushion sand (leveling sand) not be placed at the areaof the slab-on-grade floor. If cushion sand becomes wet. erosionand/or settling of the sand may occur which can result in the formation of voids beneath the floor and associated structural distress.
If a structural floor slab is used. a minimum four inch high voidspace should be provided beneath the slab.
1.4.3 Rigid Pavement Design For Pavements at Proposed Parking Areas/A ccess Drives Rigid pavements for the proposed parking areas and access drives should consist of six inch thick reinforced concrete pavement. Rigid pavement at areas where heavy waste hauling equipment is used to load refuse should consist of seven inch thick reinforced concrete pavement. Pavement subgrade soil preparation should comply with the recommendations provided in Section 1.4.1.2 above. Pavement design assumptions and material properties are discussed in Section 5.3 of this report.
1.4.4 Reconvnended Foundation Types and Allowable Loadings -Pavilion Belled drilled piers and grade beams should be used for support of the proposed pavilion columns and walls. The pavilion floor may consist of a slab-on-grade floor with site preparation completed as described in Section 1.4.1.3 above. or alternatively, a structural floor slab (suspended floor slab) may be used. Foundation recommendations pertaining to pavilion columns. walls. grade beams. and the pavilion floor are as follow:
•Building Columns and WallsThe pavilion columns should be founded on belled drilled piers whichbear at a depth of eight feet below the ground surface at the time ofthis investigation. Walls should be supported by grade beams whichare founded on drilled piers. The drilled piers should be designedfor allowable net bearing pressures of 3,000 psf for axial compressiondead loads plus sustained live loads and 4.500 psf for axial compression dead loads plus sustained and transient live loads. The centerto center spacing of the drilled piers should be equal to a a minimumof three times the drilled pier bell diameter. The maximum bell-toshaft diameter ratio for drilled piers should be three.
Allowable shaft friction in compression and tension for the portionsof the drilled pier shafts below a depth of five feet beneath thefinished grade surface is 200 psf. The ultimate shaft friction whichcould be exerted against the drilled pier shafts as a result of swelling soils is 400 psf.
Use of the above recommended allowable net foundation bearing pressures provides for:
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. a safety factor of at least 3.0 against a drilled pier bearing failure under axial compression dead loads plus sustained live loads.
- a safety factor of at least 2.0 against a drilled pier bearingfailure under axial compression dead loads plus sustained and transient live loads. and
-drilled pier maximum total settlements of about one inch.
Drilled piers should be belled in order to provide resistance against pullout forces which may be exerted on the drilled pier shafts by swelling soils. Because of the presence of slickensides in the overburden soils. severe caving of pier bells may occur during construction. The adverse effects of pier bell caving can be limited by:
-the designer using a maximum bell-to-shaft diameter ratio of three.
-the designer minimizing pier bell diameters. and
-the construction contractor minimizing the time between the comple-tion of pier bell underreaming and concrete placement.
•Grade BeamsGrade beams should be founded on drilled piers and extend at least 1.5feet below finished grade. Minimum four inch high carton forms (voidboxes) should be provided beneath the grade beams.
•Ground Level Floor SlabThe floor for the proposed pavilion may consist of a slab-on-gradefloor with site preparation performed as described in Section 1.4.1.3above. or alternatively, a structural floor slab (suspended floorslab) may be used. If a slab-on-grade is used. it is suggested thatcushion sand (leveling sand) not be placed at the area of the slab-ongrade floor. If cushion sand becomes wet. erosion and/or settling ofthe sand may occur which can result in the formation of voids beneaththe floor and associated structural distress.
If a structural floor slab is used. a minimum four inch high voidspace should be provided beneath the slab.
1.4.5 Excavation Dewatering Reguirements It is expected that sumps and sump pumps will be effective in removing ground water entering site excavations which are less than 20 feet in depth.
1.4.6 Earth Pressure Design Parameters for Design of Below Ground Structures Below ground structures may be designed by using equivalent fluid pressures. earth pressure coefficients. and soil strength properties. Below ground structures at the proposed city hall site or pavilion site may be designed by using the following values of weight of equivalent fluid in pounds per cubic foot (pcf). active earth pressure coefficient (Ka). passive earth pressure coefficient (Kp), angle of internal friction in degrees. cohesion in psf. and average soil wet unit weight in pcf:
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Weight of Weight of Active Passive Eguiva· Eguiva-Earth Earth Angle of Soil lent lent Pres-Pres-Internal Cohe-Wet Description Fluid for Fluid for sure sure Friction. sion, Unit Active Passive Coeffi-Coeffi--Weight Case Case cient cient � (pcf) (pcf) (Ka) (Kp) (degrees) (psf) (pcf)
Site clays 97 185 0.53 2.1 18 200 127
The weights of equivalent fluid shown above include hydrostatic forces but do not include surcharge forces imposed by construction equipment or vehicles. Surcharge forces must be considered in order to compute maximum stresses for use in the design of below ground structures.
The weight of equivalent fluid for the passive case and passive earth pressure coefficient shown above do not include a safety factor. It is recommended that a safety factor of 2.0 be applied to the weight of equivalent fluid for the passive case and passive earth pressure coefficient as shown above. With the use of a safety factor of 2.0. the weight of equivalent fluid for the passive case will be 151 pcf for the site clays and the passive earth pressure coefficient will be 1.4 for the site clays.
1.4.7 Earth Pressure Design Parameters for Design of Temporary Shoring/Bracing for Excavations Temporary shoring/bracing for excavations may be designed by using the following design parameters:
Weight of Weight of Active Passive Eguiva-Eguiva-Earth Earth Soil lent lent Pres-Pres-Angle of Description Fluid for Fluid for sure sure Internal Cohe-Wet Active Passive Coeffi-Coeffi-Friction. sion. Unit Case Case cient cient � C Weight (pcf) (pcf) (Ka) (Kp) (degrees) Cpsf) (pcf)
Site clays 109 154 0.71 2.1 10 1,000 127
The weights of equivalent fluid shown above include hydrostatic forces but do not include surcharge forces imposed by construction equipment or vehicles. Surcharge forces must be considered in order to compute maximum stresses for use in shoring and bracing design.
The weight of equivalent fluid for the passive case and passive earth pressure coefficient shown above do not include a safety factor. It is recommended that a safety factor of 2.0 be applied to the weight of equivalent fluid for the passive case and passive earth pressure coefficient as shown above. With the use of a safety factor of 2.0. the weight of equivalent fluid for the passive case will be 139 pcf for the site clays and the passive earth pressure coefficient will be 1.5 for the site clays.
1.4.8 Temporary Shoring and Bracing Requirements for Excavations If Title 29. Part 1926. Section 1. Subpart P of the July 1. 1992 Code of Federal Regulations is used for temporary excavation shoring/bracing design, the overburden soils should be categorized as Type C soil. The definition of Type C soil is provided in Appendix A of the above-refer-
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enced July 1. 1992 Code of Federal Regulations. It is expected that severe caving of trench excavations will occur during construction due to the presence of slickensides within the site surficial soils.
1.4.9 Sewer Bedding Reguirements Bedding for sewers should be designed and installed as specified by "City of Houston Specifications for Sewer Construction, Form E-14-62." with amendments. The site clays sampled during this investigation are considered to be representative of satisfactory soil conditions with regard to pipe bedding design. Bedding for sewers should be designed in accordance with Drawing No. 529-S-1 or 530-S-1 for sewers with the site clays in the area from three feet below the pipe invert to one foot above the pipe crown.
1.4.10 Requirements for Backfilling Excavations Backfill for excavations which are not below proposed pavements or the building floor should consist of suitable earth fill compacted to a uniform dry density equal to at least 90 percent of the maximum standard dry density CASlM D 698) at a moisture content within± 5 percent of the optimum moisture content.
For the sections of excavations below proposed pavements. the backfill should consist of compacted suitable earth fill or select fill as defined in Section 1.4.1.2 above. The upper eight inches of suitable earth fill or select fill subgrade soils below pavements should be lime stabilized with seven percent hydrated lime by dry soil weight.
For the sections of excavations below the proposed building floor. the backfill should consist of compacted select fill as defined in Section 1.4.1.1 or 1.4.1.3 above.
2.0 FIELD INVESTIGATION
2.1 Site Surface Conditions
The proposed city hall building and parking areas/access drives sites are located
about 650 feet northwest of the intersection of FM 518 and Shadwell Lane in Friends
wood. Texas. The proposed pavilion site is located about 750 feet southwest of the
intersection of FM 518 and Shadwell Lane in Friendswood. Texas. The sites were
generally flat lying at the time of this investigation and site vegetation consisted
of low to medium high native grasses and a few isolated 15 to 20 feet high trees.
2.2 Subsurface Investigation
The subsurface investigation for this project included the drilling of five geotech
nical borings (Boring Nos. 1 through 5) at the locations shown in Figures 2 and 3.
The locations of Boring Nos. 1 through 4 were established by HTS. Inc. The boring
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locations of Boring Nos. 1 through 4 were staked in the field by HTS. Inc. with a
tape wheel being used to measure distances to boring locations from reference points
consisting of the existing corners of the property boundaries. The location of
Boring No. 5 was established and staked in the field by the City of Friendswood.
Drilling, sampling, and testing at Boring Nos. 1 through 4 were performed in ac
cordance with applicable ASlM procedures by using a Mayhew 200 drill rig mounted on
a truck and conventional auger drilling methods. Drilling. sampling, and testing at
Boring No. 5 were performed in accordance with applicable ASlM procedures by using a
Mayhew 200 drill rig mounted on an all terrain vehicle and conventional auger drill
ing methods. Van and Sons Drilling Service performed the drilling under contract to
lffS and under the supervision of an lffS engineer and engineering technician.
Soil sampling during the drilling of the geotechnical borings consisted of continu
ous sampling or sampling on five foot intervals with relatively undisturbed samples
being obtained. Relatively undisturbed samples were obtained by hydraulically forc
ing sections of three inch O.D. tubing (Shelby tube) into the subsoils. The tube
samples were extruded in the field. sealed with foil. and placed into airtight plas-
) 1 tic bags. Estimates of the undrained shear strengths of the cohesive soils were
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obtained with pocket penetrometer readings being taken on each end of the tube
samples.
The soil samples obtained from the geotechnical borings were transported to HTS'
laboratory where selected samples were subjected to laboratory testing.
3.0 LABORATORY TESTING
A laboratory testing program was conducted to obtain engineering properties for use
in performing engineering analyses and to adjust field soil classifications. The
following laboratory tests were performed:
•moisture content determinations (ASlM D 2216).•dry density determinations (ASlM D 2937).
1 Atterberg limits (ASlM D 4318).•percent soil particles passing a No. 200 sieve (ASlM D 1140). and
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•unconfined compression tests (ASTM D 2166).
The numbers of tests and the test results are presented in Table 1. All tests were
performed in accordance with applicable ASTM specifications and soils classifica
tions were completed in accordance with the most recent requirements of ASTM D 2487.
4.0 SUBSURFACE CONDITIONS
4.1 Subsoils
The subsurface soil conditions as determined from the drilling of the geotechnical
borings are provided in:
•Sections 1.3.1 and 1.3.2 of this report, and•the boring logs presented in Appendix A.
The boring logs were prepared by using both field visual classifications and the
results of laboratory testing. The stratification lines shown on the boring logs
represent the approximate boundaries between soil types and the transitions between
soil types may be gradual.
4.2 Ground Water
Ground water conditions are described in Sections 1.3.3 and 1.3.4 of this report and
on the boring logs contained in Appendix A. The depth to ground water was obtained
by:
•observing the drilling operations and the free moisture contained in the samplesrecovered during drilling,
•measuring the water levels in the borings upon the completion of drilling, and
•measuring the water levels in the borings 24 to 72 hours after the completion ofdrilling
It is noted that recommendations contained in this report are based on ground water
depths at the time of this investigation and that an accurate determination of the
true ground water level may require several days or even months of observations.
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5.0 ENGINEERING ANALYSES
Engineering analyses were performed in order to develop design recommendations for
the proposed city hall building and pavilion foundations. parking area pavements.
and access drive pavements. Engineering analyses included:
•analyses of the potential heave (potential vertical rise) of the proposed buildingslab-on-grade floor. the proposed pavilion slab-on-grade floor. pavement anddrilled piers due to the presence of expansive soil.
•bearing capacity and settlement analyses for drilled pier foundations.
•pavement design analy ses for rigid pavements.
•analyses to define pavement subgrade soil stabilization requirements. and
•analyses to determine lateral earth pressure design parameters which can be usedin the design of below ground structures and trench shoring/bracing.
This section briefly addresses the analyses performed and the analyses assumptions.
5.1 Potential Vertical Rise Analyses
Potential vertical rise analyses were completed for the proposed building slab-on
grade floor. the proposed pavilion slab-on-grade floor. pavements. and drilled
piers. The depth of seasonal moisture variation at the proposed city hall site and
the proposed pavilion site was estimated to be eight feet. The estimated depth of
seasonal moisture variation was based upon moisture content versus depth data ob
tained from the soils sampled/tested.
The potential vertical rise analyses for the proposed building slab-on-grade floor.
pavilion slab-on-grade floor. and pavements were performed by using Texas State
Department of Highways and Public Transportation Test Method Tex-124-E. the Van der
Merwe Method and the results of laboratory index tests.
The potential for the heaving of drilled piers was estimated by using:
•the results of laboratory index tests to estimate potential maximum swell pressures at the bases of drilled piers.
•the subsurface soil shear strength properties to estimate uplift forces due toupward-acting shaft friction caused by swelling soils. and
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•the subsurface soil shear strength properties to evaluate the uplift resistanceprovided by pier bells.
5.2 Bearing Capacity and Settlement Analyses -Drilled Piers
Drilled piers were analyzed for embedment depths of 13 feet below the existing
ground surface at the city hall building site and eight feet below the existing
ground surface at the pavilion site. The assumed eight to 13 foot shear embedment
depths provide for founding the piers at. or below the depth of seasonal moisture
variation. on competent bearing soils and. establishing a drilled pier depth which
will minimize expected caving of the site soils during belling operations.
Bearing capacity analyses for drilled piers were conducted by using the a coeffi
cient method to define ultimate shaft friction values and general shear bearing
capacity factors to define ultimate end bearing values (Pile Foundation Analysis and
Design by Poulos and Davis. 1980: and "Behavior of Drilled Piers Under Axial Load
ing", by Reese. Touma and O'Neill. 1976). A safety factor of 2.0 was used to deter
mine allowable shaft friction values and a safety factor of 3.0 was used to define
allowable end bearing values.
Potential settlements of drilled piers were evaluated by using:
•elastic theory and the elastic modulus values shown in Table 2 to estimate invnediate settlements. and
•three dimensional consolidation theory and the consolidation parameters shown inTable 2 to estimate long term settlements.
5.3 Pavement Design Analyses
Pavement design analyses were performed in accordance with the American Association
of State Hi ghway Of ficials (AASHTO) "AASHTO Gu ide for Design of Pavement
Structures". 1986. The AASHTO "Low-Volume Road Design" method was used for the
pavement design.
Concrete pavement design recommendations provided in Section 1.4.3 of this report
are based upon:
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• 200.000. 18 kip equivalent single axle load CESAL) applications for a 20 yearperiod.
• a U.S. Climatic Region Category of Region I CMSITTO 1986 Guide. Section 4.1. Page11-72. Figure 4.1).
• a level of reliability, CR) of 75 percent (MSITTO 1986 Guide. Section 4.2.1. Page11-80).
• a California Bearing Ratio value of 2.0 (PCA Soil Primer. 1973).
•a roadbed soil resilient modulus (MR) of 3.000 psi for the unstabilized subgrade soil where MR= 1,500 x (CBR) (MSITTO 1986 Guide. Appendix FF. Page FF-11. Figure FF.6 and Section 1.5. Page 1-14).
•an effective modulus of subgrade reaction CK) value of 200 pci CMSHTO 1986 Guide.Section 4.2.2. Page II-84. and
• a "Poor" Relative Quality of Roadbed Soil (MSITTO 1986 Guide. Section 4.2.2. PageIl-74. Table 4.3).
Traffic counts used for design assumed a total of 74 parking spaces for the proposed
parking area and a total of four vehicle trips per day per parking space. A truck
factor of 0.06 as reconvnended by the Asphalt Institute was used to convert the total
vehicular volume for the parking areas to 18 kip ESAL applications. The use of a
truck factor of 0.06 yielded 200.000. 18 kip ESAL applications for a 20 year period.
On this basis. the MSHTO "Low Volume Road Design" low range for 18 kip ESAL appli
cations (50.000 to 300.000 18 kip ESAL applications for a 20 year period) was used
for design.
5.4 Pavement Subgrade Soil Stabilization Analyses
Lime stabilization requirements were developed based upon the results of laboratory
testing (Atterberg Limits. percent soil particles passing a No. 200 sieve. and unit
weight determinations). These requirements should be verified based upon the re
sults of laboratory compaction tests performed as part of the construction quality
j ( control program.
j j 5.5 Earth Pressure Design Parameter Analyses
Earth pressure coefficients as provided in this report were computed by using Ran-I !
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kine's method s. The reco1TK11ended lateral earth pressure coefficients and equivalent
fluid weight values provided in this report are based upon soil properties as su1IH11a
rized in Sections 1.4.6 and 1.4.7 above. Earth pressure design parameters provided
in this report for use in designing underground structures are based on effective
stress shear strength parameters Cc and j). Earth pressure design parameters pro
vided in this report for use in designing temporary excavation shoring/bracing are
based on total stress shear strength parameters Cc and �).
6.0 CONSTRUCTION CONSIDERATIONS
6.1 Foundation Construction
•Excavations for found ations should be clean and free of all loose materials priorto the placement of concrete. Concrete should be placed at the foundation areasimmediately upon forming, reinforcing steel placement. cleaning, and inspection.
•Fill material and fill compaction should comply with the specifications providedin Section 1.4.1 of this report. Materials excavated during drilled pier construction should be removed from the building area prior to the placement ofconcrete for the building slab-on-grade floor.
•To facilitate cleaning and inspection of belled drilled piers. it is suggestedthat drilled pier shafts have a minimum diameter of 24 inches.
•The edges of drilled pier bells should have a minimum thickness of six inches inorder to prevent edge cracking.
•Concrete placed for drilled piers should have a four to six inch slump and beplaced in the shaft in one continuous placement.
•Concrete may be allowed to drop freely in dry drilled pier excavations containingone inch or less of water. provided that the concrete does not fall against thesteel reinforcing or the shaft sides. Drilled piers with more than one inch ofwater in the bottom should be filled with concrete by the tremie method of concrete placement.
•There is a potential that casing will be required to maintain an open drilled pierexcavation. If casing is required. the casing may be removed as concrete is beingplaced. The casing should be removed in a manner which precludes the surroundingsoil from invading the fresh concrete. This requires a vertical. smooth removalof the casing while maintaining the bottom of the casing a sufficient distancebelow the top of the concrete so as to offset the surrounding material pressure.
• A qualified representative of the soil engineer should verify that drilled piersare bottomed on competent bearing materials. that the floor slab is founded oncompetent bearing soils and that acceptable construction procedures are used.
•Materials testing should be performed during construction to assure that acceptable materials and construction methods are provided by the contractor.
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6.2 Backfill Around Structures
Backfill around structures should consist of suitable earth fill compacted to an in
place dry density equal to at least 90 percent of the maximum standard dry density
(ASTM D 698) at a moisture content within± 5 percent of the optimum moisture con
tent. Care should be taken so as not to overcompact backfill or allow heavy equip
ment adjacent to the existing structures. The backfill placement operations should
be monitored and the backfill tested to assure compliance with the project specifi
cation.
6.3 Surface Drainage
The following drainage precautions should be observed during construction and main
tained at all times after construction has been completed:
•The ground surface surrounding the exterior of the structures should be providedwith erosion protection and sloped to drain away from the structures in all directions. We reconvnend a minimum slope of six inches in the first ten feet.
•Roof downspouts and drains should discharge well beyond the limits of the edges ofthe foundations and be channeled to drain invnediately away from the foundations.
•Excessive wetting or drying of foundations should be avoided. Trees and othervegetation capable of withdrawing significant amounts of moisture from the subsoils should be located a distance from the nearest foundation equal to at leastthe expected ultimate height of the vegetation. or appropriate moisture barriersshould be provided.
7.0 CLOSING REMARKS
HTS. Inc. Consultants has performed a geotechnical investigation and provided recom
mendations pertaining to foundation design for the City of Friendswood proposed city
hall building, pavement for the proposed parking areas and access drives at the city
hall site. and foundation design for the proposed pavilion. This report has been
prepared for the exclusive use of the City of Friendswood in accordance with gener-l ( ally accepted soil and foundation engineering practices. No other warranty. ex-
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pressed or implied. is made. In the event that changes in the nature. design. or
location of the proposed facilities are made. the conclusions and recommendations
contained in this report shall not be considered valid unless the changes are re-
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-23-contained in this report shall not be considered valid unless the changes are reviewed and the findings/recommendations of this report are modified or verified in writing. The analyses and recommendations presented in this report are based upon data obtained from five geotechnical borings drilled on January 11 and 24. 1994. The nature and extent of variations within the subsurface soils may not become evident until after construction is initiated. If significant variations in the subsurface soils are encountered during construction. it may be necessary to re-evaluate the recommendations provided in this report. We appreciate the opportunity to be of service to the City of Friendswood. If we can answer any questions concerning the contents of this report. or be of further service. please do not hesitate to contact us.
r:::;;:;� Fouad Hammoud. P.E.
��
f ;J; Services
Ronald E. Langston. Pr President REL:jas ITTS-771T
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TABL E 1
LAB ORAT ORY TEST SUHH ARY
PROJECT: Proposed City Hall Building and Parking Areas/Access Drives and Proposed Pavilion
LOCATION : Friendswood. Texas
CLIENT: City of Friendswood
Atterberg Bor-Sample Moisture Dry Limits(%) ing Depth Type of Material Content Density No. (feet) (%) (pcf) LL PL PI
1 0 - 2 Fat clay with sand (CH). 24.6 97.6 74 18 56 fill
2 0 - 2 Fat clay with sand (CH). 33.5 96 27 69 fill 4 - 6 Fat clay with sand (CH) 25.8 95.7 91 23 68 6 - 8 Fat clay (CH) 23.0 102.8 8 -10 Fat clay (CH) 20.4 104.5 18 -20 Fat clay (CH) 30.3 95.5
3 2 - 4 Fat clay with sand (CH) 28.3 65 20 45 4 -6 Fat clay with sand (CH) 28.6 96.0 6 - 8 Fat clay (CH) 26.4 103.0 13 -15 Fat clay (CH) 20.4 105.1
4 0.5-2 Fat clay with sand (CH) 26.1 77 21 56
5 0 - 2 Fat clay (CH) 27.2 2 - 4 Fat clay (CH) 26.7 99.9 79 23 56 4 - 6 Fat clay (CH) 25.4 69 21 48 6 - 8 Fat clay (CH) 26.5 101.6 8 -10 Fat clay (CH) 23.9 13 -15 Lean clay (CL) 17.7 107.8 37 18 19
Unconfined -200 Compressive Strain Sieve Strength (%) (%) (psf)
71.4 2,010 (1.2) 3.0 2,470 (1) 11.9 3,070 (1) 11.4 3,470 (2) 2.3
77.8 2,240 (1) 8.1 2,880 (1) 14.0 3,850 (2) 5.4
89.0 2,500 (1) 10.0
2.890 (2) 9.4
3,590 (1,2. 4.6
Lateral Pressure (psi)
0 0 0 0
0 0 0
0
0
0
PROJECT NO.: 93-S-189
PAGE 1 OF 1
Reaarks
(1)Sample bulged at failure(2)Sample failed along slickensides
(3)Sample failed along sand seam
[HTS, IX('.0 -· ---CAnsu/tan�J
Layer Soil No. Description
(1) (1)
IC Fill consisting of fat clay with sand
IIC Fat clay with sand and fat clay
IIIC Fat clay
IP Fat clay
IIP Fat clay
IIIP Lean clay
IVP Fat clay
TABLE 2
Smt1ARY OF SOIL PROPERTIES USED FOR ENGINEERING ANALYSES PROPOSED CITY HALL BUILDING AND PARKING AREAS/ACCESS DRIVES AND PROPOSED PAVILION FRIENDSWOOD. TEXAS
Depth Below Wet Moisture Dry Cohesion (2) Friction Angle (2) Ground Density Surface
(feet) (pcf)
0 - 3 126.0
3 - 6 122.0
6 -25 126.8
0 -3.5 126.9
3.5 -13 127.3
13 -17.5 126.9
17.5 -25 127.3
Content
(percent)
29.1
27.2
24.1
27.0
25.3
17.7
- -
Density
(pcf)
97.6
95.9
102.2
99.9
101.6
107.8 ..
(psf) (degrees)
C C ¢ j
1.000 200 10 18
1.000 200 10 18
1,550 200 10 18
1,250 200 10 18
1,400 200 10 18
1.750 250 10 23
2.000 230 12 19
(1)See boring logs at Appendix A for detailed soil descriptions.
PROJECT NO.: 93-S-189
PAGE NO.: 1 OF 1
Modulus of El asti city. Cc Ccr eo·Es(ksf)(3)(3) (3)
150 0.54 0.11 0.73
150 0.52 0.11 0.76
200 0.52 0.11 0.68
150 0.45 0.09 0.72
200 0.39 0.08 0.69
250 0.20 0.04 0.56
400 0.39 0.08 0.69
OCR
(3)
10
10
4
10
7
3.5
7
(2)¢ & c represent total stress shear strength parameters and¢ and c represent effective stress shear strength parameters.
(3)Consolidation properties: Cc= compression index: C cr = recompression index: eo = void ratio at effective overburden stress:
OCR= overconsolidation ratio.
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FIGURE 1
VICINITY MAP PROPOSED CITY HALL BUILDING AND PARKING ARE AS/ ACCESS DRI VES AND PROP OSED PAVILION CITY OF FRIENDSWOOD FRIENDSWOOD, TEXAS
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�,� --�i--PROPOSED ._,_ PA RKING AREA _ · · --· ·:,. r·\~---f\, .�-., ,"'� 0
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PROPOSED j,·e , � CI TY HALL '>J. •IBUILDING : . ('
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LEGEND
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S BORING LOCATION
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PLAN VIEW
SCALE 1" = 100'
FIGURE 2 BORING LOCATIONS
PROPOSED CITY HALL
BUILDING AND PARKING
AREAS/ ACCESS DRIVES
CITY OF FRIENDSWOOD
FRIENDSWOOD, TEXAS
� ' -� FM 518
-----------
1 -�
EXISTING ONE STORY BRICK HOUSE
5
PROPOSED/PAVILION
SHADWELL LANE
PLAN VIEW
SCALE 1" = 200'
DRAWN BY I M
CHECKED BY I F
LEGEND
S BORING LOCATION
FIGURE 3 BORING LOCATION
PROPOSED PAVILION
CITY· OF FRIENDSWOOD
FRIENDSWOOD, TEXAS
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11 APPENDIX A
BORING LOGS 11 {Boring Nos. 1 through 5)
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DESCRIPTION OF BORING LOG TERMS
I CLEAR I U.S. STANDARD I.. VE OPENNINOI SIEVE OPENINGS
I I I I I I I I I I I I (1)
• • • • 00., N •'° 0 0 0 : 0 • 0 ..... ..... ..... • p N • tO P N p ., ., ...... ... ... ............
p
1000, 100. 10. 1,0 0,1 0,01 0.001 0.0001 SIZE IN mm . ORAVl!L IAND "' "' a COBBLES I en en :, I SILT I CLAY I COLLOIDS II: II: C 0
[I]. core
'ci "' C 0 "'
(,) a I&. U S C S CLASSIFICATION FOR SOILS BORING LOG LEGEND
� -Penetration Sample !2J -No Recovery J -Jar
'7 -Ground Water Level Encountered During Drilling T-Static Water Level
SPLIT-SPOON SAMPLER DRIVING RECORD
Blows Per Foot Description
8-1 0-1 2 .................................... Number of blows for each six inch increment of split spoon penetration
60/8" ..................................... 60 blows drove sampler 8 inches
ST RENGTH OF COHESIV E SOILS (2)
Unconfined
Compressive Strength,
Tons Per Square
Foot (Pocket
Penetrometer)
DENSITY OF GRANULAR SOILS (2)
Consistency
��s�
Soft
Fl�
ffim
��ffim
H�
Undrained
Shear Strength,
Tons per Sq. Ft.
0.1 2
0.12 to 0.25
0.25 to 0.50
0.50 to 1.0
1.0 to 2.0
Greater than 2.0
less than 0.25
0.25 to 0.50
0.50 to 1.0
1.0 to 2.0
2.0 to 4.0
Greater than 4.0
Blows
Per
Foot
0-4
5-10
11-30
31-50
Over 50
SOIL STRUCTURE
Descriptive Relative
Term Density 0/o
Very Loose less than 20
Loose 20 to 40
Medium Dense 40 to 60
Dense 60 to 80
Very Dense Greater than 80
Slickensided .......... Having planes of weakness that appear slick and glossy. The degree of slickensidedness depends upon
the spacing of slickensides and the ease of breaking along these planes.
Fissured ............. Containing shrinkage or relief cracks, often filled with fine sand or silt: usually more or less vertical.
Pocket .............. Inclusion of material of different texture that is smaller than the diameter of the sample.
Parting .............. Inclusion less than 1/8 inch thick extending through the sample.
Seam ............... Inclusion 1/8 inch to 3 inches thick extending through the sample.
Layer ............... Inclusion greater than 3 inches thick extending through the sample.
Laminated ........... Soil sample composed of alternating partings or seams of different soil types.
lnterlayered .......... Soil sample composed of alternating layers of different soil types.
Intermixed ........... Soil sample composed of pockets of dif ferent soil types and layered or laminated structure is not evident.
Calcareous ........... Having appreciable quantities of carbonate.
Notes:
The boring logs and related information depict subsurface conditions only at the specific locations and dates indicated. Soil conditions
and water levels at other locations may differ from conditions occuring at these boring locations. Also the passage of time may result
in a change in the conditions at these boring locations.
References:
(1)ASTM D422
(2)Soil Mechanics in Engineering Practice, Terzaghi and Peck, 1967.
{ ff'n"'ll"al•• ) HTS-72/0 OP b&Gi -
j j PROJECT: Proposed City Hall Building and Parking Areas/Access Drives
LOG 0 F B O R I N G
BORING NO.: 1 BORING LOCATION: See Figure 2 BORING TYPE: Auger I PROJECT LOCATION: Friendswood, Texas HTS PROJECT NO.: 93-S-189 DATE: January 11, 1994 PAGE: 1 OF 1 I CLIENT: City of Friendswood
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Depth (ft.)
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3 -----4------5---------------------------------------------------------
Pene-SPT Sam >le trometer Blows Type No. Reading Per <tsf) Foot 2.25 1
4.5
2 2.5
3 1.5
Desc ription of Stratum
Dark gray and brown FAT CLAY WITH SAND (CH). FILL. very stiff to hard with shells
3' Dark gray FAT CLAY (CH). stiff to very stiff
5' Boring terminated at 5'Ground water was not encountered during drilling. The boringwas dry and open to a de�th of 4.5' below the existing groundsurface 72 hours after t e completion of drilling.
HTS, INC.
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L O G 0 F B O R I N G
PROJECT: Proposed City Hall Building and Parking Areas/Access Drives BORING NO. : 2 BORING LOCATION: See figure 2 BORING TYPE: Auger PROJECT LOCATION: Friendswood. Texas
CLIENT: City of Friendswood
Pene-SPT Depth Sam 1le trometer Blows (ft.) Type No. Reading Per <tsf) Foot
-2-1 2.25
-4-2 1.5
-6-3 0.75
-8-4 2.25
10 5 2.25 --
13
� 6 3.0 --
-----is
20 7 2.25 --
23
25 8 2.5 ----------------------------------------------
HTS PROJECT NO.: 93-S-189 DATE: January 11. 1994 PAGE: 1 OF 1
Description of Stratum
Dark gray and brown FAT CLAY WITH SAND (CH). FILL. stiff tovery stiff with shells and gravel 3' Gray FAT CLAY WITH SAND (CH). firm to stiff with slickensides
6' Tan and light gray FAT CLAY (CH). very stiff with slickensides. 8' calcareous nodules, and ferrous nodules Dark tan and light gray FAT CLAY (CH). very stiff with slicken-sides. calcareous nodules. and ferrous nodules
25' Boring terminated at 25'
Ground water was not encountered during drilling. The boring was dry and open to a de�th of 24' below the existing groundsurface 72 hours after t e completion of drilling.
HTS,1sc.
'------.<. onsultonts
L O G 0 F B O R I N G
PROJECT: Proposed City Hall Building and Parking Areas/Access Drives BORING NO. : 3 BORING LOCATION: See Figure 2 BORING TYPE: Auger I : PROJECT LOCATION: Friendswood, Texas HTS PROJECT NO.: 93-S-189 DATE: January 11, 1994 PAGE: 1 OF 1 j � CLIENT: City of Friendswood
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Depth
(ft.)
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-4-
-6-
-8-
10 --
13
15 --
18
20 --
23
25 ----------------------------------------------
Sample Type No.
1
2
3
4
5
6
7
8
Pene-SPT trometer Blows Reading Per <tsf) Foot
4.0
2.0
0.75
1.0
2.5
2.5
2.75
2.5
Description of Stratum
Dark gray and brown FAT CLAY WITH SAND (CH), FILL, very stiff 2' with shells Gray FAT CLAY WITH SAND (CH). firm to stiff
6' Dark tan and light gray FAT CLAY (CH). firm to very stiff with slickensides. calcareous nodules. and ferrous nodules
25' Boring terminated at 25'
Ground water was not encountered during drilling. The boring was dry and open to a de�th of 24.2' below the existing groundsurface 72 hours after t e completion of dri lling.
HTS .,1sc
...__ _____ co11sulfa111s
L O G 0 F B O R I N G PROJECT: Proposed City Hall Building and ParkingAreas/Access Drives BORING NO. : 4 BORING LOCATION: See Figure 2BORING TYPE: Auger PROJECT LOCATION: Friendswood, Texas
11 CLIENT: City of Friendswood
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3 ----
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-5---------------------------------------------------------
Pene-SPT Sam 1le trometer BlowsType No. Reading Per <tsfl Foot
1.75
2 2.5
3 1.75
HTS PROJECT NO. : 93 · S -189DATE: January 11, 1994 PAGE: 1 OF 1
Description of Stratum
Dark gray and brown FAT CLAY WITH SAND (CH). FILL, stiff with0.5' shells Brown and tan FAT CLAY WITH SAND (CH). stiff
2' Dark gray FAT CLAY WITH SAND (CH). stiff to very stiff
5' Boring terminated at 5'Ground water was not encountered during drilling. The boringwas dry and open to a de�th of 4.2' below the existing groundsurface 72 hours after t e completion of drilling.
HTS, INC.
~-----.L'ons11/tanrs
r I PROJECT: Proposed Pavilion L O G 0 F 8 0 R I N G BORING NO. : 5 BORING LOCATION: See Figure 3 BORING TYPE: Auger
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PROJECT LOCATION: Friendswood, Texas
CLIENT: City of Friendswood HTS PROJECT NO. : 93-S-189 DATE: January 24. 1994 PAGE: 1 OF 1 Pene-Depthl Sample ltrometer
(ft.) TypelNo. Reading (tsf -2-
-4-
-6--8----ur---13 7:51 I18 20 I I23 25 I I--------------------------------------------
0.5 1 2.25 2 1.75 3 2.25
4 2.0 5 3.5
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1 °1 4.25
SPT Blows Per Foot Description of Stratum
Dark gray FAT CLAY (CH). soft to very stiff with roots and 2' ferrous nodules Dark gray FAT CLAY (CH). stiff to very stiff with ferrous r-,-.3.5' nodules / Gray FAT CLAY (CH). stiff to very stiff with ferrous nodules 5.5' / Dark tan FAT CLAY (CH). stiff to very stiff with calcareous 8' ��nodules. ferrous nodules. and�silt seams Light gray and tan FAT CLAY (CH). very stiff with slickensides -with dark tan color at 9.5'
1.3' Dark tan. gray, and light gray LEAN CLAY CCL). very stiff with silt pockets. silt �artings, and sand seams -tan silt layers from 16' to 17.5'f--17.5' Dark tan and gray FAT CLAY (CH). hard with slickensides and calcareous nodules �21.5' -becomes gray with tan at 23'25' Boring terminated-at 25 · Ground water was not encountered during drilling. Ground water level was measured at a depth of 21.5' 24 hours after the completion of drilling and the boring was open to a depth of 23'. Depths were measured below the existing ground surface.
HTS, ·,.-we.
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