Soil-Structure Interaction Seminar - Foundation Performance ...

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The borings for the residential lots should be performed after the streets are cut and fill soils have been placed and compacted on the lots. This will enable the geotechnical engineer to identify the fill soils that have been placed on the lots. All fill soils should have been tested for compaction during the placement on the lots. A minimum of one density test for every 2500 square feet per lift must be performed once a subdivision is being developed. Fill soils may consist of clays, silty clays, and sandy clays. Sands and silts should not be used as fill materials. Typical structural fill in the Houston area consists of silty clays and sandy clays (not sands) with liquid limits less than 40 and plasticity index between 8 and 20. The fill soils should be placed in lifts not exceeding eight-inches and compacted to 95 percent of the maximum dry density • (ASTM D698-91). In the case of a subdivision development, the developer should perform only the borings for the streets and underground utilities. The borings for the lots should wait until all fill soils from street and underground utility excavations are placed and compacted on the lots. In g€neral, the geotechnical• testing of the soils for the lots should be the builders responsibility. We recommend that all of the foundations in the subdivision be engineered by a registered professional engineer specializing in residential foundation design. In the areas where no fill will be placed on a lot prior to site development, the borings on the lots can be performed at the same time as the time as the borings for streets. The soils data from the street and underground borings should never be used for the slab design. This is due to potential in variability in the soil conditions, including soils stratigraphy, compressibility, strength, and swell potential. <strong>Soil</strong> borings must be performed prior to foundations underpinning for distressed structures. This is to evaluate the subsoil properties below the bottom of the drilled footings. The depth of drilled footings for foundation underpinning should be determined by a geotechnical engineer. Unfortunately, this is not always followed, and many "so called" foundation repair jobs are performed incorrectly, causing significant financial loss for the client. In the event of building additions, a minimum of one boring is recommended on residential additions of less than 1,000 square feet. A minimum of two borings is recommended for additions greater than 1,000 square feet. In general, a scope of typical geotechnical exploration does not include the evaluation of fill compaction. These studies should have been performed at the time of fill placement. GEOTECH ENGINEERING AND TESTING, INC. ____________ _. 11
<strong>Foundation</strong> Design Considerations In the areas where highly expansive soils are present, the drilled footings should be founded in a strong soil stratum below the Active Zone. Active Zone is the zone at which Houston soils experience shrink and swell movements. This depth is about 10-feet. Therefore, we recommend a drilled footing depth of about 10- to 11-feet in the areas where the soils stratigraphy and groundwater depth allow the pier installation. The depth of the active zone should be verified by a geotechnical exploration. Drilled footings founded at shallower depths may experience uplift due to expansive soils. In the areas where non-expansive soils are present, the footing • depth can be as low as eight-feet. Void boxes may be used under the grade beams to separate the expansive soils from the grade beams. The grade beams for a floating slab foundation should penetrate clay soils a minimum of 12inches. The grade beam penetrations for a floating slab foundation into the surficial sands should be at least 18-inches to develop the required bearing capacity. A minimum grade beam width of 12-inches is recommended in sands and silts. In the event that a floating slab (post-tensioned slab or a conventionally-reinforced slab) is constructed in sands or silts, the geotechnical engineer must specify bearing capacity, assuming saturated subsoil conditions. This results in bearing capacities in the range of 600- to 900 psf in a typical sand or silt soils in the Houston area. Higher bearing capacity values can be used if the sands/silts do not get saturated during the life of the residence. This assumption is generally unrealistic due to the presence of sprinkler systems, negative drainage, and cyclic rainfall in the Houston area. Design parameters for a post-tensioned slab on expansive clays must carefully evaluated by a geotechnical engineer. It should be noted that the current post-tensioned slab design manual does not properly model the poor drainage, the effect of the trees, and the depth of the active zone. Revisions to the post-tensioned slab manual is under way to correct some of the short comings. In the mean time, the designer must use experience and judgment when designing post-tensioned slabs. The following design parameters are recommended for design of a post-tensioned slab in the Houston area in parts of the city with highly expansive soils (plasticity indices greater than 40): Edge Moisture Variation, em, feet Edge Lift Center Lift Differential Swell Ym, inches Edge Lift Center Lift 5.5 4.5 0.9 1.0 GEOTECH ENGINEERING AND TESTING, INC. ____________ _. 12
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SOIL STRUCTURE INTERACTION SEMINA
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FOUNDATION FAILURE DEFINED IN TERMS
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FOUNDATION FAILURE DEFINED IN TERMS
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FOUNDATION FAILURE IN THE HOUSTON A
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FOUNDATION FAILURES IN THE HOUSTON
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Inspections of the foundation had b
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J CASE NO. 10 - THE USE OF SPREAD F
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GARAGE 0" ·-0.2" -0.8 11 -0.3" •
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V) IJ.J u
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Page 40 and 41: CURRENT PRACTICES FOR DESIGN OF TRA
Page 42 and 43: INTRODUCTION CURRENT PRACTICES FOR
Page 44 and 45: and rigidity to control, dissipate
Page 47: 4.0 DESIGN PARAMETERS 4.1 General T
Page 62: I I. I I APPENDIX B TYPICAL GENERAL
Page 66: FUTURE OF POST-TENSIONED SLABS ON G
Page 72 and 73: GUIDLINES FOR GEOTECHNICAL DESIGN,
Page 74 and 75: GEOTECHNICAL GUIDELINES FOR DESIGN,
Page 76 and 77: INTRODUCTION The variable subsoil c
Page 78 and 79: South, Southwest, Southeast, and pa
Page 81: Geotechnical Foundation Design Crit
Page 85 and 86: Vegetation Control We recommend tre
Page 87 and 88: 8. The subgrade and fill moisture c
Page 89 and 90: Concrete Placement Monitoring The c
Page 91 and 92: Area drains can be used around the
Page 93 and 94: Inspections Every homeowner should
Page 95 and 96: Moisture Barriers Moisture barriers
Page 97: RECOMMENDED QUALITY CONTROL AND INS
Page 108 and 109: FOUNDATION REPAIR TECHNIQUES FOR RE
Page 110 and 111: PROFESSIONAL RESUME of DONALD E. LE
Page 112 and 113: FOUNDATION REPAIR TECHNIQUES PAGE 1
Page 115: FOUNDATION REPAIR TECHNIQUES PAGE40
Page 119: A P P E N D I X- DRAWINGS SAMPLE FO
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EXAMPLE OF HELICAL ANCHORS Pipe Typ
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RESIDENTIAL SOIL AND FOUNDATION REQ
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Section 6-52. Exceptions CITY OF WE
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Soil Structure Interaction Seminar
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July 21, 1994 Page3 corporation, as
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Residential Construction Liability
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July 21, 1994 Page 8 E. Defenses to
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The Texas Deceptive Trade Practices
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construction or design of the house
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(5) Arguably, implied warranties do
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(3) Includes any diminution in mark
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D. Who Is a Proper Plaintiff? 1. An
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a. claimant's damages are limited t
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a. May be based on hearsay (i.e., e
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d. The Broker (1) Absent specific a
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VI. More Honored in the Breach HORA
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