Introduction to Geotechnical Engineering

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Introduction to Geotechnical Engineering : 

Introduction to Geotechnical Engineering Robert G. Trazo, M.Sc., PE, GE Principal Engineer Southern California Geotechnical, Inc.

Introduction : 

Introduction B.S. Civil Engineering, UCLA; M.S. Civil Engineering, CSULB State of CA Licensed Civil and Geotechnical Engineer Cal Poly Pomona Lecturer – Civil Engineering Department CE 325 Intro to Geotechnical Engineering CE 326 Geotechnical Engineering II CE 327L Geotechnical Engineering Lab CE 210/210L Computers in Civil Engineering Lecture and Lab CE 422L Concrete Lab CE 491/492/493 Senior Project Geotechnical Engineer License Exam Preparation Team 2005-Present 21 Civil License Exam Review Classes (Geotechnical) taught since 2001 Work History: Engineer with Lockwood-Singh & Associates (1993-1997) Forensic Geotechnical Firm Engineer with Goffman, McCormick & Urban (1997-2003) Residential/Municipal/Commercial Engineer with Southern California Geotechnical (2003-present) Commercial/Industrial

Synopsis of SoCalGeo’s Role : 

Synopsis of SoCalGeo’s Role Part I - Geotechnical Investigation/Report Drill borings/trenches, take samples, test soil, writes report containing recommendations based on proposed development Part II - Review of Grading/Foundation Plans Grading/Concrete/Landscape/Retaining wall contractors as well as Structural Engineer, Architect, Civil Engineer use our recommendations to design project Part III - Observation and Testing of Soils during Construction SoCalGeo is at the site making sure project gets built using our recommendations and per plans and specifications We write 2 reports saying: Rough grading performed per our recommendations and project specs Precise grading performed per our recommendations and project specs

Planning the Geotechnical Investigation : 

Planning the Geotechnical Investigation Review Site Plan Check Alquist-Priolo Fault Maps Check Geology Maps Check Liquefaction Maps

Alquist Priolo Act (1972) : 

Alquist Priolo Act (1972) The Alquist-Priolo Earthquake Fault Zoning Act was passed in 1972 to mitigate the hazard of surface faulting to structures for human occupancy. It’s main purpose is to prevent the construction of buildings used for human occupancy on the surface trace of active faults. The law requires the State Geologist to establish regulatory zones (known as Earthquake Fault Zones) around the surface traces of active faults and to issue appropriate maps. Cities and counties must require a geologic investigation to demonstrate that proposed buildings will not be constructed across active faults. For the purposes of the Act, an active fault is one that has ruptured in the last 11,000 years.

Alquist-Priolo Map Sample : 

Alquist-Priolo Map Sample

Alquist-Priolo Map Detail Sample : 

Alquist-Priolo Map Detail Sample

Geologic Map : 

Geologic Map

Liquefaction : 

Liquefaction Typically are identified as zones of required investigation by the California Geologic Survey (CGS)

Seismic Hazards Map : 

Seismic Hazards Map

Liquefaction : 

Liquefaction Typically are identified as zones of required investigation by the California Geologic Survey (CGS) 50-foot deep borings or CPT Ground Motion Parameters

Liquefaction : 

Liquefaction Typically are identified as zones of required investigation by the California Geologic Survey (CGS) 50-foot deep borings or CPT Ground Motion Parameters Use of CPT values to calculate resistance to liquefaction For liquefiable layers, calculate total settlement

Liquefaction : 

Liquefaction Differential Settlement difference between settlement at 2 borings 50 – 60% of total settlement Maximum total settlement for structural mitigation typically 4” If total settlements are greater than 4” ground improvements deep foundations overexcavation

Lakewood Estates Project : 

Lakewood Estates Project Took over project from original geotechnical engineer Original recommendations included stone columns, vibro-compaction to mitigate liquefaction-induced settlements Our investigation Additional borings and laboratory testing to verify soil types and susceptibility to liquefaction Our (ultimate) design Conventional foundations No ground improvement

Geotechnical Report Contents : 

Geotechnical Report Contents Site Preparation Recommendations Corrective Grading Recommendations Foundation design parameters Floor Slab design parameters Retaining Wall design parameters Pavement design parameters Seismic design parameters

Site Preparation Condition Issues : 

Site Preparation Condition Issues These are the conditions present at the time of our subsurface exploration Pay special attention to topography, site size, ground surface cover Any existing structures? Basements?

Proposed Development Issues : 

Proposed Development Issues Is this the same development as the current site design? Same structure type? Same structure size? Are column and wall loads within 25% of assumed values? Same floor slab loads? Basement or other below grade construction? Proposed Cuts and Fills (VERY IMPORTANT) Significant new cuts could expose better or worse bearing materials, could require additional removal. Significant new fills could cause settlement of compressible soils at depth.

Exploration/Sampling Methods : 

Exploration/Sampling Methods Number of Borings and/or Trenches Exploration Method Hollow Stem Auger Backhoe Hand Auger Cone Penetration Test (CPT) Sampling Method Standard Penetration Test (SPT) California Ring Sampler Bulk Sample

Geotechnical Conditions : 

Geotechnical Conditions Boring logs contain detailed subsurface information Topsoil Pavement/Slabs Soil Types Bedrock Types Groundwater – also discussed in recommendations section

Laboratory Testing : 

Laboratory Testing Classification Moisture/Density Sulfates Consolidation Maximum Density/Optimum Moisture Direct Shear pH/Resistivity Atterberg Limits

Ground Motion Parameters : 

Ground Motion Parameters Site Acceleration (a) measured in g’s Maximum Magnitude (M) CGS Open File Report FRISKSP or other probabilistic seismic hazard software

Geotechnical Design Considerations : 

Geotechnical Design Considerations Discuss our rationale for the grading and foundation recommendations Expansive Soils Presaturation Dowelling Sulfates Shrinkage/Subsidence Based on maximum dry density and in-situ moisture contents, very approximate Grading and Foundation plan review VERY IMPORTANT – review as early in the design stage as possible, especially on complicated jobs

Site Grading Recommendations : 

Site Grading Recommendations Site Stripping Topsoil depths are approximate Can Topsoil be blended? Demolition Recommendations Disposal of asphalt and concrete debris Other unsuitable materials which should be removed from the site

Collapse Graph Sample : 

Collapse Graph Sample

Consolidation Graph Sample : 

Consolidation Graph Sample

Site Grading Recommendations : 

Site Grading Recommendations Overexcavation for Building, Slope, & Retaining wall areas To remove existing fill To remove collapsible soils To remove compressible soils

Site Grading Recommendations : 

Site Grading Recommendations Overexcavation for Building, Slope, & Retaining wall areas To remove existing fill To remove collapsible soils To remove compressible soils Try to limit total settlement to 1” On bigger structures with higher column loads, total settlements may be in the 2” range. Try to equalize settlements.

Site Grading Recommendations : 

Site Grading Recommendations Parking areas, we tend to leave existing fill in place Parking areas are relatively large and complete remedial grading would be costly Owner assumes additional risk in return for cost savings

Site Grading Recommendations : 

Site Grading Recommendations Potential Site Preparation Difficulties Slot Cutting/Shoring Very Moist Subgrade Soils

Site Grading Recommendations : 

Fill placement Are on-site soils suitable for use as fill? Requirements for imported fill soils Expansion Index Soluble Sulfates Grain Size Should always be well graded, at least 10% fines Site Grading Recommendations

Construction Considerations : 

Construction Considerations Excavation Temporary construction slope inclination Potential for caving of shallow excavations Slot Cutting Excavation difficulties Blasting/ripping Oversized Materials (Cobbles/Boulders) Protect nearby structures Groundwater Expansive Soils Moisture Conditioning Recommendations for landscape planters

Settlement Design vs. Bearing Capacity Design : 

Settlement Design vs. Bearing Capacity Design Increase in footing width causes increased settlement for the same applied pressure Increases in qa for width or depth are best made after preliminary foundation design is prepared

Foundation Design Recommendations : 

Foundation Design Recommendations Foundation depth/width Reinforcement usually based on expansive soils or liquefaction Allowable bearing pressure may be increased by ⅓ when considering short duration wind or seismic loads.

Foundation Design Recommendations : 

Foundation Design Recommendations Foundation Construction Evaluation of foundation subgrade soils Description of suitable bearing materials Recommendations for removal of any unsuitable bearing materials Moisture conditioning foundation subgrade soils

Foundation Design Recommendations : 

Foundation Design Recommendations Estimated foundation settlements Total Settlement Usually 1 inch or less Differential Settlement Usually ½ inch or less

Floor Slab Design Recommendations : 

Floor Slab Design Recommendations Thickness Steel Reinforcement Underlayment 2” sand Vapor Barrier 2” sand

Pavement Design Issues : 

Pavement Design Issues Typically assume R-value based on soil type Sands/Gravels = Higher R-value Silts/Clays = Lower R-value Large cuts or fills can change soils that are present at subgrade level CalTrans Design Procedure

Pavement Design Parameters : 

Pavement Design Parameters Pavement sections presented for AC/PCC by Traffic Index (TI) Civil/owner should decide which one to use

Percolation Tests : 

Percolation Tests Percolation testing should occur as early as possible during investigation process Large site; lots of open space – Leach lines and basins Site area limitations – Seepage pits Recommend dry well system with settling chamber

Grading Plan Review : 

Grading Plan Review Verify that the pavement sections correspond with the sections recommended in the geotechnical report. Verify that the proposed site grades, especially in the building area correspond to those assumed at the time of the geotechnical report. If not, determine the impact on the grading recommendations. Identify the locations of any retaining walls or slopes that may impact the site. Were recommendations for grading or construction of these walls/slopes given in the geotechnical report? Does the proposed grading or construction impact any adjacent sites? Is the subject site impacted by adjacent buildings or other construction? Verify adequate setbacks from any ascending slopes, per the CBC or the local building code.

Foundation Plan Review : 

Foundation Plan Review Verify that the bearing pressure used in the footing design corresponds with the recommendations of the geotechnical report. Verify that the minimum foundation widths and depths are in accordance with the geotechnical report . Verify that the strip footings incorporate the minimum steel recommended by SCG. Verify that the slab thickness and reinforcement is per the SCG geotechnical report. Verify that any sulfate-resistant concrete mix designs recommended by SCG have been incorporated into the structural plans. Verify that the CBC Seismic Design Coefficients are per the SCG geotechnical report.

Irwindale Business Center : 

Irwindale Business Center Former Calmat sand and gravel quarry. Scope of Development Previous geotechnical report was for numerous small commercial/industrial buildings <30k sf. Client wanted buildings up to 320k sf. Geotechnical issue Tailings deposits up to 60 feet in depth, covered by soil & rock fill Investigation Additional investigation to characterize the consolidation properties of the tailings Settlement monitoring Settlement potentials were high Solution Surcharge the clay deposits to decrease post-construction settlements Limited remedial grading

Why Choose SoCalGeo? : 

Why Choose SoCalGeo? Knowledgeable principal engineers who have extensive experience in commercial/industrial/retail/ residential/government projects Principal engineers who personally handle the report writing responsibilities for each project Streamlined operations Great service from professionals you can count on from the beginning to the end of the project Very competitive prices

THANK YOU. ANY QUESTIONS? : 

THANK YOU. ANY QUESTIONS?

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