Introduction to Geotechnical Engineering : Introduction to Geotechnical Engineering Robert G. Trazo, M.Sc., PE, GE
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
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”
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
Additional borings and laboratory testing to verify soil types and susceptibility to liquefaction
Our (ultimate) design
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
Hollow Stem Auger
Cone Penetration Test (CPT)
Standard Penetration Test (SPT)
California Ring Sampler
Bulk Sample Geotechnical Conditions : Geotechnical Conditions Boring logs contain detailed subsurface information
Groundwater – also discussed in recommendations section Laboratory Testing : Laboratory Testing Classification
Maximum Density/Optimum Moisture
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
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?
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
Very Moist Subgrade Soils Site Grading Recommendations : Fill placement
Are on-site soils suitable for use as fill?
Requirements for imported fill soils
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
Oversized Materials (Cobbles/Boulders)
Protect nearby structures
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
Usually 1 inch or less
Usually ½ inch or less Floor Slab Design Recommendations : Floor Slab Design Recommendations Thickness
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.
Tailings deposits up to 60 feet in depth, covered by soil & rock fill
Additional investigation to characterize the consolidation properties of the tailings
Settlement potentials were high
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/
Principal engineers who personally handle the report writing responsibilities for each project
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?