Foundations and Earthwork Stott Bushnell, Cathryn Cecil, Tyler Cecil, and Craig Fowler – BFCC...

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Transcript of Foundations and Earthwork Stott Bushnell, Cathryn Cecil, Tyler Cecil, and Craig Fowler – BFCC...

Foundations and Earthwork

Stott Bushnell, Cathryn Cecil, Tyler Cecil, and Craig Fowler – BFCC Engineering

Residential foundations are very stiff, often tied together with grade beams. They usually remain intact after liquefaction, despite large settlements (>3 in). The

structures are almost always repairable

Design-Build of the Block 25A Academic Building

The purpose of this project is to provide geotechnical evaluations and recommendations for AMEC Foster Wheeler for use in the design build of the Block 25A Academic Building for the University of California, San Francisco, Mission Bay Campus. The building will be a six story office building with a partial seventh story with a footprint of 44,000 square feet, located on the corner of 16th Street and 4th Street in San Francisco. BFCC Engineering characterized the site based on geology, existing soil, and seismic hazards and gives recommendations for retaining wall and foundation design.

Project Description

AcknowledgmentsThanks to our sponsor, Alex Wright and AMEC Foster Wheeler, for their support and guidance. Thanks as well to Dr. Kevin Franke and Levi Ekstrom for their advice and support.

University of California, San Francisco, Mission Bay Campus BFCC

The site lies in an area that has high potential for ground shaking and liquefaction due to large faults and clayey soils in the area. A design response spectrum was created to show the typical maximum accelerations for a building on the site, so that engineers could design the seismic aspects of the building accordingly. To better access the liquefaction potential, an analysis of the soil and nearby faults were done. Using liquefaction software and nearby fault data, a liquefaction hazard report was made based off the 475 and 2475 return-year earthquake. It was found that the site has high potential for liquefaction. To mitigate these hazards, it is recommended to do soil improvements, and design the foundation to resist the effects of liquefaction.

Seismic Hazards

A description of the subsurface soils was created using field exploration and laboratory testing of samples. There were about 3 boring logs and corresponding analyses completed and the raw data was given to us. There were also about 8 cone penetration tests completed in various locations on the site. This data was used to complete a soil profile to make it easier to see what type of soil is present and other properties of the soil. The groundwater levels for the site is an important property gained.

Soil Description

Depth (ft) Description Plasticity PI LL Water Content (%) Dry Unit Weight (pcf)1 Asphalt Concrete (4 in.), Aggregate Base (3 in.)2 10 1193 4 106456789 9 131

101112 Groundwater131415161718 HP19202122 34 68 57 67232425 HP2627 56 6728293031 48 74323334 HP 53 97 74 563536373839404142 73 5643444546 HP 39 73 60 6447484950515253545556 MP57585960616263646566

Clayey Sand

Poorly Graded Sand

Clayey Sand

Clayey Gravel with Sand

Elastic Silt to Fat Clay

Silty Sand

Sandy Lean Clay

Serpentine and Shale (Bedrock)

Depth (ft) Blow counts per ft Sample # ASTM Symbol Description Plasticity PI LL Water Content % Dry Unit Weight (pcf)

2.5 50 1 SC Clayey Sand 10 119

5 18 2 SP Poorly Graded Sand 4 106

6.5 100 3 SP Poorly Graded Sand

10 24 4 SC Clayey Sand 9 131

15 14 5 GC Clayey Gravel with Sand

21.5 1 6 CH Elastic Silt to Fat Clay 34 68 57 67

26.5 1 7 CH Elastic Silt to Fat Clay 56 67

31.5 1 8 CH Elastic Silt to Fat Clay 48 74

35 50 psi 9 CH Elastic Silt to Fat Clay HP 53 97 74 56

36.5 1 10 CH Elastic Silt to Fat Clay

41 1 11 CH Elastic Silt to Fat Clay

46.5 1 12 CH Elastic Silt to Fat Clay HP 39 73 60 64

51.5 65 13 SC Silty Sand

56.5 16 14 CL Sandy Lean Clay

60.5 120 15 Serpentinite and shale

65.5 140 16

Figure 3: Site Layout with Boring Hole Locations

Figure 5: Site Location In Liquefaction Hazard Zone Map

Figure 6: Liquefaction Hazard Report

Figure 7: Site Design Response Spectrum

Figure 1: Soil Profile of Northeast Section of Site

Figure 2: Boring Log Data for Northeast Section of Site

Figure 4: AutoCAD Details of Recommended Foundation Pile and Retaining Wall