LACHEL FELICE & Associates Advances in Finite Element Modeling Using PLAXIS SILVER REEF HOTEL/CASINO EXPANSION
The Design/Construction Team OWNER: Silver Reef Casino; Harlan Oppenheim Architect: Morris and Brown Architects Kathy Perrino Contractor: AECON Greg Evans Stone Columns: Hayward Baker Mark Koelling, PE Geotechnical Engineer: LACHEL FELICE & Associates
Presentation Outline Existing & Proposed Site Features Geology & Other Constraints Geotechnical Parameters Preliminary Recommendations & Settlement (by others) LF&A Recommendations Geotechnical Data & Design Approach (Explorations, Tests, Settlement History) FEM (Plaxis ) Model & Geotechnical Soil Properties Wick Drains (Spacing) Final Comments
Existing and Proposed Site Features Existing Casino 48,000 sq. ft. Expansion includes: 23,360 sq. ft. of New Construction 6-Story Cast-in-Place Concrete Hotel 60,000 Gallon Water Tank Related Grading/Landscaping/Parking Additional Future Expansion Possible Complex Previous Grading and Settlement This Project
Complex Previous Grading At least three episodes of previous grading Fill Thickness varies from 0 to 10 feet No Settlement Monitoring performed following mass grading This Project Grey contour lines Phase I grading Pink Contour lines Phase II grading Orange contour lines Phase III Grading
Geology (1 of 4) Bellingham (Glaciomarine) Drift Typically consists of unsorted, unstratified silt and clay with varying amounts of sand, gravel, cobbles, and occasional boulders derived from sediment melted out of floating glacial ice that was deposited on the sea floor (WSDOT GDM). Alluvial Material from Nearby Nooksack & Lummi Rivers Very Soft Clay (CH) Overlain by 20 to 45 feet of Loose Liquefiable Sand (SP, SP-SM) Natural Ground Surface and Groundwater at Approximately Elevation 3-Feet.
Geology (2 of 4) Fill SP & SM-SM Liquefiable Sand (Improved with Stone Columns) SP & SP-SM Liquefiable Sand CL; Soft Clay CL; Very Soft to Med Stiff Clay CL; Very Soft to Med Stiff Clay CL; Med Stiff to Stiff Clay CL; Very Stiff to Hard Clay Existing Casino 60 100
Geology (3 of 4) 7 Borings 4 Cone Penetration Tests (2 after the preload) >17 Atterburg Limit / Grain Size Determinations >34 Moisture Content Evaluations 5 Consolidation Tests
Geotechnical Data Fill SP & SP-SM (Improved with Stone Columns) SP & SP-SM CL; N=3; Cc= 0.19, 0.25, 0.28, 0.32 CL; N=1; Cv=3.4*10-3 ; Cc = 0.42 CL; N=1; Cv=1.6*10-3 ; Cc = 0.46 CL; N=13; Cv=4.0*10-3 ; Cc = 0.36 CL; N>25???; problems with data reporting 5 TESTS 13 TESTS
Geotechnical Data Selection of Soil Properties for (FEM) Model 4 Compressible Soil Layers Clay Layer 2 is Typical Soil Parameter Based on Lab Tests Only Based on Verification Exercise After Preload Unit Weight (pcf) 110 114.5 116.5 E oed (lb/ft 2 ) 86607 138666 635555 K X&Y (ft/day) -- 0.005 0.005 G ref (lb/ft 2 ) 32076 32000 113333
Other Constraints Existing casino is 60 from the new hotel. Maximum Differential Settlement: Existing Casino = 2.5 ; How much is left? Cast-in-Place Hotel: 0.5 inches Existing casino must remain operational. What do we KNOW and what do we THINK? (Regarding settlement we re not sure) You want it when? IN CASINO CONSTRUCTION, TIME IS MONEY!!
Other Constraints (An Example) What do we KNOW and what do we THINK? We know settlement has occurred. We just do not know when or how much. Not Possible to verify calculated settlement due to lack of elevation readings Figure Taken From LF&A Geotechnical Report; Silver Reef
Preliminary Recommendations (by others) 18 to 24 inches of Settlement Settlement will take 20 years Use Stone Columns to Prevent Liquefaction Recommended Length (35 ) Fully Compensating Foundation Build a basement that removes an amount of soil equal to the weight of your building $$$ >1 Million Build Somewhere Else Bottom Line: The project is DEAD About 12 weeks before Construction Starts
LF&A Recommendations Support Mitigation of Liquefaction using 48 Stone Columns installed at 8 on centers; L-40 Preload Hotel Tower using equivalent Preload/Surcharge Incorporate Expansion Joints into New Construction Accelerate Consolidation Settlement Using Wick Drains-Installed at 4 feet on centers Mat (or Raft) Foundation-No basement excavation Results in savings of ~$1 Million Project is Still Alive
Geotechnical Design Approach Settlement Considerations Control Geotechnical Design Step #1: Step #2: Select worst case soil profile and analysis plane Select conservative soil properties based on available lab test results Step #3: Step #4: Step #5: Refine selected soil properties to predict previously observed settlement thereby verifying FEM Model. Compare results with tolerable settlement performance criteria. Refine as required & stop refining ASAP. Because of time constraints LF&A decided to provide broad but reasonable estimates of settlement and focused our analysis on accurately estimating differential settlement.
FEM (PLAXIS) Model Analysis Parameters Plane Strain Model Long Axis of New Structure and Existing Casino (Over-predicts settlement) Wick Drain Spacing Discussed Below Consolidation & Staged Construction Analysis Methods Installation of stone columns during Phase 1 Construction; Placement of fill during Phase 1 & time delay of 90 days; Construction of the Phase 1 Casino; Time delay of about 3 years; Installation of wick drains and installation of stone columns; Construction of a preload/surcharge; Time delay to allow for consolidation induced by preload; Removal of the preload; Construction of rigid mat foundation; Fourth time delay to allow for final consolidation settlement.
Wick Drains Not installed below stone columns Did not consider permeability of stone columns Wick Drains installed at 4-feet on centers Modeled using a spacing of 2.8 Predicted and observed rate of settlement show the difference between reality and the simplified model
Wick Drains MEBRA-DRAIN MD-7407 Wick Drains were used. The wick drain spacing is 4 feet on centers as shown: 8 4 = SQRT (4 2 *4 2 ) Drainage Distance: = 0.5 SQRT (4 2 *4 2 ) = 4 Diameter Stone Column (Hayward Baker) = Wick Drain = 2 Effective Drainage Distance
Observed & Predicted (Long Direction) Settlement 0 Total Estimated Settlement (inches) -2-4 -6-8 -10-12 -14-16 5/27/2005 Preload 90% complete on 6/7/05 Preload complete on 6/10/05 6/6/2005 6/16/2005 6/26/2005 7/6/2005 7/16/2005 7/26/2005 8/5/2005 SP#1 SP#2 SP#3 SP#4 SP#5 SP#6 SP#7 SP#8 SP#9 SP#10 REBAR#1 REBAR#2 REBAR#3 REBAR#4 REBAR#5 8/15/2005 REBAR#6 MP#1 MP#2 MIN Predicted MAX Predicted
Observed & Predicted (Long Direction) Settlement An excerpt from the LF&A Geotechnical Report
Predicted Settlement Short Direction PLAN to ADD PLAXIS PLOT IN SHORT DIRECTION THE PLAXIS WORK IS DONE JUST NEED THE PLOT FROM TIM FYI PLOT shows predicted settlement much closer to what was observed
Conclusions Project is a success. PLAXIS is a useful tool; but laboratory testing and site history are very important to developing an accurate model. Modeling the short direction of the hotel more accurately predicts observed settlement. LF&A method for modeling wick drain spacing is appropriate. Placement of settlement monitoring points sooner may have shown more settlement than currently reported.