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

•Grey contour lines Phase I grading

•Pink Contour lines Phase II grading

•Orange contour lines Phase III Grading

This Project

Geology (1 of 4)

• Bellingham (Glaciomarine) DriftTypically 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

100’60’

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

13 TESTS

5 TESTS

Geotechnical Data

Selection of Soil Properties for (FEM) Model4 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

Eoed (lb/ft2) 86607 138666 635555

KX&Y (ft/day) -- 0.005 0.005

Gref (lb/ft2) 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)

Figure Taken From LF&A Geotechnical Report; Silver Reef

• We know settlement has occurred.

• We just do not know when or how much.

What do we KNOW and what do we THINK?

Not Possible to verify calculated settlement due to lack of elevation readings

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 ElseBottom 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 DesignStep #1: Select worst case soil profile and analysis plane

Step #2: Select conservative soil properties based on available lab test results

Step #3: Refine selected soil properties to “predict” previously observed settlement thereby verifying FEM Model.

Step #4: Compare results with tolerable settlement performance criteria.

Step #5: 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:

4’= SQRT (42 *42)

Drainage Distance:

= 0.5 SQRT (42 *42)8’

= 4’ Diameter Stone Column (Hayward Baker)

= Wick Drain = 2’ Effective Drainage Distance

Observed & Predicted (Long Direction) Settlement

-16

-14

-12

-10

-8

-6

-4

-2

0

5/27/2

005

6/6/20

05

6/16/2

005

6/26/2

005

7/6/20

05

7/16/2

005

7/26/2

005

8/5/20

05

8/15/2

005

Tota

l Est

imat

ed S

ettle

men

t (in

ches

)

SP#1 SP#2 SP#3 SP#4 SP#5SP#6 SP#7 SP#8 SP#9 SP#10REBAR#1 REBAR#2 REBAR#3 REBAR#4 REBAR#5REBAR#6 MP#1 MP#2 MIN Predicted MAX Predicted

Preload 90% complete on 6/7/05Preload complete on 6/10/05

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.