FOUNDATIONS ON SHRINKING AND SWELLING SOILS (Prediction of Movement, Construction Issues)

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1 FOUNDATIONS ON SHRINKING AND SWELLING SOILS (Prediction of Movement, Construction Issues) by Jean-Louis Briaud, Sangho Moon, Xiong Zhang Department of Civil Engineering, Texas A&M University, College Station, Texas , USA

2 ACKNOWLEDGEMENTS ENVIRONMENTAL SOIL STABILIZATION LTD. Russ Scharlin Johny Sherwood SPENCER J. BUCHANAN PROFESSORSHIP GILES ENGINEERING ASSOCIATES INC. Doug Dayton

3 OUTLINE FUNDAMENTAL BEHAVIOR SHRINK TEST WATER CONTENT METHOD CASE STUDY SMART FOUNDATION

4 soil grain water soil grain water air soil grain water air Saturated u w 0 u a = 0 σ = σ - u w Occluded Air u w = u a σ = σ - u w Continuous Air u w 0 u a = 0 σ = σ - αu

5 T α Glass Contractile Skin α T h c = 4 T cos á d ã where T = w 72 mn/m 0 kpa h c γ w - 1,000 kpa Water d h c Atmospheric pressure Water h u hγ w

6 initial state after time, t h = Osmotic Suction after time, t Initial state Pure Water Salt Water

7 Water State Examples Suction pf cm kpa Degree of Saturation Water Content Swell Shrink Oven Dry Suction Air Dry YES NO Tension Shrinkage Limit Near 100 % 8 to 15 % Field Capacity Swell Limit to 50 % YES % Large River NO Compression Deepest Offshore Platforms Bottom of Deepest Ocean

8 Soil State Swell Shrink u Unsaturated Yes No Saturated Yes Yes GWL Saturated No Yes

9 PHASE DIAGRAMS

10 w w SW Saturated or Occluded Air w i w max w SH ( V/V) max 0 V/V

11 SHRINK TEST PARAMETERS D o D H o W o SHRINK W H t = 0 t

SHRINK TEST Shrink Test Shrink Test Example (B/RF1/6) 25 20 0.3-0.9 m,ew = 0.86, w = 17.15 % 1.2-1.8 m, Ew = 0.69, w = 21.66 % 2.

12 SHRINK TEST Shrink Test Shrink Test Example (B/RF1/6) m,ew = 0.86, w = % m, Ew = 0.69, w = % m, Ew =0.83, w = % data chosen for calculation of Ew Water Content, % Volumetric Strain, V/V

13 SHRINK TEST RESULTS (1) Porecelain Clay and Bentonite Clay H/H o Porcelain Clay Bentonitic Clay t, hr H/H o f V/V o 1 f Porcelain Clay Bentonitic Clay w E w w 1 E sh w w sh 0.1 Porcelain Clay Bentonitic Clay w o w o V/V o

SWELL TEST Swell Test Swell Test Example (B/RF1/6 0.3 0.9 m) L load Recompression under Overburden Pr essure Swell under Overburden Pressure Swell with no Overburden Pressure 1 2 0.010 0.

14 SWELL TEST Swell Test Swell Test Example (B/RF1/ m) L load Recompression under Overburden Pr essure Swell under Overburden Pressure Swell with no Overburden Pressure Porous stone Soil sample Consolidometer Porous stone H/H % Recovery, ( H/H) P Maximum Free % Swell, ( H/H) FS Max. Swell Under Overburden, ( H/H) PS Time, hrs

15 EXAMPLE OF THE PREMISS METHOD

16 SHRINK TEST RESULTS (3) Influence of Vertical Pressure w Sample(S) Overburden(O) S (S1) S+O (S2) V/V o w w 0.15 Sample(S) 0.10 Overburden(O) S (S1) 0.05 S+O (S2) Sample(S) Overburden(O) S (S1) S+O (S2) H/H o D/D o

17 SHRINK AND SWELL TEST RESULTS Porecelain Clay and Bentonite Clay Shrink Swell 0.0 w Porcelain Clay V/V o Shrink Swell 0.0 w Bentonic Clay V/V o

18 SUCTION VARIATION WITH DEPTH After Mitchell (1979) u 0 u 0 0 u e Suction, u u(z,t) Depth, z Suction Envelope Suction Envelope z max u(z max ) = u 0

19 After Mitchell (1979) Äu(z) = 2 Äu 0 exp (-( / T 0 á ) 0.5 z) Äw = f (Äu) characteristic curve 0.5 max T0 á ) z = 1.3( where u = change in suction at depth z u 0 = change in suction at ground surface T 0 = period of weather cycle α = diffusion coefficient z = depth below ground surface w = change in water content z max = maximum depth of water content change

20 After Styron et al. (2001) LI LL (%) = ± 30 Äw = 0.6 (PI/LL)

21 WATER CONTENT VARIATION AS A FUNCTION OF TIME From Posey, Briaud, 1995, Woodfin, Briaud, Time for CS Fall Winter Spring Summer Fall Winter Spring SA OUTSIDE CC UNDER CC OUTSIDE Average Water Content SA UNDER CC = Corpus Christi (0-0.5m) SA = San Antonio (0-0.5m) CS = College Station (0-1.5m) OUTSIDE = Outside the Foundation Imprint UNDER = Under the Foundation Imprint Fall Winter Spring Summer Fall Winter Spring Time for SA and CC CS OUTSIDE

22 MOISTURE INDUCED MOVEMENT S = H i Äå i = H i f Äw E i w i w w w i + w i H i w i w i w i z ε i ε i + ε i ε v

23 WEIGHT INDUCED SETTLEMENT S = H Äå = i i H i Äσ i E i P σ v σ v H i σ ov σ i σ ov σ ov + σ i z ε i ε i + ε i ε v

24 PLAN VIEW OF THE SITE Site in Arlington, Texas W Boring location RF Boring order. 1 - deep 2m North 2m 0.6m W1 0.61m m B/W1/7 redrill - deep RF1 7. BM BM m m 3m Boring date # 1 : 06/24/99 # 2 : 07/13/99 # 3 : 10/25/99 # 4 : 02/11/00 # 5 : 05/11/00 # 6 : 08/11/00 # 7 : 11/17/00 # 8 : 03/13/01 # 9 : 07/15/01

SOIL STRATIGRAPHY Site in Arlington, Texas RF1 10m W1 20m W2 A 10m A North BM1 BM2 RF2 0 A A 2m 2m Depth,m 0.5 1 1.5 2 2.5 3 Dark Gray Silty Clay : Trace Fine Sand S u = 151.5 kpa w mean = 20.

25 SOIL STRATIGRAPHY Site in Arlington, Texas RF1 10m W1 20m W2 A 10m A North BM1 BM2 RF2 0 A A 2m 2m Depth,m Dark Gray Silty Clay : Trace Fine Sand S u = kpa w mean = % h = 3.42 pf LL = 51.3, PL = 22.3 Brown Silty Clay, trace fine Sand : Calcareous S u = kpa w mean = % h = 3.41 pf LL = 40.4, PL = 17.1 γ t = 20.3 kn/m 3 E w = 0.752, f = 0.39 %SW = 5.17 %<0.002= 47.7 γ t = 20.4 kn/m 3 E w = 0.869, f = 0.39 %SW = 4.31 %<0.002= m GWL : 4.27 m (Jun./25/99) 4.8 m (Feb./1/01) 4 m (Jul./15/01) Legend RF : Reference W : Water injected BM : Benchmark

26 WATER CONTENT AND SUCTION vs. DEPTH Footing RF1 at a site in Arlington, Texas Depth, m Depth, m B:Boring B1 B2 1.0 B3 B4 1.5 B5 B6 B7 B8 2.0 B B:Boring B1 B2 1.0 B3 B4 1.5 B5 B6 B7 B8 2.0 B Water Content Suction, pf

27 GARNER S STUDY (1999) 3 samples at 3 water contents sent to 5 laboratory. Water Content, % Sample 1 Sample 2 Sample 3 Suction, pf Sample 1 Sample 2 Sample 3 Suction, kpa Sample 1 Sample 2 Sample % pf kpa kpa

28 SHRINK TEST RESULTS (2) Three Samples From Arlington, Texas w B/RF1/ m, E w = m, E w = m, E w = V/V o w B/RF2/ m, E w = m, E w = m, E w = V/V o

29 SELECTED SOIL TEST RESULT FOR RF1 E w f % SW Depth, m B3 B4 B5 B6 B7

30 Displacement, mm 08/1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/2001 FOOTING MOVEMENT OVER TWO YEARS RF1 RF2 W1 W2-60 Date summer fall winter spring summer fall winter spring summer

31 Rainfall, mm RAINFALL AND TEMPERATURE Date 08/1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/2001 Temperature, o C Ave. Monthly Temperature Ave. Monthly Rainfall

32 WATER CONTENT VARIATION AND MOVEMENT Date 06/1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/2001 Water Content, % Displacement, mm Average of 4 Footings at a site in Arlington, Texas Average Measured movements Average Water content

33 PREDICTED AND MEASURED MOVEMENTS Average of 4 Footings at a site in Arlington, Texas RF1+ RF2+ W1+ W2 4 Displacement, mm Average Measured movements Water Content Method Time, days

34 HOUSES ON EXPANSIVE CLAYS MOST EXPENSIVE NATURAL HAZARD IN THE COUNTRY

35 FOUNDATION SOLUTION Stiffened Slab on Grade Stiffened Slab on Grade & on Piers Elevated Structural Slab on Piers air gap Thin Post Tensioned Slab

36 HOUSES ON EXPANSIVE CLAYS VERY DIFFICULT TO PREDICT THE SOIL MOVEMENT (WEATHER, VEGETATION, DRAINAGE) MUCH EASIER TO DESIGN AN ADJUSTABLE FOUNDATION

37 SMART FOUNDATION

38 SMART FOUNDATION 3.5 ft (1.1 m) 3.5 ft (1.1 m) 1ft (0.3 m) 13.1ft (4 m) 1ft (0.3 m) 52.5 ft (16 m) 13.1ft (4 m) 52.5 ft (16 m)

39 SMART FOUNDATION CONSTRUCTION Make Cavity Cast Footing & Place Spacer Back Fill Excavate Trench Cast Beam Finish 1ft

40 COST COMPARISON Conventional Waffle Slab 16 m 16 m 0.1 m Slab on Grade with 0.9 m deep 0.3 m thick Beams every 4 m $24,000 Smart Foundation 16 m 16 m 0.1 m Slab on Grade with 0.9 m deep 0.3 m thick Beams every 4 m and 1 m 1 m 0.3 m Footings $26,200 ~ 10 % Increase in Cost

41 SMART FOUNDATION ADJUSTMENT Shrinking Excavation Jack up Front View of Jack up Replace Spacer Finish Back Fill 1ft

42 FOUNDATION ANALYSIS BY SAFE Edge drop case beam moment distribution

43 FOUNDATION ANALYSIS BY SAFE Edge drop case + jacking beam moment distribution jacking

44 CONCLUSIONS FUNDAMENTAL BEHAVIOR SHRINK TEST WATER CONTENT METHOD PROPOSED SHRINK TEST WATER CONTENT METHOD VERIFIED SMART FOUNDATIONS = ADJUSTABLE SOLUTION

DISTRIBUTION OF EXPANSIVE SOILS

HOW TO DESIGN? DISTRIBUTION OF EXPANSIVE SOILS WIDE VARIETY OF CLIMATE SAME SOIL -- DIFFERENT CLIMATE RESIDENCE COMPLICATIONS DESIGN NEEDS ENVELOPES EDGE LIFT EDGE DRYING DESIGN AIDS SOIL MOVEMENT SOIL