Soil Mechanic for Unsaturated soil- MTech Lec09.pptx

Soil mechanics;
Unsaturated soil;
Stress state variables;
Flow rules;
Steady state flow;
shear strength theory;
Volume change theory;
Volume change indices;
1 D Consolidation;
Plastic Equilibrium;
Limit equilibrium;
2 & 3 D Steady state flow;

1. SOIL MECHANICS FOR NSATURATED SOILS Prof. Samirsinh P Parmar Mail: [email protected] Asst . Professor, Department of Civil Engineering, Faculty of Technology, Dharmsinh Desai University, Nadiad-387001 Gujarat, INDIA

2. P u b l i s h ed b y J o hn W il e y & S o ns , 1 993

3. Soil Mechanics for Unsaturate d Soils TABL E OF C O NTENTS Chapter 1 2 3 4 5 6 7 8 9 I ntroduction t o Unsaturate d Soi l Mechanics Phas e Propertie s an d Relati o n s Stres s Stat e Varia b les Measuremen t o f Soi l Suction F low Laws Measuremen t o f Permeability Stead y Stat e Fl ow Por e Pressur e Parameters Sh e a r Strengt h Th e ory 10 11 Measuremen t o f Shea r Strengt h Parameters Plastic and Limit Equilibrium 12 Volum e Chang e Theory 13 Measuremen t o f Volum e Chang e Indices 14 15 16 Volum e Chang e Predic t ions One-dimensional Consolidatio n an d Swelling Two - an d Three-dimensional Unstead y - stat e Flow an d Non-isot h erma l Analyses Estimations o f --- Estimations o f --- Estimations o f ---

4. Note s a t the botto m o f eac h PowerPoint Slide Notes: Different approaches could be taken towards synthesizing the material on the behavior of un s aturated soil mechanics. The approach deemed most desirable w a s to maintain a relatively close parallel to classic a l saturated soil mechanics. The emphasis was not focused solely on “problematic soils”, but rather on the areas of seepag e , shear strength and volume change of all soils with negative pore-water pressures. The prepared notes closely follow the material in the textbook. Additional notes have been prep a red on new and important subjects that have emerged during the years subsequent to 1993. The textbook appears to have f i lled an important role in centralizing our understanding of the behavior of unsaturated soils from the standpoint of two independent stress state variables .

5. Forma t Fo r Eac h Constitutiv e Behavior Constitutive Relationship (e.g. , seepage, shea r strength , volum e change) Theor y associate d with the Constitutive Relationship Measuremen t of th e associate d unsaturated soi l properties Estimation of th e unsaturated soi l property function s (throug h use of SWCC) Applicatio n of the constitutiv e relationship t o practical engineerin g problems

6. Important Objective of This Course To teach Geotechnical Engineers to think the way the Unsaturate d Soil behaves Th e Physics mus t be correct Many behavioral aspects related to Unsaturate d S o ils are the opposite to saturated soil behavior (e.g. , hydraulic conductivity of sands capillary barriers)

7. Categorizatio n o f Soi l Mechanics

8. CATEGORIES OF UNSATURATED SOIL MECHANICS PROBLEMS Based on Constitutive Behaviour

9. CLIMATI C CHARACTERISTICS Couple d mass- transport & thermal analysis Moistur e flux i s a n aspect originally omitte d from Soil Mechanics

10. CAPILLAR Y FLOW PHENOMENA Water Table

11. EXAMPLES OF PROBLEMS REQUIRING AN UNDER- STANDING OF UNSATURA T ED S O IL M E CHANICS an d R a pid Drawdown Compacted Soils Infiltration

12. Bernatzik , 1948 Problematic Soils

13. Water phase ENVIRONMENTAL EFFECTS DURIN G THE OPERATION OF THE RESERVOIR SOME RELEVANT QUESTIONS MIGHT BE ASKED AS STEADY STATE CONDITIONS ARE ESTABLISHED ?

14. SOME RELEVANT QUESTIONS THAT MI G HT BE ASKED ARE REFERRED TO THE STABILITY OF THE EXCAVATION SLOPES ? STABILITY O F VERTICA L OR NEA R VERTICAL EXCAVATIONS Cove r of som e type

15. SOME RELEVANT QUESTIONS MIGHT BE ASKED PER T A I N I NG TO LAT E RAL EARTH PRESSURES ? LATERAL EARTH PRESSURES Effect of a membrane?

16. ? LATERAL EARTH PRESSURES AGAINS T WALLS

17. IS THERE A NEE D FOR UNSATURATED SOIL MECHANICS? YES! The Geotechnical Engineer has the greates t potentia l to assist the public in circumventin g problems associate d with Unsaturated Soils Concern for the environment a n d advances in computing power greatly assisted in the promotion of Unsaturate d Soil Mechanics

18. AN UNSATURATED S O IL ELEMENT WITH A CONT I N U OU S A I R PHASE

19. TERMINOLOGY AN D DEFINITIONS

20. Categorizatio n o f Soi l Mechanics Base d o n Stres s Stat e Variables S a t u r a t e d S (  - u w ) Effective stress Positive pore-water pressures oil M e c h a n i c s Negativ e pore-water pressures Matric suction ( u a - u w ) Ne t norma l stress (  - u a ) Visualization of the World of Saturated- Unsaturated Soil Mechanics

21. (  z - u a ) (  y - u a ) (u a - u w ) (u a - u w )  zx  zy  xz  x y  yz  yx U n s a t e d S o e n i c s S a t a t c s S o i l h a n i c h r u a a t c e d r u  zy (  z - u w ) (  y - u w )  zx  xz (  x - u w )  xy  yz  yx (u a - u w ) i l M M e Stress State a t a Poin t in an Unsaturate d Soil an d in a Saturate d Soil (  x - u a )

22. Summar y of the description of the Stress State fo r an Unsaturated Soil Elemen t with the Preferred Stress State Variables

23. Stres s Stat e Variable s (Unsaturate d Soils) Ne t Total Stress Tensor    x  u a   yx  x y   y  u a   zy  x z  yz 0 0  u a  u w  0 0   z  u a     zx          u a  u w   u a  u w           Stress Tensors form th e basis for a Science becaus e we live in a 3-D Cartesian coordinate world Matric Suctio n Stress Tensor

24. Variations in Stress State Description  ’ = (  – u a ) +  ( u a – u w )  ’ = effective stress  = parameter relate d to saturation  * i j =  ij – [ S u w + ( 1 – S) u a ]  ij  ij  ij = total stres s tensor, = Kroneke r delta or substitutio n tensor,  * ij = Bishop’ s soi l skeleto n stres s (Jommi 2000) S = degree of saturation Abov e propose d equation s ar e constitutiv e relations

25. Separatio n o f th e Zone s abov e th e Wate r Table Unsaturate d Soil Dr y s o il Two fluid phases Capillar y fringe Legend Solids Wa ter Air Saturate d Soil Occluded ai r bubbles

26. Constitutive Relations for Classic Problems in Unsaturate d Soils Mechanics  Empirical , semi-empirica l an d theoretical relationship s ar e proposed an d verified Volume change (Stress versu s Strain) Shear strength (Stress versu s Stress) Flow (Velocity versu s Stress)  Demandin g laboratory experiments - Careful experi m ents requir e d for uniqueness studies - Ma y alte r tes t procedures fo r economi c reaso n s

27. Unsaturated Soil Seepage Volume change Shear strength v = k (- u ) ∂ h / ∂ y w w Saturated Soil v = k w dh/dy where : h = u w /  w + Y v = k ∂ h / ∂ y w  = c’ + ( σ - u ) t a n φ ’ n a + ( u - u ) t a n φ b a w   = c ’ + (  n – u w ) tan  ’ = c’ + ( σ - u ) t a n φ ’ n w de = a d ( σ - u ) + 1 a a d ( u - u ) 2 a w de = a d ( σ - u ) v w v = k w (- u w ) dh/dy  = c ’ + (  – u ) tan  ’ n a + (u a – u w ) tan  b de = a v d (  – u w ) d e = a d (  – u ) + 1 a a 2 d(u a – u ) w Fundamentals of Soil Mechanics in One Diagram Constitutive Relations for Saturated/Unsaturated Soil Mechanics

28. Selected Readin g Materials Fredlund, D.G . (2000) . “Th e 199 9 R.M . Hard y Lecture: The Implementation of Unsatura t e d Soil Mechanics into Geotechnical Engineering”, Can a dian Geotec h n ical Journal, 3 7 (5) , 963-986 Fredlund, D.G . (2002) . “Us e of the Soil-Wate r Characteristic Curv e in the Implementation of Unsaturate d Soil Mechanics”, Keynote Address, March 10-1 3 ,UNSAT 2002 , Recife , Brazil, Vol . 3. Ha , T.V. Pham , an d Fredlund, D . G. (2002) . “Th e Application of Dynami c Programming to Slope Stability Analysis” , Canadian Geotechnical Journal , pp. 830-847. Gitirana , G ilson , an d Fredlund , D . G. , (2003) . “From Experimental Evidence Towards the Assessmen t of Weather- Related Railwa y Emba n kmen t Hazards " Proc . Of the Conf . on “ From Experimental Evidence Towards Numerical Modelling of Unsaturated Soils ” , Sept . 18-19.

29. Revie w of Procedur e Typical to Saturate d Soi l Mechanics 1. ) Define geometry of t h e problem (Surface & Sratigraphy) 2. ) Determin e pore-wate r pressures 3. ) Determin e the soi l parameter s (c ’ &  ’) 4. ) Us e analysis to incorporate tota l stresses Pore-wate r pressures mus t be assessed beca u s e behavior is controlled by (  – u w )

30. Additiona l Features to Accommodate Rainfal l Induced Landslides Slop e mus t b e visualize d a s a transient analysi s on a saturated-unsaturate d soi l profile Unsaturate d soi l has water storag e capabilities Unsaturate d soi l ha s highl y varyin g coefficien t of permeabilit y an d infiltration conditions Shea r strengt h of th e unsaturated soi l mus t be take n into account Actua l (or real-time ) flux moistur e condition s (i.e., rainfall ) mus t be take n into account Calculatio n of facto r of safet y mus t accoun t for unsaturated soi l behavior

31. Analysi s Ca n B e Viewed as a Combination of the Following Elements of Physics Saturated-unsaturated seepage analysis (Permeabilit y an d Storage) Stress analysis for the shea r and normal forces (Metho d o f Slice s o r Stress Analysis) Shear strength evaluatio n of the unsaturated soil (angl e  b ) Evaluatio n of surfac e moistur e flux condition s (Percentage of k sa t ) Calculatio n of factor of safety, F s

32. RELEVANT QUESTIONS? ? NATURAL SLOPES SUBJECTED TO ENVIRO N MENTAL CHANGES

33. Initial stead y stat e conditions 208 mm / yea r = 6. 6 x 1 -8 m/s Quite an extrem e condition

34. Initial stead y stat e conditions along Section X - X 23 kPa 40 kPa

35. Afte r 12 minutes Flux = 1. 3 x 1 -5 m / s

36. Afte r 48 minutes When th e rain stops Flu x = 0.0

37. Afte r 108 minutes

38. Heav y rainfal l creates a wetting front

39. Rain stops Regain of strength Loss of strength 50 % of  ’

40. Thank you..!