1. GEOTECHNICAL ENGINEERING ECG 503 LECTURE NOTE 07 TOPIC : 3
GEOTECHNICAL ENGINEERING ECG 503 LECTURE NOTE 07 TOPIC : 3.0 ANALYSIS AND DESIGN OF RETAINING STRUCTURES

2. LEARNING OUTCOMES Learning outcomes:
At the end of this lecture/week the students would be able to:
Understand natural slope and made engineered soil slope assessment which include rainfall induced failure and role of suction.

3. Types of Retaining Structures
TOPIC TO BE COVERED
Types of Retaining Structures
Sheet Pile Wall – Cantilever and Anchored Sheet Pile

4. 2.1 Introduction and overview
LATERAL EARTH PRESSURE
Introduction & Overview
2.1 Introduction and overview
Retaining structures such as retaining walls, basement walls, and bulkheads are commonly encountered in foundation engineering, and they may support slopes of earth mass.
Proper design and construction of these structures require a thorough knowledge of the lateral forces that act between the retaining structures and the soil mass being retained.

5. Retaining walls are used to prevent the retained material from assuming its natural slope. Wall structures are commonly use to support earth are piles. Retaining walls may be classified according to how they produce stability as reinforced earth, gravity wall, cantilever wall and anchored wall. At present, the reinforced earth structure is the most used particularly for roadwork

6. 3 basic components of retaining structure
Facing unit – not necessary but usually used to maintain appearance and avoid soil erosion between the reinforces.
Reinforcement – strips or rods of metal, strips or sheets of geotextiles, wire grids, or chain link fence or geogrids fastened to the facing unit and extending into the backfill some distance.
The earth fill – usually select granular material with than 15% passing the no. 200 sieve.

7. Component of E.R. Wall

8. Retaining Wall EARTH RETAINING STRUCTURES Types of Retaining Wall
The various types of earth-retaining structures fall into three broad groups.
Gravity Walls
Embedded walls
Reinforced and anchored earth

9. Masonry walls EARTH RETAINING STRUCTURES Gravity Walls Gravity Walls
Gabion walls
Crib walls
RC walls
Counterfort walls
Buttressed walls

10. EARTH RETAINING STRUCTURES
Gravity Walls
Unreinforced masonry wall

11. EARTH RETAINING STRUCTURES
Gravity Walls
Gabion wall

12. EARTH RETAINING STRUCTURES
Gravity Walls
Crib wall

13. Types of RC Gravity Walls
EARTH RETAINING STRUCTURES
Gravity Walls
Types of RC Gravity Walls

14. EARTH RETAINING STRUCTURES
Embedded Walls
Embedded walls
Driven sheet-pile walls
Braced or propped walls
Contiguous bored-pile walls
Secant bored-pile walls
Diaphram walls

15. Types of embedded walls
EARTH RETAINING STRUCTURES
Embedded Walls
Types of embedded walls

16. EARTH RETAINING STRUCTURES
Reinforced and Anchored Earth
Reinforced and anchored earth
Reinforced earth wall
Soil nailing
Ground anchors

17. Reinforced earth and soil nailing
EARTH RETAINING STRUCTURES
Reinforced and anchored earth
Reinforced earth and soil nailing

20. Stability of Rigid Walls
EARTH RETAINING STRUCTURES
Stability Criteria
Stability of Rigid Walls
Failures of the rigid gravity wall may occur due to any of the followings:
Overturning failure
Sliding failure
Bearing capacity failure
Tension failure in joints
Rotational slip failure
In designing the structures at least the first three of the design criteria must be analysed and satisfied.

21. States of Equilibrium Hydrostatic Pressure and Lateral Thrust
LATERAL EARTH PRESSURE
Types of Lateral Pressure
States of Equilibrium
Hydrostatic Pressure and Lateral Thrust
Earth Pressure at Rest
Active Earth Pressure
Passive Earth pressure

22. Horizontal pressure due to a liquid
LATERAL EARTH PRESSURE
Types of Lateral Pressure
Hydrostatic pressure and lateral thrust
Horizontal pressure due to a liquid

23. Earth pressure at rest LATERAL EARTH PRESSURE Earth Pressure at Rest Az σv
σh = Ko σv A B
If wall AB remains static – soil mass will be in a state of elastic equilibrium – horizontal strain is zero.
Ratio of horizontal stress to vertical stress is called coefficient of earth pressure at rest, Ko, or
Unit weight of soil = γ

24. LATERAL EARTH PRESSURE
Earth Pressure at Rest
Earth pressure at rest .. cont.

25. Active earth pressure LATERAL EARTH PRESSURE Active Earth Pressure A
Plastic equilibrium in soil refers to the condition where every point in a soil mass is on the verge of failure.
If wall AB is allowed to move away from the soil mass gradually, horizontal stress will decrease.
This is represented by Mohr’s circle in the subsequent slide.
Unit weight of soil = γ z σv σh B
Earth pressure at rest

26. σz σX = Ko σz σz σx’A ACTIVE EARTH PRESSURE (RANKINE’S)
(in simple stress field for c=0 soil) – Fig. 1 σz
σX = Ko σz ø
Ko σz σz
σx’A

28. LATERAL EARTH PRESSURE
Active Earth Pressure
Based on the diagram :
(Ka is the ratio of the effective stresses)
Therefore :
It can be shown that :

29. Active pressure distribution
LATERAL EARTH PRESSURE
Active Earth Pressure
Active pressure distribution z zo

30. LATERAL EARTH PRESSURE
Active Earth Pressure
Active pressure distribution
Based on the previous slide, using similar triangles show that :
where zo is depth of tension crack
For pure cohesive soil, i.e. when  = 0 :

31. Active pressure distribution
LATERAL EARTH PRESSURE
Active Earth Pressure
Active pressure distribution z
For cohesionless soil, c = 0

32. 2.2.4 Passive earth pressure
LATERAL EARTH PRESSURE
Passive Earth Pressure
Passive earth pressure A
If the wall is pushed into the soil mass, the principal stress σh will increase. On the verge of failure the stress condition on the soil element can be expressed by Mohr’s circle b.
The lateral earth pressure, σp, which is the major principal stress, is called Rankine’s passive earth pressure
Unit weight of soil = γ z σv σh B
Earth pressure at rest

33. σz σX = Ko σz σz σx’P PASSIVE EARTH PRESSURE (RANKINE’S)
(in simple stress field for c=0 soil) – Fig. 2 σz
σX = Ko σz ø
Ko σz σz
σx’P

35. Mohr’s circle representing Rankine’s passive state.
LATERAL EARTH PRESSURE
Passive Earth Pressure
Shear stress
Normal stress C D D’ O A σp
Koσv b a σv c
Mohr’s circle representing Rankine’s passive state.

36. LATERAL EARTH PRESSURE
Passive Earth Pressure
Referring to previous slide, it can be shown that :
For cohesionless soil :

37. Passive pressure distribution
LATERAL EARTH PRESSURE
Passive Earth Pressure
Passive pressure distribution z
For cohesionless soil,

38. LATERAL EARTH PRESSURE
Passive pressure
At-rest pressure
Active pressure
Earth Pressure
Wall tilt
In conclusion
Wall tilt

39. Rankine’s Theory LATERAL EARTH PRESSURE Types of Lateral Pressure
Initial work done in 1857
Develop based on semi infinite “loose granular” soil mass for which the soil movement is uniform.
Used stress states of soil mass to determine lateral pressures on a frictionless wall
Assumptions :
Vertical frictionless wall
Dry homogeneous soil
Horizontal surface

40. LATERAL EARTH PRESSURE
Types of Lateral Pressure
Active pressure for cohesionless soil

41. Effect of a stratified soil
LATERAL EARTH PRESSURE
Types of Lateral Pressure
Effect of surcharge
Effect of a stratified soil

42. LATERAL EARTH PRESSURE
Types of Lateral Pressure
Effect of sloping surface

43. LATERAL EARTH PRESSURE
Types of Lateral Pressure
Active pressure,
Passive pressure,
where
and

44. LATERAL EARTH PRESSURE
Types of Lateral Pressure
Tension cracks in cohesive soils

45. LATERAL EARTH PRESSURE
Types of Lateral Pressure
Effect of surcharge (undrained)

46. LATERAL EARTH PRESSURE
Types of Lateral Pressure
Passive resistance in undrained clay

47. LATERAL EARTH PRESSURE
Stability Criteria
The stability of the retaining wall should be checked against :
FOS against overturning (recommended FOS = 2.0)
(ii) FOS against sliding (recommended FOS = 2.0)

48. LATERAL EARTH PRESSURE
Stability Analysis
The stability of the retaining wall should be checked against :
FOS against overturning (recommended FOS = 2.0) Ph
∑ V A Pp
.. overturning about A

49. Friction & wall base adhesion
LATERAL EARTH PRESSURE
Stability Criteria
FOS against sliding (recommended FOS = 2.0) Ph
∑ V Pp
Friction & wall base adhesion

50. LATERAL EARTH PRESSURE
Stability Criteria
For base pressure (to be compared against the bearing capacity of the founding soil. Recommended FOS = 3.0)
Now, Lever arm of base resultant
Thus eccentricity

51. Base pressure on the founding soil
LATERAL EARTH PRESSURE
Stability Analysis Pp Ph
∑ V
Base pressure on the founding soil

52. LATERAL EARTH PRESSURE
Stability Analysis
Worked example :
Figure below shows the cross-section of a reinforced concrete retaining structure. The retained soil behind the structure and the soil in front of it are cohesionless and has the following properties:
SOIL 1 : u = 35o, d = 17 kN/m3,
SOIL 2 : u = 30o,  = 25o , d = 18 kN/m3,
sat = 20 kN/m3
The unit weight of concrete is 24 kN/m3. Taking into account the passive resistance in front of the wall, determine a minimum value for the width of the wall to satisfy the following design criteria:
Factor of safety against overturning > 2.5
Factor of safety against sliding > 1.5
Maximum base pressure should not exceed 150 kPa

53. LATERAL EARTH PRESSURE
Stability Analysis
THE PROBLEM
SOIL 2
2.0 m
0.5 m
0.6 m
2.9 m
GWT
4.5 m
SOIL 1
30 kN/m2
4.0 m

54. LATERAL EARTH PRESSURE
Stability Analysis P1 P3
SOIL 2
2.0 m
0.5 m
0.6 m
2.9 m
GWT
4.5 m
SOIL 1
30 kN/m2
4.0 m P2 P4 PP
W41 W3 W2 W1 P5
THE SOLUTION P6

55. LATERAL EARTH PRESSURE
Stability Analysis
Determination of the Earth Pressure Coefficients

56. LATERAL EARTH PRESSURE
Stability Analysis

57. LATERAL EARTH PRESSURE
Stability Analysis
To check for stability of the retaining wall
FOS against overturning
> 2.5
(ii) FOS against sliding > 1.5
Thus it is not OK

58. LATERAL EARTH PRESSURE
Stability Analysis
(iii) For base pressure
Now, Lever arm of base resultant
Thus eccentricity
Therefore

59. LATERAL EARTH PRESSURE
Stability Analysis
qb = and kPa
Since maximum base pressure is less than the bearing pressure of the soil, the foundation is stable against base pressure failure.
DISTRIBUTION OF BASE PRESSURE
80.5 kPa
120.8 kPa
In conclusion the retaining wall is not safe against sliding. To overcome this the width of the base may be increased or a key constructed at the toe.

60. Group assignment NO. 1:
Form a group of 6 members in each group. Your task is to write up a case study which involve a dam case failure in Malaysia and a slope failure in Malaysia. Your report shall consists of the history of each case, as examples; amount of dam in Malaysia, their purpose, operation, etc.
Make sure your case study are not the same as others groups. Penalties will be given accordingly for those who ignore the warnings.
Date of submission :

61. Group assignment NO. 2:
Form a group of 6 members in each group. Your task is to write up a case study which involve a ground improvement technique. Your shall selected a real project which will consists of real soil problems and technique to overcome the problems.
Make sure your case study are not the same as others groups. Penalties will be given accordingly for those who ignore the warnings.
Date of submission :