METHOD OF SLICES YULVI ZAIKA

LEARNING OUTCOMES

• SLOPE STABILITY BASED ON TAYLOR DIAGRAM

• BASIC THEORY OF SLICE OF SLOPES

• CALCULATION OF SAFETY FACTOR

TAYLOR DIAGRAM FOR COHESION SOIL( = 0)

-

Nd = stability number

Because than

STABILITY DIAGRAM FOR COHESIVE SOIL AND >53O

𝐷=h𝐷𝑒𝑝𝑡 𝑜𝑓 h𝑎𝑟𝑑 𝑙𝑎𝑦𝑒𝑟

h h𝑖𝑔 𝑜𝑓 𝑠𝑙𝑜𝑝𝑒𝑠

Hard layer

Z=depth of hard layer

High of slopes

SLOPES STABILITY FOR COHESION LESSSOIL; >0 (TAYLOR, 1948)

THE SLICED METHODYULVI ZAIKA

SLICED METHOD

• THIS METHOD CAN BE USED FOR SOIL IN DIFFERENT SHEARING RESISTANCE ALONG THE FAILURE PLANE

• PROPOSED BY FELLENIUS ,BISHOP, JANBU, ETC

• ASSUMED CIRCULAR FAILURE PLANE

REGULATION OF SLICES

1. SLICED PERFORMED VERTICAL DIRECTION

2. THE WIDTH OF THE SLICE DOES NOT HAVE THE SAME MEASUREMENT

3. ONE SLICE MUST HAVE ONE TYPE OF SOIL IN THE FAILURE SURFACE

4. THE WIDTH OF THE SLICE MUST BE SUCH THAT THE CURVE (FAILURE PLANE) CAN BE CONSIDERED A STRAIGHT LINE

5. THE TOTAL WEIGHT OF SOIL IN A SLICE IS THE SOIL WEDGE ITSELF, INCLUDING WATER AND EXTERNAL LOAD

FELLENIUS (ORDINARY) METHOD OF SLICES

• FIRSTLY IT IS ASSUMED THAT THE SIDE FORCES T AND E MAY BE NEGLECTED

AND SECONDLY, THAT THE NORMAL FORCE N, MAY BE DETERMINED SIMPLY BY

RESOLVING THE WEIGHT W OF THE SLICE IN A DIRECTION NORMAL TO THE

ARC, AT THE MID POINT OF THE SLICE

• WHERE IS THE ANGLE OF INCLINATION OF THE POTENTIAL FAILURE ARC TO

THE HORIZONTAL AT THE MID POINT OF THE SLICE

• THE DRIVING FORCE IS

FORMULATION

• IF SUBMERGED.

• WHERE:

STEP BY STEP PROCEDURE

1. DRAW CROSS-SECTION TO NATURAL SCALE

2. SELECT FAILURE SURFACE

3. DIVIDE THE FAILURE MASS INTO SOME SLICES

4. COMPUTE TOTAL WEIGHT ( WT ) OF EACH SLICE

5. COMPUTE FRICTIONAL RESISTING FORCE FOR EACH SLICE N TANΦ – UL

6. COMPUTE COHESIVE RESISTING FORCE FOR EACH SLICE CL

7. COMPUTE TANGENTIAL DRIVING FORCE (T) FOR EACH SLICE

8. SUM RESISTING AND DRIVING FORCES FOR ALL SLICES AND COMPUTE FS

BISHOP METHOD- Also known as Simplified Bishop method

- Includes interslice normal forces

- Neglects interslice shear forces

- Satisfies only moment equilibrium

3. Simplified Bishop Method

RECOMMENDED STABILITY METHODS

• ORDINARY METHOD OF SLICES (OMS) IGNORES BOTH SHEAR AND NORMAL INTERSLICE FORCES AND ONLY MOMENT EQUILIBRIUM

• BISHOP METHOD- ALSO KNOWN AS SIMPLIFIED BISHOP METHOD- INCLUDES INTERSLICE NORMAL FORCES- NEGLECTS INTERSLICE SHEAR FORCES- SATISFIES ONLY MOMENT EQUILIBRIUM

OTHERS

• SIMPLIFIED JANBU METHOD- INCLUDES INTERSLICE NORMAL FORCES- NEGLECTS INTERSLICE SHEAR FORCES- SATISFIES ONLY HORIZONTAL FORCE EQUILIBRIUM

• SPENCER METHOD- INCLUDES BOTH NORMAL AND SHEAR INTERSLICE FORCES- CONSIDERS MOMENT EQUILIBRIUM- MORE ACCURATE THAN OTHER METHODS

RECOMMENDED STABILITY METHODS

OMS IS CONSERVATIVE AND GIVES UNREALISTICALLY LOWER FS THAN BISHOP OR OTHER REFINED METHODS

FOR PURELY COHESIVE SOILS, OMS AND BISHOP METHOD GIVE IDENTICAL RESULTS

FOR FRICTIONAL SOILS, BISHOP METHOD SHOULD BE USED AS A MINIMUM

RECOMMENDATION: USE BISHOP, SIMPLIFIED JANBU OR SPENCER

REMARKS ON SAFETY FACTOR

USE FS = 1.3 TO 1.5 FOR CRITICAL SLOPES SUCH AS END SLOPES UNDER ABUTMENTS, SLOPES

• CONTAINING FOOTINGS, MAJOR RETAINING STRUCTURES

USE FS = 1.5 FOR CUT SLOPES IN FINE-GRAINED SOILS WHICH CAN LOSE STRENGTH WITH TIME