METHOD OF SLICES YULVI ZAIKA LEARNING OUTCOMES SLOPE

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

STABILITY DIAGRAM FOR COHESIVE SOIL AND >53 O High of slopes Z=depth of hard layer Hard layer

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

THE SLICED METHOD YULVI 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

FORMULATION •

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