SLOPE STABILITY

By :

Yulinda Sari, ST. M.Eng.

Assessment of Slope Stability

Simple methods

e.g Infinite slope, linear failure plane, circular plane, wedge failure plane

Use of Charts e.g Taylor’chart

Assessment of Slope Stability

Slices methods e.g. ordinary, bishop, janbu,

morgenstein & price

Introduction to computer programs e.g. Slope/w, Stabl etc.

METHODS OF ANALYSIS

After defining the shape and location of the failure surface, the limit equilibrium methods can be applied for slope stability analysis by imposing several assumptions i.e:

(1)The failure occurs in two-dimension,

(2) Rigid block movement taking place on the failure surface itself, and

(3) Uniform shear stress is mobilized over the whole length of the failure surface

In general, there are two methods of limit equilibrium analysis i.e.:

1.Linear methods which is relatively simple, and

2.The Non-linear methods or Method of Slices

In limit equilibrium method, the shear strength at the time of failure is f compared to the

stress mobilized at that plane m.

Then the factor of safety is :

SIMPLE METHODS Infinite Slope Analysis

FORMULA 

SIMPLE METHODS Finite Slope with Linear Failure plane

FORMULA 

SIMPLE METHODS 

Finite Slope with Circular Failure plane

Slope in Homogeneous Cohesive soil (= 0 Analysis)

FORMULA 

USE OF CHARTS

There are many charts available for evaluating the factor of safety of a slope, each based on various assumptions and specific use. The most popular one is the Taylor’s stability number which will be discussed in the following. Other charts include the Janbu stability charts for slope in cohesive soils, Morgenstein graphs for rapid drawdown in dam, the Bischop and Morgenstain charts for effective stress analysis, and many others.

Taylor’s chart (Figure 5.8) can be used to evaluate the stability of slope in a homogeneous cohesive soil with a hard stratum at depth of ndH

from the surface of the slope. The factor of safety can be calculated as:

Where Ns is the Taylor’s stability number obtained from the chart.

METHOD OF SLICES

FORMULA As shown in the Figure, the forces acting on slice i are:

1.The total weight of the slice, W = bhi

2.The total normal force on the base: the effective normal force N’ = ’li and the boundary water force U = li. where

is the pore water pressure at the center of the base and l is the length of the base3.The shear force on the base, T = m li4.The total normal forces on the sides, Ei and Ei-1

5.The shear forces on the sides, Xi and Xi-1

6.Any external forces working on the slope must be included in the analysis.

FORMULA 

Bischop (Routine) Method

Bischop assumed that the resultant of vertical inter-slice forces (Xi –Xi-1) is equal to zero, but the sum of the horizontal inter-slice force (Ei-Ei-1) is not zero. Then T is not equal to the soil resistance at the base of the slices

CONTOH SOAL

PENYELESAIAN CONTOH SOAL

PENYELESAIAN CONTOH SOAL

COMPUTER PROGRAM

GEO-SLOPE

● SLOPE/W for slope stability analysis

● SEEP/W for finite element seepage analysis

● CTRAN/W for finite element contaminant transport analysis

● SIGMA/W for finite element stress and deformation analysis

● TEMP/W for finite element geothermal analysis

● QUAKE/W for finite element dynamic stress and deformation analysis

GEO-SLOPE provides the following suite of geotechnical and geo-environmental engineering software products :

SLOPE/W

SLOPE/W is a software product that uses limit equilibrium theory to compute the factor of safety of earth and rock slopes.

The comprehensive formulation of SLOPE/W makes it possible to easily analyze both simple and complex slope stability problems using a variety of methods to calculate the factor of safety.

SLOPE/W has application in the analysis and design for geotechnical, civil, and mining engineering projects.

SLOPE/W is a 32-bit, graphical software product that operates under Microsoft Windows.

The common "look and feel" of Windows applications makes it easy to learn how to use SLOPE/W, especially if you are already familiar with the Windows environment.

SLOPE/W

C A S E

LANDSLIDE ANALYSIS AT OUTSIDE DUMPING AREA AIR LAYA COAL MINING SITE, TANJUNG ENIM

The Incident on November 27th, 2002

Landslide Consequences : No Sacrifice / victim Fall down of 1 electrical tower PLN Damaged MCP (KPL 701) & Dikes Destroyed Agriculture Land

LANDSLIDE SITUATION

Landslide Occured = November 27th, 2002Influenced area = 72 HaVolume of soils removed = 690.000 bcmMax. movement velocity = 72 cm/jam

Fall Down Tower

Eni

m ri

ver

Tensio

n Cra

ck

Damaged Mud Collection Pond (KPL 701)

DESCRIPTION OF SITE

Dumping Area = 650 HaLandslide Area = 72 HaBefore landslide : High Slope = 60 m Angle Slope= 15ºAfter landslide : High Slope = 48 mGeological Structure : - unsymetrical anticline - symetrical syncline - no faultDumping Soil : - sandy silt and sand/silty clay - very low cohesion, wet, and loose

GROUND INVESTIGATIONPOSITION OF BORE HOLES

Failure Area

DikeMud Collection Pond

Tower

Eni

m R

iver

Point of Failure Start (BH.SP08)

ANALYSIS OF SLOPE ANALYSIS OF SLOPE STABILITYSTABILITY

NUMERICAL SIMULATION (SLOPE/W)NUMERICAL SIMULATION (SLOPE/W)

Before Failure

At Failure

SF = 2.43

SF = 0.495

LANDSLIDE MECHANISM

Moving Mass

Seepage

River

Run off

Weak Layer

CRACK

FAILURE OCCURED

FAILURE MECHANISM

Infiltration

Moving Mass

Seepage

River

Run off

Weak Layer

CRACK

STARTING FAILURE

CONCLUSIONCONCLUSION

Landslide Occurred because : :

Develop. of Tension Crack at the Fill Surface Develop. of Tension Crack at the Fill Surface

Soil Strength decrease (same with the Interface Soil Strength decrease (same with the Interface Layer)Layer)

The Prolonged and Heavy Rainfall The Prolonged and Heavy Rainfall It resulted in It resulted in

significant water ingress into the ground that significant water ingress into the ground that triggered triggered

the mass movementthe mass movement