Abdul Rahman bin HilmiSCM 010-4127/4/2015Shear Strength Analysis on Slope FailureThe shear strength of a soil mass is defined as the magnitude of the shear stress that a soil can sustain. (Wikipedia)The shear strength is defined by the Mohr-Coulomb failure envelope:

Introduction Project Background

Slope Failure Info & StatisticsA research by JKR indicated that from 322 failed slopes, 89% are cut slopes & only 1% are natural slopes.In Slope Design Guideline by JKR stated that human factor attributed to 57% of failed slopes & only 14% are due to geological factor.Ir. Neoh (2001) stated that slope failure eventually occurs if the shearing resistance is equal to or less than the shearing force. (Practical Design Aspects for Slopes in Mountainous Terrains)Higgins & Potts (2004) mentioned that slope failure is often progressive, it does not occur simultaneously at all points of the slope involved in rupture (The Skempton Conference, Vol. 2, pg.1009)

Landview of Slope FailureView from the toe up vertically

Main factor of failure excess rainwater infiltration due to poor drainage system maintenancePalm oil plantation sits on slope head, rainwater eroded the topsoil into the drain. The drainage became heavily silted the drain became effectively shallower than designed depth. Growth of excess vegetation causes obstruction to water flow they trap water and reduce water flow Consequence - Draining capacity is significantly reduced.Problem Statement

Thick soil and excess vegetation in major part of the drainage system

slope head V-drainmid slope V-drain main drain - cascadeRain overflowing from the drain infiltrated the slope head thus causing the toe to saturate, increasing moisture content reducing toe strength.Pore water pressure is increased reducing strength.Krystina, Lenka & Pavla (2013) indicated in their research - shear strength of soils is highly affected by moisture conditions, especially if the soil contains clay materials.Finally, the shearing force from slope weight > shearing resistance of slope materials = landslideType of failure Flow (Department of Geotech, UTM)Currently, slope rectification work is halted, but necessary tests have been done To identify the basic soil properties at the selected locationTo determine and compare the shear strength of non-failure and failed slopeTo evaluate the accuracy of laboratory experiment by comparing the results obtained in the laboratory to the one obtained in professional field test.

Research ObjectivesLITERATURE REVIEWShear Strength Parameters From Previous StudiesA landslide study in Simpang Pulai-Lojing Highway done by Andrew Malone (2007) revealed that friction angle of landslide weak sample was 23 and the sample from strong sample was 42In a study in USM, Damanhuri, Fauziah & Roslan (2014) obtained 229 shear strength parameters from 29 failed slopes and 35 parameters from 10 stable slopes around Penang,

minimum value of effective friction angle = 23.2Soil TypeParametersRange for Failed SlopeRange of Stable SlopeResidual soilsC (kN/m 2)0.20-36.200.20-59.40. 3.20-44.408.60-65.80Effect of Sampling Disturbance to Lab Test Soil Properties

Gilbert (1992) stated in his research paper that Undrained shear strength increases as disturbance in soil samples decreases. Depending on the degree of disturbance in the clay involved, undrained shear strength can be 50 percent less in disturbed tube samples.Robert Day (1980) in his soil testing manual stated that Sample disturbance can cause the greatest reduction in shear strength of any other factor.Direct Shear Test is used because the triaxial test equipment is currently not working.Undisturbed sample would require the use of dedicated tools i.e. borehole which is currently not available, thus undisturbed sample will be used.

Research ConstraintsCollect soil samples at 2 sites failed slope and non-failure slope besides it. Hoe and hand shovel will be used.6 samples of 2 kg each will be collected on each slope 3 near slope head, 3 near slope toe at depth of 1 meter. Total of 12 samples.Keep samples in labelled plastic bags.Atterberg limit test to classify soil Direct Shear test to determine shear strength

Research MethodologyProject MethodologyObtain 6 samples each from failed & normal slopeAir dry samples for lab testsAtterberg Limit TestDirect Shear Test Failed Slope SamplesNormal Slope SamplesFailed Slope SamplesNormal Slope SamplesLiquid Limit, Plastic Limit, Plasticity IndexCohesion & Friction Angle Failed Slope Soil IdentificationShear Strength of Failed SlopesNormal Slope Soil IdentificationShear Strength of Normal SlopesShear Strength of Failed SlopesShear Strength of Normal SlopesCompare & Evaluate both shear strength parametersCompare lab test results with field test resultsConclusion on Lab Test AccuracyResult as expected?YesState possible reasonsNoThesis Final ConclusionAtterberg limit test is expected to reveal soil at sites are of clay, as observed during preliminary site visit.It is expected that shear strength of failed slope is lower than the non-failure slope. Field test was conducted on undisturbed samples, thus the shear strength obtained is a closer representation to in-situ soil higher shear strength is expected for undisturbed samples than the lab-measured values.

Expected Outcomes of Research

Niroumand H., Kassim K, Ghafooripour A, Nazir R, Zolfeghari S (2012) Investigation of Slope Failures in Soil Mechanics, Department of geotechnical engineering, Universiti Teknologi MalaysiaPublic Works Department Malaysia (2006) Guidelines on Slope Maintenance in MalaysiaNeoh, Cheng Aik. (2001). Practical Design Aspects for Slopes in Mountainous Terrains. Proceedings of National Slope Seminar 2001.Public Works Department Malaysia (2010) Guidelines for Slope DesignGilbert, Paul. (1992) Effect of Sampling Disturbance on Laboratory-Measured Soil Properties, Washington: US Army Corps of Engineers

ReferencesDay, Robert. (1980) Soil Testing Manual: Procedures, Classification Data, and Sampling Practices, McGraw HillDamanhuri J., Fauziah A., Roslan ZA., (2014) Threshold Values Of Shear Strength Parameters Of Soils Taken From Slope Failures And Stable Slopes In Malaysia, Universiti Sains MalaysiaD. M. Potts, K. G. Higgins (2004), Advances in Geotechnical Engineering: The Skempton Conference

References