Question

for geotechnical engineering 1

3 (a) With neat sketches explain how the method of slices can be used to determine the factor of safety of an embankment when subjected to ‘end of construction condition. (b) The stability analysis performed using the 'method of slices', on an embankment of 12 m high gave the following results: Total normal force = 2000 kN (ii) Total shearing force 500 kN Total neutral force = 300 kN (iv) Length of the arc = 23 metres (v) Value of cohesion = 30 kN/m² (vi) Angle of internal friction = 8° Determine the factor of safety.

Answer 1

criven - 1 a) Method of slices- d S v w This method of IN slices are used where the effective angle of shearing resistance is not constant over the failure surface by wing In this method Factor of safety cambe forces provided by each slices. by using the contributia to the moving. paesisting the value of Normal force N= Weasa Effective normal force N'=N-U determined - Wlasa-uay sex Also maxim resisting Force T resisting Force T = 2 (c'to'tand) axseca but the value - s maxim resisting forces so Fos {(chaxsela +Nitan Ele'sx seca + tang "(wcase - Usx seed) - sum of moments of sum of-moments of forces ETmark EWd {TmaxR {WR sina Fos 3 [e'ox seed + tau d'I w lasa-U AR SELA) Ewsina

L=23m Given data: 26 Total normal force EN = 2000KN Total shearing force et 500KN Total neutral force EU = 300 KN Length of are value of cohesion C = 30 kN/m2 Angle of internal friction &=8" By using method Fos is given by the expression FOS CL & tande (N-u) of slices. ΣΤ where c-cohesion - L- Length of are EN- Normal force ET- shearing force EU- Total neutral force gubstituto the given value in above expressia FOS 30x 23+ tan 8 (2000 - 300) 500 Fos 690+ 0.1405X 1700 500 FOS 928.85 500 FOS = 1,857 I FOS =1.86