Page 26 - Minutes of Proceedings of Civil Engineers Vol CXCV 1913-14 Part 1

66 WENTWORTII-SIIEILDS ON THE CONSTRUCTION OF flMinutes ol APPENDIXES. APPENDIX I. Srarrltrr or Quer-Wer,r,s. The two principal couditions necessary for the stability of a retaining-wall &re :- (1) That the outward horizontal forces (pressure of backing, etc.) shall be fully equallerl by the inrvard horizontal forces (i.e. pressure of waber in frtnt of wall* resistance due to slope of foundations and to friction between base of wall and material on which it rests). (2) That the vertic&l pressure between the wall and the material on which it rests shall nowhere exceed a s*fe limit, \Yhen making calculations to ascertain whether the v'alls described in this Paper complied u'ith these conditions of stability, Rankine's formula for the lalerafpressure of the earth backing was used, viz. :- o_rhz l-sinp '- 2'r+iino' where P denotes the lateral pressure of barking per lineal unit, 10 tt ,, weight of materisl per unit volume. A ,, ,, angle of rePose of eame. h ,, ,, heiglrt of wall. The problem at once arose-what value should be given to the various symbols in thie formula ? For instance, the val.ue of g must vary considerably, not only with the nature of the material forming the backing, but also with its condition wet or dry, and rvhether virgin ordeposited soil, The followingvalues -whether wero assumed in the case of walls for portion A built in the dry which lvere backecl rvith sandy clay frorn the excavatiols :- eu = 720 ltrs. per cubic foot. e - 26" (2 to 1). The coefficient of friction between the base of the wall and the material on which it rested. was assumed to be at least 0'2. With these assumptions the following results were obtained :- P""Ji"ingll,:""t Lateral pressure of backing 57'0 tons. due to surcharge 2'9 ,, Tottl outrYarrl forces . 59 I ,, 'Ions. Resistnnce due to rvater-pressure 22'8 ), ,, slope of foundatious 16'3 friction 26.I . Total inwar