Determination of the additional earth pressure on the chamber walls of twin locks

Abstract

1. Until recently there were no investigations of the conditions of the static work of chambers of twin locks. Therefore, in the design of these locks total transmission of the reaction pressure occurring behind the inner wall of the chamber being filled to the inner wall of the adjacent chamber was assumed. Such design practice led to an overestimation of the calculated loads and to an increase of weight of the chambers. 2. The instructions of SNiP II-55-79 for determining the additional earth pressure (Appendix 3, Paragraphs 8 and 9) give overestimated values of this pressure, which do not agree with the data of on-site observations. The soil reaction pressure behind the outer walls of the chamber being filled from their bending by the water determined for the case of unconfined backfill by formula (23) is underestimated and does not coincide with the data of on-site observations either in magnitude or in the form of the pressure diagram. 3. When calculating chambers of twin locks for hydrostatic loads we recommend determining the soil reaction pressure behind both walls of the chamber being filled by means of the calculation schemes used for single-lane locks. The additional earth pressure being transmitted through the backfill of the interlock space to the adjacent chamber should be determined in fractions of this reaction pressure by relations (1)–(8). 4. In calculations of the strength of lock chambers it is suggested to take into account the shear stresses (frictional forces) on the contact of the soil with the backs of the walls, which will make it possible to reduce the calculated area of reinforcement. Furthermore, consideration of frictional forces in calculations for the hydrostatic load will permit using lower levels of backfill behind the chamber walls, which will ease their work and permit designing more economical structures.