Earth pressure on lock chamber walls during construction

Abstract

1. Observations confirmed the fact of formation under natural conditions of a soil arch (noted earlier in laboratory experiments) between the rear face of the wall and the slope of the pit. This phenomenon reduces the earth pressure in the lower part of the wall. 2. The total earth pressure on lock walls under natural conditions as a rule exceeds the calculated in a number of cases by threefold. A considerable part of this excess pressure (≈80%) is formed in the construction period. An analysis of the results of full-scale observations of the Volga locks during the construction period showed the main causes of occurrence of this pressure: on the lock of the Lenin Volga station with a sectional bottom uneven settlements of the half-sections caused the walls to tilt toward the backfill, which move than doubled the earth pressure; on the dock-type lock of the 22nd Party Congress Volga station the soil, which was placed too loosely in the lower part of the backfill, on subsequent consolidation caused settlement of the overlying soil, as a result of which the earth pressure also almost doubled. At the same time, on the lock of the Votkinsk station the earth pressure during construction was close to the calculated. Thus, the implementation of a proper sequence of construction operations can prevent a considerable increase of earth pressure on the lock chamber walls during construction. 3. Until recently very little attention has been paid to full-scale observations of the displacement of lock chamber walls in the construction period and to checking of the structure of soils placed in backfills. However, these factors play a decisive role in the formation of soil stresses and earth pressure on the walls. Therefore, the setup of such full-scale observations in the future will permit taking into account for purposes of design the possible displacements of walls and the inhomogeneity of the physical and mechanical properties of soil during construction.