Stability Of Trench Excavation Under Construction Machinery Load

Because of the city infrastructures rehabilitation and construction, the modification works of old cities and the development of residential districts in the recent years, municipal pipeline works just as the water supply and sewerage works, heat supply, air supply, fiber optic cable, electric cable and oil pipeline increasing day after day. In the same time, the drag shovel is in general use in the excavation works of the municipal pipelines, owing to the general use of the construction machinery in the construction of the civil engineering in China. Trench collapse causes a considerable number of deaths and injuries of workers every year in the process of trench excavation. How to avoid this kind of construction collapse accidents is a subject which should be studied as soon as possible. This paper discussed the influence of the construction machinery such as the drag shovel on the trench stability in the process of the trench excavation. Firstly, the construction machinery load was simplified into strip load. The effects of ground condition, magnitude and location of the construction machinery load and eccentric distance on the excavation depth, the failure mechanism and the failure pattern of the trench wall were investigated by a series of centrifuge model tests which simulated the process of trench excavation. According to the centrifuge test results, the failure pattern of the trench wall and the velocity field were set up. The upper-bound value of excavation depth was given by upper-bound solution. The upper-bound solution expression of the excavation depth was simplified according to the failure features of the trench wall, and then verified this simplified expression by the centrifuge test results. Finally, the influence area division of the machinery load was made by the width expression for the sliding soil mass, and the influence area and non-influence area of the machinery load on the excavation depth were visually represented. If the machinery load is in the non-influence area, it's no influence on the excavation depth, and the value of the excavation depth given by the simplified expression of upper-bound solution equals to that of no machinery load. If the machinery load is in the influence area, the machinery load has influence on the excavation depth, and the ratio of the value of the excavation depth to that of no machinery load can be given by simplified expression of upper-bound solution. In addition, the discussion of the simplified expression of upper-bound solution indicated that the influence of the eccentric distance on the excavation depth increased with the increase of the bearing pressure of machinery load.