Effect of Groundwater Table Rising and Slurry Reduction during Diaphragm Wall Trenching on Stability of Adjacent Piles

Abstract

The process of diaphragm wall trenching normally affects the surrounding environment. The piles near a diaphragm wall trench are commonly affected by the trenching process as well. During trenching the slurry level and the natural groundwater level are assumed to be constant. However flooding may cause damage to the slurry trenches due to the increase of the groundwater table. Another possible scenario for the trench failure is due to reduction of the slurry level. The reduction of the slurry level could be due to the presence of cavities or a very coarse soil layer. Piles located near a trench could be affected greatly if the trench is subjected to reduction of slurry or increase of the groundwater level. This research focuses on studying numerically the stability of piles adjacent to the diaphragm wall during the trenching process, especially in cause of slurry reduction or increase of groundwater level. The slurry reduction were simulated numerically with the finite different analysis and compared with previous laboratory work. The increase of groundwater level is simulated for a case study in Giza, Egypt. Groundwater level was assumed to increase in the area. Piles are generally affected by the trenching process. The behaviour of the pile is related to its position from the slurry trench. The stability of the pile may not be affected greatly by a normal and successful trenching process. However slurry reduction or increase in the groundwater level may cause a great effect on the stability of the nearby piles. Trenching in general causes an increase in pile settlement, horizontal displacement and bending moment. The pile skin friction and end bearing are affected as well. The percentage of the change in slurry or groundwater levels affects piles deflection and bending moment.