Research On The Utmost Limit Piles Distance About Row Piles Retaining And Protecting For Deep Fundation Excavation In Chengdu Area

The piles distance of row piles retaining and protecting for deep foundation excavation is determined by the amount of piles which is determined by the balance of the whole protects structure. But such piles distance can not make sure that the soil between tow piles generates stable soil arch, and it is probably that the soil behind piles extrude from the stake and then cause the whole protect structure expiration. In order to obtain the outmost limit piles distance of row pile retaining and protecting for deep foundation excavation in ChengDu area, the author summarized the stamp of the two-layer-stratum in ChengDu area , and deduced to a outmost limit piles distance calculation formula based on the soil arch principle.In this article, the author summarized the stamp of the two layer stratum in ChengDu area, which presents top soft and bottom hard characteristics, and discussed its influence to the foundation excavation engineering. Put forward a concept of macro-cohesive strength, witch could be obtained by back-analysis of the autostability of the sandy pebble soil. Studied the formation process of soil arch between two piles by the FLAC-2D software, and discovered that the formation of soil arch was related to plastics flow in the soil behind two piles. Suggest that horizontal stress concentrating could be used to determine the region of soil arch , and put forward 3 conditions for soil arch' s existent: (1)There have been asymmetry move or relative displacement in soil; (2) Stable arch feet to provide support to soil arch; (3)The soil in arch area could attain new equilibrium by stress adjustment after yield. Deduced to a outmost limit piles distance calculation formula for passive piles, which considers the influence of the supports on the soil between piles, and this formula could be used for outmost limit piles distance computing both in cohesive soil and cohesionless soil. Finally some actual engineering case is given to verify the usability of the formula. At last, though the numeric simulation to the Southwest Jiaotong university deep foundation excavation project, we found that soil arch could be generated both in cohesive soil and cohesionless soil since the soil between piles was supported by certain force. Finally, the author studied the influence factor about the coefficient of support force between piles in detail, such as earth pressure, internal frictional and cohesive strength of soil, ratio of piles distance and pile diameter.