Study On The Stiffness Effect Of Cantilever Double-row Anti-sliding Piles And The Soil Arching Between Piles

Landslides are a common geological disaster in China, especially in themountainous areas of Sichuan, Chongqing and Yunnan provinces. As a key technologyin landslide treatment, vertical piles have been used successfully in many situation andnumerous methods have been proposed to design the piles. Double-row anti-slidingpiles are used to deal with the large-scale landslide where single-row piles can’t resistthe tremendous thrust force. The double-row anti-sliding piles are referred to the tworows of piles which interact with each other. The arrangement of double-row pile isflexible. It is initially used in the last century then it is widely used. But the theory aboutcantilever double-row anti-sliding piles without coupling beam is rare and researchabout the interaction between pile rows still has a long way to go.Based on the engineering practice and the related literatures at home and abroad,the design principle of piles with varying rigidity in the foundation is introduced to thedesign of double-row anti-sliding piles. The rigidities of the leading piles and the rearpiles are no longer always equal to each other, but designed according to the force theyshare; Based on the characteristics of soil arching between piles, the soil arching can bedivided into active soil arching and passive soil arching. The soil arching effect in theanchorage segment is discussed which rare literates discussing about. Based on thecoupling effect of the double-row anti-sliding piles, a design method was proposedconsidering the related displacement.In order to prove the rationality of the design method with variable stiffness andstudy the characteristics of the soil arching effect, this paper used the theoreticalanalysis, the indoor model test, the numerical analysis and the engineering monitoringtechnology to make a deep insight into the cantilever double-row anti-sliding piles. Thefollowing conclusions were drawn:(1) The indoor model test of the double-row anti-sliding piles with variable rigiditywas design by changing the pile spacing of the leading row and the rear row piles. Thepile head displacement, the soil pressure and the bending moment were monitored,which verified the rationality of the design of double-row piles with variable stiffness.The earth pressures were monitored, which verified the existence of soil arch effect.(2) Based on the indoor model experiment, the FLAC3D was used to simulate thesoil arch effect between cantilever double-row anti-sliding piles and compared with the results obtained from the model test. The soil arching not only exists in the sliding layer,but also in the anchoring segment. The existences of active soil arching and passive soilarching were verified, and the soil arching effect in the anchoring segment was studied.The development of the soil arching can be divided into four stages. The influence ofslide thrust, pile spacing, row spacing and the parameters of the contact surface, pileconstraints were discussed.(3) The finite difference method was used to simulate the double row anti-slidingpiles under horizontal load. By changing the pile spacing of the leading row and the rearrow piles, the pile spacing, the row distance, the anchoring depth of the leading and rearpiles and the reinforcement of the soil between pile rows, the variable stiffness methodwas put into application in the optimized design of double-row piles. The results showthat reducing the rigidity of the front pile properly is beneficial for the distribution ofslide thrust.(4) According to the mechanical mechanism of double-row anti-sliding piles, adesign method was proposed considering the related displacement of piles, whichconsidered the displacements of the double-row piles, the pile spacing and the rowspacing.(5) The double-row piles were applied to reinforce an existing single-row piledslope in Chongqing. The numerical simulation and field monitoring results showed thevalidity of double-row piles in reinforcement of existed single-row anti-sliding pile.The use of variable rigidity design method is effectively in adjusting the share ratio ofsliding force between the leading-row and rear-row piles. The cross-sections of theleading and rear row piles had important influences on the share ratio between theleading and rear piles, the rear piles was suggested to enlarge cross-section appropriate.Construction of the rear pile and excavation of the rock mass in front of the leadingpiles would cause disturbance to the landslide, the filed monitoring should be enhanced.