基于极限分析的桩端岩层冲切分析

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Abstract The rock stratum at pile tip is prone to punching failare for pile foundation in karst region. The Hoek-Brown nonlinear rock strength criterion has been introduced according to the characteristics of rock mass in the karst region；and then the shear stress of quadratic parabolic expression was obtained. The work-energy equation of punching failure body was established using limit analysis method. Then the generatrix equation of punching failure body was obtained through the variational extremum principle. Furthermore，the calculation formula of safe thickness for the rock stratum anti-punching failure was obtained by differential equation. Combined with the practice of pile foundation in karst area，the value range of main resistant punching shear safety thickness factors affecting were analyzed. Parameter analysis shows that：(1) The top and bottom diameter ratio d1/d of punching failure body decreased nonlinearly along with the increase of RMR value；in other words the bottom conical rotor diameter of punching failure which formed by the good karst roof of rock mass quality is small. Conversely，the greater the diameter at the bottom of the body of revolution. (2) According to the different d1/d and RMR values，the ranges of initial punching angle is between 24°–42°. (3) The ratio of thickness to diameter h/d decreases nonlinearly along with the increase of RMR. That is to say the better the rock mass quality，the smaller the safe thickness. When the rock mass quality is good(RMR＞65)，the safety thickness h/d is lower than 2.5.

Key words： pile foundations punching failure limit analysis work-energy equations safe thickness

Received: 07 May 2013

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https://rockmech.whrsm.ac.cn/EN/Y2014/V33/I3/631

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