Study On The Calculation Method Of Earth Pressure Of Excavations Retaining And Protection Structure And The Stability At The Bottom Of Excavations

Based on objective facts that earth pressure acting on the retaining and protectionstructure is actually often in the non-limit state and some excavations bottom soil is a kindof softer soft soil，and combined with the studying results of predecessor, this papermakes corresponding analysis and research, the main contents are as follows:(ⅰ) According to the study on the progressive failure mechanism of soil of the RBdisplacement mode, the play value of internal and external friction angle and soil atdifferent depth’s relational expression is established, which is introduced into thehorizontal layer analysis method. Quasi-active earth pressure and Quasi-passive earthpressure intensity strength approximate formula in non-limit state are established, andQuasi-active earth pressure and Quasi-passive earth pressure in non-limit state approximatealgorithm are given;(ⅱ) It reaches a conclusion of stress states and movement trends in different regionsof the bottom soil of the excavations, and deduces calculation formula of the slip-linesolution for the depth of the driven the excavations supporting pile by using the slip-linefield theory to analysis stability of excavations bottom soil;(ⅲ) Upper bound theorem of the limit analysis method is utilized to solve upper-bound solution for the depth of the driven the excavations supporting pile, that is to say, itshould set up a failure mechanism which satisfies the mechanical boundary conditions andcorresponding virtual work-rate equation, and then deduce upper-bound solution for thedepth of the driven the excavations supporting pile; Lower bound theorem of the limitanalysis method is utilized to solve lower-bound solution for the depth of the driven theexcavations supporting pile, that is to say, it should set up the statically admissible stressfield, on the basis of balance equation and yield criterion, and then deduce lower-boundsolution for the depth of the driven the excavations supporting pile;(ⅳ) The depth of the driven the excavations supporting pile that is deduced in slipline field method is equal to upper-bound solution and lower-bound solution in limitanalysis method. Based on that, we can make a conclusion that the slip-line solution of thedepth of the driven the excavations supporting pile is the exact solution; (ⅴ) It is verified that the reasonableness of the depth of the driven the excavationssupporting pile through stability monitoring of Heng tai excavations;(ⅵ) This paper deduces critical width of single side of excavations by referring tocritical width method, and determines the scope of the development of the plastic zone areasoil at the bottom of excavations supporting combining with a relative geometricrelationships at the bottom of excavations supporting the slip line field, and provides atheoretical basis for preventing and treating the scope of plastic damage.