Characteristic Research On Pile-anchor Excavation Supporting System

Cantilever piles and pile-composite anchor support system are widely applied in excavation engineering due to a series of advantages including the good supporting effect,small occupation space,convenient construction,low cost and wide application range.As a result,it is necessary to give systematic and comprehensive analysis in investigating the mechanisms and structural behaviors of these two kinds of supporting system.In this study,the internal force and deformation of the pile-composite anchor supporting system have been discussed by using the elastic foundation beam method.Furthermore,a h-type double-row-piles support structure,which is an improvement of the conventional gate-type double-row-piles structure,was developed and studied in detail.The main constants and results of this study are listed below:(1)The displacement and internal force of the timbering pile in the pile-composite anchor supporting system were calculated by theoretical method,in which the timbering pile was treated as a vertical cantilever beam that fixed at the pile bottom.The pile-composite anchor support system was divided into two parts from the excavation surface.The upper part of the supporting system was governed by the Rankine's earth pressure theory,and the lower part of the supporting system was governed by the elastic foundation beam assumption,while the effects of the active earth pressure was been concerned as well.Then two equations could be built and solved by introducing some boundary conditions and continuity conditions.(2)Macaulay's function was adopted in the calculation due to the reasons that there always existed soil-layers,concentrated forces caused by anchors,and internal supporting structures in the supporting system,which lead to some discontinuity load.As a result,the whole load patterns could be written in one equation by using the Macaulay's function,which made the calculating become simple.(3)The present theoretical model was verified with the measured data form two excavations in Whenzhou and Beijing.The results shown good agreement,which preliminarily indicated that the present theoretical model is reasonable and applicable in practical engineering.Also,the present theoretical model provided reference when choosing the value of m in practical engineering.(4)The h-type double-row-piles numerical model was developed by using a finite element software called PLAXIS.The distributions of deformations and inner forces of the front pile and back pile along the depth,and the ground settlement were investigated in detail.The numerical results show that supporting effects of the h-type double-row-piles is better than the conventional gate-type double-row-piles structures.Furthermore,some efficient parameters including the cantilevered height,the pile spacing,and the soil stiffness between the front pile and the back pile were discussed in detail,which have significant contribution to the engineering design.(5)Moreover,a h-type double-row-piles composite anchor supporting system FEM model was developed to investigating the effects of the composite anchor.The numerical results shown that the existence of the anchor influence the results significantly.