Numerical Analysis On The Mechanical Properties Of Multiple Underreamed Ground Anchor

With the rapid development of urban construction in our country,the demand of ground anchor with high bearing capacity in underground space engineering,slope supporting and foundation pit supporting is increasing.Compared with the common bolt,the expanded anchor has higher bearing capacity,good supporting effect and convenient operation.In this paper,multiple underreamed ground anchor is a new type of anchor,it is developed on the basis of the expanded anchor.The application of this multiple underreamed ground anchor is less in our country,so it is necessary to study it.Based on the result of model test about multiple underreamed ground anchor in the Xi'an University of technology,the bearing characteristics,failure modes and group anchor effect of the multiple underreamed ground anchor are further studied though numerical simulation.The main contents of this paper include the following aspects:(1)On the basis of the model test,numerical simulation is carried out with ABAQUS to study the influence on the failure mode in different number of expanded bodies and the buried depth.Found that the failure modes of soil around the ground anchor is the shape of "bulb ".with the number of expanded body increasing,the surrounding soil damage form has gradually developed into a series of "flame".The failure mode of shallow multiple underreamed ground anchor belongs to the whole shear failure and the failure zone is connected with the ground surface.The failure mode of deep multiple underreamed ground anchor is the local shear failure.(2)The influence on the bearing capacity in different depth and the size of expanded body was studied by the means of numerical simulation.From the analysis of the results,it is found that the bearing capacity is enhanced with the increase of the buried depth and the diameter of the expanded body.When the depth is large enough,the bearing capacity enhanced with the increase of the span,but the effect is not obvious.In addition,the bearing capacity of the anchor does not enhanced with the increase of the length and the number about the expanded body,even decrease with its increase latter.Through a number of experimental simulation data get the optimal length of the expanded body is 100mm-150 mm.The optimal number of the expanded body is related to the buried depth,the optimal number is increase with the increase of the buried depth.(3)Change the soil parameters to study the effects between soil cohesion,internal friction angle,deformation modulus and the bearing capacity.Through the data analysis,it is found that with the increase of cohesion,internal friction angle and deformation modulus,the uplift bearing capacity of multiple underreamed ground anchor will enhanced,but the contribution of deformation modulus is small.(4)In practical engineering,the application of group anchor is wide,so this paper further studies the influence between the horizontal space,depth,quantity,position and the group anchor effect.It is found that the larger the horizontal spacing is,the smaller the group anchor effect is;The deeper the buried depth is,the smaller the horizontal spacing required to reduce the group anchor effect,but not less than 4D And when there is much number of expanded body in single underreamed anchor,it is need far horizontal space to reduce group anchor effect.The more number of anchor,the effect of group anchor is more obvious,and the anchor force of ground anchor is not same in different positions.