Research On The Risk And Control Methods Of Urban Pile-anchor Support Excavation Adjacent To Important Buildings In Soft Rock Areas

Soft rocks are widely distributed in China,and many cities are built in soft rock areas.It is very essential to develop and utilize underground space in the city center with the rapid development.But the existing buildings in the urban are densely populated,and some soft rocks are prone to disintegration and the engineering properties are poor.The coupling of the two results in a greater risk of engineering deep excavation in urban centers in soft rock areas than general deep excavation.The pile-anchor support structure is widely used in the urban excavation,therefore this paper aims at the research on the risk and control method of the urban pile-anchor support excavation adjacent to important buildings in weak rock areas.By investigating the actual project to collect inspection,monitoring and test data of the project.Then,on the basis of in-depth research on the working mechanism of the anchor in the soft rock area and the attenuation characteristics of the pull-out bearing capacity,the risk assessment is carried out for the urban pile-anchor support excavation adjacent to important buildings in weak rock areas considering the key factors.Thus the control methods are proposed based on the evaluation results.This paper mainly completed the following work:Firstly,the engineering cases of urban pile-anchor support excavation adjacent to important buildings in soft rock areas are investigate d,including:(1)the case of serious deformation and cracking of surrounding buildings caused by the construction of the excavation in the strongly weathered slate stratum;(2)the case of the attenuation of the pull-out bearing capacity of the bolt anchored in the argillaceous siltstone layer in the excavation with overdue service;(3)the case of the construction safety guarantee of a deep excavation adjacent to an important building in a strongly weathered slate layer.The results of the investigation clearled the direction and provided basic data for the in-depth study of the urban pile-anchor support excavation adjacent to important buildings in weak rock areas.Secondly,in view of the problem that the bearing capacity of the bolt may decrease due to the softening and disintegration characteristics of the soft rock stratum,the attenuation characteristics of the pull-out bearing capacity of the bolt and the variation law of the calculation parameters are studied based on the load transfer model of the anchor.The whole-process load-displacement equation at the end of the bolt(at the head of the anchor)in the pull-out test is derived based on the study of he tri-polyline constitutive model of the anc hor-soil interface.The multipile field pull-out test data of bolts anchored in argillaceous siltstone in the second case are analyzed,while the whale algorithm is used to invert the calculation parameters,which revealed the attenuation characteristics o f the pull-out bearing capacity of the excavcation in the soft rock areas and the variation law of the calculation parameters of the load-displacement relationship of the bolt.Then,according to the characteristics of the important buildings adjacent to t he excavation,the risk assessment for urban pile-anchor support excavation adjacent to important buildings in weak rock areas is carried out considering the decisive influence such as the stratum lithology,important buildings,precision equipment and special users on the construction of the deep excavation.The risk evaluation index system of the general urban deep excavation construction is summarized b uilding on the existing literature,and the new index system is reconstructed through investigation and interview,which is applied to the third case to carry out risk evaluation.The results show that suppressing the collapse of soft rock and reducing the impact on adjacent buildings and users are the focus of risk control of such excavations.Eventually,the idea to inhibit disintegration and management measures to achieve low-impact construction are proposed based on the risk assessment results.And they are applied to actual projects,which lead to good results.The successful application of the methods provides reference and guidance for risk control of the urban pile-anchor support excavation adjacent to important buildings in soft rock areas.