Study On Unstable Rockmass Mechanism And Engineering Application Of Passive Flexible Protection Systems At West Victoria Peak In Zhangjiakou

The landform of China is extremely complicated,and with the increasing range of human acti-vities,the stability of the unstable rock slope is gradually paid more attention in mountainous area.As a new type of protection system,the flexible protection system has been widely used because of its low cost,good effect and strong adaptability.This paper is based on the engineering of unstable rock treatment in Zhangjiakou West Taiping Mountain,and revealed the failure mechanism of unstable rock slope by its engineering geological conditions.With application of the finite element numerical simulation method,the stability of the pull-splitting typical rock mass under the different load combination is discussed.Furthermore,the force and deformation characteristics of RXI-025 passive flexible net under the rockfall impact of 250KJ kinetic energy are analyzed.The main results are summarized below:(1)The structural plane has great influence on the force and deformation characteristics of the unstable rock.When there is no structural plane,the maximum principal stress appears above the unstable rock,the value is 0.079MPa,and there is no obvious stress concentration on the rock mass.When there is a structural plane with a length of lm in the trailing edge of the unstable rock mass,the maximum principal stress is transferred to the tip of the structural plane,the value is 0.25MPa,and the shear stress also produces stress concentration.(2)Consider three kinds of load cases for unstable rock stability calculation as load case I:natural state,load case II:natural state with rainstorm,and load case III:natural state with earthquake.The results show that stress statement of unstable rock under different load combinations are similar,all the maximum tensile stress and maximum shear stress appear in its trailing sophisticated structural surface.And the values show "load case III>load case II>load case I",which is consistent with stability coefficient of unstable rock.To sum up,the load case III makes stability of unstable rock the most dangerous.(3)The axial force of the protective net,the supporting rope and the anchor rope is changed rapidly at the beginning of contact in the process of rockfall impact,and the axial force of the protective net changed firstly as its direct contact with the falling rock.The supporting rope which bears maximum load among the three plays an important role in strengthening the whole protection system.In practical engineering,it is necessary to increase the section area of the supporting rope so as to strengthen the integral forced performance of the flexible protection system.(4)For the larger impact kinetic energy of rockfall,the deformation of the flexible protective net is faster than others,but it also recovers faster.With the increase of the rockfall initial kinetic energy,the added value of the maximum displacement of the protective net,the maximum axial force of the supporting rope and the maximum bending moment at the bottom of the steel column decrease gradually.Therefore,the relationship between the deformation of each component of the flexible protection system and the rock falling velocity is nonlinear.This studies help to further the understanding of the failure mechanism of unstable rock slope,especially to reveal the mechanism of passive flexible protection system.It can also provide guidance for the engineering design and construction,and has important reference for the practical engineering.