Research On Developmental Characteristics And Prevention Measures Of Daaoxi Unstable Rock Along Hang-shao-tai Highway In Zhejiang Province

Based on the engineering example of Da Ao Xi unstable rock,starting from the geological environment condition of unstable rock development,this paper induces the developmental characteristics and deduces the evolution of dangerous rock by field investigation.Using the limit equilibrium theory,the stability coefficient of dangerous rock mass with different failure modes is calculated and the stable state of dangerous rock mass under different conditions is evaluated.Comparing the empirical formula and the RocFall simulation,the kinematic law of the rockfall in the whole collapsing process is summarized and the kinematic parameters of the rockfall in the proposed highway position are estimated.Integrating the all research results and the distribution of proposed highway,the scientific and reasonable prevention measures are proposed.The main findings are as follows:(1)Unstable rock is aligned East-West and the bedrock is huge thick glutenite.Unstable rock can be divided into two parallel zone.The structural surface in upper zone are scarce,so block is huge.However,the structural surface in lower zone are abundant,and can divide into three types: anti-dipped lay,unloading fissure and steep joint,so the major failure modes are toppling and falling,just a few are sliding.(2)The evolution of dangerous rock can summarise as: Differential weathering cause the lower shale shaping cavity,while the upper glutenite shaping steep free face.The structural surface cut huge thick glutenite into block of varying shape and size.Effected by external factors,such as rain,the structural surface extend and penetrate,causing unstable rock separate from source rock and form rockfall.(3)The results of stability analysis indicate that: Unstable rock in upper zone are stable state under whole conditions.Unstable rock in lower zone are stable state only under natural conditions.However,under rainy and seismic conditions,that unstable rock of falling and sliding are under-stable or basic-stable state,while that toppling are basic-stable or stable state.All the stable state of dangerous rock match those result found by field investigation.(4)The kinematic parameters of the rockfall in the proposed highway position calculated by empirical formula as follows: the velocity is 19.81~32.34m/s,the kinetic energy is 2052.5~6273.9KJ and the bounce height is 0.3~3.5m.They reveal that unstable rock are destructive.(5)The results of RocFall simulation indicate that: When the slope is approximately consistent,the kinetic energy-location curve show uni-peak type.When the slope is undulate,they show serrated type.When there are long and gentle slopes in the whole steep slope,they show multi-peak type.The kinetic energy in same position under three material conditions are different(Bedrock outcrops﹥ Talus cover﹥Soil with vegetation).The motion of rockfall is mainly rolling and sliding.It cans transform into bounce only where the microtopographic slope change suddenly.The locations of maximum kinetic energy are different(Bedrock outcrops﹥ Talus cover﹥Soil with vegetation),while the locations of maximum bounce height are same.So,the slope is the key factor of bounce height.The end-points of rockfall are different(Bedrock outcrops﹥ Talus cover﹥Soil with vegetation).(6)Comparing empirical formula and RocFall simulation,the results of empirical formula are more conservative.(7)By comprehensive comparison,proposed prevention measures are local protection(general or pile-plank rock retaining wall)aiming at bridge pier and support column aiming at cavity.