Research On Failure Mechanism Of Quasi-masonry Unstable Rock Block In Limestone Area

Because of quasi-masonry feature,there are different phenomena between unstable rock block in limestone areas and sandstone areas when failure occurs.Unstable rock block in limestone area disintegrates significantly when failure,lots of small size come into being,formatted collapse disaster maybe exist massive development or a significant effect of air cushion.Therefore,researching in disintegration mechanism of unstable rock block in limestone area has an important significance for understanding the formation mechanism of collapse disaster in Three Gorges scientifically,also giving a good supporting role for the level of rockfall in limestone area mitigation level.The paper takes Wushan County of Chongqing City,Wang Xia unstable rock block for a practical engineering background,using numerical simulation method,material mechanics and fracture mechanics theory to study the failure disintegration mechanism of unstable rock block in limestone area.(1)For the unstable rock block in limestone area,geological model suitable for analysis of failure mechanism is constructed through field survey and field geology investigation.Defining the concept of unstable rock block height platform ratio(H/B),when height platform ratio H/B > 1,we call “top tensile-shear disintegration mechanism”;when height platform ratio H/B < 1,we call “bottom tensile-shear disintegration mechanism”.(2)For “top tensile-shear disintegration mechanism”,employing numerical simulation method,tensile-shear region distribution law with different suspension height ratio c/H,height aspect ratio H/b and inclination angle θ are obtained,based on this,defining an original crack at the junction of quasi-masonry unstable rock block,referring tensile-shear fracture mechanics model with edge crack,by means of fracture mechanics classical solution,quasi-masonry structure top tensile-shear disintegration mechanism is analyzed,collapse criterion of unstable rock block with different suspension height ratio c/H,height aspect ratio H/b and inclination angle θ is obtained.Taking Wang Xia unstable rock block W1 in Wushan County of Chongqing City as an example,block fissure distribution area is predicted.Also,for “bottom tensile-shear disintegration mechanism”,collapse criterion of unstable rock block with different height aspect ratio H/b and inclination angle θ is obtained.Taking Wang Xia unstablerock block W2 as an example,block fissure distribution area is predicted.(3)Taking quasi-masonry unstable rock block as an energy system,energy release quantity in sliding process is calculated,the sudden collapse criterion is built.Taking Wang Xia unstable rock block W2 as an example,it maybe disintegrate when dip angle 34°.(4)Three different heights 530 mm,795mm,1060 mm,three different widths230 mm,345mm,460 mm,three different inclination angles 80 °,70 °,60 °,three different bonding methods non bonding,clay bonding,M5 mortar bonding,in total 81 models disintegration experiment are implemented,height aspect ratio bigger,the relative height of initial cracking position lower,inclination angle bigger,the relative height of initial cracking position higher,bonding mode has no effect on height of initial cracking position,but it can decide whether cracking or not,also,cracking area,in case of non bonding,the possibility of cracking is large and the distribution range of the crack is more than of the bond.