Study On Rock Thickness Unloading Effect Andits Mechanism Of Layered Rock Mass

The layered rock mass is the type of rock mass with the largest exposed surface area.With the rapid development of China’s economy,There are many highways,railways,subways and hydropower stations have been built.In this process,it is inevitable to encounter many safety issues related to the deformation and destruction of the layered rock mass.At present,factors of the variation of layer thickness are generally not considered in engineering design related to layered rock masses.However,since the formation of the rock body,it will surely experience tectonic effect,unloading and weathering.Meanwhile,the construction of human being will also affect the structure of the rock mass with a fast speed.In the process,the rock formation will inevitably suffer damage,and its thickness will change.At present,there are few studies on the Change in thickness of the layered rock mass and the mechanism of change.Based on this,this article focuses on the study of shallow metasandstone and slate in the dam area of the Cihaxia,based on rock mass evolution theory.Firstly,we explain the engineering geological conditions,formation conditions,and original thickness.Secondly,with the aid of had been excavated of nearly 100 adits,layerby-layer measurement and statistical analysis of rock thickness.Finally,the unloading,tectonizing,weathering effects were studied of the variation range in layer thickness,layer thickness variation law and mechanism.This study provide theoretical references for the design,excavation,support in layered rock body.(1)Through the study of the combination of stratigraphic lithology,geological structure and lithologic combination in the study area,it is found that although area is inclineyan rock formation,under the influence of the Yellow River,however,due to its weak tectonic action,no large folds and faults have been found in this area.It mainly develops small stratum faults,cut faults and small folds,and thelayer of the rock complete.It provides good research conditions for statistical analysis of the law of layer thickness change.The original layer thickness did not change significantly with adit depth and elevation,and its original layer thickness was mainly affected by lithologic combinations.(2)To study the distribution and variation law of the thickness of the upper and lower faults,under the influence of different lithology and different tilt of both flanks rock formation,we found some differences in the thickness distribution of the rock.The thickness of the rock within the influence range of the fold in the same lithology is obviously thinner than the thickness of the rock within the influence range of the interlaminar fault zone and the cut fault.The effect range of thickness change in sandstone is larger than that in slate.The influence range of thickness change in the strike direction depends on the size and extension direction of the type of structure.(3)The thickness of the layer after gradually increasing after becoming steady along the depth of adits,and there is no obvious change rule with the height of rock thickness.The tectonic,unloading,and weathering action all can make the hidden layer open.The indoor unloading test verified the hidden layer open under unloading conditions,with the aid of simulation calculation and maximum positive strain theory to reveal the mechanism of layer thickness change.