| The vertical joint developed in the soft hard alternating rock is a kind of special joint.On the one hand,this kind of joint usually occurs preferentially or only in the harder and more brittle rock strata and is usually perpendicular to the stratification interface of the rock strata;on the other hand,this kind of vertical joint in the soft and hard interactive rock strata has its unique development mechanism and distribution characteristics.The in-depth study of its distribution characteristics and development mechanism can better guide the excavation of underground engineering,stress history evaluation,groundwater seepage and energy development Mining and many other aspects.In this paper,the vertical joints of interbedded sandstone and mudstone in Northern Shaanxi Province of China are taken as the research object.Through large-scale statistics of vertical joints in the field,a series of data such as the occurrence,trace length and opening degree of vertical joints are obtained.By means of regression analysis and theoretical analysis,the influence of geological comprehensive environment on the development of vertical joints and the distribution characteristics of spacing are studied in detail,and the development of vertical joints is revealed Mechanism,main research contents and achievements are as follows:(1)The influence of geological environment on the development of vertical joints isstudied.The results show that the development of vertical joints in the soft hard interbedded strata in the study area is affected by multiple geological environment factors.The direction of joint fracture is controlled by the area of structural stress,but also by the local influence of slope trend;the joint spacing is related to the thickness of sandstone layer,the thickness of upper and lower mudstone layers and the overlying stress,while the influence of slope unloading on joint fracture is not significant.(2)The classical relationship between the thickness of the brittle rock and the joint spacing is discussed.The results show that the statistical relationship between joint spacing and mechanical layer thickness obtained in a small range of mechanical layer thickness may have restrictions and limitations.(3)The causes of the diversity of the joint spacing distribution characteristics in the study area are explained,and the complementary index deviation(S_k)to characterize the joint spacing distribution characteristics and joint development degree are put forward.The joint spacing distribution pattern is related to the joint development stages.During the process of joint development from filling to saturation,the spacing distribution will transform from a negative exponential distribution to a lognormal distribution and then to a normal distribution.(4)A new joint saturation mechanism is proposed,which can cause the S/T ratio of spacing layer thickness to be larger than that of normal joint saturation.(5)The concept model of vertical joint development is established.The model shows that the difference of elastic ability and rheological property between hard brittle rock and soft rock can provide tensile stress condition for the development of vertical joint.The theoretical analysis further points out that the vertical joints under different interface conditions are controlled by different fracture mechanisms and have different joint spacing characteristics and influencing factors.(6)The influence of interface slips on joint spacing is considered.When the axial tensile strain increases,,the interface condition of rock stratum may gradually transition from non slip to full slip,so the joints in hard brittle rock stratum may not be produced under one interface condition,but may be affected by a variety of interface conditions,which makes the joint spacing show more complex characteristics. |
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