Study On Bearing Capacity Of Pressure-dispersed Anchor Cable

In engineering practice,due to the influence of various conditions,there are a large number of heterogeneous strata,such as common mudstone interbedding,faults and so on.Especially in the reinforcement of high rock slopes in the construction of expressways,the complicated distribution of rock strata often occurs,which makes the anchor cables often need to pass through the soil strata with different mechanical properties.The mechanical properties of rock and soil layers(strength,deformation characteristics,etc.)and the distribution of in-situ stress in rock mass,as well as the interlayer joints of strata,will have an impact on the shape of the borehole and the borehole wall after the drilling of anchor cables,which will lead to a great impact on the interaction between anchor and rock and soil layers.In this paper,based on a highway roadbed slope support project in Guizhou,the stress(strain)distribution law of Pressure-dispersed anchor cables in soft and hard rock interbedded rock mass is studied by theoretical induction,physical model test as the main research means and numerical simulation as the auxiliary means.The main research contents are as follows(1)Firstly,the current theoretical analysis methods of Pressure-dispersed anchorage segment are summarized,analyzed and compared.(2)The test model is a Pressure-dispersed anchor cable with two anchoring units under two working conditions: bearing plate in hard rock stratum and bearing plate in soft rock stratum.According to the similarity theory of model test and model size,the similarity ratio of physical model test is determined to be 1:10.With cement,water sand and gypsum as the main raw materials,the corresponding soft rock and hard rock are allocated respectively.According to the engineering prototype,the distribution of axial force in grouting body and shear stress in the interaction between grouting body and surrounding rock under different tension loads are analyzed by "compensating tension first" and "integral graded tension".At the same time,the difference between the distribution of axial stress and shear stress is compared when the bearing plate is located in different strata.(3)Finally,ABAQUS is used to simulate the anchor cable of two bearing bodies,and spring element is used to simulate the bonding force between grouting body and surrounding rock,which is realized by inserting the node number of spring element into the INP file.The distribution of axial stress and bond stress between grouting body and surrounding rock are analyzed under two working conditions.Through the above work,the following conclusions are drawn:(1)Ultimate bearing capacityThe ultimate bearing capacity of the anchor cable system is different under the two working conditions.The ultimate bearing capacity of the bearing plate in hard rock section is larger than that in soft rock section,which is about 2KN.The failure modes of the anchor cables are the same under the two working conditions,both of which are caused by slip between grouting body and surrounding rock.(2)Axial stress distributionUnder the two conditions,the peak value of the axial stress of grouting body appears near the bearing plate,and the farther away from the bearing plate,the smaller the axial stress is.The mechanical properties of soil layers are different.The attenuation rate of axial stress distribution curve is different in different strata.The attenuation rate of hard rock section is about 5.8-6.8 times that of soft rock section.Especially at the interface of rock strata,the attenuation rate has a certain turning point,and the turning phenomenon is more obvious with the increase of tension load.(3)Shear stress distributionUnder the two conditions,the shear stress increases with the increase of tension load,and the maximum shear stress is about 175 KPa for the bearing plate in hard rock,117 KPa for the bearing plate in soft rock,and the maximum shear stress occurs in the section of hard rock.Because of the difference of mechanical properties between hard and soft rocks,shear stress changes abruptly at the interface of rock strata.When the shear stress transfers from hard rock to soft rock,the shear stress decreases;when the shear stress transfers from soft rock to hard rock,the shear stress increases.The larger the tension load,the larger the catastrophe value.According to the distribution characteristics of shear stress of bearing plate in soft rock,it is suggested that the length of anchorage section of unit in soft rock should be increased so that each anchor cable element can mobilize the same proportion of ultimate bond strength under the same load condition,so that the anchor cable can be destroyed at the same time.