Study On The Pull-out Characteristics Of Soft Rock Bolts Under Confining Pressure

Anchoring technology is widely used in the field of engineering construction today.It has played a large safety role in transportation,construction,underground space and slope protection,and has the characteristics of low cost and high efficiency.This technology has become a solution to rock soil and tunnels.One of the important means of engineering problems.There are many weak surrounding rocks in domestic coal mine roadways,tunnels and other projects.Supporting dangerous rock formations during construction has also become the key.Because the field test is more dangerous and difficult to operate,and there are fewer studies on the drawing of larger size specimens under confining pressure,the indoor drawing test and the finite element numerical simulation method are used for research.Use similar materials such as fly ash,river sand,and engine oil to simulate weak surrounding rock,and perform grouting and anchoring with steel bars to simulate real anchoring units.When drawing,the water is compressed around the water body,which is close to the actual force.Based on this,three factors,the size of the confining pressure,the sand content of the grouting body,and the sand content of the rock mass,have been tested on the influence of the pull-out force and the stress distribution of the rock mass.The main work and content of this paper are as follows:(1)Similar materials with fly ash,standard sand,and engine oil as the ratio can simulate the properties of soft rock in tunnels.The material properties and parameters meet the requirements of similar ratio.Through the compaction process of the parts,the rock mass of similar materials has higher strength.,Change the ratio for multiple pullout tests.(2)Considering three factors,27 sets of pull-out tests are conducted,and the drawing displacement curve diagram of the anchor rod under various conditions is obtained,and the drawing force distribution and change law are studied.(2)Summarized the five failure modes of bonded anchor rods,explained the formation reasons and failure characteristics,and also pointed out two failure modes that appeared in this test: the anchor solid brought out the rock mass and became coneshaped failure;grouting Debonding failure occurred at the interface between the body and the rock mass,and the grout body was completely pulled out.(3)The influence of confining pressure,sand content of anchor solids and sand content of rock mass on resistance to pull-out force was studied through bolt pull-out tests,and it was found that the biggest factor affecting pull-out force was confining pressure,followed by sand content of grouting body,The rock mass has the least impact on sand content.The law of the curve and the position where the ultimate pull-out resistance appears are analyzed,and the cause of the failure phenomenon is pointed out in a mesoscopic view.(4)Use the finite element numerical simulation software ANSYS to simulate the drawing of the bolt,and study its drawing curve law,stress distribution law and rock deformation law.It focuses on the study of the stress law of the rock mass-grouting mass interface along the depth direction and the stress distribution law of the grout mass-rebar interface,and the deformation of the rock mass in the X-axis and Y-axis directions.