Experimental Study On Shear Performance Of Anchoring Jointed Rock Mass Under Erosive Environment

Rock and soil anchoring technology is economical,efficient and practical.It is the most commonly used reinforcement and support method in slope engineering and underground engineering.However,the anchored bolt supporting structures are mostly in a hidden,complex and harsh working environment.Thus,the existence of corrosive medium and stray current often leads to the erosion and even failure of the rock bolt in the long-term working process.Especially in offshore areas,there are many well-developed multiple joints of rock,and the seawater can easily infiltrate into the anchorage structure through joint cracks.And as a kind of catalyst,chloride ion in seawater can accelerate the erosion rate of rock bolts,which poses a serious threat to engineering structures in offshore areas.Therefore,with the rapid development of urbanization in coastal areas,the durability of anchorage structure should be paid great attention.This paper is supported by the National Natural Science Foundation of China(No.41572275)project Study on the Evolution Mechanism of Anchorage Corrosion Damage of Anchoring Jointed Rock Mass under Long-term Erosion of Seawater.Combined with laboratory test,theoretical analysis and numerical simulation,this paper studies the shear performance of anchoring jointed rock mass under long-term erosion of seawater.The main contents are as follows:Combined with laboratory test,theoretical analysis and numerical simulation method,the shear performance test of rock mass with anchor joint under long-term action of seawater is studied.The main contents are as follows:(1)The accelerated corrosion test of anchoring jointed rock mass was carried out,and the specimens with different corrosion degrees were obtained by controlling the current density and the power-on time.The actual pitting corrosion rate obtained by weighing after tests is lower than the theoretical value,but the overall error was within the ideal range.(2)The specimens of anchoring jointed rock mass with different connectivity rates,diameters and prestresses were designed,and the specimens with different corrosion degrees were obtained by electrochemical method.Furthermore,direct shear tests were carried out to study the influence of corrosion on the shear performance of anchoring jointed rock mass.The result shows that,with the increase of connectivity rate,the cohesion and internal friction angle of the specimen gradually decrease;with the increase of corrosion degree,the expansion of corrosion products has squeezing effect on the rock mass at the crack,which increases the internal friction of the joint surface.And the effect becomes more obvious when connectivity rate of the crack is large.What's more,with the increase of pitting corrosion rate of the rock bolt,the peak shear strength of anchoring jointed rock mass increases first and then decreases.(3)Considering the shear strength of jointed rock mass itself,the calculation formula of shear strength of anchoring jointed rock mass with incomplete penetration was proposed.Based on the shear strength regression curve of the uncorroded specimen obtained from the test,combined with the increment variation coefficient of equivalent cohesion converted by the corrosion to the rock bolt and that to the prestress,the relationship between shear strength and different pitting rates was obtained.The relationship is in good agreement with the indoor test data.(4)Combined with the results obtained by laboratory simulation tests and the concept of strength reduction,the model of anchoring jointed rock mass was established to simulate the corroded specimens with different pitting corrosion rates.Through the direct shear test and indoor compression test,parameters of the numerical test were calibrated macroscopically.The crack developing law during the shearing process and the influence of corrosion on the specimens were revealed microscopically by PFC discrete element analysis software.The results show that PFC can be used to evaluate the degradation behavior about shear performance of anchoring jointed rock mass under the influence of corrosion.