Study Of Interface Shear Stress Relaxation Behavior Of Anchors In Red Clay Soil

A large number of engineering practices have shown that prestressed anchors(cables)will produce different degrees of prestress loss,and the stress relaxation characteristics of the anchor solid-rock-soil interface is an important factor affecting the prestress loss of prestressed anchors(cables).Therefore,this paper developed an anchor-soil interface shear stress relaxation test device for the pre-stressed anchored slopes in the red soil area of southern my country,carried out the anchor-soil interface shear stress relaxation test and theoretical studies under the action of multiple factors(soil moisture content,soil dry density and shear displacement level).And revealed the stress relaxation characteristics of the red clay soil anchor rod under long-term load under the action of multiple factors.With the support of the National Natural Science Foundation of China(41572298),the main research work and results of this paper are as follows:(1)Basic physical and mechanical properties tests were carried out on the test soil material taken from the excavation site of a slope in Qidong County,Hunan Province,and its chemical composition,mineral composition and microstructure were tested at the same time.Independently developed an anchor-soil interface shear stress relaxation test device.And the device was used to load 12 groups of anchored unit samples with different soil moisture content and dry density in stages.According to the coordinate translation method,the whole process curve of the staged load stress relaxation was converted into a separate load stress relaxation curve.Finally,the shear stress relaxation amount and residual shear stress ratio were used to qualitatively analyze the influence of water content and dry density on the shear stress relaxation characteristics of the anchor-soil interface.(2)The stress relaxation test results of the A1 and A2 samples were selected,introduced the fractional calculus theory to improve the viscous pot element,and a fractional M||N(composed of Maxwell and Newton in parallel)relaxation model of the anchor-soil interface shear considering the influence of the shear displacement level was established.The results show that,compared with the integer-order M||N model,the Burgers model and the five-element model(H||M||M),the fractional M||N relaxation model established in this paper not only has the advantages of simple structure and fewer parameters,but also has higher fitting and prediction accuracy,which is convenient to be applied to actual engineering.(3)The stress relaxation test results of C1～C3 samples were selected,the damage variable factors were introduced into the Merchant model,and the anchor-soil interface shear stress relaxation model considering damage was established.Through regression analysis of the test results,the empirical relationship of each model parameter changing with the shear displacement was established.Then,a shear stress relaxation damage model of the anchor-soil interface was established that can simultaneously consider the influence of the shear displacement level and the dry density of the soil.The results show that the Merchant stress relaxation model considering damage can well describe the shear stress relaxation characteristics of the anchor-soil interface.(4)A set of anchor unit samples(two parallel samples)were made,and the shear stress relaxation test and creep test of the anchor-soil interface were carried out respectively.The Merchant rheological model with damage considered was used to fit the test data,and the relationship between the fitted stress relaxation model parameters and the creep model parameters was compared and analyzed.Then,the interaction relationship between the shear stress relaxation characteristics and creep characteristics of the anchor-soil interface was revealed.