Study Of Creep Characteristic And Long-term Strength For Soil-anchor Interface Under Multiple Factors

Anchor supporting structures,such as anchors(cables),are commonly used in engineering for maintaining the stability of slopes,foundation pits,tunnels and other projects.However,under the action of long-term loads,the anchor(cable)supporting structure would produce rheological problems.In particular,the soil anchors are mainly reflected as shear creep at the soil-anchor interface.In fact,the soil-anchor interface produces creep problems under the combined action of various factors,such as soil water content and dry density,stress level,grouting pressure,etc.Therefore,based on the self-developed test device,comprehensive tests of the soil-anchor interface shear creep element samples were carried out under multiple factors,including soil water content and dry density,stress level.Additionally,theoretical analyses were also carried out to explore the shear creep characteristics and long-term strength of the soil-anchor interface under multiple factors.With the support of the National Natural Science Foundation of China,the main research work and results of this article are as follows:(1)The chemical analysis,mineral analysis,electron microscope scanning and basic physical and mechanical properties of the red weathered residual soil corrected from Hengyang basin,Hunan province were all tested.A special specimen preparation device for element anchor specimens was developed based on the spiral dry drilling method.6 groups(5 pieces / group)of element anchor specimens with different soil water content and dry density were prepared using this device.The effects of soil water content and dry density on the shear characteristics of soil-anchor interface were analyzed by means of instantaneous pull-out test.In addition,combined with the direct shear test results of the corresponding soil samples,an empirical formula about the shear strength of the soil-anchor interface versus the soil cohesion and internal friction angle was established.(2)A creep pullout test device was designed and made based on the principle of force increase of pulley block.16 groups of element anchor specimens with different soil water content and dry density were all applied graded creep loads using this device.A cluster of soil-anchor interface shear creep curves in various stress levels about those specimens were obtained by T-K Tan’s method.Soil-anchor interface long-term shear strengths were obtained by isochronal curves method.Additioanlly,an empirical formula about the long-term shear strength of the soil-anchor interface versus soil water content and dry density was established by regression analysis.(3)Creep testing results of 4 groups of specimens were selected,which were the same in soil water content,but different in dry density.The empirical relationships of two hyperbolic model parameters versus time were obtained by regression analysisusing the hyperbolic model.The shear creep hyperbolic models for the soilanchor interface with different dry densities were established.Furthermore,by analyzing the relationship between the model parameters and the dry density of the soil,a soil-anchor interface shear creep model that can consider the effects of the shear stress level and the dry density of the soil was established.(4)The traditional Poyting-Thomso creep model(P-T creep model)was improved by introducing a nonlinear viscous element whose viscosity coefficient changes with time in a negative exponential function.An improved P-T creep model with the ability of describing the accelerated creep was established.Using this model to analyze the above testing results,it indicates that the improved P-T model has a better fitting effect on the creep curves with different soil water content and dry density.