Viscoelasto-plastic Cavity Expansion Theory Based Properties For Soil-grout Interface Bond Strength Of Pressure Grouted Anchors

Pressure grouting anchors have been widely used due to their technical advantages such as great bearing capacity,low cost,and easy to construct.The grouting pressure is of great importance for the soil–grout interface bond strength,and furtherly influence the bearing capacity of pressure grouted anchors.It has important theoretical and engineering significance for the design and construction of pressure grouted anchors that research the influence of grouting pressure on the bond characteristics of soil-grout interface clearly.The main work completed in this article and the results obtained are as follows:(1)Firstly,the physical and mechanical properties of red clay from Hengyang City,Hunan Province was analyzed clearly based on some tests.Secondly,element-anchor specimens have been produced on the basis of the homemade pressure grouting systems,compaction device and drilling device.Thirdly,the instantaneous pull-out tests of element-anchor specimens were carried out through a universal testing machine,and 24 shear stress-shear displacement curves(τ-s curves)of element-anchor specimens with different saturation and grouting pressure,as well as bond strength.Finally,the relationship of soil–grout interface bond strength,grouting pressure and soil saturation is gained by the regression analysis.(2)The model expression of the pressure grouted soil–grout interface shear stress-shear displacement curve(τ-s curve)which can fit part ofτ-s curve of the pressure grouted element-anchor specimens well has been established.In addition,the second-order polynomial model is used to fit the model parameters,the saturation of the red clay and the grouting pressures,so that the empirical calculation formula for the model parameters is received.From this,an interface shear model considering the grouting pressure p_iand saturation S_ris established.Theτ-s curve model and the empirical calculation formula of the model parameters can be used to predict theτ-s curve based on the soil saturation and the grouting pressure.Theτ–s curves of two unfitted samples have been predicted,and the results show that the established interface shear model has high prediction accuracy.(3)The soil-grout interactions for pressure grouted anchors were specially divided into two stages according to its construction and mechanical behaviors,including radius expansion of anchor hole during pressure grouting and attenuation of soil-grout interface normal stress after the cement grout hardening.Specially,a formula for calculating the expansion radius of anchor hole was deduced on the basis of the elastic-plastic cavity expansion theory.A formula for calculating the attenuation of soil-grout interface normal stress was then reasoned based on the viscoelasto-plastic cavity expansion theory.Thereafter,a new theoretical analysis and calculation method for soil–grout interface bond strength of pressure grouted anchors was developed in reference to Mohr-Coulomb’s failure criterion.The results obtained from the instantaneous pull-out tests and other physical model tests for pressure grouted anchors were compared with the theoretical calculations.The good agreements indicated that the proposed theoretical method was effective and accurate for calculating the soil–grout interface bond strength of pressure grouted anchors.(4)The self-built pressure grouted anchor soil-grout interfaceτ–s curve model is used to analyze the load transfer of the pressure grouted anchors,and the numerical solution of the differential equation of the pressure grouting anchor load transfer has been acquired.Apart from that,the affect of the length,grouting pressure,and soil saturation on the bond characteristics of the pressure grouting soil-grout interface is explored through a calculation example.The results show that the greater the grouting pressure and length,the greater the peak pulling force of the pressure grouted anchors and corresponding peak displacement;on the contrary,the greater the saturation,the smaller the peak pull force and peak displacement of the pressure grouted anchors.