Principle Study On Detection Of Void Condition Behind Tunnel Lining By Hammering Method

With the rapid development of tunnel construction in our country,the problem of tunnel diseases is becoming more and more serious.In many tunnel diseases,the bad bonding state between lining and ground is one of the main reasons,which can directly induce various tunnel diseases and affect the safety of tunnel structure.The hammering method is widely used in the integrity testing of pile foundation and the detection of defects in concrete slab structure,but its application and research of the tunnel structure disease detection is relatively few.This paper is based on the project "the research on the evaluation method of tunnel structure dynamic nondestructive testing(NO.2016JBM034)",which is funded by the Central University Basic Research Business Expenses.The principle level experimental and numerical study on the detection of the void condition behind tunnel lining were carried out.By means of time domain analysis,frequency domain analysis,time-frequency analysis,correlation evaluation and fractal box dimension calculation,this paper studied the influence of the soil parameters change on the void detection,and evaluated the void size and the influence range behind the concrete slab by the hammering method.This paper also made qualitative analysis and quantitative evaluation about the void condition behind tunnrl lining.The main works are as follows:1.A principle test model for the detection of void condition behind tunnel lining based on hammering method was established.Experimental study on detecting the variation of soil parameters,void size and its influence range by hammering method was carried out.2.The soil density and water content behind the concrete slab were respectively changed.Under different soil density and water content condition,the change law of the measured acceleration response of the concrete slab was analyzed.3.The cavity was buried behind the concrete slab.Under different soil parameters condition,this paper analyzed the difference of the vibration acceleration of the concrete slab between the void and without void condition.And the influence of the soil parameters's change on the void detection was studied.4.Under the condition of different size of voids behind the concrete slab,by arranging the measuring line and moving the measuring points,the fractal box dimension of acceleration response at different positions could be obtained.By analyzing the changes of the fractal box dimension,the size of void and its influence range could be deduced.5.The finite element model was established and the numerical simulation was carried out.The numerical model was checked according to the test results.Effects of soil density,dynamic elastic modulus and poisson's ratio on detecting the the void condition behind the concrete slab were analyzed.Besides,under different void condition,the size of void and its influence range were detected by hammering method.After the above study,the following conclusions were drawn:1.With the increase of soil density and water content,the acceleration response of the concrete slab is reduced,the vibration attenuation speed is accelerated,and the frequency spectrum curve is more flat;2.With the decrease of the soil density,the contact state between the concrete slab and the soil tends to be worse,which has a certain influence on the void detection.However,the change of water content has little effect on void detection.3.In the region of the void,the box dimension is stable.With the location of the measuring point away from the cavity,the box dimension decreases and will become stable again.Based on the analysis of the change of the acceleration box dimension,the quantitative evaluation of the void size and its influence range on the concrete slab was carried out.4.It was found by the numerical simulation that the change of soil density and dynamic modulus would have some influence on the void condition detection,but the change of poisson's ratio had little effect.Besides,the numerical simulation results verified the validity of the fractal box dimension in the test to determine the size of the void and the influence range.