Experimental Study Of Detecting Void Beneath Cement Concrete Pavement With Seismic Wave Method

Cavity beneath concrete slab is a common disease of cement concrete pavement, which directly affected the carrying capacity and service life of the road. The total length of cement concrete pavement up to 2012 was 165.32 thousand kilometers, while account for 39.0percent of the total highway mileage. Obviously, cement concrete pavement occupied a very important position in the highway industry of our country, so it became particularly important to detect, prevent, and treat cavitys beneath concrete slab in time. While evaluated the void conditions precisely was the precondition for dealing with voids beneath concrete slab.After analyzing the formation mechanism of the cavity beneath concrete slab and getting a comprehensive understanding about existing detecting methods, then based on mechanical vibration, regarded voids beneath concrete slab as a cut to equivalent stiffness of the concrete slab vibration system, this paper proposed a new detection method — — seismic wave detection method. With the aid of IDTS3850——a pallograp generated by Chengdu Zhongke Dynamic Instrument Co., Ltd.,we could record and analyze seismic waves of the cement concrete pavement which been under different void conditions, and explored vibration characteristics of the cement concrete pavement structure with different cavity conditions,then we could obtain a kind of fast, easy, economical detection method aimed at voids beneath concrete slab. Applied a quantitative impact load on the cement concrete pavement when we detected the cavity beneath concrete slab by seismic wave detection method, at the same time,recorded vibration signal of the cement concrete pavement which been under different void conditions by pallograp so that we could obtain vibration laws of these cement concrete slabs,and then we could take advantage of this law to judge voids of other cement concrete pavements.The results showed that: parameters of the vibration signal(maximum velocity, dominant frequency, time of vibration) were in good correlation with the void conditions, cement concrete slabs which been under different void conditions(no void, a slight void, a serious void) had its own vibration laws. The degree of the void beneath concrete slab had highly significant influence on test results, the more serious the degree of void beneath slab was, the bigger maximum velocity was, and the higher the dominant frequency was, the longer thevibration time would be, in addition, the way of hammering also had a certain influence on the test results. Therefore, the research results of this thesis provided a new way for void detection, and it also had guiding significance for dealing with voids beneath concrete slabs in the program of highway maintenance or improvement.