Research On Three Points Regression Method For Identifying The Voids Under Concrete Pavement Slab

With the increase of service time of existed cement concrete pavements, various diseases are always occurred. Voids beneath the concrete slabs are one of the principal diseases of cement concrete pavements, and it is the main reason which leads the cracks and crash of concrete slabs. So, it is significant for the pavement rehabilitation to find a method to determine whether there are voids beneath cement concrete slabs and what the size of void area. Three points regression method has been one of the most representative methods for identifying the voids of concrete pavement with the development and wide applications of Falling Weight Defiectometer (FWD). But this method lacks theoretical base, and the voids can just be qualitatively analyzed. Also the application range of this method and the development of FWD is limited to some extent. Therefor, theoretical base of three points regression method and the method of identifying the voids quantitatively would just be reseatched in this thesis. Mainly contents as following:(1) The deflections under various loadings had been caculated based on different base model. The result showed that the intercept is caused by the change of void area value, and the larger the loading, the smaller the area.(2) The model of void which tally with the actual situation is given based on the mechanism of void development. The concept of Contact Compensation is first put forward in order to explain the intercept reasonably which is expressed in the relationship between load and deflection, and also Slope Difference index is established to solve Contact Compensation. The results show that the correlation of Contact Compensation and Slope Difference is good and the correction based factors of pavement model.(3) Deflection Ratio which is used to indentify the void area qualitatively is put forward. The formula which explains the correlation of Deflection Ratio and void area is obtained, and the coefficients in the formula are modified by calculating the models under different conditions which consider the parameter variations comprehensively. Finally, the void area value should include in the value of Contact Compensation, so the calculation method of void area is obtained and verified by engineering practice.(4) The whole set of void identification of cement concrete pavement has been established by integrating the method in this thesis and three points regression method. The research results provide theoretical basis for three points regression method and obtain method for quantificationally identifying the voids under concrete pavement slab. And it is significant for the void evaluating and maintenance of concrete pavement.