Abstract
Liner sheets are welded together by welding machine for the construction of landfill liners. After welding, the seam between the sheets are carefully inspected for the detection of faulty welds. There are various inspection methods such as Visual Inspection(VI), Air Pressure Testing (APT) and Vacuum Box Testing (VBT). VI has possibility of overlooking, APT can only be applied to seams joined by double fusion welding, is easy and effective, but does not indicate the exact location of the fault. VBT is time-consuming if all the seams are to be inspected. The thermo-graph inspection (TGI) has developed as a new method of non-destructive test, which is viable and can complement the demerits of existing methods. TGI measures the temperature of the sheet surface when they are welded. To evaluate quality of the seam, this method uses threshold temperature, which is obtained by welding experiments and strength tests of the seam samples, to judge whether the seam is correctly welded. However, it requires hundreds times of experiments to obtain the value. The problems is that if the material of the sheet changes, time-consuming experiment is always needed. To solve this issue, a heat transfer model of geomembrane seam welding is attempted to develop to derive the threshold temperatures for the faulty welds detection which can be applied to various kinds of materials. To verify the model accuracy, measurement of the vertical distribution of the temperature of the seam was conducted. The temperature at jointed part and at the surface were obtained by the thermos-couples while the sheets were welded by self-propelled heat-welding machine. The model values correspond reasonably well with the experimental data on various conditions.
