Study On Image Identification Of Grouting Distribution Behind Shield Tunnel Segment With GPR And Settlement Control

Shield-driven tunneling construction in soft soil induce ground and tunnel settlements, because of three main factors, such as the proper operation of grouting slurry, the enough quantity of slurry and the suitable pressure of grouting. Therefore, the key point is to master the distribution of grouting accurately in time during the construction period. Based on this background, this thesis presents the method using ground penetration radar (GPR) to take nondestructive detection on the distribution of grouting material behind shield-driven tunnel segment. A series of examinations have been carried out including simulation and in-situ tests. This paper has simulated the propagation of ground-penetrating radar (GPR) pulse in mediums behind shield-driven tunnel segment and accomplished numerical simulation by FEM software. The main contents and conclusions are as follows:The coaxial probe technique and network analytic instrument have been used to detect the permittivities of different grouting materials, which may affect results of the GPR detection. From the results, the permittivities are obtained that vary with detecting frequency, moisture content, and curing period. Permittivity is exponentially related to detecting frequency(100MHz～1GHz).This study shows that it is important to adopt different permittivity values according to different choices of detecting frequency.In the simulation test of the distribution of grouting, the distribution shape of grouting, time of detection operation and distribution of gaps has been analyzed. It can be concluded that the imaging rules of different configuration slurry in reflection profile. Multiple-dimensioned analyse method of second-order DB wavelet has been applied during the data processing. It can restrain noise effectively and display the reflection distinction waveform of objects.In this paper, combining physical modeling results and numerical modeling results by Finite Difference Time Domain method (FDTD), the distribution of the grouting material can be identified accurately by Ground Penetrating Radar (GPR).