Research On Imaging Method During Shield Driven Tunneling

The forecast of prospecting during shield driven tunneling is based on underground medium resistivity theory. According to the distribution of electric field in different medium that the apparent resistivity is different, we study the apparent resistivity which is affected by the underground objection in different depth. Then we transform the apparent resistivity data into an image.The purpose of inversion is obtaining the minimum of the objective function. It is an optimization method in mathematics. Traditional method such as least squares method need to calculate the partial derivatives of the inversion model. Usually, the model of geophysics is strongly non-liner, the calculation need a long time because the partial derivatives of the model is too complex. This article introduces three algorithms: hooke-jeeves, simulated annealing and quantum annealing. These three algorithms need not to calculate partial derivatives, and they have fast-speed partial convergence. The model is based on the abnormity of apparent resistivity caused by globularity objection underground of middle-gradient device and double-pole device. We inverse the testing data of apparent resistivity through these three algorithms, that we can find the real resistivty, the depth, the radius and the horizontal distance of the globularity objection and the ground resistivity. Comparing these three algorithms, we can find the virtue and the disadvantage of the three methods: hooke-jeeves is an unconstrained optimization method, it has a simple principle and an easy achievement, but its initial value has a strong impact on the result data of inversion; simulated annealing and quantum annealing are both random search algorithm, they can jump out of the local convergence to obtain the global convergence value, and their initial value have little impact on the result data of inversion and good stability, so they are widely used in geological prospecting.We apply SA and QA in this inverse imaging software that is made up by C++ in VC6.0. The inverse imaging software is fit for finding the underground globularity objection that cause the abnormity of apparent resistivity, under the middle-gradient and double-pole device. We also give the experience explanation about the apparent resistivity curve. For the experiment, we design a programmable frequency signal source. Direct digital synthesize technology is used in this signal source device that is controlled by MCU.