Maoxin Su

Predicting geological hazards during tunnel construction

Abstract The complicated geological conditions and geological hazards are challenging problems during tunnel construction, which will cause great losses of life and property. Therefore, reliable prediction of geological defective features, such as faults, karst caves and groundwater, has important practical significances and theoretical values. In this paper, we presented the criteria for detecting typical geological anomalies using the tunnel seismic prediction (TSP) method. The ground penetrating radar (GPR) signal response to water-bearing structures was used for theoretical derivations. And the 3D tomography of the transient electromagnetic method (TEM) was used to develop an equivalent conductance method. Based on the improvement of a single prediction technique, we developed a technical system for reliable prediction of geological defective features by analyzing the advantages and disadvantages of all prediction methods. The procedure of the application of this system was introduced in detail. For prediction, the selection of prediction methods is an important and challenging work. The analytic hierarchy process (AHP) was developed for prediction optimization. We applied the newly developed prediction system to several important projects in China, including Hurongxi highway, Jinping II hydropower station, and Kiaochow Bay subsea tunnel. The case studies show that the geological defective features can be successfully detected with good precision and efficiency, and the prediction system is proved to be an effective means to minimize the risks of geological hazards during tunnel construction.

Multi-component and multi-array TEM detection in karst tunnels

Emerging applications of transient electromagnetic methods (TEM) in tunnelling require higher resolution on the distributions and shapes of low resistivity bodies, such as karst water and karst pipes, using multi-component and multi-array receivers. However, there are no apparent resistivity definitions for both vertical and horizontal components with offsets inside the loop. Although the raw field can show the differences of the earth electric structure, it is not straightforward. Apparent resistivity is very convenient and easy for engineers. We have developed a method for multi-component and multi-array TEM which can be applied in tunnelling and defined the expressions of apparent resistivity. This method takes advantage of the difference in resolution among components. A homogeneous half-space model and four typical three-layered models are used to test the effectiveness of the new definition. A field case history is carried out and analysed to demonstrate the viability of this technique. The results suggest that it is feasible to use the technique in tunnelling, especially for identifying the spatial distribution of karst water and karst pipes.

Study on Major Construction Disasters and Controlling Technology at the Qingdao Kiaochow Bay Subsea Tunnel

ABSTRACT Li, S.; Tian, H.; Xue, Y.; Su, M.; Qiu, D.; Li, L., and Li, Z., 2015. Study on major construction disasters and controlling technology at the Qingdao Kiaochow Bay Subsea Tunnel. The Qingdao Kiaochow Bay Subsea Tunnel was difficult because of complex geological conditions, including the 18 faults crossing the tunnel, large construction section, and high risks for collapse and water inrush. These conditions were considered as a background of this study. Geological disasters, such as collapse and water inrush, were introduced as the two main geological disasters during construction. Moreover, the advanced support pretreatment measures that aimed to address faults during construction and effectively prevented collapse disasters were introduced. For the water inrush disaster, geological forecasting was used to predict underground water location, and advanced grouting was adopted. The presented disaster control technologies were proven effective in the construction of the Qingdao Kiaochow Bay Subsea Tunnel. This study provides a certain reference value for disaster control technologies for subsea tunnel construction.

3D electrical resistivity inversion using prior spatial shape constraints

To minimize the number of solutions in 3D resistivity inversion, an inherent problem in inversion, the amount of data considered have to be large and prior constraints need to be applied. Geological and geophysical data regarding the extent of a geological anomaly are important prior information. We propose the use of shape constraints in 3D electrical resistivity inversion. Three weighted orthogonal vectors (a normal and two tangent vectors) were used to control the resistivity differences at the boundaries of the anomaly. The spatial shape of the anomaly and the constraints on the boundaries of the anomaly are thus established. We incorporated the spatial shape constraints in the objective function of the 3D resistivity inversion and constructed the 3D resistivity inversion equation with spatial shape constraints. Subsequently, we used numerical modeling based on prior spatial shape data to constrain the direction vectors and weights of the 3D resistivity inversion. We established a reasonable range between the direction vectors and weights, and verified the feasibility and effectiveness of using spatial shape prior constraints in reducing excessive structures and the number of solutions. We applied the prior spatially shape-constrained inversion method to locate the aquifer at the Guangzhou subway. The spatial shape constraints were taken from ground penetrating radar data. The inversion results for the location and shape of the aquifer agree well with drilling data, and the number of inversion solutions is significantly reduced.

Practice of TEM tunnel prediction in Tsingtao subsea tunnel

Summary Introduce the TEM tunnel prediction and its application in Tsingtao subsea tunnel. Give an introduction about the apparent longitudinal quadratic differential conductance imaging method. It has the characteristic of more sensitivity to geological surfaces. Finally, give a field test case of TEM prediction in Tsingtao subsea tunnel. The result forecast two water bearing structure ahead of the tunnel face successfully.

Technology of transient electromagnetic synthetic aperture method in tunnel prediction

Summary As an electromagnetic induction method, TEM (transient electromagnetic method) is sensitive to low resistivity water-filled fracture zone, and has made some achievements in the advanced prediction. However, as the geological and hydro geological conditions encountered in the excavation of buried long tunnel become more and more complicated, it is difficult to forecast the water hazard problems in the construction process of complex geological conditions, so new interpretation methods that fit to such conditions is in urgent need. In this paper, the principle of transient electromagnetic synthetic aperture method is introduced. Firstly, we get longitudinal conductivities with equivalent conductive plane method. Then, by borrowing ideas from synthetic aperture radar, correlation superposition can be used in the processing of differential conductance signals. Lastly, draw profiles with synthesized signals and give a joint interpretation combined with apparent resistivity sections. The results of imaging and interpretation for measured data have shown that this method is sensitive to geological disasters in front of the tunnel face, and compared with previous methods, the resolution has improved greatly.