The Research on the Advanced Geological Forecast of LXS-3Section in the Second Line of Lanzhou-Xinjiang Railway
|School||Southwest Jiaotong University|
|Keywords||Advanced geological forecast Tunnel Tunnel Seismic Prediction Groundpenetrating radar FDTD forward modeling GprMax2D|
Today, tunneling plays an important role in the construction of many engineering projects. As one special engineering body, it has its own particularity which makes the risk during tunnel construction over that of any other projects. To minimize the risk of tunnel construction and ensure the construction safety and quality are the primary tasks of tunnel advance geological forecast, which is also an enormous challenge for the usage of advance geological forecast. Driving studies on tunnel geological prediction technology will play a huge role in promoting the development of the construction technologies in tunnel engineering and other underground engineering.Based on the analysis of collected previous data and research methods at home and abroad, this paper presents the results of advanced geological forecast along the LXS-3section in the second line of Lanzhou-Xinjiang railway by the combined application of TSP (Tunnel Seismic Prediction) and GPR (Ground Penetrating Radar). And then, compared the results with the field condition after excavation to analyze the accuracy of tunnel advanced geological forecast and summarize experience for geological advanced prediction of tunnel. This paper mainly focuses on the following aspects.(1) Summarize various tunnel prediction methods systematically and elaborate the basic principle, operating methods and interpretation signs of GPR.(2) Elaborate the basic principle, operating methods and interpretation signs of TSP. The results of previous studies show that TSP has a better effect in mid-and long distance prediction during tunnel excavation process and surrounding rock classification.(3) Take the LXS-3section in the second line of Lanzhou-Xinjiang railway as investigated object, the response characteristics of seismic wave and electromagnetic wave on some unfavorable geological phenomenon (such as, the distribution of groundwater-rich zones, fracture zones, joint concentrated areas and loess caves) of surrounding rock are summarized in this paper according to the image features obtained with the combined application of TSP and GPR.(4) Based on the long distance detection results obtained with the TSP forecast system, the dynamic surrounding rock classification was conducted in this paper according to the distribution of detected unfavorable geological conditions of surrounding rock to make scientific and rational guidance for the plan of tunnel construction scheme and support measures. The field construction results show that the application of TSP in surrounding rock classification is an efficient way in tunnel advanced geological forecast and is of great significance to design change during construction.(5) Based on the TSP detected results, GPR was applied to the mid-and short distance detection of tunnel construction to obtain a detailed forecast for the development of unfavorable geological conditions. The detected results show that the combined application of TSP and GPR is not only favorable for the saving of detection cost, but also can accurately forecast the distribution of unfavorable geological conditions in detection range due to the high accuracy of GPR.(6) After excavation of tunnel, the field conditions revealed by excavation were contrasted with the detected results obtained with TSP and GPR to evaluate the accuracy of combined detection of TSP and GPR. The comparison reveals that the combined application of both methods can efficiently improve the accuracy of advanced geological forecast in tunnel construction.(7) Based on the finite difference time domain method, an imagined model was built in GprMax2D software to simulate the theoretical reflection image of electromagnetic wave under such geological condition.which promoted the continuous improvement of advanced geological forecast technology.By the study of advanced geological forecast technology used in the LXS-3section in the second line of Lanzhou-Xinjiang railway, a systematical advanced geological prediction method is summed up:firstly, obtain the surrounding rock classification of tunnel construction by TSP method, and then, detect the distribution of unfavorable geological conditions by GPR based on the primary data obtained by TSP; finally, conduct the short distance forecast using face sketch method according to the results obtained by TSP and GPR.