The commonly used methods are TSP, TST, and TST, both of which are used to forecast in the tunnel. TSP and TST can forecast the geological conditions 1～15m in front of the tunnel face, and GPR can forecast the geological conditions 2 ~ 3m in front of the tunnel face.
In recent years, high-density electrical method has been introduced into tunnel geological prediction, that is, high-density electrical section is arranged along the tunnel direction on the mountain directly above the tunnel. The advantages of this method are high speed, intuitive image and sensitive response to water and structure.
Yunnan Aerospace Exploration has used long-term (high-density resistivity method), medium-term (TSP, TST) and short-term (ground penetrating radar) methods to predict tunnel geology earlier in China, and achieved good results.
beam (Bore Tunnelling Electrical Ahead Monitoring) detection technology is a more advanced electrical tunnel advanced detection technology in the world at present. It was developed by GETGEO EXPLORATION TECHNOLOGIES of Germany (GET for short) in 1998, and obtained the German national patent in 24.
as an advanced detection technology of the induced polarization method in the frequency domain of focusing current, BEAM is developed from a comprehensive electrical parameter called the PFE-Pereentage frequency effect, and also applies the focusing current technology to keep the detection data within a certain range.
the principle of p>BEAM testing technology is to find out the rock quality, cavities and water bodies through the electrical method (induced polarization method) of testing the resistivity of rock strata. The phenomenon that the rocks of electron conductor and ion conductor are polarized in artificial current field is called induced polarization, which was discovered by Conrad Schfumberger of France in about 1913.
the BEAM test system developed by GET company in Germany is a technology that uses AC induced polarization method as detection means.
AC induced polarization method uses two different fixed frequencies in ultra-low frequency band (.1～1Hz) to supply power (f1 and f2) respectively, and then respectively observes the voltages of f1 and f2 when supplying power, and obtains two kinds of resistivity R(f1) (observed with lower frequency f1) and R(f2) (observed with higher frequency f2). Therefore, the percentage frequency effect PFE can be calculated (the formula is as follows):
R(f1) =U(f1) /I(f1) and r (F2) = u (F2)/I (F2)
pfe = [r (f1)-r (F2)]/r (f1) X1. F2 )
PFE is a characteristic parameter of rock mass, which represents the ability of rock to store electric energy, and the porosity is inversely proportional to PFE. In the tunnel advanced prediction, the corresponding PFE of karst caves, faults, fracture zones and other bad geological bodies with high porosity is lower; The high porosity section filled with water and gas can only store a little electric energy, so the PFE is low; Sand, clay layers, piles, boulders and concrete can also be detected by BEAM because of their typical PFE values.
the interpretation of p>BEAM's forecast results is based on the above definitions of different rock masses, in which high, medium and low indicate the degree of porosity of rock masses, and the PFE values of fault zones and caves in hard rock areas with high porosity are the lowest, followed by similar geological conditions in soft soil areas, and the PFE values of compact rock masses are the highest, and the porosity and PFE values are obviously inversely proportional. Different resistivity will also correspond to different rock mass conditions. Dry and dense rock mass has higher resistivity, while water-bearing rock mass with large porosity has lower resistivity. BEAM system uses AC induced polarization method to make advance prediction, and obtains two parameters of percentage frequency effect PFE and resistivity R. Based on these two parameters, the geological conditions ahead are comprehensively predicted.
Since the beginning of 2, this technology has been applied to tunnel projects under various complicated geological conditions abroad. Up to now, the cumulative length of the tunnel has exceeded 1km. The main applications are Ginori Tunnel in Italy, Gotthard Base Turnnel in Switzerland (the longest tunnel in the world at present), Lotschberg Base Tulnnel in Switzerland, Irlahull, Geisbers and Stammham Tunnel in Germany (connecting the high-speed railway from Nuremberg to Ingolstadt) and so on.
Europe and America Geodetic Equipment China Co., Ltd. took the lead in introducing technology to China.
monograph on advanced tunnel geological forecast "Tunnel Geological Forecast"