| Through reading massive literature materials, this paper summarizes and analyzes the Karst cause, zonal regularity and the characteristics of engineering geological hazards, and studies the theory of seismic wave. Meanwhile, the TST12A Seismic Prediction System ("TST12A System"as below) is applied in Yingzuiyan Tunnel construction of Yu-xiang Highway project in Chongqing, where the Karst is commonly. TST12A System takes advance geological predictions for the tunnel, and receives good effect, according to engineering geological materials and feedback information as construction.(1) This paper synthetically analyzes and evaluates kinds of advance geological prediction methods including long-distance and short-distance prediction. Analyzing lots of practical projects, it explains their applicable conditions, characteristics and limitations, and then shows the present situation and developing trend.(2) Through studying characteristics of Karst causes and zonal regularity, according to the condition and requirement of tunnel construction, this paper systematically concludes the harm, categories, gushing water and influence to tunnel construction, which caused by Karst. Meanwhile, it shows that the key factors of gushing water possibility and scale are Karst of tunnel body, Karst's growing structural planes and position in space.(3)The prediction method used by this paper predicts the geological condition ahead of and around the tunneling face, which is based on rules of seismic waves reflecting in different strata. It introduces geophysical conditions, wave field principle, types of seismic waves, wave impedance, wave amplitude, wave-front diffusion and wave-front absorbing, as well as time-distance curve which is very important to geological prediction. Forward, backward and refracted waves which produced by reflecting, transmitting, refracting and diffracting when seismic waves meeting wave impedance interface, spread in space and time by their own rules. So the arranged sensor can receive wave's characteristics in space and time, namely characteristic time-distance curves.(4)TST12A System mainly reveals poor geological bodies'existing, orientation and the rule of lithology changes ahead of the tunneling face, which is different from the traditional geoexploration method. The seismic wave prediction method, which is carried out inside the tunnel, takes special processing rather than one-dimensional semi-infinite space in elastic wave field. TST12A System is a new prediction method, which is based on classic theory of elastic wave and chiefly uses vertical seismic profile technique and multi-channel wave seismic exploration technique for reference. This system adopts the one-blast to one-receipt mode, whose sensor is arranged far away from the tunneling face.The data collecting system consists of the collecting equipment, the sensor and the seismic source, which is designed for special construction environment. The sensor adopts three-component velocities mode so that it can be arranged inside the bare holes coupled with water. And then this paper puts forward excitation energy selection principle in aspect of seismic energy's effect to the test data. The parameter's setting of data collection consists of excitation modes, seismic energy, blast holes'distance, number of recording channels, sampling rate, recording length, the minimum migrating distance and spacing of the channels.The data processing software system is designed for the particularity of tunnel geological prediction and the natural characteristic of data information, which is based on vertical seismic profile technique, multi-channel wave multi-component seismic exploration technique, the tomography of seismic wave and the data processing of petroleum exploration. This system takes a consider of the rules and characteristics of seismic wave transmitting in rock mass to extract and analyze effective waves by the spherical spreading compensation, extraction of up reflected waves, separation of P and S waves, Back Q filtering, velocity scanning, and migrating and imaging techniques. Considering of the complexity and diversity of collected data in field, optional processing mode according to the demand takes the place of the single-fixed one.(5)Yu-xiang Highway is located in the southeast of Chongqing, acrossing Nanchuan, Wuling, Pengshui, Youyang, Qianjiang and Xiushan. There are tunnels in a big proportion of the project, with complicated and variable geological conditions. Moreover, the region belongs to the rich-Karst area in the southwest of China, which makes great trouble to the tunnel construction.TST12A System is applied in Yingzuiyan Tunnel project, which is located between Dahan village in Youyang County and Shihezi village in Qianjiang District. It is an up-down separated and four-lane road long tunnel with S-line shape, whose entry is connecting with Yandengbao Big Bridge. The double line's distance varies from 14.8m to 35m at Youyang side, and from 35m to 16.5m at Qianjiang side. The left line ( ZK39+520～ZK42+767) is 3247m long and the right (YK39+470～YK42+780) is 3310m long in total. This paper adopts the results of predictions for the right line of Yingzuiyan Tunnel to prove the accuracy of TST12A System. And it found six belts of rock fault, cracking rock zones and a Kars cave ahead of tunneling faces YK42+590,YK42+180,YK42+095,YK41+477,YK41+198,YK40+737,YK39+913, which agrees with practical condition during the tunneling construction at accuracy 90%. In addition, this paper continues to discuss on the rules of Karst cave's prediction through analyzing the typical testing section (YK41+198～YK41+098). |
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