The early closure tunnel construction method can restrict deformation around tunnel face by inner pressure induced in immediate ring closed supports of tunnel section. In this paper, the characteristics of early closure method on inner support pressure, acting earth pressure, distance of closure and ratio of radius of support to invert are clarified. As a result, the support effect of early closure method is heightened by arranging the distance of closure according to ground characteristics, and earth pressure ratio of arch to invert has a correlation. These lead the guide of rationalization of support system.
The authors developed a new survey method, called Tunnel Seismic Probe Drilling (T-SPD), in which drilling vibration data are used (for the evaluation of ground conditions). T-SPD only needs drilling a borehole on a side wall to set receivers as preparation works. Since drilling vibration data is recorded during drilling, T-SPD doesn't prevent a drilling work (at the tunnel face). So far, we have conducted field demonstration tests of the T-SPD using a middle-long boring with a drill capacity of 50 - 150m at three tunneling projects and confirmed its effectiveness. In this paper, we will report the results of two field demonstration tests using an ultra-long controlled boring with a drill capacity of 1,000m. The T-SPD results shows a relatively good agreement with verification data such as P-wave velocity distributions estimated from the ground surface and from the tunnel floor (in other survey methods). In addition, T-SPD can properly evaluate the ground situation where the drilling energy might have been overestimated because of considerable jamming.
Heaving in some mountain tunnels after completion occurs in roadbeds that were built without an invert because the ground was relatively stable during construction. The stress-release by excavation, along with subsequent swelling of groundwater, cause the roadbed to lose strength, allowing upheaval of the road surface.
In this study, we analyzed geological degradation characteristics and the state of past tunnels in cases where inverts were installed. And, we used measurement data to compare axial forces of inverts with axial forces of early-closure primary inverts in other tunnels at the construction stage. Based on these, we discuss the necessary performance. As a result, we used numerical analysis to compare support effectiveness of the invert shape and considered a rational structure.
Sprayed concrete lining is often applied to the excavated rough surface of face and its circumference in order to prevent the accidents due to rock falls in a cutting face of tunnel construction. Around 10 minutes time, workers approach the face to mount the steel arch support on the circumference. In this study, we aim to reveal the resistance and mechanism of a sprayed concrete punched into by an unstable rock came off the face, and so we developed the experimental equipment which could punch a rock into a early-age base concrete and then evaluated the strength and deformation characteristics of the concrete using a three-dimensional laser scanner etc. In addition, its experimental test was simulated by Discrete Element Method and then the mechanism of punching failure was revealed. Especially, the punching behavior of the concrete was expressed using the tensile softening curve based on the fracture process zone and then its punching resistance was supposed to be arisen by tension rather than shear.
As a measure to preserve groundwater environment during the construction of mountain tunnels, usually waterproof materials are injected around the tunnel to control the leakage of spring water. However, there have been only a few examples on the use of post grouting for the injection of waterproof materials after tunnel excavation. In this research, we present a design and construction method for the injection of waterproof materials by post-grouting using a dam consolidation grout method and examine its effects based on construction data. In addition, we analyze the tunnel behaviors at the time of groundwater recovery at a level exceeding 150 m following the injection of waterproof materials, and discuss the applicability of water-reducing measures under a high groundwater level condition.
The health monitoring for tunnels, especially over 50 years old, became a serious issue after the ceiling panel collapse accident at Sasago highway tunnel occurred in 2012. Following this accident, MLIT (Ministry of Land, Infrastructure, Transport and Tourism of Japan) required administrators to conduct periodic inspections of road tunnel. One of the authors has already proposed Tunnel-lining Crack Index (TCI) to assess the health monitoring for tunnel lining quantitatively. Periodical inspection data of twin road tunnel were applied for the estimation of TCI. However, health monitoring by using TCI is usually performed focus on each span or each tunnel. In this study, the effectiveness of TCI separating the section of tunnel lining become clear by comparing the difference of area by four patterns. Thus, benefits of employing TCI become clear for quantitative priority health assessments of tunnel lining.