Applied Mechanics and Materials Vols. 501-504

Abstract: In order to avoid heavy casualties and economic losses, and to get an insight into engineering and hydrogeological conditions, Tunnel Seismic Prediction (TSP) method is applied for advanced geological prediction in tunnel engineering. Basic principle, data analysis method, prediction criterion of TSP are studied. Seismic reflection characteristics of karst caves and fractured zones are analyzed and demonstrated in Qiyueshan Tunnel. Results indicate that TSP is sensitive to karst caves and fractured zones, but may have errors in location. The location of the prediction results should be checked with comprehensive geological prediction methods. In some extent, research of the prediction principles and engineering application in the present study is instructive for further applications.

Abstract: A Ground Penetrating Radar (GPR) method was conducted for advanced geological prediction in Wuchiba Tunnel field, Hubei Province, China. A 100 MHz antennae is applied. Reflection characteristics of water are studied. Theoretic and case studies indicate that the reflection characteristics of water or mud are: The reflection energy (amplitude) is high; the reflection frequency is low and the reflection phase is inverse (the phase difference is 180°). These characteristics are the main criterion of water and is instructive for further GPR advanced geological predictions in similar geological fields.

Abstract: In this paper, with the in-situ engineering project Shiziyang tunnel of Guangzhou-Shenzhen Railway, under the disturbance of high-speed train vibration load, the shield tunnels dynamic response and foundations sand liquefying phenomenon are studied ,where they are mainly located in saturated and soft soil. Due to the tunnel going through the paralic deposited silt layer, silty soil, alluvial clay layer and the layer of fine sand or coarse sand layer, under the condition that enduring a long time of high-speed train running, which may easily lead to the foundation liquefaction and asymmetric settlement. At the entrance of the tunnel, with the poor geological conditions and weak cladding, which can easily induce sliding and collapse, where the geological conditions of this part is the most unfavorable place. Through numerical simulations, the main factor the constitutive model is explored, which may affect the single high-speed train loads on the vibration response of the train in shield tunnel and the law of accumulation and dissipation for pore water pressure.

Abstract: With the development of tunnel technology, the number of tunnels becomes huge in some area, and adjoining tunnels turn into tunnel group in some highway sections. So, to ensure the traffic safety, the linkage ventilation control system for the tunnels of the whole highway section is necessary and essential. In this research, obtaining the live traffic information of each tunnel is the key point. This article attempts to build up an intelligent ventilation system which makes traffic flow data of every tunnel available and predictable. The system achieves information sharing and build up weight-based traffic forecasting model. In addition, the composition of fuzzy-logic ventilation control model is introduced. The research might expand the application of intelligent tunnel ventilation control system and could provide references to other linkage ventilation control system of tunnel groups.

Abstract: This paper researched the high press and broken drift deformation mechanism of 1424m filling roadway by theoretical analysis and on-site monitoring. Strengthening rock residual strength by improving roadway pressure contributed to enhancing drift stability. The roadway deformation could be controlled effectively with the method of improving rock self-carrying capacity. The monitoring results showed anchor supporting resistance and reinforcement depth were inadequate. And supporting method was not coordinate with rock deformation, which was the main reason of roadway deformation increasing gradually. Improving bolt pre-stress and increasing the anchoring range are the key to limit roadway deformation. And the support way should provide a greater supporting resistance. It recommends that the combination reinforcing method, "strong prestressed anchor + long cable+ grouting behind the surrounding rock" is appropriate for controlling the drift displacement, and it can save supporting costs 390 yuan per year for per meter drift compared with previous supporting way while reaching the same effect.

Abstract: Based on hydraulic model test, overflowing capacity, water flow state, flow speed distribution, pressure, fluctuating pressure, downstream erosion of flood discharging tunnel and other parameters while total opening and part opening of No. 1 flood discharging tunnel of Hekoucun Reservoir have been observed. It is indicated in experimental study, water at the contraction section at the end of the sluice chamber gets fierce fluctuation, with spray reaching the tunnel top, and results in great negative pressure on the lateral walls on both ends of the contraction section in the original design scheme. After changing the shape of the transition, flow state has been improved, negative pressure reduced, so the design is adaptable; It is recommended in the test guiding plate can be added on the both sides of the cleaning door so as to reduce water-wing height; Three medium-size piers have been compared with the better pier recommended in the test.

Abstract: In order to study the failure process and mechanism of rockburst of underground cavern, the physical model materials of hard brittle rock which is gotten though similar material test and have the tendency of rockburst are prepared for making cavern physical models of 1000mm*1000 mm*1000mm and φ 150mm. Then plane strain physical model test is carried out on the machine for large-scale physical model test in geotechnical engineering. The results show that the state of rock switches from the elastic to the plastic on the condition that horizontal and vertical load of the model is equal and increase synchronously. The failures of hard brittle rock burst in surrounding rock are mainly in the initial crack of rock. The phenomenon of separation by layer appears around the cave walls. Damage occurs in very short time and extremely narrow loading range and is sudden with chippings popping or fragments falling. After failure rock stress readjusts and keeps relatively stable in a relatively long time and loading range.

Abstract: A tunnel in Chengde collapsed several times and cracks existed in the second lining. Using non-destructive testing equipment, tunnel support was detected to find out the hidden trouble early. In the section of K16+890~K16+950, the quality of tunnel support was assessed, with GPR and anchor measuring apparatus. In the tunnel, the thickness of composite lining was 25cm, and the second lining was 38cm, both of which met the design requirements. Positive peak method was selected to locate on I beam. The average longitude space of I beam was 127cm, while the design value is 120cm. Many rock bolts was lacked at the right crown. Moreover, the bolts in the haunch did not kept in diamond layout, close to I beam. Through analyzing waveforms of impact-echo, the number of qualified bolts only made up 74 per cent of the total bolts. The large space of I beam led to the lack of holding power. Meanwhile, the disqualified bolts limit the coordination deformation between surrounding rock and support. All the support defects led to tunnel collapse. These tests results demonstrate that NDTcan be used to mitigate the risks of tunnel construction.

Abstract: Taking the longwall mining face area in steeply dipping seam as the research object, the stability of asymmetrical rock mass structure is analyzed using shell theory and masonry beam theory. The results show that asymmetrical shell structure is formed at the top strata of mining stope and its magnitude is mainly determined by the mechanical characteristic of overburden strata of working face, mining space size and so on. Localized instability of the shell structure is the main factor that leads to the overall structural instability in the stope. The instability modes includes: the shell roof instability dominated by tensile failure, shell shoulder instability initialized by compression-shear failure, and shell bases composite instability occurs in tensile and compression-shear modes. The shell structure stability dedicates rational strata control measures to choose, and the caving height of overburden strata is the key for shell structure instability.

Abstract: The deformation and failure problems in soft rock supporting cannot be effectively controlled with conventional methods. This paper put forward the coupling support technologies by the use of large deformation constant-resistance bolt, large deformation constant-resistance cable and bottom-grouting pipes, with the analysis of deformation and failure reseasons, combing with verifications in field-test project at B103W01 working face, State Grid Energy abundance Coal Limited Shajihai Coal Mine. It also provides the reference for the tunnels supporting under similar conditions.