Performance of Super-Large-Span Tunnel Portal Excavated by Upper Bench CD Method Based on Field Monitoring and Numerical Modeling

The number of super-large-span tunnels is increasing in both new construction and reconstruction projects in China recently. In super-large-span tunneling engineering, the deformation properties and mechanical behaviors of tunnel portal structure are more complex than those of common tunnel due to the flatter shape and larger construction span. The mechanical behaviors of rock mass change in response to different sequential excavation methods and supporting parameters. The upper bench CD method has been gradually applied in the construction of super-large-span tunnels in China. In this paper, the design parameters for the supporting structure of super-large-span tunnel were studied by the field monitoring and numerical modeling in a case study of Laohushan tunnel. It was found that the crown settlement was larger than the clearance convergence, and the stress of arch was greater than that of the side wall in tunnel portal section. The invert structure was flat with small curvature. Therefore, the shotcrete was mainly subjected to tensile stress. The use of H200 × 200 steel rib with spacing of 60 cm and C25 shotcrete with thickness of 30 cm is recommended. The results of this paper provide basis for the development of design specifications and construction standards for super-large-span tunnels and provide reference for similar projects in the future.

A Simplified Viscoelastic Solution of the Frost Heaving Force of Cavity Water behind Tunnel Linings

With the high demand for construction of tunnels in China’s severe cold regions, the problem of frost heaving has become an important factor that endangers tunnel safety. This paper attempts to investigate the effect of frost heave of cavity water that widely exists in the tunneling engineering on the tunnel stability. According to the actual deformation of the surrounding rock of the tunnel, the viscoelastic behavior is considered to the surrounding rock. On the premise of the elastic solution of stagnant water frost heave, the viscoelastic solution of frost heaving pressure is deduced by Laplace transform using the generalized Kelvin model based on the elastic-viscoelastic correspondence principle. The frost heaving force is analyzed through a case study with variations in the size of the cavity defect as well as the constitutive model parameters. It is concluded that the frost heaving force increases with the cavity defect size; over time, the frost heaving force gradually increases, but it will eventually stabilize. It is found that when the frost heaving force reaches a certain level, the surrounding rock with low strength or the lining with insufficient strength will crack, and the frost heaving force will not continue to increase.

Mechanical and Acoustic Emission Characteristics of Sandstone through Triaxial Unloading Test after Cyclic Freezing-Thawing Treatment

The dynamic failure behaviour of tunneling rock in the cold region where freezing-thawing frequently occurs is unclear. This study aimed to test and understand the damage characteristics of tunneling sandstone samples in the cold region via triaxial unloading test and acoustic emission (AE) technique. The sandstone samples were first subject to different cycles of freezing-thawing. Their stress-strain curves, deformation modulus, and the AE characteristics were then measured under triaxial unloading conditions and through the AE test. The results showed that the freezing-thawing treatment with less than 60 freezing-thawing cycles caused rather less damage compared to the triaxial unloading condition. For the samples subject to more severe freezing-thawing treatment, more cracks were produced. These cracks were not closed under small confining pressure during the triaxial test, causing weaker mechanical properties of samples. We also found that the freezing-thawing treatment had a significant deterioration on the mechanical properties of the sandstone samples when the number of freezing-thawing cycles exceeded a certain threshold (between 60 and 80 in this study). As the AE characteristics matched well with the key stages of the measured axial stress-strain curves and the deformation modulus that varied with the decreasing confining pressure, the AE characteristics can be potentially used to quantify the released energy of rock cracking and identify the critical damage phases during the tunneling engineering process.

Application of Grouting Technology in the Geotechnical Engineering

Through detailed investigation to development status of grouting technique, summarizes the classification of geotechnical grouting technology, selection of materials grouting, Finally, by anchoring engineering and tunneling engineering described in detail grouting process，grouting order, grouting parameters and grouting end standard in the geotechnical engineering application，This research has practical guidance and theoretical reference value for similar projects.

Optimal Design of Working Face Ventilating System of Huoerxinhe Company

In order to guarantee the safe and efficient production of coal mine of Huoerxinhe Company, for the problems of gas exceeding limitation, excavating replacement tension, resource waste air leaking and so on, the ventilation mode was optimized and Y type ventilation mode was adopted. Practices indicate that this ventilation mode is entirely feasible on working face of Huoerxinhe Company. Through this mode, we can (1) decrease the tunneling engineering quantity, improve the excavating replacement tension of double U type mode; (2) reduce the protective coal pillars to cut down resource waste; (3) solve the problem of gas exceeding limitation on upper corner thoroughly.

Experimental Study on Mutual Effects of Rock Tunneling Positions with High Underground Pressures

Using the mould pattern contrasting experiments the carrying capacities and deformation effects of underground tunnels within soft bed and top or floor strata are studied under high ground pressures in this paper. Through measuring mould strengths and deformation with different stratum and space position the relations of tunneling positions in different strata with carrying capacity and strains are obtained. It is shown that the soft seam tunneling under high ground pressure can bring about higher secondary stresses and have more acting effects than top or floor tunnels. In the same pressure conditions the carrying capacity of having top tunneling above soft tunnel decreases near 30% with that of having floor tunnel. The mutual effects with double horizontal spaces of tunnels decrease 25%. The experiment conclusions are important significance of conducting and applying for reasonable designing underground tunneling engineering.

Ground Settlement Prediction Model and its Application for Tunneling Engineering above Mined-Out Regions

Although many types of curve fitting methods were used in ground settlement prediction, it is due to every prediction method was not perfect, they have some defects and shortcomings to some extent and ground settlement prediction be up against huge challenge. Usher model, being used for economic and resources prediction, is introduced to ground settlement prediction as a new method, and its mathematics features are also analyzed. After comparative analysis, Origin software is selected for parameters solution of Usher model with an explanation of the solving process. Based on the Shipogou tunnel project which through the mined-out regions in Qingdao-Yinchuan highway, the Usher model for ground settlement is established combining to the field data, of which the parameters are solved with the user-defined function and nonlinear tool of Origin. The predicting results being compared with that of grey model and hyperbolic model, it shows that Usher model is of good adaptability, high accuracy, simple and coinciding well with measured data.

Application of HHM in Risk Identification of Tunnel Project

Tunnel project contains complex and diverse risk factors. Risk management has an important role on tunneling engineering projects. Risk management is based on risk identification. Only with sufficient knowledge of risk can we analyze,evaluate and control the risk .Traditional risk identification methods are generally targeted at a certain stage of the tunnel project or a particular content of the tunnel project. It can not consider all factors of the tunnel projects. This paper presents a new risk identification method - hierarchical holographic modeling. The method provides a multi-angle decomposition to the perspective of the tunnel features and in order to find the tunnel project risk source. It can provide a basis for risk management.