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The most crucial role in the safe construction of shield tunneling is how to keep up the tunnel face stability, especially for those in saturated sand. An issue of collapse associated with insufficient support pressure can be observed during shield tunneling when the face support pressure is not well managed. In this regard, the face stability of slurry shield tunnels with an impermeable filter cake in saturated sand was analyzed in this study. A series of finite element models were developed and verified against published experimental data. The failure mechanism of tunnel face and limit support pressure at collapse were investigated with consideration of the effects of cover depth (d1), water level (d2), and internal friction angle (φ). The results indicated that the wedge-prism model could represent the tunnel face’s failure zone. The internal friction angle had a significant impact on the failure zone of the tunnel face. The increasing friction angle caused the reduced height of the failure zone and the increased slope of the failure surface. As the cover depth increased, the size of the wedge-prism model increased until the soil arch formed (i.e., h ≈ 0.5D in this paper). The collapse mode of the tunnel face was less affected by changes in water level. When the cover depth reached the height of the soil arch, the hydraulic head pressure above the soil arch determined the limit support pressure (phh = γw(d1 + d2 − h)). The limit support pressure increased linearly with d1 and d2, while the impact of internal friction angle on the limit support pressure of a tunnel in saturated sand was slight. About − 0.16 kPa increments are added to the limit support pressure as the internal friction angle reduces 1°. Moreover, an empirical approach to estimate the limit support pressure on the slurry shield tunnel face in saturated sand was proposed. The calculated limit support pressure by the prediction approach was consistent with the numerical results. Overall, the conducted investigations could offer helpful references for the slurry shield operation in saturated sand.

With the rapid development of high-speed railways (HSRs) in seasonally frozen regions in China in recent years, there is an increasing need for better understanding of how the construction materials behave. In particular, the dynamic behavior of granular base course materials used for China's HSRs subjected to combined actions of cyclic loading and freeze-thaw (F-T) cycles has attracted much attention. In this study, a series of cyclic triaxial tests were performed to investigate the characteristics of granular base course materials. A number of factors including effect of F-T cycles were considered in these tests. As such, representative test results of dynamic shear stress amplitude ( τ ¯ d ), dynamic shear modulus (Gd), and damping ratio (λ) are presented and discussed. Based on the Hardin-Drnevich model, a fitting equation for determining maximum dynamic shear modulus (Gd,max) is proposed. Then, a unified normalized dynamic shear modulus (Gd/Gd,max) curve is drawn and well validated by the test results. Furthermore, equations for λ are expressed in terms of an exponential function of Gd/Gd,max. The test results show that the Gd/Gd,max curves are not completely consistent with previous studies. Overall, this study provides further insights into the dynamic behavior of granular base course materials subjected to F-T cycles.

This research is aimed at developing a practical method for estimating the vertical acceleration of a ballasted railway track bed subjected to trainload in seasonally frozen regions. For this purpose, an indirect thermal-dynamic coupled two-dimensional (2D) finite element (FE) modeling was developed to simulate the thermal and dynamic responses of Harbin–Qiqihar Railway (HQR). Results show that peak values of vibrational acceleration level increase with train speed and axle load increase, but decrease with elastic and height of ballast increase. Taking the effects of the factors mentioned above, two fitting formulae were formulated to estimate vibrational acceleration level of the embankment with an attenuation coefficient, which can be used to describe the attenuation characteristics of ground vibration. In this way, the numerical model and results can be used as a reference for design, maintenance, and research on other embankments in seasonally frozen regions.

The reliability of a disc cutter is critical to shield tunneling performance in compound strata. In this regard, a series of three-dimensional models were developed to evaluate the interaction between the disc cutter and the soil-rock interface. The influences of the penetration depth and the tip width were also addressed. Then, this study presented a rudimentary identification method of disc cutter's potential failure modes in compound strata. The results convincingly indicated that the cutting coefficient could be separated into two stages at the interface of soil and rock: linear reduction stage and constant value stage. For a disc cutter with a tip width of 20 mm and 22 mm, about 1.5% and 1% increments were added to Cc,r as the disc cutter penetrated every millimeter deeper, respectively. It showed that a cutter ring was apt to fracture at the soil-rock interface. The risk of cutter ring fracture was mounting dramatically as the penetration depth raised. The fracture failure possibility at the soil-rock interface for a narrow cutter ring was higher under a great thrust. And it also revealed that the cutter ring of a disc cutter might be led to non-uniform wear due to the insufficient starting torque to rotate in soft layers. Overall, the conducted research could offer helpful guidance for TBM operation in the compound stratum.

The effect of freeze-thaw (F-T) cycles on dynamic behavior of coarse-grained materials (CGMs) (i.e., coarse-grained materials used in railway subgrade named as base course materials) is critical to ensure the service status of railway subgrade in seasonally frozen regions. In this study, a series of stress-controlled dynamic triaxial tests were conducted on CGMs with various fines contents (FCs) exposed to F-T cycles. Typical test results were then analysed and discussed, highlighting the environmental effect on the dynamic properties. The results demonstrated that the dynamic shear modulus decreased with the increase of FC or the number of freeze-thaw cycles (NFT), but the damping ratio (D) results indicated just the reverse characteristic. In this regard, a modified empirical model was determined to describe the relationship between dynamic shear modulus (Gd) and dynamic shear strain amplitude ( γ ¯ d ). Meanwhile, a unified mathematical formula was proposed to characterize D. Furthermore, the two proposed empirical equations were found to be severely inconsistent with the previous ranges suit for seismic loading. The study provides a useful reference for preliminary evaluation of the response to train loading for CGMs subjected to F-T cycles.

Finite element (FE) simulations are increasingly providing a versatile environment for conducting dynamic response studies on the embankment induced by high-speed train (HST). In this environment, vibration mitigation strategies for the subgrade may be assessed to achieve economic and practical solutions. To investigate the vibration behaviors of embankment induced by HST in seasonally frozen regions, an FE modeling was developed and validated by the field test. The investigation noted significant differences in response features in different seasons. For the sake of providing useful engineering information relating to vibration mitigation, a parametric study was conducted to preliminarily investigate the effect of constructing a wave impeding barrier (WIB) at the site. The influences of the material modulus, the size and the embedded depth of WIB on the vibration mitigation were also systematically analyzed in the time domain and frequency domain and then discussed. It showed that the stiffening effect of the WIB led to a shift of response from a large one to a small one. The results convincingly indicated that the vibration mitigation effect of WIB would be improved when its modulus and size increased or the embedded depth decreased. And it also revealed that the WIB might amplify rather than reduce the ground vibration when its embedded depth was larger than a threshold value. Overall, the conducted study highlights the potency of vibration mitigation in seasonally frozen regions by installing a WIB in the subgrade.