Grouting with cementitious materials is a commonly-recognized measure to control the freezing and thawing deformation of artificial freezing strata. This study investigated the unfrozen water content of silty clay with different cement content under freeze-thaw condition, as well as the pore characteristics of the silty clay before and after freeze-thaw cycle based on nuclear magnetic resonance. It analyzed pore characteristics variation patterns of cement improved soil before and after freeze-thaw cycle and the micro-mechanism of freeze-thaw damage through scanning electron microscopy and mercury intrusion porosimetry. Results showed that: ①With the same water content, the increase of cement content would lead to the initial increase and subsequent decrease in the sensitivity to temperature of water molecule magnetization in the pores. ②When the cement content is between 0%~10% and at the same temperature during thawing process, the increase of cement content would lead to the initial decrease and subsequent increase of the unfrozen water content in the frozen soil. ③Compared with the silty clay without cement, cement improved silty clay shows little changes in its pores before and after the freeze-thaw cycle. The pore characteristics and microstructure of improved silty clay with cement content of 5% are less affected by freeze-thaw cycle. This research can provide references for the study of freeze-thaw resistance of improved soil and the stability control of strata frost heave and thaw settlement in artificial frozen engineering.

TBM hob wear is an important factor that affects the TBM tunneling efficiency and construction cost.Different blade types differ in rock breaking efficiency and wear.By analyzing the rock-breaking mechanism of the arc blade wedged hob, this study established the calculation model of hob normal cutting, and analyzed the influence of hob edge angle on normal cutting force.This study then designed three kinds of hobs with different cutter spacing and three types of hobs with different blade for rock breaking tests in laboratory.Results show that the reasonable cutter spacing is 15mm, sharp blade is prone to be worn, the tooth-like blade, which has higher rock breaking efficiency and wear resistance, is better than arc blade.Combined with the actual situation of the project site, a new hob with wedge-shaped blade is developed, which are applied to inclined shaft TBM tunneling at engineering site.Results show that the wear rate of the new wedge-shaped hob is 20 % less than that of the conventional ones, and the service life of former is longer than that of latter.Under the same geological conditions, new wedge-shaped hob can reduce the number of hobs consumption and improve efficiency of tunnelling.The development and application of the new type successfully solved the problems of hob wear and frequent replacement of hobs in the TBM inclined shaft excavation.It can provide technical support for TBM long distance inclined shaft driving, which not only shortened the construction period, but also saved the construction cost.

Coal gangue has the characteristics of complex physical and chemical properties, low strength, loose and porous, which limit its extensive use in building materials. In this paper, coal gangue was modified by soaking in hydrophobic solution under uncalcining and non-prewetting conditions. The basic characteristics of coal gangue before and after modification was systematically studied, and hydrophobically modified coal gangue mass substitution rates of 0%, 30%, 50%, 70% and 100% were set. Contact angel, flexural strength, compressive strength, electric flux were used as characteristic parameters to evaluate the influence of modified coal gangue replacement rate on the basic properties of mortar under different substitution rates.Results showed that, by using the binary cooperative complementary method, when the replacement rate of modified coal gangue was lss than 50%, the hydrophobic state of the surface of coal gangue mortar could be achieved. As the replacement rate of modified coal gangue increases, the compressive strength showed a decreasing trend, the maximum decrease was 15.7% compared with none modified coal gangue added. The 28 d compressive strength was 58.5 MPa with 30% replacement rate of modified coal gangue. The electric flux was less than 250 C under different modified coal gangue replacement rate, which indicated excellent resistance to chloride permeability. When the modified coal gangue replacement rate is 30%, the electric flux was the smallest (130 C). The hydrophobic modification method could ensure good mechanical strength and resistance to chloride penetration under the condition of uncalcined and non-prewetted coal gangue, which fully utilizes coal gangue.

The construction of shield tunneling close to risk sources in urban has been a commonly encountered problem in recent years. The establishment of the analytical model used to calculate the immediate settlement of existing structures has been a major focus in approaching construction issues. It is obvious that after shield construction, the settlement will inevitably continue to increase for a long period. In this study, a novel model applied to calculate the long-term settlement considering the influence of soil consolidation was proposed. Based on this proposed analysis model, combined with building information modeling (BIM), geographic information system (GIS), city information model (CIM), geoscience modeling (Geo Model), and internet of things (IoT), a three-dimensional (3D) intelligent management and control platform for shield tunneling construction close to major risk sources was developed and introduced. In this platform, the analysis model was embedded to calculate the long-term settlement, and the risk data were determined by comparing calculated results, monitoring results, and control standard value. The intelligent platform adopts the analytical method and computer technology to solve the problem of approaching construction, such as management of construction information, pre-warning, and control of construction risk, and it has been successfully applied in Beijing shield tunneling projects. This platform can also provide the pre-warning function and economic value for similar construction projects.