Large deformation and failure of soft rock are pressing problems in the mining practice. This paper provides a case study on failure mechanisms and support approaches for a water-rich soft rock roadway in tectonic stress areas of the Wangzhuang coal mine, China. Mechanic properties of rock mass related to the roadway are calibrated via a geological strength index method (GSI), based on which a corresponding numerical simulation model is established in the Universal Discrete Element Code (UDEC) software. The failure mechanism of the roadway under water-saturating and weathering conditions is revealed by field tests and numerical simulation. It is found that the stress evolution and crack development are affected by weathering and horizontal tectonic stresses. The roadway roof and floor suffer from high stress concentration and continuous cracking, and are consequently seen with rock failure, strength weakening, and pressure relief. Unfortunately, the current support system fails to restrain rock weathering and strength weakening, and the roadway is found with serious floor heave, roof subsidence, and large asymmetric deformation. Accordingly, a new combined support system of “bolt–cable–mesh–shotcrete + grouting” is proposed. Moreover, numerical simulation and field testing are conducted to validate the feasibility and effectiveness of the proposed approach, the results of which demonstrate the capacity of the proposed new support method to perfectly control the surrounding rock. Findings of this research can provide valuable references for support engineering in the soft rock roadway under analogous geological conditions.
The bolt support is one of the most important types of active support in anchorage engineering. The anchorage quality of the bolt is directly linked to the safety and stability of the anchorage engineering. Therefore, it is very important and necessary to monitor the stress state of the bolt. Conventional monitoring instruments are susceptible to electromagnetic interference and can not implement remote long-term monitoring and quasi-distributed measurement. A hydraulic-type FBG sensor for axial bolt load measurement is presented, comprising a pressure ring as a load-carrying structure, hydraulic oil as a transfer medium, an elastic diaphragm and a cantilever as sensitizer, and a FBG as the sensing element. The overall structure and working principle of the sensor are introduced in detail, and the theoretical relationship between the FBG wavelength shift difference and the force is established. Accurate force measurement can be obtained by monitoring the two FBGs’ wavelength shift difference. The experimental results show that the average force sensitivity is 39.61 pm kN−1 in the range of 0–100 kN, and the linear coefficient is above 99.88%. The measurement sensitivity is improved by using the wavelength shift difference as the monitoring data, which avoids the cross-sensitive influence. In addition, WDM and SDM technology is adopted for constructing a FBG quasi-distributed measurement system to realize on-line monitoring of axial bolt load. The sensor proposed in this paper has wide application prospects in the field of health monitoring in anchorage engineering.
Based on a concrete engineering example, the change law of soil deep displacement and internal force of anchor cable in the excavation process of foundation pit under pile and anchor support system is simulated by numerical analysis method, and compared with the measured results, and the synergistic action law of soil deep displacement and internal force of anchor cable is discussed. The comparison between the results of finite element numerical analysis and the field measurement shows that the two-dimensional finite element numerical analysis can reflect the variation law of the deep displacement of soil and the internal force of anchor cable in the field to some extent.
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