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This study was part of a preliminary safety assessment for a real project of existing bridge piles passing through beaded karst caves threatened by a nearby newly built embankment. To investigate the severity of the effect of the embankment on the performance of these piles, a series of reduced-scale model experiments of piles considering different cave numbers (n = 0, 1, 2, and 3) near surcharge loads were designed with a similarity ratio of 1:35. Two phases of loading, the vertical loading atop the pile and nearby surcharge loading, were imposed successively to explore the vertical bearing characteristic and lateral response characteristic of the piles passing through beaded karst caves. The effects of cave number, vertical load atop the pile, and nearby surcharge load on the responses of pile and soil were clarified and several fitting functions were presented to characterize the variations of responses with different cave numbers and nearby surcharge loads. The results and conclusions can provide a reference for the design and safety assessment of bridge piles in karst terrains. [ABSTRACT FROM AUTHOR]

When a super-large diameter shield tunnel passes through a strongly karst-developed area, in order to ensure the stability of the tunnel and economy of karst reinforcement, the reasonable treatment range for a huge number of karst caves needs to be researched. Based on a karst treatment project of a shield tunnel with a diameter of 14.5 m, this paper studies the influence of intrusive fully filled karst caves on the stability of the lining and excavation face by using theoretical calculation. In addition, the safe distance between the tunnel and karst caves outside the tunnel is proposed through numerical simulation, and the corresponding treatment range is obtained. The results show that the bearing capacity of the lining has a certain reserve when the intrusive cave is smaller than a certain size, and the caves filled with plastic or hard plastic clay have sufficient antifracturing ability. Therefore, some small fully filled caves inside the tunnel profile can be left unreinforced. On the other side, the critical safe distance is only 1–2 m for the caves with a size of 3 m, so the outside caves with a size less than 3 m can be left unreinforced in the treatment range farther away from the tunnel. The proposed treatment range is close to similar projects that have been built, indicating that analysis results are reasonable. [ABSTRACT FROM AUTHOR]

In a metal mine adopting a sublevel caving (SLC) method, life-of-mine and temporary mine infrastructures are preferred to be positioned on the footwall side of the ore body. Therefore, the footwall stability, especially well developed with steeply inclined discontinuities, is a major concern in an SLC mine. In response to this issue, a comprehensive investigation of the large-scale footwall failure mechanism has been conducted. The load-bearing structure responsible for footwall large-scale failure has been recognized. Subsequently, by adopting limit equilibrium theory, an improved mechanical model of overlapping cantilever beams is proposed for evaluating the footwall stability and determining its failure scope. In this model, a relationship between footwall movement and lateral force acting on the caved zone side of the footwall is built, considering the footwall movement and its compression effect on the caved zone. A validation study of this improved mechanical model is conducted and the calculation results are compared with the in situ monitoring data. It is shown that this improved model offers a more realistic simulation of lateral force acting on the caved zone side of the footwall. The proposed improved model can be utilized for other practical applications involving footwall large-scale failure under similar geotechnical conditions. [ABSTRACT FROM AUTHOR]

The U-steel support structures of underground caverns are prone to instability and failure under blast loads. The purpose of the underground cavern reinforcement is to mobilise the self-supporting capacity of the surrounding rock to resist the blast. To better understand the mechanical performance and failure mechanism of the U-steel support, the fracture process and vibration behaviour of the support structure under blast loading are investigated by the microseismic monitoring experiment. The dynamic responses of the cavern support structures under blast loading are investigated, and the potentially hazardous sections of the U-steel support structure are revealed by the theoretical analysis. The microseismic monitoring results show that the blast induced microseismic events are concentrated in the arch shoulder of the small chaînage, correspondingly the U-steel structures in this region have been partially extruded and deformed. The failure mechanism of the supporting structure is presented. In order to effectively inhibit the internal fracture evolution or macroscopic failure of the rock mass, the synergetic reinforcement scheme of the structures is proposed. The results of the research can be used as a reference for the design and control method of the U-steel support in similar projects. [ABSTRACT FROM AUTHOR]

Aiming at the technical problems of frequent dynamic pressure disturbance of regenerated roof and roadway stability control in the process of forming large-section support return channel under the delamination mining, taking 1200-2 fully mechanized caving face of Baiyinhua No. 4 Mine as the engineering background, numerical simulation and theoretical analysis were adopted. The overburden structure of the lower stratified caving face and the loading characteristics of the roof after the expansion are analyzed, and the breaking forms and the limiting conditions of the roof are given.The combined support scheme of anchor rod + metal mesh + steel ladder belt + I-beam insertion + suspension beam + anchor cable + single pillar is studied to form a set of safe and efficient construction support technology system. Practice shows that this scheme can effectively reduce the roof subsidence, narrow the scope of plastic failure zone, and ensure the stability of roadway surrounding rock during the support withdrawal period. Successfully complete the efficient withdrawal of hydraulic support. The research results can provide a good reference for the roof management and the smooth output of coal resources under similar conditions. [ABSTRACT FROM AUTHOR]