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Underground coal mining activities are prone to cause movement and breakage in geological strata and also lead to mining subsidence and even ground fissures. Along the direction working panel advancing, ground fissures may occur in roof in front and/or behind working panel. However, the investigations of previous similarity tests in lab only emphasize on the region behind working panel. By improving strata material property in construction and mounting artificial pressure devices, two physical simulation tests were conducted and successfully investigated the simulated results. Then, the mechanical model of “cantilever beam and elastic foundation beam” was proposed to calculate the stress distribution and the crack initiation angle in overlying strata and it well explains the mechanisms of ground fissures generation and propagation. Results show that, the maximum internal force in roof always occurred in front of working panel. However, because the void space in gob due to excavation is large enough to cause the bend and rotation of roof strata, compare to the triaxially compressed region in front of working panel, the roof always broke off at some positions above gob since the stress concentration resulting from such bend and rotation of strata could easily reach the limit strength of strata rocks. Also, the length of cantilever beam changed dynamically as respect to the panel advancing and the breakage intervals. Thus, the breakage position where the internal force first reached the limit tensile strength is not fixed and there will be two different kinds of relative positions between the crack initiation point and the working panel. The crack initiation direction is always perpendicular to the internal force, and the crack propagation direction is affected by the initiation angle, overburden-separation degree and the position of the hydraulic shields. If there is no overburden-separation or less, the roofs will break off as a composite beam and the propagation direction will be roughly along the central line between the initial broken point and the support position. Otherwise, the roof strata will bend with the support shields moving forward, then the fracture angle will be close to the initiation angle and the fault surface will be stepped.

Practices show that hydraulic supports crushing accidents or roadway supports failure often take place when a longwall face advances toward an abandoned roadway or a predriven equipment recovery room. erefore, a 2D similar simulation experiment is conducted to reveal the loading mechanism. e result shows that when the workface advances close to roadways, the main roof breaks ahead of the workface and leads to instability of higher strata. ese two changes induce a sharp increase of the load on supports and lead to an accident. us, more attention should be paid to the advanced fracture. erefore, mechanical analysis is used to explain the advanced fracture. Results show that the failure of coal pillar being excavated induces a sharp increase in the main roof's hanging length. Once the hanging length reaches the limit, the advanced fracture takes place. erefore, the stability of the coal pillar and the hanging length of roof strata are two key factors that may induce an accident. To prevent the a similar supports crushing accident, the partial backfilled technology which partly backfills the abandoned roadway in height and length to maintain the stability of the coal pillar is put forward and put into practice. e field test shows a good effect.

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In this paper, Ground deformation in shield tunneling construction is researched. It is put forward that ground deformation is caused by three reasons, which are ground loss, the positive thrust and the friction. By solving the three-part respectively, the three-dimensional solution formula can be obtained after superposing these. This method is used to calculate the tunnel construction phase at any point in the level of vertical settlement and horizontal displacement. As shown in analytical calculation, the predicted ground displacements of this method are in good agreement with the measured values.

In order to study the occurrence mechanism of advanced coal pillar instability failure and support crushing accidents during a long-wall face passing across abandoned roadways period, the Panel LW3101 in Shenghua Colliery was taken as a typical engineering background. By means of in situ investigation, physical simulation experiment, theoretical analysis, in situ tests, and relevant monitoring methods, the occurrence mechanism and prevention measures are studied. The results show that the bearing stress in advanced coal pillar is accumulated larger and larger with the width of advanced coal pillar gradually decreasing, and meanwhile, the key stratum in overlying strata would also be sliding instability under some minimum critical width condition; the sudden failure of advanced coal pillar which leads to a sharp increase of bending moment is the key factor that induces fracture of the main roof in front of long-wall face, and the advanced fracture of the main roof can be prevented by changing the stress state of the advanced coal pillar from a two-dimensional state to a three-dimensional state; the method of backfilling abandoned roadway is used to improve the stability of advanced coal pillar and the corresponding monitoring results verify that this method is effective. The research conclusions provide a theoretical foundation and new guidance for preventing advanced coal pillar instability failure and support crushing accidents under a long-wall face passing across abandoned roadways condition.