Experimental Study on the Brittle-Ductile Response of a Heterogeneous Soft Coal Rock Mass under Multifactor Coupling

Abstract

After a gas drainage event causes different degrees of initial porosity in the coal seam, the heterogeneity of the coal mass becomes much more obvious. In this paper, soft coal testing samples with different degrees of heterogeneity were prepared first by a new special experimental research method using hydrogen peroxide in an alkaline medium to generate oxygen. Then, a series of mechanical tests on the soft coal mass samples were carried out under multiple factor coupling conditions of different heterogeneities and confining pressures. The results show that with a low strength, the ductility failure characteristic and a kind of rheology similar to that for soft rock flow were reflected for the soft coal; i.e., the stress-strain curve of the coal mass had no apparent peak strain and residual strength. An interesting phenomenon was found in the test process: there was an upwardly convex critical phase, called the brittle-ductile failure transition critical phase, for the heterogeneous soft coal mass between the initial elastic compression phase and the ductile failure transition phase in the stress-strain curve of the coal mass. An evolution of the brittle-ductile modulus coefficient of the soft coal was developed to analyze the effect of the internal factor (degree of heterogeneity) and external factors (confining pressure) on the transition state of the brittle-ductile failure of soft coal. Further analysis shows that the internal factor (heterogeneity) was also one of the essential factors causing the brittle-ductile transition of soft coal.

Combined support technology for main roadway passing through goaf: A case study

“…[42][43][44] In addition, a high-strength concrete spray layer can seal the shallow surrounding rock to effectively limit the arbitrary expansion of the surrounding rock fracture zone, thereby maintaining the integrity of the surrounding rock. [45][46][47][48][49][50][51][52][53][54][55][56][57] It can be seen that the coupled actions of the high-strength pretensioned anchor bolts and anchor cables with surface protecting components such as the plate and steel mesh, along with the high-strength concrete spray layer, constitute the high-strength "anchorage-mesh-shotcrete" support system for the goaf roof, as shown in Figure 5…”

“…However, the combined support of the high‐strength pretensioned anchor bolts and anchor cables can place the surrounding rock in a compression state and effectively control the deformation and failure of the surrounding rock in deep and shallow anchorage zones 42‐44 . In addition, a high‐strength concrete spray layer can seal the shallow surrounding rock to effectively limit the arbitrary expansion of the surrounding rock fracture zone, thereby maintaining the integrity of the surrounding rock 45‐57 . It can be seen that the coupled actions of the high‐strength pretensioned anchor bolts and anchor cables with surface protecting components such as the plate and steel mesh, along with the high‐strength concrete spray layer, constitute the high‐strength “anchorage‐mesh‐shotcrete” support system for the goaf roof, as shown in Figure 5.…”

Coupling numerical model of hydraulic fracturing seepage in soft coal based on elastoplastic damage

“…Zhao Zhigen et al [8] studied the difference in strength between soft coal and hard coal, and the stress-strain curve is also very different. Weijian Yu et al [9] experiments show that internal factors (heterogeneity) are also one of the important factors causing brittle ductile transition of soft coal. Zhang Tianjun et al [10][11] established the damage evolution model of soft coal under loading, which reflects the inelastic mechanical effect of soft coal in meso damage.…”

Stability of Coal Pillar and Roof Movement Characteristics in Roadway Backfill Mining

“…e stability of the coal pillar is the key factor that determines the roof movement and the overlying strata structure. Most of the studies focused on the strength of a single coal pillar [12][13][14][15][16], and the stability of the coal pillar group of RBM are ignored. In terms of roof movement and control mechanism, Zhang et al [17] explored the development mechanism of waterconducting fracture in the overlying rock in RBM; Sun et al [18] established a mechanical model of the roadway backfilling stope, deduced the stope roof equation and the coal pillar load-bearing formula, and put forward the basis for coal pillar instability; Deng et al [19] established a mechanical model for the roof movement of extrathick coal seams and proposed the roof instability and fracture conditions; the above studies explored the roof and overlying strata movement mechanism of RBM and promoted the field application of RBM.…”