Thin spray-on liner (TSL) is a surface protection technology used by spraying a polymer film, which is widely used for mine airtightness and waterproofing. A reinforcing TSL can replace steel mesh, which is a new method for roadway support. This paper reviews the development of a reinforcing TSL. Considering the deterioration of geological conditions in deep underground mining and the demand for reinforcing automation, two kinds of polymeric reinforcing TSL (RPTSL) materials are developed. The mechanical characteristics of the new TSL materials are studied experimentally. Results show that the average compressive strength, tensile strength, cohesion, and internal friction angle of the two TSL materials are 52 and 32 MPa, 12 and 8 MPa, 6.2 and 17.2 MPa, and 33.6° and 25.9°, respectively. The bonding strength between the two materials and coal is greater than the tensile strength of coal itself, and the mechanical properties of the material for comparison are lower than those of both materials. Based on the TSL support mechanism, we examine the application of the two TSL materials to the mining environment and compare the mechanical properties of polymer materials and cement-based materials. The advantages of polymer materials include versatile mechanical properties, good adhesion, and high early strength. This study provides a new support material to replace steel mesh for roadway surface support, which satisfies the needs of different surface support designs under complex geological conditions, and promotes the automation of roadway support.

The short encapsulation pull-out test (SEPT) is extensively used in rockbolting research or engineering. The field SEPT is time-consuming and labor-intensive, and its result is only applicable to the tested in situ. The laboratory SEPT is usually employed in theoretical rockbolting research due to its easily controlled variables. However, the design of laboratory SEPT is quite different, as there is no standard testing method, resulting in the applicability and limitations of each study not being clear. Accordingly, the aim of this paper is to bridge the gap between laboratory SEPT research and field application. On the basis of thick-walled cylinder theory, a mechanical model of a rock bolt subjected to axial load was established under consideration of the deformational behavior of confining materials around the bolt. Plane stress analysis was introduced to derive the analytical relationship between the axial force of the bolt and the deformation of the confining materials. A new approach of laboratory SEPT sample design was established, namely, equivalent radial stiffness theory, to simulate anchorage performance in a specific in-situ geocondition. Consequently, the field SETP could be replaced by laboratory testing using properly designed bolting samples with a certain level of accuracy. In addition, the application scope of previous laboratory SEPT research could be accurately defined. Laboratory SEPT was carried out to study the anchoring performance of right spiral rebar bolts under different confining materials. Poly Vinyl Chloride (PVC) tubes with a thickness of 31 mm, #60 aluminum (Al) tubes with a thickness of 5.8 mm, and #20 steel tubes with a thickness of 5.5, 7.0 mm were used in sample preparation to simulate soft, medium, and hard surrounding rocks in the field. The anchorage performance of the bolt under different geoconditions was systematically proposed, which provides a technical approach for similar research using different anchoring materials. A negative exponential expression formulating the axial load capacity of the right spiral bolts for the full spectrum of the surrounding rocks’ strength was derived on the basis of theoretical analysis and data regression. It can be used for preliminary reinforcement design, as well as the accurate key parameter setting in the numerical calculation of roadway deformation using right spiral bolts. The theoretical prediction is highly consistent with the testing results in the literature, which confirms the validity and reliability of this research. This study contributes to the establishment of a laboratory SEPT standard in rock mechanics.

Coal bump occurring in longwall roadways accounts for more than 87% of total coal bump events. However, there is no practical mechanical model that can explain the causality and process of coal bump, resulting in that the prediction and prevention of rockburst heavily depend on engineering experience or lessons. Considering the mechanical characteristics of surrounding rock, the suspended roof behind working face and stress state of the rib coal, a seesaw structure model related to incentive of the coal bump and a mechanical model related to instability of rib coal block are established in this paper based on theoretical analysis and numerical calculation, which is capable to clarify the causality mechanism, process, key factors and critical state of coal bump. The hard suspended roof behind the working face produces periodic abutment pressure on the coal around the working face. The result of numerical calculation shows that, under the condition of high compressive stiffness of hard coal around the working face, the roof in front of the working face rebounds upward. The phenomena of roof rebound suggests that the overlying strata of the working face form a seesaw structure. In the area of roof rebound, the normal stress on the roof-coal interface is reduced. Stress analysis of a rib coal block has been conducted. Result shows that, the tectonic stress perpendicular to the rib can overcome the fractional resistance pushing the rib coal into the roadway once the normal stress on the roof-coal interface de-stresses to a certain level. Accordingly, a critical state equation of coal bump has been established. It can be concluded that, de-stressing of the roof-seam interface caused by roof rebound triggers coal bump. The tectonic stress is its force source, and the tensile strength of coal and the shear strength of the coal seam with roof and floor are bump resistances. This study clarifies the causality mechanism and process of coal bump occurred in longwall roadway that provides a theoretical basis for prediction and prevention technology.