| The ground surface in tunnels is prone to fracture and deformation,and the maintenance of the surrounding rock surface is an important link in the support system.Compared with the existing surface protecting methods such as mesh and thich shotcrete,the sprayed-on membrane has its unique advantages in terms of deformability,mechanical properties,and construction performance.Spray-on membrane is rarely used in coal mine bolting,and there are still many deficiencies in the study of its supporting function and mechanism.This paper comprehensively employed the methods of theoretical analysis,laboratory experiments,numerical simulation,application research,etc.to study the mechanical properties of a typical sprayed-on membrane,reveal its effects and mechanisms under the bolt support system,and then carried out relevant evaluations and recommendations.The main conclusions are as follows:(1)The mechanical characteristics of the spray-on membrane,including fast loadbearing response,large deformation capacity and high bonding strength,were revealed.The rapid build strength of the tested membrane at the initial stage of tension determined that it could quickly play a mechanical role at the initial stage of rock deformation;the maximum elongation was close to 60%,showing it was applicable to large deformation conditions in coal mine tunnels.No failure was observed inside the membrane or from the bonding surface both in the normal and tangential bonding tests,revealing the good adhesion of the membrane.(2)The mechanical effect of the membrane on the rock mass surface to improve the compressive strength and maintain integrity was analyzed.Through numerical simulation,it was found that the compressive strength of small-scale intact rock and fractured rock mass with membrane had been increased;it had been found through tests that the compression strength of raw coal substrates with membranes had increased by 25%.When the sample matrix failed in the compression and tensile experiments,the membrane did not exhibit integral debonding and peeling,and maintained good adhesion with the loosen rock blocks,showing the role of maintaining the integrity of the surrounding rock surface.(3)The effects of the membranes to restrain the deformation of rock mass between bolts,prevent block collapse,and improve the integrity and self-bearing capacity of rock mass was revealed.The membrane suppressed the appearance of the “basket” effect between the bolts through its adhesion capacity.The test obtained the linear loading capacity index of the membrane,revealing that it could theoretically bear the self-weight of 752 kg loose blocks,indicating that it had the ability to prevent the collapse of small loosen rocks on the roof.(4)It was discussed that spray-on membrane could restrain the weakening of the strength of mudstone and realize the sealing effect of the rock in grouting.The membrane reduced the moisture content of the mudstone matrix,which in turn suppressed the weakening of the matrix strength.The experiment found that there were three forms of failure when the membrane was subjected to the internal pressure of the rock surface,and the maximum sealing pressure was 1.05 MPa.Compared with the simulation results of grouting pressure gradient in fractured rock masses,it was found that the spray-on membrane had the sealing ability of the rock surface in grouting and had the potential to improve the grouting effect.(5)The collabrative supporting action to bolt support was revealed.Through numerical simulation of roadway bolting,it was found that the amount of sinking on the surface and inside of the roof rock mass with membrane was suppressed,the stress in the y direction of the rock mass inside the roof increased,and the average value of the maximum axial force of the roof bolts was significantly reduced.It showed that the membrane improved the integrity and self-supporting capacity of the roof rock mass.(6)The action mechanism of spray-on membrane under the bolt support system was summarized.The bolt plays the main role of support.Due to its special mechanical properties,the spray-on membrane has a reinforcing effect on the surface rock mass,and prevents the deformation and movement of the rock mass and blocks between the bolts through rapid loading capability,maintaining the integrity of the rock mass;It inhibits the weakening of rock mass,and has the potential to prevent corrosion of metal supporting parts.Meanwhile,it has the ability to seal the wall in grouting.The function of spray-on membrane and bolts complement each other,and play a collaborative role in the control of ground.(7)The engineering characteristics of spray-on membranes was discussed.Supporting principles of spray-on membranes were studied.The supporting performance and construction characteristics of spray-on membranes and sprayed concrete and mesh,were compared and analyzed.and proposed a differentiated development plan for sprayed film materials.Suggestions for the development of construction techniques and equipment principles were given.And the application limitations of membranes were analyzed,and the applicability of the membranes was evaluated.(8)A mechanized slurry preparation and spraying process was developed.The according integrated construction equipment with self-propelled ability using compressed air as power was proposed,of which the three-dimensional prototype model of the was established.Two engineering practices of spray-on membranes for metal supporting components sealing and gas blocking of refuge chamber wall were carried out,through which the sealing effects of membranes was verified.There are 125 figures,30 tables and 186 references in this dissertation. |
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