Analysis Of The Mechanical Characteristics For The Concrete Block In Gob-side Entry Retaining

The concrete block structure used in tunnel side supporting for gob-side entry retaining can overcome a series of problems such as the early-strength,dust-free,low labor tension and the rapid mechanized construction.Therefore,this paper mainly studies the requirements of mechanical characteristics of the concrete block in tunnel side supporting,based on which industrial tests was carried out.Firstly,according to the analysis result of movement laws of overlying rock strata,the passive caving is more difficult to control than the initiative caving.Therefore,cutting the overlying rock strata along the outer edge of the roadside support promptly is needed to reduce the pressure during the overlying rock strata collapse process.The analysis of interaction between the movement laws of overlying strata and the tunnel side supporting shows that the mechanics performance of tunnel side support for gob-side entry retaining is a function of both bearing capacity and deformation.The mechanical resistance formulas during primary supporting,roof cutting supporting,and the late supporting were calculated and deduced by establishing models of working resistance during the three supporting periods.The results show that the work resistance during top cutting supporting period is the largest one,which should be used as a design value for the calculation of concrete block structure.For the structure of concrete block,the method of calculating the compressive strength and bearing capacity was calculated by using the Hilsdorf damage theory.Under the guidance of the matching between the roof and floor strength and the support strength of the roadway,the reasonable range of width of the concrete block structure was determined;and the design process of the concrete block structure in tunnel side supporting was obtained.By using the numerical simulation software to study the whole wall and the large masonry wall,it was found that bearing performance of the concrete block structure has little change than the whole wall.However,there is a large lateral tensile stress in the vicinity of the mortar layer and the concrete block,which becomes the weak parts of the structure.This study indicates that if the strength of mortar is similar with that of the concrete block,the whole structure of the concrete block will be more uniform and reasonable.Therefore,in the design of the tunnel side supporting,the strength of concrete block structure should be similar with that of mortar.The compressive strength of the concrete block structure decreases with the increase of the number of layers.The strength of the five-story concrete block is about 4.6%,which is lower than that of the three-story concrete block;and the strength of the twelve-story concrete block is lower than that of the three-story concrete block about 6.8%,which further illustrates the feasibility of concrete block structure.Finally,combined with the actual geological conditions and the above mentioned research results of the 3203 working face of the Longmeng Coal Mine,the engineering practice of the concrete block structure wall was carried out on the 3203 working face.The result of good stay and the economic benefit are achieved.This study provides a valuable experience for mechanized construction.