| Aeolian sand is a kind of loose sand body widely distributed in the northwest of China.It has low cohesion and poor water retention,and it is a fine-grained soil sand with poor gradation.During the tunnel excavation process,engineering disasters such as detachment behind the lining,quicksand and even collapse of the face are likely to occur.The existing engineering experience shows that the improved step method has a good effect on controlling the stability of the aeolian sand tunnel,but the selection of the length and height of the step has no research on the influence of the stability of the face of the aeolian sand tunnel.There is no theoretical basis for the control of the stability of the face and the instability of the face of the face under different steps is unresolved.In view of the above problems,this paper relies on literature research,laboratory tests,numerical calculations and theoretical analysis to study the engineering characteristics of aeolian sand strata by means of literature research,laboratory tests,numerical calculations and theoretical analysis,and to simplify different types of stepped face faces into inclined plane face faces.In order to study the stability of the face of the deep tunnel and the deformation characteristics of the stratum after the collapse of the face,the main contents are as follows:(1)The physical parameters of aeolian sand were measured and analyzed by laboratory tests.A series of indoor mechanics experiments were carried out.The effects of water content and compactness on the mechanical properties of aeolian sand were analyzed.The mechanical properties and parameters of aeolian sand were summarized.(2)The similarity model test of the face instability was carried out to measure the surrounding rock stress field during the collapse process,and the influence of the face angle was analyzed from the changes of the stress field in the vertical and horizontal planes.The stress field difference caused by the angle of the face is discussed.(3)The experimental model of discrete element mechanics was established to calibrate the mesoscopic parameters of aeolian sand.On this basis,the three-step excavation model of the aeolian sand tunnel was established,and the gap between the inclined face and the real construction step in the stability of the face was evaluated.It was verified that the stepped face was simplified to the inclined face.Rationality.At the same time,the results of similar model tests are verified by the stress path,and the three-dimensional instability morphology of the face after collapse,the stress deflection phenomenon in the surrounding rock and the variation characteristics of the pressure arch are further analyzed.(4)Under the framework of the limit equilibrium theory,the upper form of the collapsed body is described with reference to the particle ellipsoid theory,and the internal collapse pressure is derived,so that the ultimate support force of the face is obtained.Based on the theory,the morphological characteristics and force state of the collapsed body are described,and the influence of the angle of the face on the collapsed body is quantitatively analyzed. |
