Analysis Of Static And Dynamic Characteristics Of Loess Tunnel Basement Rock

With the rapid development of railway in our country, more and more thetunnels are across the loess strata. Due to the special mechanical properties of loess,the bearing capacity of the basement is often difficult to meet the mechanicalperformance of the structure. Bearing capacity of tunnel base depends on the staticand dynamic characteristics in Loess basement region whether it can satisfy structureand operation safety. In this paper, tunnel basal pressure of surrounding rock isstudied from the angle of stress. At the same time, the bottom of the tunnel rock is thebase of the whole tunnel structure. The characters under the effect of long loops andtrain load, unload have significant effect on the bottom of the tunnel and even thewhole tunnel structure. With the improvement of train speed, higher requirements forthe basement of the surrounding rock deformation are put forward. So the research onbasement subsidence deformation under long-term train load is particularly important.In this paper, the main research contents and results are as follows.(1)The methods of traditional experience to determine the surrounding rockpressure theory have carried on the contrast analysis. The traditional experiencemethod has many disadvantages by the contrast analysis. Analysis result showed thatthe soil column method was the maximum and Kake formulas was minimum.(2)Basement surrounding rock stress of the loess tunnel is studied by using themethod of numerical simulation form different construction methods, mechanicalparameters of different buried depths, loess tunnel itself (cohesion, internal frictionAngle). It is concluded that the different construction methods have more influenceon the vertical stress of surrounding rock of tunnel basement; tunnel vertical stress ofsurrounding rock of the basement also increases with the increase of tunnel burieddepth; mechanical parameters of loess itself (cohesion, internal friction Angle) effectsare so small that it can be neglected, etc.(3)The dynamic response characteristics of base rock are systematicallyanalyzed. The train load is simulated in the form of an incentive function. Four different speed (200km/h and250km/h,300km/h and350km/h) train load aresimulated. The vertical acceleration and the vertical stress distribution laws wereanalyzed with four different train loads. Numerical simulation results show that theacceleration and basal total vertical stress peak value are increased with the increaseof train speed.(4)The train cumulative settlement of basement rock of the tunnel undercirculating load was analyzed. This paper used DingQing Li model to analyze thecumulative plastic strain. Accumulated subsidence value was calculated to fourdifferent train speed loads. It was concluded that early cumulative settlement wasdeveloping very fast, then the cumulative settlement development was very slow, andfinally tended to a stable state. Tunnel basement accumulated subsidence value wasincreased along with the increase of train speed.