Design Method For Soil Nail Wall Between Piles For Stability Of A Cut Slope Along Bazhong-Dazhou Railway Considering Horizontal Soil Arch Effect

Beside decision on the spacing of stabilizing piles, soil arch effect remains far from wide application in load calculation for combinations of stabilizing piles and structures between them despite well acceptance of its existence. Soil nail wall between piles is one of the combinations, which is widely used in slope stabilizing practices and has obtained good engineering results. However, its design method for soil nail wall between piles remains to be improved basing on soil arch effect between piles. In nowadays, the load applying on a soil nail wall is usually evaluated basing on the driving force acting on its nearby piles or roughly calculated by increasing the value of shearing strength indices, such as increasing frictional angle, and the load on the piles is considered to be the driving force at the location of the piles by neglecting the soil arch effect. The existing method usually overestimates the load on a soil nail wall and underestimated the load on the piles.In this paper, the effect of soil arch between piles on the loads acting on a soil nail wall and the nearby piles is firstly theoretically analyzed, resulting in that (1) due to the soil arch, the driving force at the apex of the soil arch, rather than what at the location of piles should be taken as the load on the piles, and that (2) the load on the soil nail wall is the active earth pressure or the driving force by the soil before the soil arch. Basing on the results, the method for the calculation of load on the soil nail wall and the nearby piles are produced.In the paper, a slope along the railway from Bazhong to Dazhou was taken as an example, for which the reinforcing soil nail wall between piles was assigned load with the method presented here in this paper, and the effect of the soil arch is then illuminated through the example. Finally, numerical stimulation is carried out to reproduce the soil arch between piles and verify the rationality of the presented calculation method by showing the loads on the soil nail wall and the nearby piles.(1) By engineering geological survey and rock mechanic Lab. tests are determined rock physics and mechanics parameters of the slope. Using the sampling soil of the slope site for conducting soil arch physical model experiments to probe the soil arch shape, size and its influencing factors.(2) According to the current design specifications, the method for the calculation of the driving force arrangement on the structures and the nearby piles is produced by considering horizontal soil arch effect are produced.(3) The stability of the example slope is calculated by the use of transferring coefficient method, resulting in a FS smaller than 1 and a consequent necessary of pre-reinforcing. The horizontal soil arch effect between piles and the method for the calculation of load arrangement are introduced to discuss the ultimates values on the stablizing piles and the soil nail wall when existing soil arch.(4) According to the shape and size of the soil arch and the load value on the soil nail wall, a design method of soil nail are proposed by considering soil arch effect. Combined with the current design specifications for soil nail wall design calculations are completed of the structure size and the spatial location arrangement design of soil nails. At the same time compared with the traditional design method, the here presented design method is proved to be optimized.(5) The finite element numerical simulation software, FLAC3D is employed to analysis the stability and reinforcement effect of the combination reinforced slope by piles and soil nail wall between piles. And then by comparing the stability coefficient and reinforcement effect, the rationality and effectiveness of the design method proposed in this thesis is validated.The research results has been applied to the reinforcement design for stability of some slopes along the railway from Bazhong to Dazhou. It may also be taken as a reference for slope stabilizing under similar geological conditions to the slope mentioned in this thesis.