The Research Of Soil Arching Effect In Pile-Net Supported Embankments

The theoretical studies of soil arch is not meet the requirement of engineering application until now, and the calculated results based on different assumptions are quite different,so far a unified theory of soil arch have not been formed. It is difficult to research the soil arching effect in pile-net supported embankments, such as the vertical stress distribution in embankment, the height and shape of soil arch by tests at the site. The accuracy of numerical calculation needs to be improved because constitutive model and patameters are too diffcult to be confirmed. This paper use theoretical calculations, tests at the site and numerical calculation to research the soil arching effect in pile-net supported embankments based on Hai-dong passenger dedicated line and Liu-nan passenger dedicated line. The main results are as follows:1、The results of vertical stress distribution in embankment by Terzaghi’s method and German recommendations are more consistent with numerical modeling, with the depth of embankment increasing, vertical stress in embankment upper the soil increases linearly at first, and then reduces with curve.2、The pile-soil stress ratio by Terzaghi’s method and Low’s method is more consistent with tests at the site, with the height of embankment increasing,the pile-soil stress ratio increses with "S" shape curve.3、When not to consider ground reaction, the results by theoretical calculation methods are arranged from small to large as follow:Guido’s method, Japanese Handbook, the new method in this paper, British Standard8006, Nordic Handbook, German recommendations. With the coefficient of ground reaction increase, the geogrid tension and strain decrease, and with the geogrid stiffness increase, the geogrid strain decrease, the geogrid tension increase. When the foundation soil is soft (the coefficient of ground reaction is from0to500kN/m3), with the pile net increase, geogrid tension increase. When the foundation is hard (the coefficient of ground reaction is greater than1000kN/m3), with the pile net increase, geogrid tension keep unchanged mostly. For the medium and low compression foundation, British Standard, Nordic Handbook, Japanese Handbook and German recommendations are not applicable; the method in this paper considering ground reaction is more applicable.4、The results of numerical model in this paper are consistent with tests at the site, and the same results as follows:with the height of embankment increasing, pile tip stress and soil stress among piles increases, the pile-soil stress ratio is essentially the same. With the height of embankment increasing, the pile tip stress, soil stress among piles, and the pile-soil stress ratio increases for Liu-nan passenger dedicated line on low compression foundation with cement flyash gravel pile. With the pile spacing increasing, the pile tip stress, soil stress stress ratio and settment increase. The values of both methods are similar.compression foundation and low compression foundation with flexible pile,属性不符stiffness increasing, the soil stress among the piles and settlement reduce属性不符foundation is treated with rigid pile, with the pile stiffness increasing, the soil stress among the piles and settlement decrease slightly.6、The pile tin stress in center is less than the pile tip stress on the edge, and the soil stress among pile属性不符a the centroid position is less than the stress in the center of soil between属性不符pile stress, the stress toward the embankment center is greater than属性不符of slope.set to reduce the pile tip stress, soil stress among the piles, pile-soil stress ratio, settlement and height of soil arch,but increase the ratio of height of soil arch to the pile net spacing.With the reinforced cushion modulus increasing (from50Mpa to150MPa), the pile tip stress increase, the soil stress among the piles decrease slightly, pile-soil stress ratio increase, but the distribution of vertical stress in embankment, the height of soil ar属性不符ment less affected.8、When the eight of embankment is less than8meters, vertical stress in embankment with depth属性不符into linear increase phase and the curve phase. The boundary of the two phases is defined as the height of soil arch, then when the pile diameter is0.5meter and the pile spacing is from1meter to2meters, the height of soil arch is1.4~1.8times pile net spacing, and属性不符pile spacing is smaller, the height of soil arch is larger.