EXPERIMENTAL RESEARCH ON FACTORS AFFECTING SHEAR STRENGTH OF HALOPHYTE ROOT-SOIL COMPOSITE SYSTEMS IN COLD AND ARID ENVIRONMENTS

This paper aims to study the contribution of halophytes roots in increasing shear strength of soil in cold and arid environments. The Gasikule Salt Lakes and the surrounding areas in the Qaidam Basin are selected as the test area. Five predominant halophytes(Triglochin maritimum Linn., Phragmites australis Trin., Carex enervis C.A.Mey., Leymus secalinus Tzvel., Koeleria cristata(L.)Pers.) are selected as test species. Direct shear tests are carried out to the samples of soil without roots and root-soil composite system collected in-situ by the method of digging soil from shallow layers to the deep layers of the ground, where layer-by-layer excavation is applied to investigate the effect of moisture content, vertical pressure, the pattern of roots arrangement, root content and root area ratio on shear strength of soil. Results exhibit the following results. With the increasing of soil moisture content, the cohesion force decline. The relationship between vertical pressure and shear strength satisfies Mohr-Coulomb law. The roots play a role in soil reinforcement in shallow layer. The increment amplitude of shear strength is 3.26%~57.18%.With decreasing in root area ratio(RAR)for T.maritimum Linn. and P.australis Trin. and the decreasing in root content for C.enervis C.A.Mey., L.secalinus Tzvel. and K.cristata(L.)Pers., the cohesion force of root-soil composite system decreases. Root area ratio(RAR)has a relatively larger effect on cohesion force of T.maritimum Linn. and P.australis Trin. root-soil composite system than soil moisture content. The effect of root content on cohesion force of C.enervis C.A.Mey., L.secalinus Tzvel. and K.cristata(L.)Pers. root-soil composite system is bigger than soil moisture content, too. The cohesion force of root-soil composite system at different depths is significantly larger than that of non-rooted soil, with the corresponding increment amplitude ranging from 9.61%~182.56%. In contrast, the variation in internal friction angle is relatively small. Reinforcement effect of shear strength for T.maritimum Linn.roots is relatively significant, followed by P.australis Trin., C.enervis C.A.Mey., L.secalinus Tzvel. and K.cristata(L.)Pers. The conclusion plays a role in assessing the reinforcement of roots in increasing shear strength and has an instructive meaning in implementing measures in soil erosion prevention and shallow landslide and other such geological hazards by halophytes in testing site and other regions with similar geological conditions.