Experimental Research On Mechanical Properties Of Terraced Field Ridge In Southern Shannxi Province And The Cause Analysis Of Collapse

Terrace project is an important Soil and Water Conservation measures in southern Shaanxi and its peripheral province, which can solve the masses life full belly and welcome to the local people. However, the ridge collapsing phenomenon is serious, due to some natural factors, such as the high content of soil clay, a heavy rainfall intensity, a steep slope gradient, soil expansion under the influence of water and so on, and construction quality, the effect of irrational socio-economic activities in development and utilization. The main reason of the terraced field ridge collapsing is lack of awareness of the particularity of local soil.Terraced field ridge in Southern Shaanxi as the research object,a study is performed on strength characteristics of Terraced field ridge in local by means of the indoor conventional triaxial shear test; The stress-strain relationship and shear strength characteristics of ridge soil were analyzed. The free expansion ratio and strength of soils were studied by means of the indoor free expansion ratio tests and unconfined compressive strength tests. Meanwhile, the correlations between the stability of free expansion ratio and unconfined compressive strength were analyzed; The change trend of expansion force in different soil layers deep is studied through expansion force test. the main research results are as follows:(1) Stress-strain relationship: Strength-deformation relationship of soil samples presented a hardening type at high confining pressure, structure failure and strain hardening level enhanced with the increase of confining pressure, while low confining pressure was showing a weak softening characteristic.(2) Strength characteristics: Terraced field ridge of the shear strength change over water content and the influence of cohesion c’ changing on the terraced field ridge collapsing is greater than Internal friction angle. Shear strength parameters had no obvious regularity along the depth distribution within the scope of 120 cm deep soil, and they were sensitive to changes in moisture content, may be due to the different moisture content resulting in differences for shear strength between different soils, which may lead to the instability of ridge.(3) There are three stages of expansion rate changes over time on the different depth of soil samples: accelerating expansion、decelerate expansion、stabilizing phase; three stages of stress-strain relationship: elastic 、 yield 、 strain strengthening. The finally expansive deformation increases with soil depth of terraced field ridge in Yang County, and unconfined compressive strength is cut down in 120 cm deep soil, which is consistent with cohesion c’ value, yet having no obvious rules in Black Town’s. The soils of unconfined compressive strength and the stability of free expansion ratio showed an exponential relationship.(4) The expansive force is constantly increasing with soil depth of terraced field ridge in Yang County, which is consistent with the variation rate of expansion, yet having no obvious rules in Black Town’s.When terracing, expansive soil easily weathered, swelling and strength degradation such properties must be acquainted. The water content have a great impact on the soil shear strength. The ridge collapsing phenomenon is worse in rainy season. In expansive soil distribution area, drainage problems must be paid attention, which can construct of drains between terrace and its upper steep ground to divert rainfall runoff, centered on the drainage and firming the terraced field ridge to establish a comprehensive prevention and control system of cultivated measures, engineering measures and biological measures.