Effect Of Ferric Oxide Colloid On Shear Strength Of Landslide Soil Under Dry And Wet Circulation Condition

Collapse is a part of the unique types of soil erosion in the south.During development of the collapsed hill,the dry-wet cycle of the soil plays a decisive role in the occurrence and development of the fallen hill.At the same time,the mechanical properties of the soil surface oxide content on the soil have a greater impact.Therefore,this study used DCB method to remove some free iron oxides to analyze soil particle composition changes and indoor triaxial and direct shear tests,and to explore the developmental laws of shear strength and fracture of collapsing soil under dry and wet cycles.The results show:(1)After the three soil layers were abducted by DCB method,the composition of soil particles changed.The content of clay in the laterite layer increased significantly at 20-2?m and<2?m,and the increase was larger than that of the sand layer and the debris layer,because the aggregate formed by the interaction between the free oxide and the clay mineral adsorbed by the large particles was destroyed,so that the clay mineral It is released and the cosmic content is significantly increased.The development of cracks in laterite is more affected by the content of colloidal iron oxide and the number of dry and wet cycles.When the number of dry and wet cycles is 1 time,there is no observable change in the surface of the red soil layer sample,the soil sample is not cracked,the crack length and the crack area ratio are 0.When the content of iron oxide colloid is low,the number of dry and wet cycles is higher.For a long time,the red soil sample is not hard to crack,and the characteristic parameters such as the crack length and the crack area ratio increase.The smaller content of iron oxide colloid,the more the number of dry and wet cycles,the more severe the cracking of red clay.The sand layer and the debris layer have lower expansion and contraction,and no cracks are shown on the surface of the sample under the action of seven dry and wet cycles.(2)The relationship between the deviating stress value of the soil and the number of dry and wet cycles indicates that the iron oxide colloid plays a cementing role in the soil and is the foundation for ensuring the structural strength of the soil.The dry-wet cycle softens the connection strength between the soil particles.To a certain extent,the destruction of the soil structure has been accelerated.The internal friction angle of the red soil layer decreases with the increase of the number of dry and wet cycles,and the decrease is lower than the cohesion.The internal friction angle of the sand layer and the debris layer gradually reduces and stabilizes with the dry-wet cycle.The decrease in cohesion of the red soil layer and the sand layer is much larger than that of the internal friction angle.There is a substantial correlation between the shear strength index of the red soil layer and the fracture area ratio.The cohesive force of the red soil layer decreases with the increase of the fracture area ratio.Under the dry-wet cycle,the fracture area ratio tends to stabilize and the cohesive force decreases.The polynomial function is utilized to curve the fracture area ratio and the number of dry and wet cycles.The curve fitting correlation coefficient R~2 is greater than 0.95,which indicates that the relationship between the fracture area ratio and the soil shear strength can be well expressed.(3)By comparing the two shearing modes,it can be observed that the cohesive force obtained by the direct shear test is lower than that of the triaxial test,and the internal friction angle is greater than the triaxial test.The result of.Both experiments have their advantages and disadvantages.In the future,when the indoor test simulation is performed,the actual situation will be considered,and the optimal test method is selected according to the actual situation.