干湿循环条件下重庆地区三种土壤抗剪强度的动态变化

DYNAMICS OF SOIL SHEARING STRENGTH OF THREE TYPES OF SOILS UNDER WETTING-DRYING ALTERNATION IN CHONGQING AREA

选择广泛分布于重庆丘陵山区的黄壤、钙质紫色土和中性紫色土3种土壤，通过对室内三轴剪切试验，测定含水率和容重交互作用对土壤抗剪强度指标的影响。在含水率和容重对土壤抗剪强度影响分析的基础上，3种土壤按各自最优含水率和容重制作干湿循环试验土样，进行干湿循环条件下土壤抗剪强度的动态变化分析。试验结果显示：（1）在相同容重情况下，3种土壤黏聚力c值随着含水率的增加呈现出先增加后减小的趋势，在相同土壤含水率水平下，土壤黏聚力C值随容重增大而增大；3种土壤内摩擦角φ值在各容重条件下均随着含水率增加呈明显减小的趋势。（2）含水率和容重的交互作用对土壤黏聚力C值有显著影响。黏聚力c值在1．3～1．7gcm-3容重范围内随着容重的增大而增大，且每一个容重均有一个含水率与之对应。在这样一个交互作用下黏聚力C值达到最大，含水率和容重的交互作用对内摩擦角φ值影响相对较小。同一容重下，其φ值差异不大，随容重的增大缓慢增大。（3）3种土壤的黏聚力c值均随干湿循环次数的增加均呈减小趋势，且前两次循环C值衰减幅度都很大，从第三次干湿循环至第五次干湿循环黏聚力C值衰减幅度很小，趋于稳定。（4）3种土壤在干湿循环后内摩擦角φ值总体呈减小趋势，但不同土壤类型间存在差异，第五次循环结束后，黄壤为24．6°，中性紫色土为22．6°，钙质紫色土为19．3°。

By means of triaxial shearing test in laboratory, effect of the interaction of soil water content and bulk density on soil shearing strength in yellow soil, calcareous purple soil and neutral purple soil was explored. The three types of soils are extensively distributed in the hilly regions of Chongqing. Dynamics of the soil shearing strengths of the three types of soils under wetting-drying alternation were analyzed, using soil samples adjusted to be optimal in soil water content and bulk density specific of the three soils, separately, based on the analysis of effect of soil water content and bulk density on soil shearing strength. Results show that the soil cohesive force first increased and then decreased with theincreasing soil water content in all the three soils unchanged in soil bulk density, and it increased with the increasing soil bulk density in the soils the same in soil water content. Internal frictional angle decreased significantly with the increasing soil water content in all the three soils, regardless of bulk density. The interaction of soil water content and bulk density affected soil cohesive force significantly, which increased with increasing soil bulk density in the range of 1.3 - 1.7 g cm-3, and would peak when bulk density interacted with a matching soil water content. The interaction did not have much effect on internal frictional angle, which did not vary much when bulk density remained the same, but increased gradually with increasing soil bulk density. In all the three soils, soil cohesive force decreased with increasing number of wetting-dr- ying alternations, and it dropped sharply in the first 2 cycles of wetting and drying and very slowly during the following three cycles, and then leveled off. Internal frictional angle as a whole decreased with increasing number of wetting-drying alternations in all the three soils, however, differences were found between the soils different in soil type. The angle was 24.6°, 22.6° and 19.3° in yellow soil, neutral purple soil and calcareous purple soil, respectively after the fifth cycle of wetting-drying alternation.