秸秆长度对黑土力学特征的影响

【目的】研究了秸秆还田时不同长度秸秆对黑土力学特性的影响机制,为黑土压实与恢复、侵蚀与保护提供理论依据。【方法】试验于2016年6月以黑龙江省西北部的克山农场境内典型黑土区未经开垦(高有机质低黏粒含量)以及耕作40 a(低有机质高黏粒含量)的土壤为研究对象,在还田秸秆质量分数为1%、土壤含水量为20%,以及土壤容重为1.1 g/cm³的条件下,采用室内固结和三轴剪切相结合的方法,通过压缩指数、回弹指数、黏聚力及内摩擦角的测定与分析,模拟研究了不同长度(1、5、15、25 mm和空白对照)小麦秸秆对黑土压缩、回弹及抗剪切行为的影响机制。【结果】模拟秸秆还田可以有效改善黑土力学特性,长期耕作的低有机质高黏粒含量的土壤在添加秸秆后抵抗剪切能力的增强效果最为显著。秸秆长度分别与压缩指数呈负相关,与回弹指数呈正相关,且添加15 mm长度秸秆的黑土压缩指数最低而回弹指数最高,即此时其抗压能力及压实后自然恢复能力最强。随着秸秆长度的增加,黑土的抗剪强度逐渐显著增强,但增幅逐渐减小。【结论】秸秆还田措施对黑土力学特征有显著的改善效果,且模拟试验结果的秸秆最佳长度为15 mm。

Influences of chopped straw length on mechanical properties of black soil

【Objective】This study aims to explore the influences of chopped straw length on mechanical properties of black soil. It will provide theoretical basis for compaction and restoration, erosion and protection of black soil.【Method】We chose typical black soil without reclamation(high organic matter and low clay content)and tillaged for 40 years(low organic matter and high clay content)as subject simples on Keshan Farm of the northwest of Heilongjiang Province in June 2016. The adding mass fraction of the straw was 1%, soil gravity water content was 20%, and the initial density was 1.1 g/cm³. We combined the indoor oedometer test and triaxial test, to obtain and analyze the compression index, rebound index, cohesion and internal friction by simulating different chopped straw lengths returning(1, 5, 15, 25 mm, soil treatment without straw), then investigated their effects on soil compression, rebound and shearing properties.【Result】 Straw returning could effectively improve the mechanical properties of black soil. The effect of straw returning on low organic matter high clay soil samples due to long term tillage were more significant with the increase of chopped straw length. With the chopped straw length increasing, the compression index and rebound index was negatively and positively correlated with straw length, respectively; especially when straw length was 15 mm, the compression index decreased to the minimum value, and at the same time rebound index significantly increased to the maximum value; or black soil is hard to be compressed, and most easily rebound to the natural state after compaction. Soil cohesion significantly increased with straw length increasing, leading to higher shear strength, but the increase amplitude was decreasing gradually.【Conclusion】Straw returning measure has significant positive effects on the mechanical characteristics of black soil, and the optimum straw length of simulated experimental results is 15 mm.