改良盐渍土强度变形及其微观特性试验研究

盐渍土的盐胀溶陷等不良工程特性对交通基础设施建设及其安全运行有着极其不利影响。现以南疆地区路基氯盐渍土为研究对象,开展了不同龄期改良氯盐渍土2种试验方案的无侧限抗压强度试验及SEM-EDS试验,研究水玻璃、水泥、石灰、粉煤灰及纤维等多种材料联合改良盐渍土的机理及其微观特征。研究结果表明:以28 d抗压强度作为评价标准,方案1中最优组合为水泥8%+石灰12%+纤维0.2%+纤维长度18 mm+含盐量3%,适用于中盐渍土改良;方案2中最优组合为粉煤灰20%+石灰6%+纤维0.2%+纤维长度12 mm+含盐量1%,适用于弱盐渍土改良。2种方案改良盐渍土越过应力峰值后仍能保持较高的抗压强度值,改良盐渍土应力-应变曲线呈应变软化型,试样呈脆性破坏。根据微观结构及EDS分析,改良盐渍土的矿物颗粒相对较大,颗粒完整性较好,胶凝物由絮状水化硅酸钙和针状钙矾石构成,其微观结构较致密,颗粒间接触方式以面-面接触方式为主;相比方案2,方案1内部结构排列致密,内部完整性好,强度性能优越。该研究成果丰富了氯盐渍土改良技术,为盐渍土在路基处理中再循环利用提供了技术参考。

Experimental Study on Strength Deformation and Micro-characteristics of Improved Chloride Saline Soil

The unfavorable engineering characteristics of saline soil such as salt expansion and solution subsidence have extremely adverse effects on the construction of transportation infrastructure and its safe operation. The mechanism of improving saline soil by adding sodium silicate, cement, lime, fly ash and fiber and the microscopic characteristics of improved soil were investigated via unconfined compression test and SEM-EDS test on the chloride saline soil of subgrade in south Xinjiang. Results manifest that with the 28 d compressive strength as the evaluation standard, the optimal combination in scheme 1 (cement content 8%, lime content 12%, fiber content 0.2%, and fiber length 18 mm, with a salt content of 3%) is suitable for improving medium chloride saline soil; the optimal combination in scheme 2 (fly ash content 20%, lime content 6%, fiber content 0.2%, and fiber length 12 mm, with a salt content of 1%) is suitable for improving weak chlorine saline soil. The improved saline soil modified by the aforementioned two schemes could both retain high compressive strength after reaching stress peak, and the stress-strain curves display strain softening feature with brittle failure. Microstructure and EDS analysis illustrate that the mineral particles of the modified and solidified saline soil are relatively large with sound particle integrity. The cementitious material is composed of flocculent calcium silicate hydrate and acicular ettringite with dense microstructure. The contact mode between particles is mainly face-to-face contact. Compared with those in scheme 2, the improved soil specimen in scheme 1 is of dense internal structure, good internal integrity, and superior strength performance.