干湿循环作用下高压实膨胀土及改性土裂隙演化规律及机理研究

Study on the evolution law and mechanism of cracks in high compacted expansive soil under dry wet cycling

干湿循环作用下膨胀土裂隙发育是影响南水北调工程渠坡安全的主要因素之一。为研究不同干湿循环作用下高压实膨胀土及水泥改性土的裂隙演化规律及机理,分别对为20 mm和40 mm高度的渠坡膨胀土及水泥改性土的环刀试样进行了7次室内干湿循环试验。试验结果表明:(1)随着干湿循环次数的增加,高压实膨胀土试样的最终裂隙率和分形维数不断增大并趋于稳定,达到一定的循环次数后,试样高度对裂隙率的影响减弱,而对分形维数的影响增大。(2)高压实水泥改性土在经历7次干湿循环后,试样表面没有出现裂隙,表明水泥可以有效的抑制膨胀土裂隙的发育。(3)在第2~3次干湿循环过程中,试样表面裂隙出现了自愈合现象。随着干湿循环次数的增加,膨胀土试样裂隙起裂时间提前,试样出现了不可逆转的损伤,自愈合现象消失。试样高度越高,试样裂隙的起裂时间越长。(4)由于高压实膨胀土团聚体失水收缩使得其空隙空间增加,加速了水分子的逃逸,导致高压实膨胀土和改性土的失水速率可分为3个阶段:加速率阶段、常速率阶段、减速率阶段。(5)在加速率和常速率阶段,试样高度对失水速率几乎没有影响。在减速率阶段,与40 mm高度试样相比,20 mm高度试样的失水速率降低的更快,进入减速率阶段的时间更早。随着干湿循环次数的增加,试样失水速率明显降低。

The development of cracks caused by dry wet cycles is one of the main factors affecting the safety of the canal slope project in the South to North Water Diversion Project.To study the evolution law and mechanism of cracks in high compacted expansive soil and modified soil under the action of dry wet cycles,the paper takes the expansive soil and modified soil of a canal slope in the middle route of the South to North Water Diversion Project as the research object. Seven tests were conducted on twotypes of expansive soil ring samples with different heights (20 mm and 40 mm). The test result show that: (1)The final crackrate and fractal dimension of high compacted expansive soil continuously increase with the increase of dry wet cycles, and afterreaching a certain number of cycles, the crack development speed gradually slows down and tends to stabilize. As the number ofwet and dry cycles increases, the influence of sample height on crack rate weakens, while the influence on fractal dimension increases.(2) After 7 cycles of wet dry cycles, no cracks appeared on the surface of the sample of high-pressure cement modifiedsoil, indicating that cement can effectively suppress the development of cracks in expansive soil. (3) With the increase of thenumber of wet dry cycles, the crack initiation time of the expansive soil sample is advanced, and the sample shows irreversibledamage, and the self-healing phenomenon disappears. The higher the height of the sample, the longer the initiation time of thecracks in the sample. (4)Due to the water loss and shrinkage of high-pressure compacted expansive soil aggregates, their voidspace increases, accelerating the escape of water molecules. As a result, the water loss rate of high-pressure compacted expansivesoil and modified soil can be divided into three stages: acceleration rate stage, constant rate stage, and deceleration rate stage.(5) During the acceleration rate and constant rate stages, the height of the sample has almost no effect on the water loss rate. Inthe deceleration stage, the water loss rate of the sample with a height of 20 mm decreases faster and enters the decreasing ratestage earlier than that of the sample with a height of 40 mm. As the number of wet dry cycles increases, the water loss rate of thesample significantly decreased.