Effects of ambient air humidity and temperature on crack development of compacted expansive soils
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摘要: 裂隙是影响膨胀土工程性质的重要因素。以南阳某高速公路膨胀土为对象,采用大尺寸压实膨胀土试样进行不同环境湿度与温度下的裂隙发育试验,通过数码相机摄影并基于自编程序进行土样表面图像的定量化分析,获得裂隙率、均宽及总长等典型特征参数,进而探讨环境湿度与温度对膨胀土裂隙发育规律的影响。结果表明：大尺寸土样裂隙发育特征相较环刀样和薄层饱和泥浆样更接近路基与边坡等工程实际；环境湿度越高,初期裂隙发展越慢,发育持续时间越长,后期裂隙特征统计参数反而越大；环境温度越高,初期裂隙发展越快,但裂隙回缩稳定速度也越快,后期裂隙特征统计参数反而越小；低湿度或高温度使土样表面易于产生更多肉眼不可见的微裂隙,是裂隙特征统计参数与理论分析相比偏小的重要原因,而高湿度与低温度则有利于收缩应力向深层土体传递,促使裂隙偏向数量更少但更宽和更深方向发展。Abstract: Cracks are one of the most significant influences on physical and mechanical properties of expansive soils. Some expansive soils, taken from Nanyang Expressway, are compacted to large-size samples and then dehydrated gradually in a closed greenhouse with various ambient air humidities and temperatures for desiccation tests, and a camera is utilized to record the development of cracks on the surfaces of samples. The captured images are disposed and then analyzed quantitatively to obtain typical characteristic parameters of surface cracks, such as crack ratio, average width and total length, for further exploration of crack developing laws. The results show that the cracks observed from the large big-size samples are more similar to those on the site such as embankments and slopes compared to the ring-knife-made or thin-saturated-slurry samples. The higher the ambient air humidity, the slower the cracks develop in the early stage, and the longer the developing time lasts, while the larger the statistical characteristic parameters of surface cracks in the later stage. The higher the ambient air temperature, the faster the cracks develop in the early stage, and the faster the cracks retract and become stable, while the smaller the statistical characteristic parameters of surface cracks in the later stage. Low ambient air humidity or high ambient air temperature makes it easy for the surface of soil samples to generate more invisible micro-fissures, which is an important reason for the small statistical characteristic parameters of cracks compared with the theoretical analysis. High ambient air humidity or low ambient air temperature may be beneficial to the transfer of shrinkage stress to deeper soil layer, and promote the development of cracks with fewer branches, larger width and deeper depth.
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Keywords:
- compacted expansive soil /
- humidity /
- temperature /
- crack ratio /
- crack width /
- crack length
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图 9 不同环境湿度下的裂隙均宽变化
Figure 9. Change of average crack widths under different air humidities
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图 10 不同环境温度下的裂隙均宽变化
Figure 10. Change of average crack widths under different air temperatures
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图 11 不同环境湿度下的裂隙总长变化（T=20℃,30℃,40℃）
Figure 11. Change of total crack lengths under different air humidities
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图 12 不同环境温度下的裂隙总长变化（RH=40%,60%,80%）
Figure 12. Change of total crack lengths under different air temperatures
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图 14 试验后土样含水率（#9）
Figure 14. Distribution of water content along depth of post-test soil sample (No. 9)
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图 15 不同湿度下蒙脱土样收缩裂隙对比试验
Figure 15. Shrinkage comparison of montmorillonite samples under different air humidities
表 1 试验终止时裂隙特征参数统计
Table 1 Final statistical characteristic parameters of cracks
编号 温度/℃ 湿度/% 裂隙率/% 裂隙均宽/mm 裂隙总长/mm #1 20 40 9.78 4.16 3758 #2 20 60 10.40 4.07 4089 #3 20 80 12.11 4.73 4135 #4 30 40 6.88 3.42 3268 #5 30 60 11.09 4.13 4290 #6 30 80 11.80 4.44 4147 #7 40 40 6.76 3.01 3591 #8 40 60 9.96 2.92 5446 #9 40 80 10.54 3.74 4100 
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