Properties of Pore Air Pressure in Loess During Soaking: Insights from Field Immersion Test
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摘要:
在黄河流域的黄土高原，黄土灾害频发，其关键的地质基因在于对水极为敏感。其中黄土场地遇水后的湿陷变形的科学评价，是黄土灾害研究的主题之一。黄土场地湿陷性逐渐由“最大湿陷势”向“可能湿陷势”转变，迫切需要查明现场试坑浸水试验过程中，黄土中水分入渗–气体迁移–湿陷变形的多场耦合过程。目前，有关现场浸水试验过程中真实测定孔隙气压演化规律鲜有报道。因此，笔者开展黄土高原大厚度自重湿陷性黄土场地现场浸水试坑试验，在典型剖面不同深度布置湿度传感器和孔隙压力传感器，直接测定浸水过程中水分运移和孔隙气体压力，揭示水分运移和气压形成规律。研究结果表明，试坑浸水–停水过程中，呈现出水分入渗的感知–增湿–饱和–减湿–稳定的5阶段变化规律；打设注水孔，明显地改变了试坑中的水分扩散路径，以注水孔的径向渗流——古土壤富水向上迁移的扩散路径为主；首次实现了在大厚度湿陷性黄土大型试坑浸水过程中土体孔隙气压力的原位测定，呈现波动特征，提出了浸水过程中孔隙气压的形成模式。成果为非饱和黄土中水–气运移过程提供实测证据，为进一步精细化预测大厚度黄土的增湿湿陷过程奠定基础。
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关键词:
- 黄土灾害 /
- 大厚度自重湿陷性黄土 /
- 浸水试验 /
- 水分入渗 /
- 孔隙气压
Abstract:In the Loess Plateau of the Yellow River Basin, loess disasters are frequent, and the key geologic gene is that the loess is extremely sensitivity to water. Among them, the scientific evaluation of wetting-induced collapse deformation of loess site is one of the themes. The wetting-induced collapse deformation of loess site gradually changes from "maximum potential" to "possible potential", and there is an urgent need to find out the multi-field coupling process of water infiltration, gas migration, and wetting-induced collapse deformation in loess during the on-site pit immersion test. At present, there are few reports about the measured pore gas pressure and its evolution law during the on-site pit immersion test. Accordingly, the site immersion test in loess plateau site on large thickness of self-weighted wetted loess were carried out. Moisture sensors and pore pressure sensors were arranged at different depths of typical profiles, to directly measure the water transport and pore gas pressure during the water immersion process, and thus then reveal the water transport and gas pressure formation laws. The results show that the 5-stage change rule of perception of water infiltration - wetting - saturation -drying - stabilization during the on-site pit immersion after stoping. The installation of water injection holes has obviously changed the water diffusion paths in the pit, and the radial seepage from the injection holes and the enrichment of water near paleosoil stratigraphy, whereby resulting in a predominantly upward migration of water. Having realized for the first time, the in-situ measurement of pore gas pressure of the soil during soaking in a large test pit on large thickness of the collapsed loess site. It showed fluctuating changes, and the formation mode of the pore gas pressure during soaking was proposed. The results provided experimental evidence of the coupled water-gas transport in unsaturated loess, and lay the foundation for further refinement of the prediction of the wetting-induced collpase of the large-thickness loess.
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图 1 浸水试坑试验场地区域位置（a）、典型地质剖面（b）、观测点布置（c）、实景图（d）
Figure 1. (a) Regional location, (b) typical geologic profile, (c) measured point, (d) actual view of the test site for immersion pits
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图 2 探井中水分计埋设剖面图和安装过程
Figure 2. Moisture meters and their installation process in exploratory excavations
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图 3 钻孔中液位计埋设剖面图和安装过程
Figure 3. Liquid level meters and their installation process in drill
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图 8 试坑浸水过程中土体孔隙压力变化的时程规律
Figure 8. Changes in pore pressure of the soil during immersion test
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图 9 试坑浸水过程中土体孔隙压力变化的时程规律
Figure 9. Changes in pore pressure of the soil during immersion test
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