In some engineering projects near the ocean, rivers, lakes, etc., a special type of gas often develops in soft soil strata, which is called “shallow gas” in engineering geology. These gases are mainly methane, with small amounts of nitrogen and carbon dioxide. They may come from biological decomposition or thermogenic processes [1], and are mainly formed in fine-grained soils (clay, silt soil) under the seabed [2, 3]. In the era of promoting the use of new energy, shallow gas can be regarded as an important resource. However, in engineering construction, it is a potential geological hazard. In engineering projects in soft soil areas, geotechnical engineering problems caused by shallow gas often occur, and in severe cases, major disasters may even be triggered. In seabed sediments, gas exists in three forms: dissolved in the liquid phase, undissolved gas in the form of voids, and in the form of natural gas hydrates [5]. The release of these undissolved gases, the exsolution of dissolved gases, and the gas release caused by the decomposition of natural gas hydrates will have a significant impact on the engineering properties of the marine sediments that carry them. Liu et al. [6] conducted an experimental study on the bubble growth characteristics of natural gas-bearing sediments (sand and clay) through high-resolution X-ray scanning technology, and the results are shown in Fig. 5.1. For fine-grained soils, with the increase of time, the accumulation of bubbles will generate relatively large gas cavities, while for sandy soils, the gas mainly exists in the form of small bubbles [7]. At present, the engineering geological research on gas-bearing soils mainly focuses on sand layer foundations. Many scholars [7–10, 35] have studied the experimental characteristics of gas-bearing sand (with small bubbles in pore water). There are relatively few reports on experimental research data of gas-bearing fine-grained soils (soils with large bubbles) [2, 11–13], possibly due to the long experimental period caused by the low permeability of clay and the difficulty of sample preparation. Gas-bearing fine-grained soil strata mainly include silt, silty clay, and silty (silty fine-grained soil). These strata are rich in a large amount of organic matter. Under suitable conditions, these organic matters are decomposed and fermented by biological action to form shallow gas. After the formation of shallow gas, apart from the part that escapes to the outside, the remaining gas is generally adsorbed by the soil layer and dissolved in the pore water of the soil. Only when the adsorption capacity of the soil layer and the dissolution effect of the pore water reach saturation will free gas be formed and exist in the soil layer in the form of bubbles.

Model Description of the Mechanical Properties and Temperature Effects of Fine-Grained Gassy Soils

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发表日期：

2026年

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Guangchang Yang

摘要

In some engineering projects near the ocean, rivers, lakes, etc., a special type of gas often develops in soft soil strata, which is called “shallow gas” in engineering geology. These gases are mainly methane, with small amounts of nitrogen and carbon dioxide. They may come from biological decomposition or thermogenic processes [1], and are mainly formed in fine-grained soils (clay, silt soil) under the seabed [2, 3]. In the era of promoting the use of new energy, shallow gas can be regarded as an important resource. However, in engineering construction, it is a potential geological hazard. In engineering projects in soft soil areas, geotechnical engineering problems caused by shallow gas often occur, and in severe cases, major disasters may even be triggered. In seabed sediments, gas exists in three forms: dissolved in the liquid phase, undissolved gas in the form of voids, and in the form of natural gas hydrates [5]. The release of these undissolved gases, the exsolution of dissolved gases, and the gas release caused by the decomposition of natural gas hydrates will have a significant impact on the engineering properties of the marine sediments that carry them. Liu et al. [6] conducted an experimental study on the bubble growth characteristics of natural gas-bearing sediments (sand and clay) through high-resolution X-ray scanning technology, and the results are shown in Fig. 5.1. For fine-grained soils, with the increase of time, the accumulation of bubbles will generate relatively large gas cavities, while for sandy soils, the gas mainly exists in the form of small bubbles [7]. At present, the engineering geological research on gas-bearing soils mainly focuses on sand layer foundations. Many scholars [7–10, 35] have studied the experimental characteristics of gas-bearing sand (with small bubbles in pore water). There are relatively few reports on experimental research data of gas-bearing fine-grained soils (soils with large bubbles) [2, 11–13], possibly due to the long experimental period caused by the low permeability of clay and the difficulty of sample preparation. Gas-bearing fine-grained soil strata mainly include silt, silty clay, and silty (silty fine-grained soil). These strata are rich in a large amount of organic matter. Under suitable conditions, these organic matters are decomposed and fermented by biological action to form shallow gas. After the formation of shallow gas, apart from the part that escapes to the outside, the remaining gas is generally adsorbed by the soil layer and dissolved in the pore water of the soil. Only when the adsorption capacity of the soil layer and the dissolution effect of the pore water reach saturation will free gas be formed and exist in the soil layer in the form of bubbles.