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Immersion is an important part of reservoir engineering investigation and evaluation. Determining the reasonable and effective burial depth of the critical immersion water table is one of the key scientific issues in the impact assessment of the bearing capacity of reservoir immersion foundations. In this study, basic physical and mechanical property tests were carried out on the soil in the typical immersion area of Xiaonanhai Hydropower Station, and the influence mechanism of saturation on the mechanical properties of building foundation soil and immersion on the bearing capacity of a shallow foundation was obtained. According to the test results, the influence depth of the rising groundwater level on the stability of the building foundation is analyzed, and a method to determine the critical depth of immersion groundwater in the reservoir is proposed. Taking the typical building foundation of Luohuang Town in the immersion area of Xiaonanhai Reservoir as an example, the validity of the critical water depth is further verified. The results show that the safety limit depth of the independent foundation affected by the rise of the water table increases with the increase of the width of the foundation and decreases with the increase of the buried depth of the foundation. Considering the safety limit depth, the critical depth of building immersion is 4.830 m, and without considering the safety limit depth, the critical depth of building immersion is 4.05 m. To a certain extent, it can reduce the impact of water table changes on the bearing capacity of shallow foundations. [ABSTRACT FROM AUTHOR]

Immersion is an important part of reservoir engineering investigation and evaluation. Determining the reasonable and effective burial depth of the critical immersion water table is one of the key scientific issues in the impact assessment of the bearing capacity of reservoir immersion foundations. In this study, basic physical and mechanical property tests were carried out on the soil in the typical immersion area of Xiaonanhai Hydropower Station, and the influence mechanism of saturation on the mechanical properties of building foundation soil and immersion on the bearing capacity of a shallow foundation was obtained. According to the test results, the influence depth of the rising groundwater level on the stability of the building foundation is analyzed, and a method to determine the critical depth of immersion groundwater in the reservoir is proposed. Taking the typical building foundation of Luohuang Town in the immersion area of Xiaonanhai Reservoir as an example, the validity of the critical water depth is further verified. The results show that the safety limit depth of the independent foundation affected by the rise of the water table increases with the increase of the width of the foundation and decreases with the increase of the buried depth of the foundation. Considering the safety limit depth, the critical depth of building immersion is 4.830 m, and without considering the safety limit depth, the critical depth of building immersion is 4.05 m. To a certain extent, it can reduce the impact of water table changes on the bearing capacity of shallow foundations.

ABSTRACT: There are many factors affecting the instability of the submarine hydrate-bearing slope (SHBS), and the interaction with hydrate is very complicated. In this paper, the mechanical mechanism of the static liquefaction and instability of submarine slope caused by the dissociation of natural gas hydrate (NGH) resulting in the rapid increase of pore pressure of gas hydrate-bearing sediments (GHBS) and the decrease of effective stress are analyzed based on the time series and type of SHBS. Then, taking the typical submarine slope in the northern South China Sea as an example, four important factors affecting the stability of SHBS are selected, such as the degree of hydrate dissociation, the depth of hydrate burial, the thickness of hydrate, and the depth of seawater. According to the principle of orthogonal method, 25 orthogonal test schemes with 4 factors and 5 levels are designed and the safety factors of submarine slope stability of each scheme are calculated by using the strength reduction finite element method. By means of the orthogonal design range analysis and the variance analysis, sensitivity of influential factors on stability of SHBS are obtained. The results show that the degree of hydrate dissociation is the most sensitive, followed by hydrate burial depth, the thickness of hydrate and the depth of seawater. Finally, the concept of gas hydrate critical burial depth is put forward according to the influence law of gas hydrate burial depth, and the numerical simulation for specific submarine slope is carried out, which indicates the existence of critical burial depth.

Critical burial depth plays an important role in tunnel design and analysis. So, the division method for deep tunnels and shallow tunnels is perceived as a main concern. Considering the soil stress path dependency, this paper investigates the construction mechanical behavior of soil mass at different burial depths, and aims to explore a method for identifying critical burial depth. Firstly, using the Eulerian method and stress return mapping scheme, an elastoplastic algorithm applicable to double loading criteria was developed for a soil constitutive model considering complex stress paths. Then, the developed algorithm was implemented into a user-defined material subroutine (UMAT) and validated through numerical triaxial tests under different stress paths. Subsequently, the UMAT was used to model tunnel excavation in soils. The simulated results were compared with the results that from practical engineering, which shows that the UMAT could accurately predict the ground surface settlement. On the basis of this, the stress distribution and deformation performance in soil during tunneling at different burial depths were explored. Finally, the division method for differentiating shallow tunnels and deep tunnels in soil was discussed and a method for determining the critical depth was proposed. [ABSTRACT FROM AUTHOR]