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Measuring stiffness of soils in situ
Published in Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto, Computer Methods and Recent Advances in Geomechanics, 2014
Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto
Artificial ground freezing is an effective temporary ground improvement technique in soft soils. The freezing improves the properties (strength, stiffness and permeability) of the soil and provides a local supporting structure. Ground freezing is a reversible process with no environmental impact and it has many applications in geotechnical engineering such as slope stabilization, ground water control and supporting excavation during underground construction. In tunnelling, a closed arch of frozen ground is formed after a period of time, around the excavated area which provides a protected area for the excavation of the tunnel cross-section. For a safe geotechnical design and construction of the freezing process, a reliable prediction of the coupled thermo-hydro-mechanical behaviour is required. A three-phase freezing soil model is implemented in the presented finite element model to capture the various couplings during freezing process.
Ground improvement techniques and lining systems
Published in David Chapman, Nicole Metje, Alfred Stärk, Introduction to Tunnel Construction, 2017
David Chapman, Nicole Metje, Alfred Stärk
The freezing method is only applicable when the ground contains water, ideally still fresh water. Ground with a moisture content greater than 5% will freeze. Water can be added via a fire hose, a sprinkler system, a borehole or injection device to raise the moisture content in the ground. The principle of ground freezing is to use a refrigerant to convert in situ pore water into a frostwall, with the ice bonding the soil particles together.
Experimental evaluation of uniaxial strength and creep behavior of frozen gravel
Published in Journal of the Chinese Institute of Engineers, 2022
Yaqin Zhang, Ping Yang, Lin Li
During construction of urban subway system, a water-rich gravel stratum is sometimes encountered during tunnel construction. Owing to the high permeability associated with the gravel stratum, the tunnel is usually vulnerable to seepage, piping, and quick sand problems. With consideration of the outstanding performance in water sealing, high strength, and negligible environmental impact, artificial ground freezing (AGF) technology is typically adopted to freeze the surrounding soil to ensure tunnel safety during excavation. The performance of AGF technology is highly dependent on the mechanical properties (e.g. strength and creep behavior) of frozen soil. Research findings on frozen sand and silt show that there usually is a noticeable deforming process before failure (e.g. Xu et al. 2017; Liu et al. 2019; Fei and Yang 2019; Zhao et al. 2020; Sengal and Ou 2021). As a result, structural instability can be avoided by monitoring deformation. Unlike frozen sand or silt, frozen gravel is usually associated with brittle failure. In other words, there may not be an early warning sign before failure. Very serious engineering accidents can be a direct result of this phenomenon. Consequently, considering tunnel safety, the strength characteristics of frozen gravel deserve special attention.
Evolution mechanism of temperature field of the frozen wall of the vertical shaft under cold energy extraction
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Hanwen Zhang, Weipei Xue, Zhishu Yao, Zongjin Wang, Feng Wang, Cheng Wu
Artificial ground freezing was first put forward by Friedrich Poetsch in the 19th century and was originally used in mining engineering (Cheng 2016). Artificial ground freezing is to use artificial refrigeration technology to freeze the ground water into ice to form frozen wall (Lu, Chen, and Chen 2021). The frozen wall will increase the stability and strength of the soil and form temporary support, which is convenient for underground engineering construction (Yang and Rong 2020). After the construction of the artificial ground freezing, the average temperature of the frozen wall is very low, in which a large amount of cold energy is stored. Frozen wall is bulky, just finished construction of frozen wall is equivalent to a huge cold storage tank (Ji 2017). If the cold energy of the frozen wall is not extracted and applied, it will gradually dissipate under the action of geothermal, resulting in a serious waste of resources. Taking Wanfu Coal Mine as an example, the frozen wall at the end of shaft construction is used as an underground cold source to extract cold energy and apply it to the refrigeration system to save nearly 1.36 × 106 kWh of electric energy (Fan, Zhang, and Zhou 2016). At the same time, artificial ground freezing is not only used in shaft sinking construction but also widely used in subways, tunnels, foundation pits, and other engineering fields (Rong et al. 2022). If the excess cold energy of the frozen wall in all freezing projects is reasonably extracted and applied, it will save a lot of energy and alleviate the problem of national energy shortage. Therefore, it is urgent to study the extraction technology from excess cold energy of frozen walls.
Closed-form solutions for large strain analysis of cavity contraction in a bounded Mohr-Coulomb medium
Published in European Journal of Environmental and Civil Engineering, 2022
Xiu-Guang Song, He Yang, Hong-Ya Yue, Xu Guo, Hai-Sui Yu, Pei-Zhi Zhuang
Artificial ground freezing has been widely used to stabilize temporarily the ground in order to provide ground support and/or exclude groundwater from an excavation until the final retaining and lining structures are constructed (Andersland & Ladanyi, 2004; Sanger & Sayles, 1979; Viggiani & Casini, 2015; Zhang et al., 2018). From a structural point of view, determination of the geometry and the thickness of a frozen wall is one of the main concerns for practitioners. Because of the relatively high compressive and low tensile strengths of frozen soil, curved arch walls, particularly circular walls, are often selected with priority. The unloading model of a cylinder unloading from an in-situ stress state that was studied previously has been commonly used to determine the thickness of a circular frozen wall (Andersland & Ladanyi, 2004; Klein & Gerthold, 1979; Sanger & Sayles, 1979). For example, assuming and (i.e. no internal support), Sanger and Sayles (1979) proposed Equation (77) to estimate the minimum thickness of a cylinder wall. Klein and Gerthold (1979) extended this solution to the case where the internal pressure acting on the wall equals (i.e. ), thereby Equation (78) was given. These solutions were obtained by solving the equilibrium equation (1) and the Mohr-Coulomb yield function (6). Therefore, they can be recovered by Equation (26) or (30) considering the boundary conditions they adopted.