Effects of material and drilling uncertainties on artificial ground freezing of cement-admixed soils

Abstract

The artificial ground freezing method can be used jointly with the deep cement mixing method during break-in and break-out processes of shield machines in a tunnel shaft. The frozen ground can fully cut off groundwater seepage, thus ensuring a watertight working platform. Cement-admixed soils can restrict frost heave and thaw-induced settlement because of the decreased permeability. Both methods can also enhance mechanical strength of the soil to enable construction to proceed. Two main sources of heterogeneity are likely to influence the freezing effect: spatial variability in in situ water content in natural soil and spatial variability in binder concentration in cement-admixed soils. Furthermore, positioning error when installing freeze pipes can also affect freezing efficiency. This study simulates in situ water content and binder concentration as Gaussian random fields, whereby variations in the thermophysical properties are estimated. Positioning error is also assessed by prescribing an incline angle in freeze pipes. The influences of those two sources of spatial variability as well as positioning error are examined with random finite-element analyses and statistical characteristics are estimated based on the results. Results are tabulated to offer practitioners a rule of thumb for estimating additional efforts needed in artificial ground freezing, accounting for variations in the thermophysical properties and positioning errors in installing freeze pipes.

Site Measurement and Study of Vertical Freezing Wall Temperatures of a Large‐Diameter Shield Tunnel

“…However, deep-mixed or jetgrouted mixing piles usually have random untreated areas due to inevitable error though they were installed with due discretion [20][21][22][23][24][25][26]. ese untreated areas have an adverse effect on the strength and water-tightness of the treated ground [24,25,[27][28][29]. In the latter case, the temperature of the surrounding soil is lowered to freezing point by a supply of low-temperature-concentrated saline solution into the freezing pipe, so that the pore water of the soil is frozen, thereby temporarily improving the strength and watertightness of the soil.…”

Artificial Ground Freezing Impact on Shear Strength and Microstructure of Granite Residual Soil Under an Extremely Low Temperature

“…Meanwhile, urban environments and geotechnical properties have been inevitably influenced by subway tunnel excavations at a varying degree during construction and operation periods (Fu et al, 2014). Currently, the artificial ground freezing (AGF) method is widely used in tunnel excavations due to its advantages of broad applicability, high strength performance, seepage prevention, and environmental protections (Lackner et al, 2008;Liu et al, 2017). Although the AGF method has great advantages, the frost heaving damage and thaw-induced deformations of geotechnical materials during construction adversely affects the stability of underground structures (Vitel et al, 2015).…”

Numerical simulation of coupled liquid water, stress and heat for frozen soil in the thawing process

“…Saturated frozen soils composed of solid soil particles, ice, and unfrozen water, are multi-phase and porous materials, and the interactions among these phases can affect their deformation and mechanical features greatly (Liu and Lai, 2020). When temperature reduces to a value at which water in the soil begins to freeze, the pore ice can be formed and a large amount of pore ices gathers to form an ice lens, thus leading to frost heave (Xu et al, 2010;Liu et al, 2017;Sweidan et al, 2020Sweidan et al, , 2021. Once the temperature rises, the ice lens will melt and transform to water, the internal equilibrium within the soil will be destroyed in the thawing process (Wang et al, 2015;Antonova et al, 2018).…”