Freezing Pressurized Water into a Standard Cylindrical Ice Sample in a Triaxial Cell

Baosheng Wang,Tingting Luo,Peixin Sun,Tao Zhang,Weihao Yang,Chun Zhu

doi:10.1155/2021/6678966

Abstract

The mechanical characteristics of high-pressure frozen ice are a basis for the design of deep underground frozen walls, the drilling of thick permafrost and ice sheets, and the probing of extraterrestrial ice. The continuous control of the sample stress state from freezing to testing is essential for the experimental study of in situ mechanical response of high-pressure frozen ice. In the context, we developed a preparation technique for freezing pressurized water into a standard cylindrical ice sample in a triaxial cell. Through theoretical analysis, a cylindrical water sample with precise dimensions and strong sealing was fabricated using heat shrinkable tubing, sectional end caps, and an assembly cylinder. A mounting device was designed to insert the water sample into the triaxial cell without deformation. In order to deal with the lateral surface irregular of the resulting ice sample caused by freezing expansion, we proposed a pressurization method in which the volume of the confining medium is controlled to restrict the radial deformation of the sample, and the axial pressure on the sample is kept constant; thus, the freezing expansion will develop along the height direction through releasing the expansion pressure. Based on the analysis of sample deformation and finite element numerical simulations, the control method of the temperature fields of the sample and the confining medium was obtained, and the standard cylindrical ice sample which satisfies the geometric accuracy requirements was produced. The comparison of ice samples frozen by different freezing methods showed that the control of the confining medium mean temperature and the sample unidirectional freezing is necessary to improve the dimensional precision of the ice sample.

Highlights

As the underground resource exploitation goes deeper, engineering disasters have become increasingly prominent in unstable aquifers [1,2,3,4,5,6], and the artificial ground freezing is the primary sinking method in such thick stratum [7]
This means that once the sample begins to freeze, the volume of the confining medium should be slightly decreased by changing the mean temperature by ð−0:25 – 0:073 pcÞ°C to allow the freezing expansion to develop to a small extent along the radial direction to compensate for the small radial shrinkage of the water sample caused by cooling and compression, the mean temperature of the confining medium should remain constant until the sample is completely frozen, and the permissible fluctuation of above temperature control is ±1.85°C
A preparation technique for freezing pressurized water into a standard cylindrical ice sample in a triaxial cell was developed, in which the dimensional accuracy of the ice sample is guaranteed by the following measures: Figure 18: Ice sample frozen with two freezing fronts developing towards each other

Summary

Introduction

As the underground resource exploitation goes deeper, engineering disasters have become increasingly prominent in unstable aquifers [1,2,3,4,5,6], and the artificial ground freezing is the primary sinking method in such thick stratum [7]. The depth of the permafrost in the Arctic can exceed one kilometer [12], but the deep permafrost is difficult to be drilled and sampled [13], which restricts the process of related scientific investigation. To solve these problems, the mechanics experiments of deep frozen soil [14,15,16] and frozen rock [17,18,19] have been widely studied, whereas little attention has been paid to the coupling problems of icesoil and ice-rock and the mechanical characteristics of the ice in deep environment are the basis of the above problems. The influence of such high freezing pressure on the mechanical characteristics of the ice needs to be further studied

Methods

Results

Conclusion