Jilin Qi

Laboratory Investigation of the Heat Transfer Characteristics of a Trapezoidal Crushed-Rock Layer Under Impermeable and Permeable Boundaries

Crushed-rock layer can be taken as a highly porous medium, which is often used in highway/ railway embankment of permafrost regions. In this study, in order to investigate the characteristics of heat transfer of a trapezoidal crushed-rock layer, laboratory tests were carried out on the porous material with impermeable and permeable boundaries under wind condition. Case 1 was closed crushed-rock layer and Case 2 was open crushed-rock layer. The results for the two cases were analyzed and compared with each other. It can be concluded that the heat transfer rate of Case 2 is higher than that of Case 1, but long-term cooling capability of Case 1 is larger than that of Case 2 under the same experimental conditions. Furthermore, we found that the heat transfer mechanisms of the two cases are quite different from each other, namely, the energy exchange of the Case 1 mainly relies on the internal natural convection which is caused by thermal variations, while in Case 2 it is from the heat transfer enhancement because of the internal forced convection induced by the external air flow. Therefore, the boundary conditions (impermeable and permeable) of crushed-rock layer can have a very large impact on the heat transfer pattern, especially under windy condition.

Analysis on the Settlement of Roadway Embankments in Permafrost Regions

In permafrost regions, the embankment settlement results from several physical and mechanical processes taking place in the different soil layer, making its mechanism very complicated. Under the thermal influence of embankment, climate warming as well as geothermal source, permafrost may degrade downwards or upwards, which continuously changes the thicknesses of the permafrost layer and the also unfrozen soil layers. Thus, any attempt to analyze the embankment settlement seems to be very troublesome and difficult. In this paper, based on ground temperatures of embankment sections in five typical regions along the Qinghai-Tibet Highway (QTH), the trends of variation of different soil layers and the thermal gradients are investigated. On this basis, four types of sections, which can represent most of the sections of QTH, are deduced to clarify the possible settlement sources in different soil layers. In order to further confirm and investigate of the settlement sources, an embankment model test was carried out. Combing the in-situ monitoring data with the results from the model test, the main settlement sources in embankment settlement are discussed for the four types of sections respectively. The results will facilitate the analysis of embankment settlement in permafrost regions.

A Review on Creep of Frozen Soils

Creep of frozen soils is one of the most important topics in engineering activities when frozen soils are involved. This paper firstly gives a review on the previous studies on creep of frozen soils. It is found that extensive experimental work has been carried out, which has facilitated recognition of creep behaviors of frozen soils. As for modeling, due to so many factors such as soil classification, density, water (ice) content as well as especially temperature, focus has been put on empirical models which often precisely describe creep behaviors of frozen soils under certain conditions but with serious limitations for extension. Closed-form models have been a pursuit while they are more theoretical explorations rather than applications so far. Considering this state of the art, a simple method was proposed in modeling the constitutive relations of frozen soil.

Temperature Effect on the Compressive Strength of Frozen Soils: A Review

Among the numerous influencing factors on the strength behavior of frozen soil, such as grain size, temperature, water content, strain rate, and confining pressure, etc. the temperature is a crucial one. In this paper a number of references concerning the temperature effect are reviewed. It is found that the strength of different frozen soils increases with the decrease of temperature below the freezing point of water, and the quantitative dependence of the strength on temperature can be primarily described by two kinds of functions, namely power function and linear function. The function parameters, including the exponent and slope, are collected. Moreover, how the other influencing factors affect the temperature parameter is also analyzed. It is found that, for example, the decrease in strain rate for testing or the increase in dry density of specimen will cause an increase in the exponent in the power function of temperature. Besides the temperature often encountered in engineering problem, the strength behavior of frozen soil at cryogenic temperatures is also reviewed.

A Visco-Hypoplastic Constitutive Model and Its Implementation

This paper presents a hypoplastic constitutive model for the viscous behaviour of frozen soil. Then the model is implemented into \(\mathrm{FLAC3D}^{\circledR }\). The performance of the model is demonstrated by simulating a compression creep test with the tertiary stage and the deformation of an embankment.

Modeling Deformation Wave in Rock Mass near Deep-Level Tunnel

In this paper deformation wave is studied on the basis of continuous phase transition theory. Relative shear strain is taken as an order parameter. The potential energy is obtained by analogy with the Ginzburg–Landau expansion of free energy. Hamilton’s variational principle is used to obtain the motion equation by which several types of deformation waves can be modeled. The results show that the proposed model is effective in modeling deformation waves.

A triaxial creep model for frozen soil based on hypoplasticity

This paper presents a triaxial constitutive model for the creep behaviour of frozen soil within the framework of hypoplasticity. The model is obtained by introducing a time-dependent function and b...