Jilin Qi

• Ph. D.
• Professor at Beijing University of Civil Engineering and Architecture

In seasonally frozen regions, the seasonal appearance of the frozen layer may have certain influence on the ground motion features of the area. In this paper, a site in a seasonally frozen region in northwestern China is taken to investigate the ground motion features in different seasons. As an easy method to obtain the linear features of the grou...

The strength of frozen soils has been one of the most extensively studied aspects in frozen soil mechanics. When carrying out deep excavations using freezing methods, high stress states are often encountered. Therefore, the strength of frozen soils under high confining pressures is of major concern. This paper first reviews the present failure crit...

Freeze-thaw cycling affects the geotechnical properties of soils and must be taken into account when selecting soil parameters for stability and deformation analysis of slopes, embankments and cuts in cold regions, especially those underlain by permafrost. This review examines methods of investigation, testing techniques and the impact of freeze-th...

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...

Temperature changes and deformations were monitored on various embankment types on the Qinghai-Tibet Railway. Some of these embankments utilized permafrost protection techniques such as duct ventilation, crushed-rock embankments, crushed-rock protected slopes, or thermal-insulation treatments. Some embankments were built conventionally without cons...

In the construction of cold region engineering and artificial freezing engineering, soil–rock mixture (SRM) is a frequently encountered geomaterial. Understanding the mechanical properties of frozen SRM is crucial for ensuring construction safety. In this paper, frozen SRM is considered as a multiphase material consisting of a soil matrix and rock....

In vast areas with frozen ground, the surface soil layer undergoes freezing and thawing with the changing seasons, which impacts the stress distribution in the underlying soil layers. However, there is a lack of systematic experimental and theoretical research on the stress transfer in this process, which makes the current calculations and analyses...

The strength criterion of frozen soil is necessary for the evaluation of failure problems of the engineering constructed in cold regions or by artificial ground freezing method. Due to the combining effect of stress conditions and temperature, the unique feature of the three-stage development in shear strength of frozen soils has been widely recogn...

To obviate the complexities of the straight forward couple stress finite element method, the penalty-based couple stress finite element method (named PcouFEM) within the framework of the Cosserat continuum is utilized to obtain the approximate solution by relaxing the C1 continuity. To examine the performance of the PcouFEM, three well-known numeri...

In order to investigate the development of thermal regime and frost heave of a gravelly soil under seepage during artificial freezing, a large-scale model test system was designed. The typical gravelly soil in Beijing obtained from a construction site was taken as the study object. Artificial freezing tests were carried out on the soil layer under...

The bimodal structure in expansive soils that refers to the bimodality of the pore size distribution significantly affects the soil freezing characteristic curve (SFCC). In this paper, the artificial samples with different bimodal structures are prepared by mixing Qinghai-Tibet silty clay and bentonite in different proportions. The influence of the...

For geotechnical stability analysis involving the Drucker-Prager (DP) criterion, both the c-φ reduction scheme and the M-K reduction scheme can be utilized. With the aid of the second-order cone programming optimized finite element method (FEM-SOCP), a comparison of the two strength reduction schemes for the stability analysis of a homogeneous slop...

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...

Silty soils are usually with poor mechanical performance and thus need reinforcement to meet the requirements in geotechnical practices. Wheat straw is low-cost, environment-friendly and wide spread, which has a great potential for use as reinforcement of the silty soils. In this study, the anti-corrosion effect of polyvinyl alcohol (PVA) treated w...

The excavation disturbed zone plays an important role in the evaluation of tunnel stability. The identification of the excavation disturbed zone is perceived as a main concern. Taking the material meso-structure into account, this paper investigates the construction mechanical behavior in heterogeneous sand cobble stratum, and aims to precisely pre...

Clay is under the coupling influence of both time and temperature in some innovative geomechanical problems. Previous experimental researches have confirmed that time and temperature affect the overconsolidation degree of clay and induce overconsolidated characteristics. However, the experimental findings have not been included in constitutive mode...

Frozen gravelly soils are often encountered in both cold regions engineering and urban underground constructions by artificial freezing method. This work takes a gravelly sand in Beijing as the basic material. Gravel grains of 10–20 mm in size are obtained and mixed with sand grains at certain ratios and then saturated frozen samples are prepared....

Frozen gravelly soils are often encountered in both cold regions engineering and urban underground constructions by artificial freezing method. This work takes a gravelly sand in Beijing as the basic material. Gravel grains of 10-20 mm in size are obtained and mixed with sand grains at certain ratios and then saturated frozen samples are prepared....

This study presents a rate-independent constitutive model for granular materials which is based on the analysis of discrete element modelling (DEM) results. We examine the elastic and plastic strain rate at any state of shear, and explore how the plastic strain rate and the stress rate are related to some state variables (e.g. stress, void ratio, e...

The influence of seepage on the development of the frozen wall must be considered when artificial ground freezing (AGF) is applied to the coarse-grained soil layers. In this paper, the influence of groundwater flow in a sandy layer on the temperature field during artificial freezing is studied. Model tests were carried out with different seepage ve...

Brine leakage is a common phenomenon during construction facilitated by artificial freezing technique, threatening the stability of frozen wall due to the continual thawing of already frozen domain. This paper takes the frequently encountered soft clay in Wujiang District as the study object, and remolded specimens were prepared by mixing calcium c...

In this paper, we investigate the mechanical behaviour of a compressed air energy storage (CAES) pile through finite element analyses. A simple hypoplastic constitutive model is used for the soil surrounding the pile. The analyses are carried out on two numerical models, namely a plane-strain model and an axisymmetric model. The numerical results s...

An optimal hydraulic section is critical for irrigated water conservancy in seasonal frozen ground due to a large proportion of water leakage, as investigated by in-situ surveys. This is highly correlated with the frost heave of underlain soils in cold season. This paper firstly derived a practical model for frost heave of clayey soils, with temper...

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 incre...

The brine leakage is a tough problem in artificial freezing engineering. This paper takes the common soft clay in Wujiang District as the study object, and calcium chloride solutions with six salinity levels were considered. The ‘classic’ cooling curve method was employed to measure the freezing point of specimens after freeze-thaw. Results indicat...

The extended hypoplastic constitutive model for frozen soil developed previously by the authors was applied to simulate the mechanical behavior of frozen soil under various stress path conditions, such as conventional triaxial shearing with constant confining pressure, triaxial shearing with constant mean principal stress, pure shearing with a circ...

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 deformatio...

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 breaking the stress-homogeneity and rate independence of the basic hypoplastic constitutive model for sand. Parameters in the model are classified into tw...

Plastic yield pressure is a key factor influencing mechanical behavior of frozen soil. In this paper, an isotache model taking account the effect of creep on plastic yield pressure was modified to describe the mechanical behavior of frozen soil. A series K 0 compression tests after different creep time and at different temperature were carried out...

This paper examines viscosity of rock mass at different structural hierarchies. The study shows that viscosity and characteristic strain rate of rock mass vary at different structural levels. There exists one-to-one correspondence between characteristic scale level and strain rate. High viscosity with low characteristic strain rate occurs under mac...

A combined constitutive model is developed for the creep behavior of frozen soil in an unconfined condition. The model is obtained by coupling two stress- and time-dependent models, which are responsible for the primary and tertiary creep stages. The model parameters are dependent on temperature and can be readily determined from the strain rate–ti...

A novel apparatus was developed for measurement of pore water pressure distribution and dissipation during thaw consolidation. Thaw consolidation tests were conducted to verify the applicability of nonlinear stress–strain relationship in 3-D large strain thaw consolidation theory. During thawing process, the measured pore pressure at different laye...

In this study, freeze-thaw cycles were conducted on samples of a fine grained soil from the Qinghai-Tibetan plateau which had been prepared with different dry unit weights. During freeze-thaw cycles, electrical resistivity was measured. The soil samples were also scanned by X-ray computed tomography (CT) before and after freeze-thaw cycles. Unconso...

The Qinghai–Tibet Highway (QTH) in China has been experiencing a serious embankment settlement/heave for more than half a century. The settlement/heave is resulted from several mechanical processes taking place in different soil layers. In this paper, four typical settlement/heave patterns of road embankments in permafrost regions, namely “steady-l...

This paper presents a hypoplastic constitutive model for the viscous behavior of frozen soil. The model is composed of a 'solid' part and a 'fluid' part. The solid part is based on the extended hypoplastic model, and the fluid part is dependent on the second time derivative of strain. The performance of the model is demonstrated by simulating some...

This paper presents a hypoplastic constitutive model for frozen sand. The model is obtained by introducing temperature-dependent cohesion and a deformation-related function for strain softening. The extended model is simple in mathematical formulation and contains only eight parameters, which can be easily obtained from conventional triaxial tests....

Settlement of foundations in permafrost regions primarily results from three physical and mechanical processes such as thaw consolidation of permafrost layer, creep of warm frozen soils and the additional deformation of seasonal active layer induced by freeze-thaw cycling. This paper firstly establishes theoretical models for the three sources of s...

Two-phase closed thermosyphon (TPCT) is a popular way to prevent permafrost layers from degrading, and consequently ensure the stabilities of engineering constructions in permafrost regions. Although TPCTs have been numerically and experimentally investigated for many years, long-term field monitored data concerning the cooling performance of TPCTs...

A reasonable height of embankment is beneficial for maintaining the thermal and mechanical stability of highway in cold regions. This paper firstly introduced theoretical models for two main sources of settlement, including an improved consolidation theory for thawing permafrost and a simple rheological element based creep model for warm frozen soi...

The BaSO4/cellulose composite fibers were prepared using Lyocell process, and the influences of BaSO4 content on structure and properties of the fibers were investigated. The results of SEM show that the surface of the fiber is more and more rough with the increase of content of BaSO4. The results of XRD show that the crystallinity of composite fib...

Large uncertainty exists in soil testing due to the randomness in sampling and system errors, especially in tests on frozen soils. In order to reduce the randomness and improve the test accuracy, the sample preparation method is improved to obtain more homogeneous samples. The standard Chinese sand is used as the soil. An environmental material tes...

Particle crushing is one of the important factors to change mechanical properties of frozen sand, which is hardly studied quantitatively so far. Triaxial compression tests are carried out on a saturated frozen sand at -0.5℃, -1℃, -2℃ and -5℃ under the confining pressure of 0.5, 2, 5 and 10 MPa, respectively. The particle crushing ratio, Br, defined...

Based on CU triaxial tests on basalt fibre-reinforced silt (BFRS), a shear strength and stress-strain relationship analysis was conducted under various cell pressures, fibre mixing ratios and fibre lengths. It was found that basalt fibre can effectively increase the shear strength of BFRS and that the improvement is mainly in the cohesion but sligh...

Creep of frozen soils is one of the most important issues in cold regions engineering. This paper first reviews the state-of-the-art of creep models for frozen soils. It is found that the elementary rheological models are more feasible in describing the creep of frozen soils. The authors propose a simple model by combining Maxwell, Kelvin and Bingh...

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...

Freeze-thaw cycle effect is one of the most important reasons that cause engineering problems in cold zone. Freeze-thaw cycles may lead to great changes of soil engineering properties, and subsequently cause unacceptable deformation or failure of engineering facilities. The research achievements of the soil engineering change caused by freeze-thaw...

When permafrost thaws, consolidation occurs under surcharge loads, leading to settlement which is one of the largest threats to infrastructures constructed in permafrost regions. This paper proposes a three dimensional thaw consolidation theory combining Biot’s consolidation theory with heat conductive equations considering ice-water phase change e...

Ground temperature and settlement at different soil layers are monitored at four typical sections of the Qinghai–Tibet Highway (QTH) and one section of a newly built test road (NBTR) in Beilu River basin, for the purpose of extensive investigation on the rather complicated mechanism of embankment settlement owing to several physical and mechanical...

The lateral earth pressure coefficient at rest, K-0, is an important parameter in geotechnical engineering. There have been many studies for unfrozen soils; however, this is not the case for frozen soils, which impedes reasonable calculation concerning cold regions engineering. This paper introduces a novel triaxial apparatus for frozen soils with...

Embankment settlement is closely related to the process of degrading of underling permafrost. Previous studies have focused on the process of permafrost degradation under natural ground surfaces, and the degradation process under roadway embankments has yet to be investigated. With the influence of climate warming, this study becomes more and more...

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 modeli...

Thaw consolidation of ice-rich permafrost is a typical problem in cold regions engineering. This paper proposes a three dimensional analysis of large strain thaw consolidation for post-thawed zone of permafrost, which is defined by a moving thawing boundary problem with phase changes. The theory is implemented in a numerical code and the numerical...

To get a better understanding of relaxation process of warm permafrost and find factors influencing on this process, a series of laboratory triaxial relaxation tests are conducted. The results indicate that the instantaneous relaxation increases with pre-strain and the relaxation stabilization duration prolongs. For the constant strain rate loading...

Stress relaxation is one of the main concerns in geotechnical engineering, especially in permafrost regions with warm frozen soil. This paper investigated the mechanical behaviors of a warm frozen soil during relaxation process. A series of triaxial relaxation tests were carried out on the warm frozen soil samples under the temperature from −1.0°C...

The pre-strain process can be considered to be the effect of stress history. To investigate the stress relaxation characteristics of Lanzhou loess, a series of laboratory stress relaxation tests under confined conditions are conducted. The relaxation curves of loess under different pre-strains are analyzed. The experimental results indicate that th...

The China–Russia Crude Oil Pipeline (CRCOP) faces significant challenges due to differential frost heaving and thaw settlement resulting from significant variations of oil temperatures along the pipeline. Oil temperature distribution along the pipeline during the long-term operation period is a very important factor in pipeline foundation design un...

The proposed China–Russia Crude Oil Pipeline (CRCOP) will be subjected to strong frost heave and thaw settlement of the surrounding soil as it traverses permafrost and seasonally frozen ground areas in Northeastern China. The freezing–thawing processes, the development of the maximum frozen cylinder in taliks and thawed cylinder in permafrost areas...

Buried pipelines are one of most economical and convenient methods for the transportation of large volumes of oil and gas. When a pipeline is buried in cold regions, it may suffer frost damage. Previous studies of pipelines and the surrounding soils in cold regions have tended to concentrate on the theory and practical engineering problems. This pa...

The China–Russia Crude Oil Pipeline (CRCOP), 813mm in diameter, is designed to transport 603,000 barrels of Siberian crude oil per day across 1030km of frozen-ground. About 500 boreholes, with depths of 5 to 20m, were drilled and cored for analyses, and the frozen-ground conditions were evaluated. After detailed surveys and analyses of the permafro...

Preconsolidation pressure (pc) is an important parameter in soil mechanics. For conventional unfrozen soils, pc is an index of the loading history and has a close relationship with the mechanical properties of soils. For frozen soils, special structures exist due to the interaction between ice and soil grains. A similar index like pc may exist in f...

China has a large area with seasonally and perennially frozen soils. It is necessary to study mechanical properties of frozen soils for the sake of constructions in cold regions, so as to guarantee their stability. In this paper, the distribution of frozen soils in China and the main features of frozen soils differing from unfrozen soils, are brief...

Under the impact of frost heave, thaw settlement and salt heave on the embankment and pavement of the highways in the zones of seasonally frozen ground in Gansu province, Northwestern China, many road damages, which has serious influence on road stability and security, occurred such as pavement cracks and road boiling etc. In this paper, repeated f...

In K0 consolidation, i.e. laterally confined compression, the axial pressure creates some plastic work on the soil samples. Part of this plastic work is dissipated by friction between soil grains. The other part is stored as free energy (SFE) in the soil. When the soil micro-structure is disturbed, SFE is either accumulated or released. In this pap...

The preconsolidation pressure (Pc) is an important parameter in soil mechanics. For conventional unfrozen soils, Pc is an index of the loading history and has close relationship with mechanical properties of soils; for frozen soils, special structure exists due to the interaction of ice and soil grains. Similar index like the preconsolidation shoul...

To evaluate the thermal protection effects of the insulation treatment, a 307 m long railway test section was constructed on the Qinghai–Tibetan plateau in 2001. Over 5 years observation data were collected and analyzed. The results showed that there was an obvious temperature difference between the top and the bottom of the insulation. The tempera...

Freeze–thaw cycling is a weathering process which considerably changes the engineering properties of soils. Therefore, the influence of freeze–thaw must be taken into account for modeling of stress–strain behaviors in stability and deformation analyses for slopes, embankments and cuts in cold regions with soil layers experiencing freeze–thaw cyclin...

In order to investigate the method and the theory on the assessment of the permafrost environment in the mining area, the catastrophe theory was used in analyzing the permafrost environment. Based on the integrated indicator system, which consisted of three subsystems: permafrost freezing-thawing erosion sensibility, permafrost thermal stability an...

There are many defects, such as fissures and cavities, in warm frozen clay and in warm ice-rich frozen clay. These defects are distributed randomly, which make some mechanical properties of these clays exhibit great uncertainty. Thus it is unreasonable to take some deterministic values as the mechanics parameters of these frozen clays. Furthermore,...

It has become a common understanding that freeze-thaw cycling is a kind of weathering process which considerably changes geotechnical properties of soils due to cryogenic actions. Therefore, the influence of freeze-thaw must be taken into account when selecting soil parameters for stability and deformation analysis of many geotechnical engineering...

Due to special engineering geological characters of the permafrost, it is inevitable for the embankment above the permafrost to come into being deformation, even failure. To ensure the railway unblocked, it is necessary for the embankment in permafrost regions to meet not only the requirement of the thermal stability, but also the requirement of th...

According to the in-situ experiment results of embankment settlement and deformation at Beiluhe test site along Qinghai-Tibet Railway in permafrost regions, it was found that, even though the permafrost table under the embankment moved up after the railway was built, the embankment has suffered quite a lot of settlement, and the settlement was main...