Due to the rigid deformation limit of high-speed railways, the anti-frost heave design has become a critical concern in seasonally frozen regions. In this study, the authors explained the frost heave mitigation techniques adopted for the high-speed railway between Harbin and Dalian in northeast China and then presented the thermal, deformation, and water content data monitored on the Gongzhuling test site. According to these data, the authors proposed the possible frost heave mechanisms of the high-speed railway foundation. The foundation is composed of well-graded gravel with cement and A/B group fill, which are treated as non-frost-susceptible materials in general. Based on the monitored data, the authors found that the surface layer (0–0.5 m) contributed most to the total frost heave and this might be caused by local water accumulation inside the foundation (0.6–1.2 m). In order to demonstrate the frost heave ability of these “non-frost-susceptible” materials, the authors conducted an indoor frost heave test with a mixture of gravel and 3% Kaolinite clay. Through this experiment, it was demonstrated that, with sufficient water supply, gravel with a limited amount of fine material can produce significant frost heave. Accordingly, we can conclude that the accumulated water inside high-speed railway foundation causes the frost heave deformation. Therefore, the treatment of the water accumulation within the fills needs to be considered for frost heave elimination or prevention.

The study of frost heave mechanism of high-speed railway foundation by field-monitored data and indoor verification experiment

Study on the influence of hydro-thermal-salt-mechanical interaction in saturated frozen sulfate saline soil based on crystallization kinetics

Artificial ground freezing (AGF) has been widely used as a temporary soil stabilization and waterproofing technique in geotechnical practices (e.g., tunnel construction). Many sources of uncertainty exist during AGF. Firstly, groundwater seepage flow can adversely affect the freezing efficacy. Secondly, freeze pipe inclination inevitably occurs during installation, which is likely to yield an unfrozen path and elevate construction risk. Thirdly, as a key soil parameter, the spatial variability in thermal conductivity can also affect the freezing process. In this work, a unit cell model of freeze pipes is established by a coupled thermo-hydraulic finite element method to examine the effects of these sources of uncertainty. The pipe inclination is considered in the unit cell model by prescribing various values of freeze pipe spacing. The thermal conductivity of soil solid is simulated as a three-dimensional lognormal random field to account for the spatial variability of soil. Results are tabulated to evaluate the additional freezing time required in the AGF system due to the existence of these uncertainties. The findings are capable of determining a reasonable range of freeze pipe spacings and the corresponding critical seepage velocity, and can offer practitioners a rule of thumb for estimating freeze pipe spacing.

Coupled thermal–hydraulic modeling of artificial ground freezing with uncertainties in pipe inclination and thermal conductivity

Frost heave is a process of coupled heat–water–mechanics, which refers to heat transfer, water migration, water–ice phase change, deformation, etc. The mechanism of the frost heave for saturated–unsaturated soils was investigated to establish a frost heave model. As the freezing continues, for saturated soils, because all pores are filled with pore water, the total increased volume due to water migration and water crystallization will separate soil particles and induce frost heave. For unsaturated soils, because of the existence of unsaturated pores, volume expansion generates by water and vapor migration and water–ice transition will firstly fill into the unsaturated pores until a critical state is reached. After that, further increased volume will separate soil particles and induce frost heave. Therefore, effective strain ratio was introduced to establish the relationship between frost heave strain of unsaturated soils and the fields of moisture and temperature. Tests were carried out for silty soil. Then, based on the inverse theory, a simplified criterion was proposed to determine the effective strain ratio, and the effective strain ratio was back-calculated according to the test results. Finally, an innovative universal frost heave model for saturated–unsaturated soils was proposed.

Investigation on frost heave of saturated–unsaturated soils

The transversely isotropic (TISO) constitutive and frost heave models for the freezing of fine-grained soils are more accurate than the isotropic model and simpler than the orthotropic models. First, in combination with the mesoscopic composition of freezing soils, a mechanical model for the interaction between the equivalent ice lens and the soil in frozen soils is established based on the series and parallel models in the theory of composite mechanics. Second, the TISO constitutive model together with the analytic expression of five elastic constants is provided for analysis of the freezing soils. Third, a preliminary elastoplastic model for TISO freezing soil is established based on the Hill plastic model. Fourth, the heat–moisture–deformation coupling TISO model and the hydrodynamic frost heave model are derived according to a thermodynamics equation, a soil water motion equation, and generalized Hooke’s law. Synchronization and uniformity of the TISO constitutive model and the TISO frost heave model are realized for analyzing the interaction between permafrost soils and buildings. Finally, an indoor standard frost heave test and the frost heave of a prototype canal are simulated based on the above models. The numerical results indicated that the models presented in this paper accurately described the frost heave and revealed the interaction between permafrost and buildings.

/pdf/transversely-isotropic-frost-heave-modeling-with-heat-5dui3ogrr0.pdf

Transversely isotropic frost heave modeling with heat–moisture–deformation coupling

For one-dimensional soil freezing process, a separate-ice frost heave model is established, and the coupled process of heat transfer, fluid flow and stress development is considered in the model. First, a coupled heat–fluid–stress model describing the growth of a single ice lens is developed by extending the coupled heat–fluid model presented by Zhou and Zhou (Can Geotech J 49(6):686–693, 2012). Second, the mechanism for the formation of a new ice lens in the frozen fringe is studied, and we indicate that if the total vertical disjoining pressure at certain place exceeds the sum of the external pressure and the critical pressure, a new ice lens will emerge. By combining the growth model of a single ice lens and the criterion for the formation of a new ice lens, the separate-ice frost heave model is then established. The difference between the separate-ice model and the rigid-ice model is explained, and the relations for different mathematical models which describe the soil freezing process are also discussed. Numerical analysis of the separate-ice model is conducted using the finite volume method. The freezing tests for Devon silt under no external pressure and Xuzhou silty clay under a constant external pressure are applied to verify the computational results. The consistence between the calculation and the observation validates the separate-ice frost heave model.

Separate-ice frost heave model for one-dimensional soil freezing process

The invention relates to quick preparation device and method of a saturated soil sample. Saturated clay is extruded by utilizing a load-vacuum combined consolidation principle so as to obtain a saturated clay sample with a low water content (the water content is lower than a plastic limit). The device comprises a sleeve, a base, a piston, a vacuum cavity and a fixing sleeve, wherein the sleeve is sequentially and respectively provided with a slide-fit piston, a cylindrical porous stone internally embedded with a horizontal pressure sensor and the fixing sleeve; the piston, the base and the sleeve are respectively provided with upper draining holes, lower draining holes and side draining holes; and a vacuum extraction hole is arranged on the vacuum cavity. The draining process of the saturated clay is accelerated under the extruding effect of the piston through the negative pressure (about 101.325kPa) condition of the vacuum cavity, and meanwhile, horizontal stress and vertical stress applied on the saturated clay are obtained through the horizontal pressure sensor and a vertical pressure sensor so as to further obtain a coefficient k0 of earth pressure at rest (a specific value of the horizontal pressure to the vertical pressure applied to the soil sample under the condition of no lateral deformation).

Quick preparation device and method of saturated soil sample

The invention relates to a geogrid strain testing device and a testing method thereof. The device comprises a rigid shell, a flexible sealing body, a sensitive component and an electrode connected with a data line, wherein the side surface of the shell is provided with a line outlet hole for leading out the data line, the bottom of the shell is provided with a base interlocked with the bottom, and the middle part of the base is provided with a groove sleeved on the geogrid in a clamping mode. The strain of the geogrid is tested by the pulling sensitivity of the conductive rubber composite; and when in testing, the sensitive component is stuck with the geogrid; and when the geogrid is deformed, the resistance of the sensitive component is changed, and the strain of the geogrid can be obtained via testing the resistance change.

Geogrid strain testing device and testing method thereof

The invention relates to a device and a method for testing the coefficient of a static earth pressure. The device comprises a base, a pressure chamber, a piston, a radially-deformed resistive strain gauge and a hydraulic sensor, wherein a sample is arranged on the base; the pressure chamber is covered on the sample base; the piston is arranged in the centre of the top part of the pressure chamber and is matched with the pressure chamber in a sliding way; the radially-deformed resistive strain gauge sensor is fixed on the middle section of the sample; and the hydraulic sensor is connected to the base. The section of the piston is as large as and of the same shape as that of the sample to be specifically tested in the pressure chamber. The internal volume of the pressure chamber is adjusted by nesting a plurality of sleeves which are all equal in height and thickness. The volume of the pressure chamber is varied to improve the rigidity thereof, reduce the amount of compression of liquid in the pressure chamber and finally obtain the pressure chamber meeting a condition on the ratio Kopt of the volume of the optimal pressure chamber to the volume of the sample, namely the condition that the maximum of the variable of the diameter of the sample corresponding to different liquid pressures does not exceed 10 microns at the premise of a certain volume of the initial liquid within the pressure chamber, thereby improving the testing accuracy of the coefficient K0 of the static earth pressure.

Device and method for testing coefficient of static earth pressure

The utility model provides a combined telescopic anchor rod, which is suitable for soft rock with a large deformation amount or a roadway surrounding rock support greatly influenced by the mining. The combined telescopic anchor rod comprises a front section of anchor rod body and a back section of anchor rod body which are inserted into a drill hole injected with cement size, wherein at least one fusiform spring is arranged between the front and back sections of anchor rod bodies and is respectively welded with the front and back sections of anchor rod bodies via a casing pipe; an elastic backing plate fixedly arranged at an orifice is arranged at the tail part of the back section of anchor rod body; and a nut for fixing the backing plate is arranged on the elastic backing plate. The telescopic amount of the anchor rod is partially replaced through the fusiform spring, the yielding performance of the anchor rod is remarkably increased, and an anchoring layer of surrounding rock is steadier on the premise that the self-supporting ability of the surrounding rock is furthest utilized by the anchor rod. The structure of the anchor rod is simplified, the telescopic effect of the anchor rod is good, a telescopic cavity body is reserved at the out-extending head part of the anchor rod when the anchor rod is mounted and used, and the combined telescopic degree of the anchor rod can be increased. The anchor rod has the characteristics of low support cost, convenience in processing, easiness in manufacturing, and the like.

Kun Hu

Papers

Separate-ice frost heave model for one-dimensional soil freezing process

Quick preparation device and method of saturated soil sample

Geogrid strain testing device and testing method thereof

Device and method for testing coefficient of static earth pressure

Combined telescopic anchor rod