Effect of temperature and strain rate on mechanical characteristics and constitutive model of frozen Helin loess

Frost heave and thaw settlement are the cause of substantial damage to infrastructure in regions of seasonal freezing as well as seasonal thawing (permafrost). While frost heaving of soils has been researched for decades, less attention has been paid to quantitative estimates of settlement and loss of strength of soils due to thawing. A constitutive model is developed, capable of simulating freezing and thawing of soils, and associated changes in the soil strength. While the porosity growth parameters describing frost heaving have been calibrated and validated for a specific soil, the description of the thawing phase has not been validated due to a lack of experimental data. The yielding of the frozen soil is described using the critical state concept, with the pore ice content being an important parameter affecting the yield function. The model was calibrated using available laboratory test data and used in the simulation of a freezing–thawing cycle in the soil with embedded footing.

Thermal-Hydro-Mechanical Analysis of Frost Heave and Thaw Settlement

A new approach to modeling the behavior of frozen soils

Mechanical properties of frozen soils (e.g., triaxial compressive strength, σtc and Young’s modulus, E) are important in tunnel, shaft, or open pit excavation projects. Although numerous at...

Predicting Triaxial Compressive Strength and Young’s Modulus of Frozen Sand Using Artificial Intelligence Methods

The mechanical properties of frozen ground are key parameters in design and implementation of artificial ground freezing (AGF) in underground projects. Soil samples were obtained from the urban underground railway project site in Tabriz, Iran. The specimens were classified as SP and CL according to the USCS. The specimens were remolded in accordance with the site conditions. Over 120 triaxial compression tests were conducted on the frozen samples at different temperatures, confining pressures and strain rates. The results show that the frozen SP and CL soils exhibit strain-softening and strain-hardening behaviour, respectively. In all cases, Young’s modulus increases with decreasing temperature and increasing strain rate and confining pressure. Also, the shear strength increases with decreasing temperature and increasing strain rate. In all tests, the Young’s modulus and shear strength of the SP soil are greater than the CL soil. Based on the results of this research, the application of artificial ground freezing was recommended for coarse-grained and non-cohesive soils like SP in the Tabriz underground railway project.

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Experimental Study of the Mechanical Behavior of Frozen Soils - A Case Study of Tabriz Subway

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

Triaxial compression deformation for artificial frozen clay with thermal gradient

A series of triaxial compression tests for frozen clay were performed by K0DCGF (freezing with non-uniform temperature under loading after K0 consolidation) method and GFC (freezing with non-uniform temperature without experiencing K0 consolidation) method at various confining pressures and thermal gradients. The experimental results indicate that the triaxial compression strength for frozen clay in K0DCGF test increases with the increase of confining pressure, but it decreases as the confining pressure increases further in GFC test. In other words, the compression strength for frozen clay with identical confining pressure decreases with the increase in thermal gradient both in K0DCGF test and GFC test. The strength of frozen clay in K0DCGF test is dependent of pore ice strength, soil particle strength and interaction between soil skeleton and pore ice. The decrease of water content and distance between soil particles leads to the decrease of pore size and the increase of contact area between particles in K0DCGF test, which further results in a higher compression strength than that in GFC test. The compression strength for frozen clay with thermal gradient can be descried by strength for frozen clay with a uniform temperature identical to the temperature at the height of specimen where the maximum tensile stress appears.

Triaxial compression strength for artificial frozen clay with thermal gradient

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.

Guozhou Chen

Papers

Quick preparation device and method of saturated soil sample

Triaxial compression deformation for artificial frozen clay with thermal gradient

Triaxial compression strength for artificial frozen clay with thermal gradient

Geogrid strain testing device and testing method thereof

Device and method for testing coefficient of static earth pressure