TECHNICAL FIELD

[001] The present subject matter described herein, in general, relates to a setup that is designed to determine the shear- strength and volumetric deformation undergone by frozen soil sample in its fully- or partially- saturated states, compacted to a target dry-density and subjected to different normal stresses.

BACKGROUND

[002] In permafrost regions, establishing the mechanical behavior of frozen soils is important for designing foundations of structures. In situation like railway track construction or mining or tunneling in permafrost region, where soils get frozen, determination of the soil shear- strength, volumetric deformations and its dependence on the rate of shearing becomes essential.

[003] The construction of infrastructures, offshore structures and stabilization slopes etc. by employing artificial ground freezing requires investigation on the shear strength parameters of the partially- or fully- saturated frozen soils when subjected to different normal stresses.

SUMMARY

[004] This summary is provided to introduce aspects related to an apparatus to determine the shear-strength of the frozen soil and the aspects are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

[005] In one implementation, an apparatus (100) to determine shear strength of a frozen soil sample is disclosed. The apparatus comprises of a chiller unit (102) connected to a pair of a chiller plates (116) with corrugation through thermally insulated tubes (104). Further a thermally insulated loading cap (106) is attached to the chiller plates (116). Further the apparatus comprises a direct shear box (108) attached to the chiller plates (116), wherein the direct shear box (108) further comprises an upper half and a botom half. Besides, a mechanized system (110) configured to provide shearing loads, and to measure vertical- and horizontal- deformations of the frozen soil sample.

BRIEF DESCRIPTION OF THE DRAWINGS

[006] The detailed description is mentioned with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to refer like features and components.

[007] Figure 1, illustrates a cross-section of the apparatus in accordance with the present disclosure.

DETAILED DESCRIPTION

[008] According to an exemplary embodiment of the present subject matter, a setup to determine the shear strength of the frozen soil corresponding to different temperatures (ranging between 0 °C to -25 °C) is disclosed. Further the setup can be used to determine the volumetric deformation undergone by the soil samples in their fully- or partially- saturated states, compacted to a target dry-density and subjected to different normal stresses.

[009] Referring to Figure 1, illustrates a cross-section of an apparatus in accordance with the present disclosure. The apparatus /DetFroSS apparatus (100) comprises a chiller unit, designated as CU (102). The coolant at a specified temperature inside the CU (102) is carried to a thermally insulated loading cap LC (106) and direct shear box DSB (108) with the help of thermally insulated tubes, designated as TB (104). The LC (106) is placed in such a manner that it will be in touch with the sample at the top with load frame resting on it. The upper DSB (108) is connected to the load cell for measuring the resistance offered by the frozen soil against shearing. While the bottom DSB (108) is connected to the direct shear motor, which manoeuvres the horizontal movement. Further to apply pre-defmed normal stress to a specimen in the apparatus (100), a mechanized system, designated as MS (110) may be provided. The MS (110) is configured to provide shearing loads, and measure vertical- and horizontal- deformations of the sample. [0010] The CU (102), TB (104), LC (106) and the DSB (108) are configured to facilitate freezing of the specimen without allowing significant heat losses. The CU (102) may further comprise a refrigeration unit and coolant circulation system, wherein Ethylene glycol (EG) may be used as coolant. The cooling coils provided in the refrigeration unit may be submerged in ethylene glycol and wherein the temperature of EG is continuously modulated by refrigeration process with a loop feedback mechanism designed with a proportional integral derivative (PID) controller. The temperature of EG may be monitored continuously with the help of a thermocouple, TC, connected to a display unit. EG at a target temperature is circulated continuously through the tubes housed inside LC (106) and the DSB (108) with the help of a motor submerged in the ethylene glycol.

[0011] In accordance with the exemplary embodiment a pair of corrugated aluminium plates, that is chiller plates (116), are attached to the LC (106) and the lower DSB (108). The plates are corrugated in the direction perpendicular to shearing of the sample to ensure proper grip between the sample and the plates. The pair of chiller plates (116) provide isothermal boundaries at the top and bottom of the specimen. The pre-cooled EG is circulated inside the LC (106) and the bottom direct shear box (108) continuously using the TB (104) to freeze the specimen. Further the LC (106) may be fabricated using a perspex sheet. A provision for placing a steel ball (118) may be provided at the top the LC (106) for uniform transmission of the vertical stress on the specimen. Further, Linear Variable Differential Transformer (LVDT) connected to the top of the LC (106) measures the vertical deformation, AV, of the soil sample during freezing and shearing.

[0012] In another exemplary embodiment of the present disclosure, temperature of the top chiller plate (116) maybe sensed and captured, and data logged using the thermocouple (114).

[0013] Further in accordance to the present disclosure the DSB (108) may be fabricated from acrylic, a material for which the thermal conductivity is low. Further the upper half of the DSB (108) may be connected to a horizontally placed load shaft (120) with a collar of 10 kN capacity by a load shaft to measure the resistance, T, offered by the sample/soil mass against shearing, which when divided by the cross section of the specimen, A (=60 mm*60 mm), would yield the shear stress, t. While, the bottom the DSB (108) is attached to the water chamber with the help of stainless- steel box (124), SSB, and threaded rod. The water chamber, resting on four roller bearings, is connected with the direct shear motor with the help of a steel shaft, which manoeuvres the horizontal movement of the bottom the DSB (108) at the desired strain rate. A horizontal LVDT is connected to the outer chamber of the apparatus, to measure the horizontal displacement, AH, undergone by the specimen/sample. Further, the thermocouples (114) are installed in the DSB (108), along the height of the specimen so as to monitor its temperature at l/4th and 3 /4th of the heights, designated as TC2 and TC3.