Soil Frost Heave Shear Force Determination: Testing Methods, Standards, and Applications in Cold Reg

Soil frost heave shear force determination is a specialized geotechnical laboratory and field test that quantifies the tangential forces developed at soil–structure interfaces and within frozen soil masses during freezing. Accurate measurement of these shear forces is essential for the safe design of piles, pipelines, towers, and foundations in seasonal frozen and permafrost regions. This article explains the technical principles, sample types, test items, testing methods, and engineering applications of frost heave shear force determination.

Technical Overview

When frost-susceptible soils freeze, capillary water migrates toward the freezing front and accumulates as ice lenses. The growth of these ice lenses causes the soil to expand, and when this expansion is restrained by a foundation, pile shaft, retaining wall, or pipeline, significant forces are generated. Among these, the tangential frost heave force acts as a shear stress along the vertical surfaces of embedded structures and is one of the most important parameters in cold regions foundation design. Soil frost heave shear force determination measures the magnitude and development characteristics of these interface shear forces under controlled freezing conditions.

Frost heave related forces are generally classified into three categories:

• Tangential frost heave force, a shear force acting along the sides of foundations, piles, walls, and anchors, which may uplift or damage structures;
• Normal (vertical) frost heave force, a pressure acting on the base of shallow foundations;
• Horizontal frost heave force, a lateral pressure acting on retaining walls, buried pipes, and trench linings.

The tangential force is fundamentally a shear phenomenon governed by the adfreeze bond between soil and structure and by the shear strength of the frozen soil itself. Relevant reference standards include ASTM D5918 for frost heave and thaw weakening susceptibility testing, ASTM D7300 for laboratory strength testing of frozen soil, ASTM D3080 adapted for direct shear testing at subfreezing temperatures, and GB/T 50123 together with JGJ 118, which specify frost heave and frozen soil test procedures and design values used in frozen ground engineering.

Testing Samples

Undisturbed Soil Samples

Undisturbed samples are recovered from the project site using thin-walled sampling tubes or block sampling methods, preserving the natural structure, density, moisture content, and, where applicable, the frozen state of the soil. Samples from permafrost are transported and stored under frozen conditions to prevent thawing and refreezing artifacts. These specimens provide the most realistic representation of in-situ interface behavior.

Remolded (Reconstituted) Specimens

Remolded specimens are prepared by compacting or consolidating soil at target dry densities and water contents inside cylindrical molds or shear rings. Reconstituted samples allow systematic parametric studies of the influence of moisture content, density, gradation, fines content, and saturation on the mobilized shear force during freezing.

Soil–Structure Interface Specimens

Interface specimens are prepared by casting or placing soil against concrete, steel, wood, or pipeline coating coupons that simulate actual foundation materials and surface roughness. These specimens are used to evaluate the adfreeze bond strength and the tangential frost heave stress transferred to the structure as ice lenses form in the surrounding soil.

Testing Items

Typical parameters determined in a frost heave shear force testing program include:

• Tangential frost heave force and average tangential frost heave stress acting on the interface, expressed in kN or kPa;
• Adfreeze (freeze bond) shear strength between soil and construction materials at various subfreezing temperatures;
• Frozen soil shear strength parameters, including cohesion and internal friction angle, derived from Mohr–Coulomb failure envelopes;
• Peak and residual shear strengths under different normal stress levels;
• Complete shear stress–displacement and shear force–time curves during the freezing process;
• Frost heave displacement and frost heave ratio, defined as the ratio of heave amount to the frozen depth of the specimen;
• Influence factors such as temperature gradient, water supply conditions (open versus closed system), cooling rate, soil salinity, and freeze–thaw cycling.

Testing Methods

Laboratory Frost Heave Shear Test

In the laboratory frost heave shear apparatus, a cylindrical soil specimen, with or without an embedded structural interface element, is placed inside an insulated ring. A cold top plate and a temperature-controlled base establish a one-directional temperature gradient, while an optional external water supply simulates open-system groundwater migration. Load cells and highly sensitive displacement transducers continuously record the tangential force and heave displacement as freezing progresses. Testing is typically conducted in walk-in environmental chambers or refrigerated cabinets capable of maintaining temperatures from approximately 0 °C down to −20 °C with an accuracy of ±0.1 to ±0.5 °C.

Temperature-Controlled Direct Shear Test

Frozen soil and interface shear strength can be determined using a direct shear apparatus installed inside an environmental chamber. Specimens are first frozen to the target temperature and equilibrated, then sheared under several constant normal stresses at slow, controlled displacement rates appropriate for frozen soil behavior. The resulting failure envelopes yield the cohesion and friction angle of the frozen soil or the adfreeze strength of the interface, following procedures consistent with ASTM D3080 as adapted for subzero temperatures and with the frozen soil strength methodology of ASTM D7300.

Field and Model-Scale Tests

For critical projects, in-situ tests instrument instrumented piles, anchors, or concrete plates embedded through the seasonal freezing active layer, with load cells, strain gauges, and thermistor strings monitored over one or more complete freeze–thaw seasons. Large-scale frost heave tank tests in cold rooms can further verify design parameters under realistic boundary and restraint conditions.

Data Interpretation

The average tangential shear stress is calculated as the measured force divided by the effective frozen contact area. Peak values, residual values, and the temperature dependence of the adfreeze strength are reported, and regression analysis is applied to obtain design shear parameters. Reported tangential frost heave stresses commonly range from several tens of kPa to more than 200 kPa, depending on soil type, moisture supply, temperature, and surface conditions, which is why project-specific testing is strongly recommended by design codes such as JGJ 118.

Applications

Test results from frost heave shear force determination are applied across a wide range of cold regions engineering projects:

• Design of pile foundations, piers, and anchors, including verification of uplift stability and determination of required embedment depth below the maximum seasonal frost penetration line;
• Oil, gas, and water pipelines in frozen ground, for evaluating constraint forces, trench backfill interaction, burial depth, and insulation requirements;
• Transmission towers, wind turbine foundations, and communication structures exposed to seasonal freezing;
• Highways, railways, and airport pavements, for assessing subgrade frost susceptibility and designing anti-frost heave layers;
• Retaining walls, canal linings, dams, and hydraulic structures subjected to horizontal or tangential frost action;
• Research and consulting studies on frozen soil mechanics, permafrost degradation under climate change, and the performance of frost jacking mitigation measures such as smooth casings, isolation layers, and soil replacement.

FAQ

What is soil frost heave shear force?

It is the tangential force developed along the contact surface between a freezing, frost-susceptible soil and a structure that restrains soil expansion. It acts essentially as an uplift shear stress on pile shafts, walls, and other embedded elements and is a controlling load case in seasonal frozen and permafrost foundation design.

How does frost heave shear force differ from adfreeze strength?

Adfreeze strength is the maximum bond capacity of the frozen soil–structure interface at a given temperature, whereas the frost heave shear force is the force actually mobilized when ice lens growth and water migration drive heave against a restrained structure. Adfreeze strength testing provides an upper bound for interface shear transfer used in design calculations.

Which standards are commonly referenced?

Commonly referenced documents include ASTM D5918 for frost heave susceptibility, ASTM D7300 for frozen soil strength, ASTM D3080 for direct shear testing adapted to subfreezing conditions, and GB/T 50123 and JGJ 118 for frost heave testing procedures and frozen ground design values. Accredited third-party laboratories typically conduct these tests under ISO/IEC 17025 quality systems.

What factors most influence the measured shear force?

The dominant factors include soil type and fines content, water content and external water supply, freezing temperature and temperature gradient, freezing rate, normal stress, structure surface roughness and material, and the number of freeze–thaw cycles experienced by the soil.

How long does a typical test take?

A single temperature-controlled direct shear test may be completed within one to several days including freezing and equilibration. A complete open-system frost heave shear test, in which the specimen is frozen under a controlled gradient while forces are monitored, typically requires one to four weeks depending on specimen size and freezing rate. Field instrumentation programs require at least one full winter season.

How are the results used in engineering design?

Designers use the measured tangential frost heave stresses to check uplift and frost jacking stability of foundations, to compute required anchorage depths in stable strata below the active layer, and to select mitigation measures such as anti-frost heave coatings, smooth sleeves, insulation, or soil replacement.