Soil Frost Heave Shear Force Evaluation: Testing Methods, Standards, and Engineering Applications

Soil frost heave shear force evaluation quantifies the tangential and normal forces that freezing, heaving soils exert on foundations, piles, pipelines, and other buried structures. Using temperature-controlled environmental chambers and shear testing apparatus operated by accredited third-party laboratories, these evaluations determine frost heave susceptibility, adfreeze bond strength, and the design parameters required for safe construction in seasonal frost and permafrost regions. This article explains the testing principles, sample requirements, methodologies, applicable standards, and typical engineering applications of frost heave shear force assessment.

Technical Overview

Frost heave is the volumetric expansion and ground displacement that occurs when freezing temperatures penetrate a water-bearing soil. As the freezing front advances, cryogenic suction draws unfrozen pore water toward the frozen zone, where it crystallizes into segregated ice lenses. Combined with the approximately 9% expansion of freezing pore water, this ice segregation can lift, squeeze, and shear the surrounding ground, generating significant forces on any structure that restrains the soil movement.

When a foundation, pile, retaining wall, or pipeline restricts heave, the soil mobilizes forces in several directions. The tangential frost heave force, sometimes called the frost heave shear force, acts along the soil–structure interface and is transmitted through the frozen bond between soil and structural surface. The normal frost heave force acts perpendicular to a confining surface, while horizontal components may act on vertical walls. Among these, the tangential shear force is frequently the governing design load for slender elements such as piles, anchor rods, and posts, because a strong adfreeze bond combined with active heave can uplift and damage foundations.

Evaluation of frost heave shear force therefore combines three complementary assessments: the frost susceptibility of the soil, the shear strength of the frozen soil and frozen soil–structure interface, and the magnitude of the forces developed under realistic thermal gradients. Standardized approaches are described in ASTM D5918 for frost heave susceptibility, ASTM D3080 and ISO 17892-10 for direct shear testing, and Chinese national codes such as GB/T 50123, GB 50324, and JGJ 118, which provide systematic procedures for tangential and normal frost heave force testing in frozen ground engineering.

Testing Samples

Undisturbed Soil Cores

Undisturbed samples recovered with thin-walled samplers or frozen coring techniques preserve the natural fabric, density, moisture distribution, and ice structure of in-situ soil. Cores are transported and stored under strict temperature control to prevent thawing or moisture migration. In the laboratory, specimens are trimmed to the required dimensions for frost heave, direct shear, or interface shear testing while maintaining field representative structure.

Remolded and Compacted Soil Specimens

For engineered backfill, borrow materials, or projects where undisturbed sampling is impractical, remolded specimens are prepared at controlled dry density, gradation, and moisture content. These specimens allow systematic evaluation of how compaction quality and water content influence frost heave potential and shear force development, and they are commonly used for frost susceptibility screening of construction materials.

Soil–Structure Interface Specimens

Because tangential frost heave force is transmitted through the adfreeze bond, interface specimens are prepared with actual construction materials, including cast concrete, structural steel, coated or fusion-bonded epoxy steel, timber, and geosynthetics. Material plates or coupons are frozen in contact with the soil specimen so that the adfreeze shear strength of the real engineering surface can be measured directly.

Model Foundation Elements

For critical projects, reduced-scale model piles, piers, or anchors are installed in soil-filled tanks and subjected to controlled one-dimensional freezing. These model tests reproduce the interaction between an advancing freezing front, migrating water, and a restrained structural element, allowing the full development of tangential frost heave force to be observed under simulated field boundary conditions.

Testing Items

Typical measured parameters in a frost heave shear force evaluation program include:

• Frost heave displacement and frost heave ratio (heave per unit frozen depth or specimen height)
• Tangential frost heave force and unit tangential frost heave stress acting on the structure surface, expressed in kPa
• Normal frost heave force acting beneath foundation bases or bearing plates
• Adfreeze bond shear strength between frozen soil and concrete, steel, or coated surfaces at multiple negative temperatures
• Frozen soil shear strength parameters, including apparent cohesion and internal friction angle at subfreezing temperatures
• Unfrozen water content and its variation with temperature, which controls residual strength and creep behavior
• Segregation potential and water intake flux during stepped freezing
• Frost susceptibility classification of the soil based on gradation, heave rate, and heave ratio criteria
• Residual and long-term shear strength after cyclic freeze–thaw conditioning

Testing Methods

Frost Heave Susceptibility Testing

Frost susceptibility is evaluated using a stepped-freezing procedure consistent with ASTM D5918. A cylindrical soil specimen is mounted in a frost cell between a cold top plate and a warm bottom plate, typically establishing a freezing front at approximately -4°C at the cold end and +4°C at the warm end while free access to external water is maintained. A surcharge load representing overburden is applied, and heave displacement, water intake, and temperatures along the specimen are monitored continuously until heave stabilization. The measured heave rate and heave ratio allow classification of the soil as non-frost-susceptible or progressively more susceptible categories, which is the first step in judging whether significant frost heave shear forces can develop.

Direct Shear Testing of Frozen Soil

The shear strength of frozen soil is determined by adapting the direct shear test of ASTM D3080 and ISO 17892-10 to subfreezing conditions. Specimens are conditioned in an environmental chamber to target temperatures such as -1°C, -2°C, -5°C, and -10°C, reflecting the service temperature range of the foundation. Normal stresses are applied across several stages, and shear load is applied at a controlled displacement rate while temperature is held constant. Peak and residual shear stresses yield temperature-dependent cohesion and friction angle values used in bearing and lateral resistance calculations.

Adfreeze Shear Interface Testing

Adfreeze strength is measured by freezing a soil specimen against a plate of the actual structural material and shearing the interface in a temperature-controlled shear box. Tests are repeated at several negative temperatures and normal stress levels because adfreeze strength increases sharply as temperature decreases and ice bonding strengthens. Both peak and residual adfreeze values are recorded, since large structural displacements may destroy the bond and reduce the available shear transfer. These values directly define the upper bound of the tangential frost heave stress that the ground can apply to the structure.

Tangential Frost Heave Force Testing on Model Piles

Following the principles of GB/T 50123, GB 50324, and JGJ 118, a model pile or anchor is rigidly fixed to a reaction frame within a soil tank equipped with distributed thermal control. Freezing is induced from the top surface under a controlled thermal gradient while the pile is held stationary, and the uplift force transferred through the frozen soil–pile interface is measured with load cells until a peak tangential frost heave force is reached. Dividing the peak force by the frozen surface area of the pile gives the design unit tangential frost heave stress, which is corrected for scale effects and compared with analytical design charts for anchor depth, anti-frost heave measures, and surface treatment selection.

Field Monitoring and Verification

For major infrastructure, laboratory results are verified by instrumented field programs in which anchored piles or sacrificial footings are fitted with load cells, thermistor strings, and heave gauges and monitored through complete freeze–thaw seasons. Field data calibrate the laboratory-derived adfreeze parameters and confirm the seasonal peak of tangential frost heave force under actual climatic, hydrological, and snow cover conditions.

Applications

Frost heave shear force evaluation supports design, verification, and failure analysis across a wide range of cold-regions and geotechnical engineering projects:

• Pile and drilled shaft foundations for buildings, bridges, and viaducts in permafrost and deep seasonal frost zones, where differential frost heave and uplift govern the embedment design
• Buried oil, gas, and water pipelines, where tangential forces along the pipe wall and differential heave at thaw-unstable transitions control stress analysis
• Transmission line towers, telecom masts, and wind turbine foundations subject to seasonal freezing and annual freeze–thaw cycling
• Highway, railway, and airport subgrades, including assessment of frost-susceptible fill materials and insulation or replacement designs
• Retaining walls, sheet piles, ground anchors, and tieback systems exposed to horizontal and tangential freezing pressures
• Solar farm pile foundations, fence posts, signage, and lighting structures in cold climates
• Artificial ground freezing projects for shafts and tunnels, where frozen soil strength and interface behavior must be verified before excavation
• Forensic investigation of frost jacking, uplifted foundations, cracked walls, and displaced pipelines, together with the design of mitigation measures such as surcharge, insulation, soil replacement, and slippery or low-adhesion surface coatings

FAQ

What is the difference between frost heave force and adfreeze strength?

Adfreeze strength is the maximum shear stress that a frozen soil–structure interface can carry, essentially the bond capacity of the ice and soil against the material surface. Frost heave force is the actual force the heaving soil applies to the structure, which is limited by the adfreeze strength and driven by frost heave deformation. The tangential frost heave force can never exceed the adfreeze bond capacity over the frozen contact area, which is why both parameters are measured together.

Which soils are most susceptible to frost heave?

Silty soils, silty sands, lean clays, and low-plasticity fine-grained soils with high capillary conductivity and an active water supply are typically the most frost-susceptible. Clean gravels and coarse sands drain freely and rarely heave significantly, while dense clays with low permeability limit water migration. Laboratory classification per ASTM D5918 and gradation-based criteria in GB/T 50123 and JGJ 118 are used to confirm susceptibility.

At what temperatures are the shear tests performed?

Interface and direct shear tests are usually run at a matrix of negative temperatures, commonly -1°C, -2°C, -5°C, and -10°C, because frozen soil and adfreeze strength increase nonlinearly as temperature drops. The selected range should envelope the minimum expected ground temperature at the structure depth over the design service life.

How are the results used in foundation design?

The unit tangential frost heave stress is multiplied by the frozen surface area of the foundation within the active frost zone to obtain the total uplift force. This force is compared with the anchorage resistance of the foundation below the frost depth plus the applied structural load, with an appropriate safety factor as required by design codes such as JGJ 118. Where uplift resistance is insufficient, designers increase embedment, apply anti-adhesion coatings or sleeves, replace frost-susceptible backfill, or add insulation to limit freezing depth.

What sample quantity and quality are required for testing?

For undisturbed testing, several intact cores of sufficient diameter, commonly 100 mm or larger and at least twice the specimen height, are required for each soil stratum, along with moisture content and density determinations. For interface testing, representative soil plus structural material coupons matching the intended surface finish are needed. Accredited third-party laboratories can advise on project-specific sampling plans, thermal handling requirements, and turnaround times based on the applicable standards.