Soil freezing force testing measures the bonding force and heave force that develop between freezing or frozen soil and structural elements such as pile foundations, anchors, and buried utilities. Accurate quantification of adfreeze strength and frost heave forces is essential for the safe and economical design of foundations in permafrost and seasonally frozen ground. This article explains the test principles, sample requirements, testing items, methodologies, applicable standards, and typical applications of soil freezing force evaluation performed by accredited third-party laboratories.
Technical Overview
Soil freezing force refers to the force generated at the interface between soil and a structural surface as a result of ice cementation. When pore water in the soil freezes, the ice bonds soil grains to the surface of a foundation element, producing a tangential adfreeze strength along shafts and walls, and a normal freezing force perpendicular to the interface. In frost-susceptible soils, water migration toward the freezing front and the growth of ice lenses additionally generate frost heave forces that can uplift or fracture foundations. Soil freezing force testing is therefore a critical geotechnical evaluation for cold-region projects, covering both the beneficial adfreeze resistance used to anchor piles in permafrost and the detrimental heave forces that must be resisted or mitigated.
The magnitude of freezing force is governed by several interacting factors, including ground temperature, soil gradation and fines content, dry density, water content and degree of saturation, salinity of pore water, interface material and roughness, loading rate, and the duration of load. Adfreeze strength generally increases approximately linearly as temperature decreases below 0 °C, but it decays under sustained load due to ice creep, which is why both short-term and long-term values are evaluated. Testing in China is typically performed in accordance with GB/T 50123 (Standard for Geotechnical Testing Method), with design application guided by JGJ 118 (Code for Design of Soil and Foundation of Buildings in Permafrost Regions) and GB 50324 (Code for Engineering Geological Investigation of Frozen Ground). Frost susceptibility screening can also reference international methods such as ASTM D5918 for frost heave and thaw weakening susceptibility of soils.
Testing Samples
Undisturbed Frozen Soil Samples
Undisturbed samples are obtained from test pits or frozen core drilling in permafrost or seasonally frozen strata. Blocks and cores are trimmed in a cold room at temperatures matching in-situ conditions, sealed against moisture change, and transported in insulated containers with continuous temperature logging to preserve the natural ice structure, fabric, and water content of the specimen.
Remolded and Reconstituted Specimens
When undisturbed material is unavailable or when parametric studies are required, remolded specimens are prepared at controlled dry density, water content, and grain-size distribution. Specimens are compacted into molds, saturated or brought to target moisture conditions, and frozen under controlled unidirectional or isotropic regimes to reproduce the desired ice formation pattern.
Soil–Structure Interface Specimens
Because freezing force acts at the soil–structure boundary, specimens commonly incorporate representative structural surfaces, including concrete, steel, and timber pile segments, coated or bitumen-treated surfaces, anchor plates, and geosynthetic layers. The interface material, surface roughness, and curing history are documented so that measured bond strengths can be transferred to design.
Field Test Elements
For projects requiring full-scale verification, instrumented model piles, anchor systems, and load plates are installed on site, allowed to freeze in equilibrium with the surrounding ground, and later loaded. Thermistor strings installed at multiple depths record ground temperatures throughout the test program.
Testing Items
Typical testing items included in a soil freezing force evaluation program are listed below:
- Tangential adfreeze strength at specified temperatures, commonly in the range of −0.5 °C to −10 °C
- Normal freezing force and normal frost heave force acting on foundation bases and retaining surfaces
- Tangential frost heave force acting along pile shafts and walls in frost-susceptible soils
- Frost heave displacement, heave rate, and heaving ratio under open-system and closed-system freezing conditions
- Complete shear stress–displacement curves, including peak and residual adfreeze strength
- Long-term adfreeze strength and creep behavior under sustained load
- Influence of freeze–thaw cycling on residual interface bonding
- Temperature-dependent regression relationships and design reduction coefficients
Testing Methods
Laboratory Adfreeze Strength Test
A soil specimen is molded and frozen against a model pile segment or interface ring inside a temperature-controlled cryostat or walk-in cold chamber. After the specimen reaches thermal equilibrium at the target negative temperature, a temperature-controlled direct shear or specialized adfreeze apparatus applies normal stress and shears the specimen along the soil–structure interface at a standardized displacement rate. Peak and residual shear stresses are recorded, and the test is repeated at multiple temperatures and normal stresses to establish the strength envelope. The procedure follows the frozen soil testing provisions of GB/T 50123.
Frost Heave and Heave Force Test
A soil column is placed in a freezing cell with a controlled cold-side temperature applied to the top plate and a warm-side temperature at the base, reproducing unidirectional freezing from the ground surface. In open-system tests, external water is supplied through the base to simulate groundwater inflow, promoting ice lens growth. Vertical displacement is measured with linear variable displacement transducers, while the heave force is captured by restraining the soil surface with a load cell at essentially zero displacement or by applying graded surcharge pressures. The test setup and susceptibility criteria are consistent with the approach of ASTM D5918.
Field Pull-Out and Anchor Testing
For field verification, model piles or anchors are installed at the project site and instrumented with strain gauges, load cells, and thermistors. A hydraulic jacking frame applies uplift load in increments while load–displacement and ground temperature data are recorded. The measured ultimate and long-term allowable adfreeze resistances are then compared with laboratory predictions and with design values permitted by JGJ 118.
Data Reduction and Interpretation
Adfreeze strength is defined at the peak shear stress or at a specified displacement limit, whichever governs. Results are regressed against negative temperature, and design values are derived by applying long-term reduction factors that account for ice creep and sustained loading. Frost heave force results are correlated with heave rate, segregational potential, and applied surcharge to classify frost susceptibility and to size anti-heave measures. All reductions, statistical treatment, and reporting are documented in accordance with the applicable GB and ASTM standards.
Applications
Soil freezing force testing supports a wide range of cold-region engineering activities:
- Design of pile foundations, anchors, and micropiles embedded in permafrost, where adfreeze resistance provides axial capacity
- Uplift stability verification for transmission towers, communication masts, wind turbine foundations, and guy anchors in frozen ground
- Assessment of tangential and normal frost heave forces acting on foundations, retaining walls, buried pipelines, and culverts in seasonally frozen soils
- Selection and verification of anti-frost-heave measures, including smooth coatings, casings, isolation layers, and ground improvement
- Artificial ground freezing projects for mine shafts, tunnels, and deep excavations, where freeze wall strength and interface behavior must be confirmed
- Railways, highways, bridges, and airports constructed on permafrost or deep seasonal frost, including evaluation of thermal regime changes over the service life
- Frost damage investigation and remedial design for distressed structures, providing objective data for engineering arbitration and insurance purposes
- Research into climate change effects on warm permafrost and long-term foundation performance under rising ground temperatures
FAQ
What is the difference between adfreeze strength and frost heave force?
Adfreeze strength is the shear bond capacity developed along the soil–structure interface due to ice cementation, and it is used beneficially to resist uplift and provide pile capacity in permafrost. Frost heave force is the pressure generated by ice lens growth and water migration in freezing soil, which acts to heave or uplift structures and must be resisted or mitigated. A complete evaluation quantifies both quantities.
At what temperatures is testing performed?
Tests are commonly conducted at multiple temperature points between −0.5 °C and −10 °C so that a strength–temperature relationship can be established. For warm permafrost sites, temperatures near −0.5 °C to −2 °C are emphasized, while colder projects extend the range to −5 °C or below.
Can testing be performed on undisturbed permafrost cores?
Yes. Undisturbed frozen cores are preferred whenever available because they preserve natural ice fabric and water content. Accredited third-party laboratories trim and test these cores in cold rooms at in-situ temperatures, with continuous temperature monitoring during storage and handling.
How is long-term adfreeze strength determined?
Long-term strength is evaluated by sustained-load creep tests or by applying long-term reduction factors to short-term peak values, in accordance with the design provisions of JGJ 118. The reduction accounts for stress relaxation and ice creep at the interface under permanent loading.
How long does a typical test program take?
Laboratory adfreeze and frost heave programs generally require two to six weeks, depending on the number of temperatures, interface conditions, and freeze–thaw cycles specified. Field pull-out programs require one full freezing season or longer for in-situ freeze-back of installed test elements before loading.
Which standards govern soil freezing force testing?
Primary references include GB/T 50123 for laboratory frozen soil testing methods, JGJ 118 for permafrost foundation design, GB 50324 for frozen ground investigation, and ASTM D5918 for frost heave susceptibility testing. Projects with international requirements may also reference applicable ISO procedures for geotechnical monitoring and laboratory practice.