🏗️ Soil Moisture Content
In short
Determination of natural moisture content of soil by drying in laboratory oven at 105–110°C to constant mass. The test is performed according to PN-EN ISO 17892-1:2015; Drying temperature: 105–110°C. The procedure comprises 9 steps (about 18 h 9 min–1 days 3 h 24 min in total); it is used for: Classification of construction soils (PN-EN ISO 14688), Determination of consistency index and soil state, Control of compaction of road and construction embankments.
At a glance
- Standard: PN-EN ISO 17892-1:2015
- Category: Construction
- Procedure steps: 9
- Total time of stages: 18 h 9 min–1 days 3 h 24 min
- Drying temperature: 105–110°C
- Constant mass criterion: Mass change <0.1% after 1 h drying
- Minimum sample mass: 30 g (fine-grained soil) to 3000 g (coarse-grained)
Overview
Natural moisture content of soil (w or wn) is one of the most important and simplest geotechnical parameters, defined as the ratio of mass of water contained in soil to mass of dry soil, expressed as percentage. Moisture determination is the starting point for almost all geotechnical tests and soil classification.
Standard PN-EN ISO 17892-1 describes laboratory method for determining natural moisture content of soil by drying sample in oven at 105–110°C to constant mass. Constant mass is considered the state where mass change after an additional hour of drying does not exceed 0.1% of sample mass. At this temperature, free water (capillary and gravitational) and adsorbed water are removed from soil, leaving mineral skeleton with chemically bound water.
Soil moisture determines its mechanical behavior — cohesive soils (clays, loams) drastically change their properties depending on water content. Moisture affects compactability, shear strength, deformability and permeability of soil. Combined with Atterberg limits (liquid limit wL and plastic limit wP), it allows determination of plasticity index and soil state (hard, semi-solid, plastic, liquid).
Testing is mandatory in every geotechnical investigation program — from simple geotechnical opinions to geological-engineering documentation. It is performed on every collected soil sample, often at many points in the profile.
Method principle
A soil sample of known mass is placed in a weighing container and dried in laboratory oven at 105–110°C until achieving constant mass. Moisture is calculated from formula: w = (m₂ - m₃)/(m₃ - m₁) × 100%, where m₁ = mass of empty container, m₂ = mass of container with wet soil, m₃ = mass of container with dry soil. Result is expressed as percentage of dry soil mass.
Applications
- Classification of construction soils (PN-EN ISO 14688)
- Determination of consistency index and soil state
- Control of compaction of road and construction embankments
- Geotechnical investigations for building foundations
- Assessment of soil suitability for construction purposes
- Testing of subgrade for road pavements
- Control of moisture in soil stabilization with cement/lime
- Monitoring of landslides and slope stability
Key parameters
| Parameter | Value |
|---|---|
| Drying temperature | 105–110°C |
| Constant mass criterion | Mass change <0.1% after 1 h drying |
| Minimum sample mass | 30 g (fine-grained soil) to 3000 g (coarse-grained) |
| Balance accuracy | 0.01 g (samples <100 g) or 0.1 g (>100 g) |
| Drying time | Usually 16–24 h (to constant mass) |
Standard
- Standard number
- PN-EN ISO 17892-1:2015
- Title (PL)
- Rozpoznanie i badania geotechniczne — Badania laboratoryjne gruntów — Część 1: Oznaczanie wilgotności naturalnej
- Title (EN)
- Geotechnical investigation and testing — Laboratory testing of soil — Part 1: Determination of water content
Step-by-step procedure
-
Preparation of weighing containers
Dry weighing containers with lids in oven. Cool in desiccator. Weigh to 0.01 g accuracy. Record mass m₁.
-
Soil sample collection
Take representative soil sample immediately after opening core/sampler. Prevent moisture loss. Sample mass dependent on soil type (30–3000 g).
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Wet sample weighing
Place soil in weighing container. Close lid. Weigh to 0.01 g accuracy. Record mass m₂.
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Sample drying
Place container (with lid ajar or removed) in oven heated to 105–110°C. Dry minimum 16 h or to constant mass.
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Cooling in desiccator
After removal from oven, close lid and place container in desiccator. Cool to room temperature (approx. 30–45 min).
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Dry sample weighing
Weigh container with dry soil with lid. Record mass m₃. If first weighing — place back in oven for 1 h and weigh again.
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Constant mass check
If difference between successive weighings ≤0.1% of dry sample mass — constant mass achieved. If not — continue drying.
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Moisture calculation
w = (m₂ - m₃) / (m₃ - m₁) × 100%. Round to 0.1% (samples >100 g) or 1% (samples <100 g).
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Documentation
Prepare report: sample number, sampling depth, soil type, masses m₁, m₂, m₃, moisture w [%].
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Laboratory oven with forced circulation | POL-EKO SLW 240/400, Binder FD 115/260, Memmert UF110 | 5 000–18 000 PLN |
| Laboratory balance | Radwag PS 4500/C/2, KERN PCB 3500-2, accuracy 0.01–0.1 g | 1 500–5 000 PLN |
| Weighing containers with lids | Aluminum or stainless steel, capacity 50–500 mL | 15–50 PLN/pc |
| Desiccator with silica gel | Glass Ø200–300 mm with dry desiccant | 300–800 PLN |
| Tongs / forceps for hot containers | Steel, thermally insulated | 50–150 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Silica gel (silica gel) | 112926-00-8 | Desiccant for desiccator — absorbs moisture from air during sample cooling |
| Calcium chloride (alternative desiccant) | 10043-52-4 | Granulated, for desiccator as alternative to silica gel |
| Distilled water | — | For periodic verification of weighing containers and cleanliness control |
Health and safety (OHS)
- Oven 110°C — burn hazard, use thermal gloves when removing containers
- Hot weighing containers — do not place on plastic surfaces, use ceramic pad
- Glass desiccator — implosion risk when opening (vacuum), open slowly
- Soil dust — protective mask when handling dry samples
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 17892-1:2015 — “Geotechnical investigation and testing — Laboratory testing of soil — Part 1: Determination of water content”.
How does this method work?
A soil sample of known mass is placed in a weighing container and dried in laboratory oven at 105–110°C until achieving constant mass. Moisture is calculated from formula: w = (m₂ - m₃)/(m₃ - m₁) × 100%, where m₁ = mass of empty container, m₂ = mass of container with wet soil, m₃ = mass of container with dry soil.
What is the measuring range and accuracy?
Drying temperature: 105–110°C; Constant mass criterion: Mass change <0.1% after 1 h drying; Minimum sample mass: 30 g (fine-grained soil) to 3000 g (coarse-grained); Balance accuracy: 0.01 g (samples <100 g) or 0.1 g (>100 g).
How long does the test take?
The times given for the individual stages add up to approximately 18 h 9 min–1 days 3 h 24 min. The procedure comprises 9 steps.
What equipment is required?
Laboratory oven with forced circulation, Laboratory balance, Weighing containers with lids, Desiccator with silica gel, Tongs / forceps for hot containers. Indicative cost of the core instrument (Laboratory oven with forced circulation): 5 000–18 000 PLN.
Where is this test used?
Classification of construction soils (PN-EN ISO 14688); Determination of consistency index and soil state; Control of compaction of road and construction embankments; Geotechnical investigations for building foundations; Assessment of soil suitability for construction purposes; Testing of subgrade for road pavements; Control of moisture in soil stabilization with cement/lime; Monitoring of landslides and slope stability.
What safety precautions apply?
Oven 110°C — burn hazard, use thermal gloves when removing containers; Hot weighing containers — do not place on plastic surfaces, use ceramic pad; Glass desiccator — implosion risk when opening (vacuum), open slowly; Soil dust — protective mask when handling dry samples.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 17892-1.