What is a Disturbed Sample (DS)?
A Disturbed Sample (DS) refers to a soil or rock specimen whose natural structure has been altered during the sampling process. This disturbance may include changes in density, particle arrangement, or moisture distribution.
Although a Disturbed Sample does not represent the exact in-situ condition of the soil, it still plays an important role in geotechnical laboratories. For instance, engineers use it for index property tests such as moisture content, Atterberg limits, grain size distribution, and specific gravity (ASTM International).
When is a Disturbed Sample Used?
Disturbed Samples are typically collected in several situations:
During the preliminary stages of geotechnical investigation or feasibility studies.
When engineers need a large volume of soil for laboratory testing.
For soil classification using USCS (Unified Soil Classification System) or AASHTO methods.
⚠️ However, a Disturbed Sample is not suitable for mechanical property tests such as shear strength or consolidation, which require an Undisturbed Sample (UDS).
Objectives of Disturbed Sample Collection
The main purposes of collecting Disturbed Samples include the following:
Determining moisture content, Atterberg limits (LL, PL, SL), and soil gradation.
Conducting soil classification for engineering projects.
Providing preliminary data for foundation, embankment, and pavement design.
Supporting an early estimation of soil engineering parameters.
Methods of Collecting Disturbed Samples
a. Using a Drilling Rig
Engineers can collect DS through several methods such as wash boring, rotary drilling, or auger boring. In these cases, the drilling process collects soil cuttings and brings them to the surface.
In addition, DS can also come from the SPT split-spoon sampler when the sample is not intact.
📘 Relevant ASTM Standards:
ASTM D1586 – Standard Penetration Test (SPT)
ASTM D1587 – Thin-walled tube sampling
ASTM D420 – Site characterization
ASTM D4220 – Preserving & transporting soil samples
b. Using a Hand Auger
Another option is to use a manual hand auger with a 2–4 inch diameter. The soil retrieved from the auger becomes disturbed due to the retrieval process. This method is particularly useful for shallow soil layers.
Sampling Locations and Conditions for Disturbed Samples
In practice, engineers often collect DS from clay, silt, sand, or mixed soils. On the other hand, it is less ideal for hard rock unless core drilling is applied. Typically, sampling occurs every 1.5–2 meters or whenever a soil layer changes.
Handling Disturbed Samples in the Field
To ensure reliable laboratory results, engineers must carefully handle Disturbed Samples:
Store them in strong PE plastic bags with clear labeling.
Furthermore, avoid direct sunlight exposure.
Use sealed containers such as buckets or cool boxes.
Finally, keep samples airtight to prevent moisture loss.
Transporting Disturbed Samples to the Laboratory
During transportation, engineers should:
Use ziplock bags, jars, or sealed buckets.
Moreover, attach borehole logs and chain of custody forms.
Minimize vibration or shock that may affect the soil.
Maintain natural moisture conditions, especially in soft clay.
Laboratory Testing for Disturbed Samples
| Parameter | ASTM Standard |
|---|---|
| Moisture Content (w) | ASTM D2216 |
| Particle Specific Gravity (Gs) | ASTM D854 |
| Sieve Analysis | ASTM D6913 |
| Hydrometer Test | ASTM D7928 |
| Atterberg Limits | ASTM D4318 |
| Soil Classification (USCS) | ASTM D2487 |
📖 Related Article: The Role Of Cyclic Triaxial Test in Analyzing Soil Dynamic Strength
Applications of Disturbed Sample Data
Disturbed Sample test results are valuable in many applications, for example:
Soil classification for geotechnical mapping.
Preliminary analysis of slope stability and bearing capacity.
Early-stage foundation and earthwork design.
Determining the need for further UDS or in-situ testing.
A Disturbed Sample (DS) plays a crucial role in the early phases of geotechnical investigation. While it does not fully preserve the soil’s natural structure, the laboratory data from DS remains essential for soil classification, project planning, and preliminary design. Therefore, proper handling and preservation of Disturbed Samples ensure accurate and reliable test results that support safe and cost-effective engineering solutions.