Disturbed Sampling

Definition

Disturbed sampling refers to the collection of soil or rock samples that have been altered or disturbed during the process of obtaining them. This type of sampling is crucial when exploring site conditions, as it helps in understanding the existing materials and their properties, even though the samples may not fully represent the in-situ conditions. Factors like drilling techniques and handling can cause these disturbances, affecting the physical characteristics and moisture content of the samples collected.

5 Must Know Facts For Your Next Test

1. Disturbed samples are often obtained through methods like rotary drilling or augering, where mechanical forces can change the soil structure.
2. While disturbed sampling provides useful data, it is important to acknowledge its limitations in accurately reflecting the original site conditions.
3. These samples are typically analyzed for properties like moisture content, grain size distribution, and plasticity index to help understand soil behavior.
4. Disturbed sampling is often quicker and less expensive than undisturbed sampling, making it a common choice in preliminary investigations.
5. Common applications for disturbed samples include environmental assessments, geotechnical investigations, and construction planning.

Review Questions

• What are the main differences between disturbed sampling and undisturbed sampling, and how do these differences impact data interpretation?
  • Disturbed sampling involves collecting soil or rock samples that have been altered during retrieval, which can lead to changes in properties such as moisture content and structure. In contrast, undisturbed sampling aims to preserve these characteristics as much as possible. The key difference impacts data interpretation significantly; disturbed samples may not accurately reflect in-situ conditions, leading to potential miscalculations in geotechnical assessments or project designs.
• Discuss how the choice of sampling technique affects the quality and reliability of disturbed samples collected during site investigations.
  • The quality and reliability of disturbed samples are heavily influenced by the sampling technique chosen. For instance, methods like rotary drilling tend to produce more disturbance than others such as hand augering. This means that while rotary drilling might yield samples more quickly, they may not provide reliable data for certain engineering analyses due to significant alterations in the soil structure. Understanding these implications is crucial for engineers when planning site investigations.
• Evaluate the implications of using disturbed samples in a major construction project, considering both benefits and risks associated with this sampling method.
  • Using disturbed samples in a major construction project can offer advantages such as cost-effectiveness and speed of collection, allowing for quicker preliminary assessments. However, the risks involve potential inaccuracies in understanding soil behavior and conditions due to disturbances caused during sample collection. If engineers rely too heavily on disturbed samples without corroborating data from undisturbed methods or in-situ testing, they may misjudge factors like load-bearing capacity or settlement risks, which could lead to structural failures or increased costs later in the project.

Related terms

Undisturbed Sampling: A method of collecting soil or rock samples that minimizes disturbance to preserve the original structure and moisture content, providing more accurate representations of in-situ conditions.

Soil Boring: A technique used to drill into the ground to obtain samples for analysis, which can produce either disturbed or undisturbed samples depending on the method used.

In-situ Testing: Testing performed directly on site to evaluate the physical properties of soil or rock, often used in conjunction with sampling techniques to assess subsurface conditions.