Disturbed Soil Samples
Disturbed soil samples are collected from the ground for laboratory analysis, focusing on the soil’s physical and chemical properties. The methods used to gather these samples range from manual excavation to mechanical digging and drilling techniques. It is important to note that these samples are considered disturbed due to the alteration of their natural structure during the sampling process. Consequently, they are not used to assess in situ properties or soil structure but rather to derive material properties that are unaffected by the soil’s structure or density.
The typical parameters derived from disturbed samples include particle size distributions, moisture content, particle density, Atterberg limits, and chemical composition. Disturbed samples are often collected in varying sizes depending on the required testing. Small disturbed samples generally weigh between 0.5 and 1 kg and are stored in plastic containers, while larger bulk samples weighing between 10 and 25 kg are sealed in heavy-duty polythene bags to preserve their original moisture content during storage and transport.
Undisturbed Soil Samples
While no soil sample can be entirely undisturbed due to the relaxation of in situ stress, efforts are made to preserve the natural structure of the soil as much as possible. Undisturbed samples are taken to measure in situ physical properties such as strength, compressibility (settlement), moisture content, unit weight, and permeability. The goal is to maintain the natural condition of the soil and provide data that reflects its behavior in the field.
Undisturbed samples are usually collected from trial pit excavations, where soil is carefully extracted from the excavator bucket and wrapped for preservation. In deeper layers, undisturbed samples may be gathered using open-ended spoon samplers or tubes like U100, UT100, or Shelby tubes. These techniques are designed to minimize disturbance to the soil and maintain as much of its natural structure as possible.
It’s essential to understand that even undisturbed samples are subject to some degree of disturbance. Factors such as the type of soil, the condition of the sampling equipment, the expertise of the driller, and the methods used for storage and transport can all influence the sample’s integrity. In cases where undisturbed samples are not feasible, disturbed samples may be reconstituted to a known state or density for advanced testing, allowing for further analysis of the soil’s behavior under specific conditions.
