Obviously, the quality of undisturbed soil sample is considerably significant. This is because crucial engineering properties for foundation design, such as soil strength, permeability, and compressibility are estimated by testing undisturbed soil samples.
There are several factors that influence the quality of undisturbed soil sample such as confining pressure of sampling equipment, volume displacement due to tubes or other collection devices, friction between collection device and the sample, water-content variation in soil specimen, sample handling and transportation, the attitude of drilling crew, and environmental conditions. These factors need to be taken into consideration while undisturbed samples are collected.
What are the Factors that Influence the Quality of Undisturbed Soil Sample?
1) Volume Displacement
Volume displacement of soil samples due to tubes or other collection equipment influence their undisturbedness. Such detrimental effects would be greater in the presence of gravel.
2) Side Friction
The side friction between soil specimen and tube would tend to compress the sample during recovery. This disturbance influence can be declined by swagging sample tubes so that the cutting edge is slightly smaller than the inside tube diameter and subsequently reduce the friction.
3) Lateral Expansion
When the sample is unloaded from the in situ confining pressure, unknown lateral expansion of the sample would certainly occur. Therefore, in situ tests using hole diameter as a reference are disturbed by an unknown amount.
4) Variation in Water-Content
There is a variation in the water content of the sample based on the recovery technique and presence or absence of water in the specimen.
5) Attitude of the Crew
The attitude of drilling crew, supervising engineer, and laboratory technicians may be poor and consequently, disturbance degree of soil sample would increase.
6) Hydrostatic Pressure
Loss in hydrostatic pressure may create gas-bubble voids in the sample.
7) Environmental Conditions
On a very hot day, the sample may lose a considerable amount of water. However, in colder days, the specimen may freeze unless it is protected properly.
8) Handling and Transportation
Handling and transportation of the sample to the laboratory and transporting samples from sampling equipment to the testing machine disturb the sample.