The area ratio for soft sensitive clay soil is:
<10%
Area Ratio for Soft Sensitive Clay Soil
The question asks about the specific area ratio required for obtaining undisturbed samples of soft sensitive clay soil. The area ratio is a crucial parameter in geotechnical engineering, as it directly impacts the quality and representativeness of a soil sample.
Understanding Area Ratio
The area ratio (\(A_r\)) is a measure that quantifies the degree of disturbance inflicted upon a soil sample during the sampling process. It is determined by the dimensions of the sampler's cutting edge. A lower area ratio generally indicates less disturbance to the soil structure.
The formula for calculating the area ratio is:
\[A_r = \frac{D_w^2 - D_c^2}{D_c^2} \times 100\%\]
- \(D_w\) represents the outer diameter of the sampler's cutting edge.
- \(D_c\) represents the inner diameter of the sampler's cutting edge.
Importance for Soft Sensitive Clay Soil
When sampling soft and sensitive clay soils, minimizing disturbance is paramount. Sensitive clays are characterized by a significant loss of strength and an increase in compressibility when disturbed. Even minor disturbance can alter their natural engineering properties, leading to inaccurate results from laboratory tests such as shear strength, consolidation, and permeability analyses.
To ensure that the collected samples truly reflect the in-situ conditions of these delicate soils, samplers are designed to cause the least possible disruption. This is achieved by using samplers with thin walls and appropriate cutting edge designs, which directly relates to the area ratio.
Optimal Area Ratio for Sensitive Clays
For most general soil types, an area ratio of less than 10-15% is often considered acceptable for obtaining good quality "undisturbed" samples. However, for particularly soft and sensitive clay soils, the criteria for minimal disturbance are much stricter. To get reliable and representative samples:
- For soft sensitive clay soil, it is widely recommended in geotechnical practice that the area ratio of the sampler should be less than 10% (<10%).
- In some extremely sensitive clay formations, engineers may even aim for area ratios as low as 5% to preserve the soil's original structure and properties as much as possible.
A smaller area ratio indicates a thinner sampler wall, which means less soil is displaced and compressed during the sampling operation. This reduction in displacement minimizes the shear strains induced in the sample, thereby preserving its natural fabric and strength characteristics. This is especially vital for the accurate determination of parameters like undrained shear strength and consolidation properties of soft sensitive clay soil.
Therefore, based on the requirements for minimal disturbance and accurate representation of in-situ properties, an area ratio of <10% is the appropriate choice for soft sensitive clay soil.
Important Questions from Site Investigation and Sub-Soil Exploration
In order to minimize sampling disturbance the area ratio A r,\(\left( {{{\rm{A}}_{\rm{r}}} = \frac{{{\rm{D}}_{\rm{e}}^2 - {\rm{D}}_{\rm{i}}^2}}{{{\rm{D}}_{\rm{i}}^2}}{\rm{\;}}} \right)\) should be
Shelby tube is one of the most widely used devices for:
Which one of the following is NOT a soil exploration technique?
If the sampler tube is pushed at the bottom of the bore hole to a distance of 585 mm with length of the sample recovered being 535 mm. Then the value of recovery ratio is ______.
If the inside diameters of the cutting edge and sample tube are 68 mm & 70 mm respectively and 76 mm & 74 mm are the outside diameters of the cutting edge and sample tube respectively, then outside clearance of the sampler is _______.
