Module 1 : Site Exploration and Geotechnical Investigation
Lecture 3 : Soil samplings and samplers [ Section 3.1 : Soil sampling, Disturbed samples, Undisturbed samples ]
   
 

Recovery ratio

Where, L is the length of the sample within the tube,

H is the depth of penetration of the sampling tube.

It represents the disturbance of the soil sample. For good sampling the recovery ratio should be 96 to 98 %.

Wall friction can be reduced by suitable inside clearance, smooth finish and oiling.
The non-returned wall should have large orifice to allow air and water to escape.
 
Fig. 1.6 Sampling tube
Table 1.1 : Sensitivity vs (L/Ds) ratio
 

Sensitivity

(L/Ds)

> 30

20

5 to 30

12

< 5

12

 
1
5