12.3 Equipment
12.3.1 Basic requirements for samplers
(1)P A sampler shall have the technical details in order to ensure the following:
- to get the soil into the sampler and keep it there during withdrawal of the sampler;
- to obtain the sample with a minimum of disturbance of the soil material during the actual sampling and before and after this operation.
(2)P A sampler shall be detailed such that it is possible to obtain samples of a required quality according to 2.3 of ENV 1997-2 from the soil in which the sampler will be used.
| Soil properties / quality class | 1 | 2 | 3 | 4 | 5 |
| Unchanged soil properties particle size water content density, density index, permeability compressibility, shear strength |
* * * * |
* * * |
* * |
* |
|
| Properties that can be determined sequence of layers boundaries of strata – broad boundaries of strata – fine Atterberg limits, particle density, organic content water content density, density index, porosity, permeability compressibility, shear strength |
* * * * * * * |
* * * * * * |
* * * |
* * * |
* |
| Sampling category to be used | A | ||||
| B | |||||
| C | |||||
12.3.2 Requirements for drive samplers
12.3.2.1 General
(1)P Drive samplers used as category A sampling methods shall fulfil all requirements presented in 12.3.2.2 to 12.3.2.7.
(2) Fulfilling these requirements does not guarantee that totally undisturbed samples will always be obtained, but it should at least minimize the disturbance of samples and thus the effect of such disturbance on the results of laboratory tests performed on these samples.
12.3.2.2 Diameter of the sample tube
(1)P For catеgory A sampling methods, sample tubes with the inside diameter less than 70 mm, and in soft clays less than 50 mm shall not be used. The cross section of the sample tube shall be circular.
(2) For catеgory A sampling methods, sample tubes having an inside diameter of 100 mm are recommended.
12.3.2.3 Length of the sample tube
(1)P For category A the maximum tube length for samplers used sampling methods shall be such that the inside wall friction and adhesion during the actual sampling do not have too much influence on the results of the laboratory test to be performed.
(2) A sample tube length of 2 to 6 times the inside diameter of the tube should be used for category A sampling methods. Sample tubes for cohesive soils may often be somewhat longer.
12.3.2.4 Wall thickness of the sample tube
(1)P The wall thickness of the sample tube shall be adequate to resist distortion while it is driven into the soil. A sample tube shall, however, be thin enough to minimize the disturbance of soil caused by displacement when the tube is inserted into the soil.
(2) In some samplers and soils liners inside the sample tube may be used.
(3)P For category A sampling methods the area ratio of the sample tube shall be kept as small as possible consistent with the strength requirements of the tube.
(4) For category A drive sampling methods in soft sensitive clays an area ratio of less than 15 % is recommended.
(5) For category A sampling methods in non-sensitive cohesive soils the area ratio of the sample tube should be less than 30 %.
12.3.2.5 Shape of the cutting edge
(1)P The cutting edge of the cutting shoe shall be sharp, and the taper angle as narrow as practicable.
(2) The taper angle should be specified in relation to the area ratio. For a sampler with an area ratio exceeding 15 % the taper angle should be less than 10° except close to the edge where the edge angle may be increased in order to avoid damaging the feather edge.
12.3.2.6 Inside clearance
(1)P The inside of the sample tube or liner shall be clean and smooth without any protruding edges or irregularities which may disturb the soil.
(2)P The inside clearance shall be sufficient to allow some lateral expansion of the sample to take place, but it shall not be so much that it permits excessive deformations and causes unnecessary disturbance of the sample. The inside clearance shall not be so much that it completely eliminates the inside wall friction thereby causing loss of the sample during withdrawal or loss of lateral support thereafter.
(3) For category A sampling methods it is recommended to have an inside clearance ratio of 0,5 % to 1,0 % for sample tubes used in cohesive soils and up to 3,0 % in other types of soils.
12.3.2.7 Sample retainer
(1) A sample retainer between the cutting edge and the sample tube may be used in soils that are difficult to sample, but preferably not for cohesive soils. The use of a sample retainer causes disturbance of the sample.
