25.11 Handling and labelling of samples
Samples are expensive to obtain and should be treated with great care. The usefulness of the results of the laboratory tests depends on the quality of the samples at the time they are tested, so a procedure should be established for the handling and labelling of the samples, as well as their storage and transport, both to prevent their deterioration and to ensure that they can be readily identified and drawn from the sample store when required.
The samples should be protected from frost, which would damage them, and from excessive heat and temperature variation, which could lead to deterioration in the sealing of the sample containers and subsequently damage the samples. The temperature of the sample store is influenced by the climate, but Class 1 and Class 2 samples should be stored at the lowest temperature practicable within the range 4 °C to 25 °C or as specified. Samples for chemical and environmental testing have different storage temperature requirements (see BS 10175 and BS ISO 18512).
All samples should be labelled with a unique reference number immediately after being taken from a borehole or excavation. If they are to be preserved with their natural water content, they should be sealed in an airtight container or coated in wax at the same time. The label should show all necessary information about the sample. If the sample is of ground that might contain hazardous substances, then the label should carry a warning to that effect.
The sample should be recorded on the daily field report. It should carry more than one label or other means of identification so that the sample can still be identified if one label is damaged. The label should be permanently marked and be sufficiently robust to withstand the effect of its environment and the transport of the sample.
NOTE The use of electronic labelling and tracking systems (barcode or chip) is now an available technology that facilitates more efficient traceability of samples. It might also provide the opportunity for initiating the electronic capturing of data in the field for subsequent use in the reporting process.
25.11.3 Disturbed samples of soil and hand specimens of rock
Where samples are required for testing, or where it is desirable to keep them in good condition over long periods, they should be treated as follows.
Immediately after being taken from a borehole or excavation, the sample should be placed in a non-corrodible and durable container of at least 1 L capacity, which the sample should fill, with the minimum of air space. The container should have an airtight cover or seal so that the natural water content of the sample can be maintained until tested in the laboratory.
NOTE For rock samples, an alternative procedure is to cover the sample in muslin or similar material and then coat in layers of paraffin wax. A microcrystalline wax is preferred because it is less likely to shrink or crack.
Larger disturbed samples that are required for certain laboratory tests may be packed in robust containers or plastic sacks.
A label, as described in 25.11.2, should be placed inside the sample container. An identical label should also be securely fixed to the outside of the container under a waterproof seal (wax or plastics). The containers may be crated during transit. During the interval when the samples are on site or in transit to the sample store, they should be protected from frost and from excessive heat.
For hand samples of rock, the reference number should be recorded by painting directly on the surface of the sample or attaching a label. Samples should then be wrapped in several thicknesses of paper and packed in a wooden box. A label of the type described in 25.11.2 should be included in the wrapping.
25.11.4 Samples taken with a tube sampler
COMMENTARY ON 25.11.4
The following recommendations are applicable to all samples taken with tube samplers. The precautions for handling and protection of samples are to be regarded as a minimum requirement for samples taken by the usual methods. In special cases it might be necessary to take more elaborate precautions.
Immediately after the sample has been taken from the boring or excavation, the ends of the sample should be removed to a depth of about 25 mm and any obviously disturbed soil in the ends of the sampler should also be removed. Several layers of molten wax, preferably microcrystalline wax (because it is less likely to shrink or crack), should then be applied to each end to give a plug of about 25 mm in thickness. The molten wax should be as cool as possible. The sides of the tube should be clean and free from adhering soil. If the sample is very porous, a layer of waxed paper should first be placed over the end of the sample.
Any remaining space between the end of the tube or liner and the wax should be tightly packed with a material that is less compressible than the sample and not capable of extracting water from it. There should be a close-fitting lid or screw-cap on each end of the tube or liner. If necessary, the lids should be held in position with adhesive tape.
In accordance with 25.11.2, a label bearing the number of the sample should be placed inside the container just under the lid. The label should be placed at the top of the sample. In addition, the number of the sample should be painted on the outside of the container, and the top or bottom of the sample should be indicated. The liners or containers should be packed in a way that minimizes damage by vibration and shock during transit.
25.11.5 Rotary core samples
Handling of rotary cores and any sub-samples required for laboratory testing is an integral part of the extrusion and preservation process and should be carried out in accordance with 25.7. Core boxes should be labelled to fully identify their content and any liners placed within the boxes should be marked with the depth range. Sub-samples for laboratory test should be labelled and also marked so as there is no doubt about which is the upper and lower end.
For each section of core removed form the core box for laboratory testing, a circular plastic pipe (or similar rigid material) of similar diameter to the core should be used to fill the gap left by the removed core sub-sample. This plastic pipe or similar rigid object should be marked to show the length of core removed and the top and base depths of the removed core. The reason for this marker is twofold; firstly to indicate where core has been removed from the stratigraphic sequence and secondly to prevent the remaining core form sliding within the box. This assists in helping to maintain the cores quality class 1.
The samples should be kept in a sample store as described in 25.11.1. It might be necessary to place rotary core samples in rigid liners to protect their structural integrity during handling and transportation. If samples are handled and transported in core boxes these might need to be packed to prevent being damaged by moving around in the box.
25.11.6 Block samples
After labels have been attached to the sample to indicate its location and orientation, the sample should be covered in muslin and then coated with a succession of layers of molten microcrystalline wax; these could be reinforced with layers of porous fabric (e.g. muslin) or plastic film. Additional labels should be fixed to the outside of samples. The sample should be packed in a suitable material and placed in a strong box or crate. Large samples should be protected with tight-fitting formwork or packed in rigid cement, expandable spray foam or wax or resin to prevent fissures from opening up under the weight of the samples.