33.4.4.6 Mineralogy and tertiary constituents

COMMENTARY ON 33.4.4.6

Tertiary constituents are relevant to identifying the geological unit rather than to the engineering properties for example, less than about 10% in a fine soil or 2% in a coarse soil.

Mineral constituents should be reported before the principal soil type, using qualitative terms such as "slightly micaceous", "glauconitic" or "very shelly". Tertiary constituents should be added at the end of the description using qualitative terms such as "with rare", "with occasional" or "with frequent", e.g. "SAND with rare gravel size brick fragments". These terms are qualitative and no definition of percentage should be given. The terms should be applied consistently on any given job. The size of the tertiary constituents can also be given in mm.

NOTE Reference samples or photographs can provide a useful record of the proportions of various quantities that the descriptors used imply.

The description of the carbonate content should be carried out in accordance with BS EN ISO 14688-1. A soil may be described as calcareous if the addition of HCL produces a clear but unsustained effervescence, as slightly calcareous if the effervescence is weak or sporadic and as highly calcareous if the effervescence is strong and sustained. The description should distinguish whether it is the clasts or the matrix or both that are calcareous. A descriptive term should be used if the presence of carbonate content is detected (i.e. the term carbonate free is not expected on field logs unless as a confirmation that the test has been carried out with a negative result). The acid used in this test should be dilute hydrochloric acid, that is 10% (0,1 M).

33.4.5 Anthropogenic ground

COMMENTARY ON 33.4.5

Anthropogenic soils ("made ground" or "fill") have been placed by man and can be divided into those composed of reworked natural soils and those composed of, or containing, man-made materials. A common and useful distinction is that "fill" is placed in a controlled manner, and "made ground" is placed without strict engineering control. Mapping geologists, such as those in the British Geological Survey, might distinguish "made ground" as placed above and "infilled ground" as placed below the original ground surface.

The description and testing of natural soils reworked by man is usually straightforward. It might not be possible to carry out significant soil tests on man-made materials, and descriptions are all that remain after the samples have been discarded or pits filled in, making them of great importance.

Good descriptions should include information on the following aspects, as well as on the soil constituents (this list is not exhaustive):

• a) origin of the material;
• b) presence of large objects such as concrete, masonry, old motor cars, etc.;
• c) presence of voids or collapsible hollow objects;
• d) chemical waste, and dangerous or hazardous substances;
• e) organic matter, with a note on the degree of decomposition;
• f) odours (see Table 18);
• g) striking colour tints;
• h) any dates readable on buried papers, etc.;
• i) signs of heat or combustion underground, e.g. steam emerging from borehole;
• j) structure, variability and any indications of the method of placement;
• k) presence of potentially reactive or expansive materials such as chert or some types of steel making slag (see Table 18); and
• l) any signs of gas such as by odour or bubbling through water.

Some examples of anthropogenic soil descriptions are given in Table 18. These materials are often heterogenous and non-ordered and so a flexible approach to the word order and use of terms can be useful. Photographs of the excavated materials should be taken to support the descriptions given.

The description of any odour in the soil should be made wherever possible using the terms in Column 2 of Table 19; these suggestions are not particularly linked to Column 1 but allow more precision than the terms in Column 1 on their own.

The description of odours is not a significant problem area in description; the logger should report any smells noticed using the terms in Table 19 for guidance. If any particularly strong smells are apparent, in an exposure, sample or container, care should be taken to avoid smelling this too closely or deeply and strong odours should not be repeatedly breathed in, in order to make an assessment. Where there is uncertainty in the nature of the odour, "strong odour" should be recorded and the assessment should be based on chemical analysis.

Many materials that emit odours are toxic or carcinogenic and health and safety considerations should override any requirement for noting odours on logs. Where the desk study has indicated that there is a risk from volatile compounds being present in the ground, an appropriate risk assessment should be made prior to carrying out any description. Where odours are unexpectedly encountered during an investigation, work should be temporarily suspended to allow for a reassessment of health and safety requirements so any additional measures can be implemented before work resumes. Where these assessments require respirators to be worn, then this should be indicated on the logs by stating "no odours on logs as description carried out wearing respiratory protective equipment".

Particular care should be taken when describing non-natural materials such as slags, clinker and ash. Unless they can be positively identified as such they should be described as, for example, slag-like, or the descriptors "probably" or "possibly" should be used.

NOTE Slags and similar materials can seldom be positively identified without mineralogical and/or chemical examination. It is often important to identify the exact nature of a slag-like material in view of the fact that steelmaking slags are often volume-unstable, whilst with the exception of a few old blast furnace slags, most blast furnace slags are stable. Similarly, non-ferrous slags might be unstable or liable to high concentrations of toxic elements (see Environment Agency Technical Reports TR P331 [50] and P5-035/TR/01 [51]).