Detailed information on tests for classification, identification and description of soil

M.1 Checklists for classification testing

(l) The number of specimens to be tested depends on the variability of the soil and the amount of experience with the soil and to a lesser extent than other soil tests on the geotechnical problem. Table M.1 gives guidance on the number of classification tests.

(2) Table M.2 presents a checklist for each of soil classification tests included in the document.

Table M.1 – Classification tests. Suggested minimum number of samples to be tested in one soil stratum

Classification test	Comparable experience
	No	Yes
Particle size distribution	4–6	2–4
Water content	All samples of Quality Class 1 to 3
Strength index test	All samples of Quality Class I
Consistency limits (Atterberg limits)	3–5	1–3
Loss on ignition (for organic and clay soil)	3–5	1–3
Bulk density	Every element test
Density index	As appropriate
Particle density	2	1
Carbonate content	As appropriate
Sulfate content	As appropriate
pH	As appropriate
Chloride content	As appropriate
Soil dispersibility	As appropriate
Frost susceptibility	As appropriate

Table M.2 – Checklist for soil classification tests

Classification test	Checklist
Water content	Check storage method of samples Coordinate testing programme with other classification tests Standard oven-drying method not appropriate for gypsum, organic soil; precautions may be needed Report presence of gypsum, organic soil For coarse soil, correction of measured water content may be needed Correction needed for saline soil
Bulk density	Test method needs to be selected Check sampling and handling methods used For large earthwork projects, method may need to be adapted, or use field method
Bulk density	For sands and gravels, correction of measured density may be needed;
Particle density	Sample preparation (oven-drying versus moist specimen) can influence results Check whether material can have enclosed pores; for such material, special techniques might be appropriate Report if material has enclosed pores If results fall outside the range of typical values, consider additional determinations; mineralogy and organic content will affect result
Particle size analysis	Selection of test method depends on particle size and gradation Carbonates and organic matter influence test results; for such materials, remove carbonates or organic matter if appropriate, or adapt testing method Check that correct quartering is used (particle size and sample representativeness)
Consistency limits (Atterberg limits)	Selection of test method for liquid limit; several methods are acceptable, but fall cone method is recommended Check storage method of samples Check specimen preparation, especially homogenisation and mixing Check whether drying has been used Drying can influence results dramatically, and should be avoided in oven Soil that oxidise should be tested quickly Results need not be reliable for thixotropic soil
Density index for granular soil	Check storage method of samples Select test type to be used Results are very dependent on procedure used Prepared specimens have high degree of non-uniformity
Soil dispersibility	Need to consider specifying different compaction conditions for specimens Avoid drying of the specimen before testing Need to select test procedures to use Need to run classification tests in addition
Frost susceptibility	–

NOTE Examples of methods for classification, identification and description of soil are given in the documents listed in X.4.1.

M.2 Water content determination

M.2.1 Evaluation of test results

(1) If the water in the soil is saline, the dissolved salts will remain in the soil after drying and may give an incorrect water content result. A more appropriate value may be the fluid content i.e. the mass of fluid (water plus salts) per unit mass of dry soil.

(2) For a coarse soil, the water content obtained in the laboratory on a sample for which the maximum grain diameter is limited by the sample size, may differ from the in place water content. In such a case, the water content should be corrected as a function of the percentage of grains that are larger than the maximum grain diameter.

NOTE Examples of methods for determination of the water content of soil are given in the documents listed in X.4.1.2.