61.4 Reporting test results (p. IV)
Table 37 Common laboratory tests for soils (9 of 10)
| Category of test | Name of test or parameter measured | Where details can be found | Remarks |
| Permeability tests Head and Epps, 2011 [132] | Laboratory permeability tests often yield results of limited value and in-situ tests are generally thought to yield more reliable data. | ||
| Constant head test | BS 1377-5, BS EN ISO 17892-11 | The constant head test is suited only to soils of permeability normally within the range 10–5 m/s to 10–2 m/s, i.e. coarse soils. Test materials should be at the required density. |
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| Falling head test | BS EN ISO 17892-11, Head and Epps, 2011 [132] | The falling head test is applicable to soils with a permeability range of 10–9 m/s to 10–5 m/s, such as silt and some clays. Undisturbed, remoulded or compacted samples may be used. Samples that swell during test might not give reliable results. |
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| Falling head with oedometer | Head and Epps, 2011 [132] | For soils of permeability of 10–11 m/s to 10–9 m/s such as clays, an adapted oedometer cell may be used. | |
| Hydraulic oedometer (Rowe cell) | BS 1377 (all parts), Head and Epps, 2013 [133] | Rowe consolidation cell allows the direct measurement of permeability under constant head with a back pressure and confining pressures more closely consistent with the field state. The Rowe cell allows either vertical or radial flow. Undisturbed or remoulded samples may be used. | |
| Triaxial constant head permeability test | BS 1377-6, Head and Epps, 2013 [133] | Measurements on a saturated and consolidated specimen under known effective stress condition, which use a constant head pressure difference between the top and base of the test specimen and measure the volume change to calculate the rate of fluid flow. This requires two back pressure systems to maintain the constant head. | |
| Triaxial falling head permeability | Head and Epps, 2013 [133] | Uses a triaxial cell with one or both of the back pressure systems replaced by a burette. This does not allow for the saturation of the sample. | |
| Triaxial permeability of low permeability soils | Head and Epps, 2013 [133] | Measurements in low permeability soils using pore pressure transducer or mercury null indicator. The sample is saturated and consolidated prior to test. | |
| Triaxial permeability test with a constant flow rate for low permeability soils | Olsen, Nichols and Rice, 1985 [138] | Generally used on very low permeability soils of less than 10–9 m/s. This triaxial test uses a constant flow rate and constant back pressure. The pressures produced by the constant flow rate should not be so high as to greatly alter the effective stress conditions. The pumped flow rate might be very low requiring sophisticated pumps. | |
Table 38 Swelling and shrinkage tests (10 of 10)
| Category of test | Name of test or parameter measured | Where details can be found | Remarks |
| Shrinkage and swelling test | There are a number of tests that can be used to understand the shrinkage and swelling characteristic of clays and extremely weak to weak mudstone. These tests are commonly identified as soil or rock tests; however, many of the tests can be carried out on both material types. | ||
| Shrinkage limit test | BS 1377-2, Hobbs et al., 2013 [139] | An indication of the minimum water content below which there is no significant shrinkage. This test is carried out using mercury (BS 1377-2). Because of the use of this poisonous liquid and the practical difficulties of this method it is very rarely carried out in the UK. New apparatus has been developed to carry out this test using laser range finding techniques and does not use mercury. | |
| Swelling strain index for radially confined specimens with axial surcharge | BS 1377-5, BS EN ISO 17892-5, ISRM, 2007 [55] | Measures the axial swelling strain developed against a constant axial pressure or surcharge, when radially confined. This test may be carried out in a standard oedometer or using an oedometer cell. |
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| Constant volume swell pressure | BS 1377-5, BS EN ISO 17892-5, ISRM, 2007 [55] | Results are used to identify if the ground beneath a foundation load might swell with increasing water content. This test is done using the standard oedometer by adding weight to negate any swell strain; automated systems are available. |
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| Three-dimensional swelling strain | ISRM, 2007 [55] | The standard apparatus is unsuitable for tests on samples that deteriorate or slake in water. An alternative apparatus, which can test firm and stiffer clay and rocks, is currently being developed. | |
| Soil suction | To assess negative pore pressures (soil suction) which provides information on volume change, deformation and strength characteristics of fine soil. | ||
| Suction plate | Manufacturer's instructions | The different ceramic plates used allows the measurement of suctions generally in the range of 10 kPa to 1500 kPa. This method is more often used in soil science. | |
| Filter paper | BRE IP4/93 [140], ASTM D5298-10 | The filter paper method has a range from 10 kPa to 100 000 kPa. | |
Table 39 Specialist laboratory tests for soils (1 of 2)
| Category of test | Name of test or parameter measured | Where details can be found | Remarks |
| Shear strength | Simple direct shear | ASTM D6528-07, Bjerrum and Landva, 1966 [141] | Determination of lateral shear strength and stress-strain parameters measured under plane strain and constant volume conditions, simulating undrained conditions for a saturated specimen. The principle stresses rotate during the application of the shear stress, simulating a number of design situations (e.g. axial loading of piles). |
| Cyclic soils testing | Cyclic triaxial testing modulus and damping properties of soils Load controlled cyclic triaxial strength of soil |
ASTM D3999-11, ASTM D5311-11 | Determination of the cyclic shear modulus, G, and damping characteristics of soils at intermediate and high strain levels. These might be relevant to dynamic, linear and non-linear analytical methods and performance evaluation of structures under dynamic or cyclic loads such as caused by earthquakes, ocean waves, or blasting. Measures reduction of shear strength as a result of cyclic loading, including liquefaction potential of soils. Test options include drained or undrained conditions, stress or strain control, and the required frequency, wave-form and amplitude of the cyclic excitation in order to model the stress that the in-situ soil experiences. The test conditions need to be carefully designed and monitored. These are expensive and highly sensitive tests and the advice of an expert in these tests is recommended to ensure that the cyclic stress expected on or in the ground is being modelled correctly in the laboratory specimen. |
| Modulus and damping of soils by resonant column | ASTM D4015-07 | Determination of small strain shear stiffness (G) and its degradation with respect to shear strain. The test is also used to determine material damping characteristics. Some test instruments also allow a torsional shear of the samples. Note that the measured resonant frequency relates only to the test specimen at its test condition, and is not representative of the resonant frequency of the in-situ bulk soil horizon. |
Table 39 Specialist laboratory tests for soils (2 of 2)
| Category of test | Name of test or parameter measured | Where details can be found | Remarks |
| Cyclic soils testing (continued) | Cyclic simple shear tests | ASTM D6528-07, Andersen, Kleven Heien, 1988 [142] | Degradation of shear strength, and liquefaction potential, with cyclic stress in the lateral plane. Tests options include drained or undrained conditions, stress or strain control, and the required frequency, wave-form and amplitude of the cyclic excitation in order to model the stress that the in-situ soil experiences. In all tests, the conditions need to be carefully designed and monitored. These are expensive and highly sensitive tests and the advice of an expert in these tests is recommended to ensure that the cyclic stress expected on the ground is being modelled correctly in the laboratory specimen. |
| Strength tests on unsaturated soils | Triaxial tests on unsaturated soils. | For instance Leong, Byunt and Rahardjo, 2013 [143] | Tests require both pore pressure and air pressure measurement. Used where the behaviour of partially saturated soil is important to design. |
| Permeability on unsaturated soils | Hydraulic conductivity of unsaturated soils | ASTM D7664-10 | Measurement of hydraulic conductivity of unsaturated soils. Measures either the relationship between hydraulic conductivity and matrix suction or that between hydraulic conductivity and volumetric water content, gravimetric water content, or degree of saturation. Applicable where the permeability of unsaturated soils is important to design. |
