BS1277: 1990 consist of 9 Parts: Part 1: General requirements and sample preparation; Part 2: Classification tests; Part 3: Chemical and electro-chemical tests; Part 4: Compaction-related tests; Part 5: Compressibility, permeability and durability tests; Part 6: Consolidation and permeability tests in hydraulic cells and with pore pressure measurement; Part 7: Shear strength tests (total stress); Part 8: Shear strength tests (effective stress); Part 9: In-situ tests.
Part 1 of this standard contains general information relating to the tests, common calibration and specification requirements and general requirements for testing laboratories and field work. It also includes details of procedures for the preparation of disturbed and undisturbed samples, where these are common to more than one type of test.
Part 2 describes tests for the classification of soils according to moisture content, Atterberg limits, density, particle density and particle size distribution. No changes in principle have been made in the test procedures, but some additional tests are included. In the preparation of cohesive soils for testing, the requirement of using the soil in its natural state, without drying, has been introduced. The main additions and amendments are as follows. a) Moisture content. Determination of the saturation moisture content of chalk has been added. The alcohol method and the sand bath method have been deleted. b) Liquid limits. A one-point cone penetration test has been added. c) Shrinkage limit. This is an addition, and two procedures are given. d) Bulk density. Determination by direct measurement has been added. e) Particle density (previously specific gravity). The pyknometer jar method has been reintroduced as a site f) Particle size distribution (sedimentation). Procedures have been rationalized and amended where necessary. Pretreatment is not now a requirement.
Determination of
This method covers the determination of In this standard, density is expressed in terms of
mass density. The In this standard the term is the definitive method for soils consisting of
clay, silt and sand-sized particles. The third is a
Part 3 describes chemical tests on soils and on water. Existing test procedures have been retained, with some modification, and additional tests have been included for the determination of the following. a) Loss on ignition; b) sulphate content of soil and ground water; c) Carbonate content; d) Chloride content; e) Total dissolved solids; f) pH value; g) resistivity; h) redox potential Tests have also been included for the assessment of the corrosivity of soils; these are the determination of the electrical resistivity and of the redox potential. In-situ methods of these two tests are given in Part 9.
Part 4 describes those tests that refer in some way to the compaction of soils. These include existing procedures for determining compaction parameters; additional tests for measurement of the limiting densities of non-cohesive soils; and tests which are related to the control and behaviour of soil placed in-situ as fill, comprising the CBR test and two procedures which have been added. These are the moisture condition test, and the chalk crushing value test, both of which require use of the same apparatus. Attention has been given to several methods of sample preparation appropriate to different soil types prior to compaction tests and the compaction of samples for the CBR test.
The principle is to determine the relationship between force and penetration when a cylindrical plunger of a standard cross-sectional area is made to penetrate the soil at a given rate. At certain values of penetration the ratio of the applied force to a standard force, expressed as a percentage, is defined as the California Bearing Ratio (CBR).
Part 5 describes test procedures in which the presence or drainage or flow of water within the pore spaces of the soil is the significant factor, but without requirinq the measurement of pore water pressure. These include the one-dimensional oedometer consolidation test, which incorporates some additional requirements. Tests for determining the swelling and collapsing characteristics have been added. Further additional test procedures are as follows. a) Determination of soil permeability (constant-head method). b) Determination of erodibility and dispersive characteristics of fine-grained soils. c) Determination of potential frost heave for which reference is made to BS 812-124.
Part 6 is a major addition to this standard. It describes tests for the determination of consolidation and permeability parameters using equipment in which the measurement of pore water pressure is an essential feature. These comprise the following. a) Determination of consolidation properties in a hydraulic consolidation cell. For samples of large diameter, either vertical or horizontal (radial) drainage can be used. b) Determination of consolidation properties in a triaxial cell under isotropic conditions.
Two types of equipment are used: (a) hydraulically loaded one-dimensional consolidation cell; (b) a triaxial consolidation cell. Consolidation or triaxial cells of large diameter enable large specimens to be tested so that some account can be taken of the effects of the soil fabric.
Back pressure (u
- pressure applied directly to the pore fluid in the specimen voids. _{b})Effective
cell pressure - the difference between the cell pressure and pore water
pressure. Effective consolidation pressure (σ’ - the
difference between the cell pressure and the back pressure against which the
pore fluid drains during the consolidation stage. Pore pressure coefficients A
and B - changes in total stresses applied to a specimen when no drainage is
permitted produces changes in the pore pressure in accordance with the equation._{3} )
Part 7 describes methods for the determination of the shear strength of soils in terms of total stress, or (in the case of drained direct shear tests) in terms of effective stress when equal to total stress. A test for determining unconfined compressive strength using standard laboratory apparatus has been added. For very soft soils the laboratory vane test has been added. Direct shear tests using the shear box and the ring shear apparatus have been added, and include the determination of drained and drained-residual shear strength parameters. The triaxial compression test procedure has been augmented by the addition of a multi-stage method which is appropriate under certain conditions.
Unconfined compression strength (q_{u}) the compressive strength at
failure of a specimen subjected to uniaxial (unconfined) compression. Sensitivity
- the ratio of the undrained shear strength of an undisturbed clay specimen to
that of the same specimen after remoulding at the same moisture content. Vane
shear strength (τ the shear strength of a soil as determined by
applying a torque in the vane shear test. _{v})Undrained shear strength (C
the shear strength of a soil under undrained conditions, before drainage of
water due to application of stress can take place. Residual strength - the
shear strength which a soil can maintain when subjected to large shear
displacement after the peak strength has been mobilized._{u})
(clauses 7 to 9) comprise: (e) unconfined
compression test procedure, in the laboratory and in a portable apparatus for
use on site; (f) triaxial compression test procedure from which the undrained
shear strength is derived; (g) triaxial compression test procedure in several stages
on one specimen, for deriving undrained shear strength. The unconfined
compression test procedure using portable apparatus, and the single-stage
triaxial compression test, are similar in principle to those given in the 1975
Standard. All the other procedures are new additions.Compression tests
The test is carried out in the triaxial apparatus on specimens in the form of right cylinders of height approximately equal to twice the diameter. Specimen diameters range from 38 mm to about 110 mm.
Part 8 is a major addition to this standard, namely the determination of effective stress shear strength parameters in the consolidated-drained and consolidated-undrained triaxial compression tests. Definitions: Effective
confining pressure - the difference between the cell pressure and the pore
water pressure. Effective consolidation pressure - the difference
between the cell pressure and the back pressure against which the pore fluid
drains during the consolidation stage. Failure - criteria for the stress
condition at failure are as follows: (a) maximum deviator stress, i.e. maximum;
principal stress difference; (b) maximum effective principal stress ratio; (c)
when shearing continues at constant pore pressure (undrained) or with no change
in volume (drained), in both cases at constant shear stress. Shear strength
- the shear stress on the failure plane at failure (τ_{f}), i.e. the
maximum shear resistance. Mohr circle of effective stress at failure -
the Mohr circle representing the state of effective stress at failure, the
diameter defined by points representing the major and minor effective principal
stress at failure. Effective shear strength parameters - the slope and
intercept of the Mohr-Coulomb effective stress envelope drawn to a set of Mohr
circles of effective stress at failure. Angle of shear resistance in terms
of effective stress (ø’) - the slope of the Mohr-Coulomb effective stress
envelope. Cohesion intercept in terms of effective stress (c’) - the
intercept of the Mohr-Coulomb effective stress envelope [NOTE The symbols f9and
c9 are collectively referred to as the effective shear strength parameters.] Pore
pressure coefficients A and B - changes in total stresses applied to a
specimen when no drainage is permitted produces changes in the pore pressure. Pore
pressure coefficient at failure (A - the value of the
coefficient A at failure. _{f})stress path parameters (s’, t’) - the stress
path parameters (in terms of effective stress) c.
Two methods of carrying out the compression test are given, which are as follows (a) The consolidated-undrained triaxial compression test with measurement of pore pressure. This test gives the undrained shear strength of a specimen subjected to a known initial effective stress, and the pore pressure changes during shear from which the pore pressure coefficient A can be derived. From a set of tests the effective shear strength parameters at failure, c’ and ø’, can be derived. (b) The consolidated-drained triaxial compression test with measurement of volume change. This test gives the drained shear strength, and volume change characteristics during shear, of a specimen from which the pore water is allowed to drain freely. From a set of tests the drained effective shear strength parameters at failure, c’ and ø’, can be derived. For many soils other than heavily-overconsolidated clays, the parameters c’ and ø’, determined from the two types of test, can be considered to be identical for most practical purposes, and are not differentiated in this standard. Both types of test are carried out in three stages: (1) saturation (clause 5); (2) consolidation (clause 6); (3) compression (clause 7 or 8). The first two stages saturate the specimen and bring it to the desired state of effective stress for the compression test, and are common to both types of test. The compression stage of the consolidated-undrained test is described in clause 7, and that of the consolidated-drained test in clause 8. The procedures described relate to strain-controlled apparatus for compression in a mechanical load frame, and a detachable triaxial cell. Alternatively, hydraulic triaxial cells may be used, provided that the essential principles are maintained (in which case the procedures may differ in detail).
Free drainage of pore water from the specimen is allowed. The test is run slowly enough to ensure that pore pressure changes due to shearing are negligible. The required rate of strain can be much slower than that for a consolidated-undrained test on a similar specimen under similar conditions. Since the pore pressure remains virtually constant, the effective confining pressure does not vary. The volume of pore fluid draining out of or into the specimen is measured by means of the volume change indicator in the back pressure line, and is equal to the change in volume of the specimen during shear. Pore pressure can be monitored at the base as a check on the efficacy of drainage. The test procedure described in 8.2 to 8.6 relates to a saturated specimen in the triaxial cell which has been brought to the required effective stress by consolidation in accordance with clause 6.
The methods described in this Part include major additions and have been formed into groups, according to either the purpose of the test or the mode of execution. These groups are as follows:
The methods described in this Part of this standard have been arranged in groups either according to the purpose of the test or the mode of execution. These groups are as follows. (a) Five methods for the determination of the in-situ density. (b) Three methods for the determination of penetration resistances. (c) Four methods for the determination of the vertical deformation and strength characteristics. (d) Two methods for the determination of the in-situ corrosivity characteristics.
This clause specifies five methods for determining the
in-situ density of soil, four of which use the direct measurements of mass and
volume, the choice of which depends upon the type of material, and one method
uses gamma rays. The last named also includes the measurement of moisture
content with nuclear gauges that combine both facilities.
This clause describes methods for determining three different types of penetration resistance of soil. All are empirical methods of testing the strength of soil at various depths below a particular location. The cone penetration test and the dynamic probing test are usually carried out independently of the borehole and other tests; the former being the more precise while the latter uses much simpler apparatus. The standard penetration test is for use in a borehole.
This clause describes four methods for
investigating in-situ strength and load settlement characteristics of soil. The
plate loading test (4.1) and the shallow pad maintained load test (4.2) are
particularly suited for the design of foundations or footings for buildings
where it is considered that the mass characteristics of the soil would differ
significantly from the results of laboratory tests, or where more precise
values of settlement are required. The in-situ CBR (4.3) is generally concerned
only with pavement design and the control of subgrade construction of soils
with a maximum particle size not exceeding 20 mm. The determination of the vane
shear strength of weak intact cohesive soils is described in 4.4.
This clause of the standard describes two methods
for determining in-situ the likelihood of underground corrosion of buried metal
structures. The results of these tests should be interpreted by a specialist.
The hand-scoop method has been deleted and substituted by a new test for coarse-grained soils based on a water-replacement method. Determination of in-situ density of fine-grained, medium-grained, and coarse-grained soils by attenuation of gamma rays has been added which includes moisture content determination.
The split-barrel sampler method has been revised to conform more closely to international practice. Two other test methods have been added as follows. a) Determination of the penetration resistance using fixed 60° cone and friction sleeve (the static cone test CPT). b) Determination of the dynamic probing resistance using a 90° cone (dynamic probing, DP).
Three test methods have been added as follows. a) Determination of the vertical deformation and strength characteristics of soil by the plate loading test. b) Determination of the settlement characteristics of soil for lightly loaded foundations by the shallow pad maintained-load test. c) Determination of the in-situ California Bearing Ratio (CBR).
Two test methods are given as follows. a) Determination of the in-situ apparent resistivity of soil. b) Determination of the in-situ redox potential of the soil. |