OR/12/032 Geotechnical properties - Revision history

Ajhil: /* Standard Penetration Test (SPT) results */

2021-08-06T09:52:35Z

Standard Penetration Test (SPT) results

← Older revision		Revision as of 10:52, 6 August 2021
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	The Standard Penetrometer Test (SPT) is a long-established method of in-situ geotechnical testing. This dynamic method employs a falling weight to drive a split-sampler and cutting shoe (or solid 60° cone in the case of coarse soils or soft rock) 300 mm into the ground from a position 150 mm below the base of a borehole; the initial 150 mm being the 'seating’ drive. The use of the test is described in British Standard 5930 (1999)<ref name="BS5930 1999">British Standards: BS 5930. 1981; 1999. Code of practice for site investigations. ''British Standards Institution'', BS5930. </ref> and the methodology in British Standard 1377: Part 9: Clause 3.3 (1990)<ref name="BS1377 1990"></ref>. There has been much discussion concerning the test method, test apparatus, and test interpretation (Stroud & Butler, 1975<ref name="Stroud 1975">STROUD, M A, and BUTLER, F J. 1975. The standard penetration test and the engineering properties of glacial materials. ''Proc. Symp. on the Behaviour of Glacial Materials''. Univ. of Birmingham, pp.124–135.</ref>; Stroud, 1989<ref name="Stroud 1989">STROUD, M A. 1989. The standard penetration test — its application and interpretation. pp.29–49 ''In: Proceedings of the Symposium on Penetration Testing in the UK''. University of Birmingham. (London: Thomas Telford.) </ref>). International variations in practice have been a feature of its use.		The Standard Penetrometer Test (SPT) is a long-established method of in-situ geotechnical testing. This dynamic method employs a falling weight to drive a split-sampler and cutting shoe (or solid 60° cone in the case of coarse soils or soft rock) 300 mm into the ground from a position 150 mm below the base of a borehole; the initial 150 mm being the 'seating’ drive. The use of the test is described in British Standard 5930 (1999)<ref name="BS5930 1999">British Standards: BS 5930. 1981; 1999. Code of practice for site investigations. ''British Standards Institution'', BS5930. </ref> and the methodology in British Standard 1377: Part 9: Clause 3.3 (1990)<ref name="BS1377 1990"></ref>. There has been much discussion concerning the test method, test apparatus, and test interpretation (Stroud & Butler, 1975<ref name="Stroud 1975">STROUD, M A, and BUTLER, F J. 1975. The standard penetration test and the engineering properties of glacial materials. ''Proc. Symp. on the Behaviour of Glacial Materials''. Univ. of Birmingham, pp.124–135.</ref>; Stroud, 1989<ref name="Stroud 1989">STROUD, M A. 1989. The standard penetration test — its application and interpretation. pp.29–49 ''In: Proceedings of the Symposium on Penetration Testing in the UK''. University of Birmingham. (London: Thomas Telford.) </ref>). International variations in practice have been a feature of its use.

	It was recommended (Clayton, 1995<ref name="Clayton 1995">CLAYTON, C R I. 1995. The Standard Penetration Test (SPT): Methods and use. ''Construction Industry Research and Information Association (CIRIA) Report'', No. 143.</ref>; British Standard 5930, 1990; International Society for Rock Mechanics, 1988<ref name="International Society for Rock Mechanics 1988">~~International Society for Soil Mechanics and Foundation Engineering~~. 1988. International Reference Test Procedure. Proc. ISOPT-1 Standard Penetration Test (SPT). ''International Society for Soil Mechanics and Foundation Engineering'', Vol. 1, pp.3–26. </ref>) that test results be reported in the form of six 75 mm penetration increments; the first two representing the 'seating’ drive and the final four the 'test’ drive, the sum of the latter providing the SPT 'N’ value. This is often not the case in site investigation reports, though it does form part of the Association of Geotechnical Specialists (AGS) format.		It was recommended (Clayton, 1995<ref name="Clayton 1995">CLAYTON, C R I. 1995. The Standard Penetration Test (SPT): Methods and use. ''Construction Industry Research and Information Association (CIRIA) Report'', No. 143.</ref>; British Standard 5930, 1990; International Society for Rock Mechanics, 1988<ref name="International Society for Rock Mechanics 1988">INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND FOUNDATION ENGINEERING. 1988. International Reference Test Procedure. Proc. ISOPT-1 Standard Penetration Test (SPT). ''International Society for Soil Mechanics and Foundation Engineering'', Vol. 1, pp.3–26. </ref>) that test results be reported in the form of six 75 mm penetration increments; the first two representing the 'seating’ drive and the final four the 'test’ drive, the sum of the latter providing the SPT 'N’ value. This is often not the case in site investigation reports, though it does form part of the Association of Geotechnical Specialists (AGS) format.

	The Standard Penetration Test (SPT) may be regarded as crude, but it is inexpensive and effective. In most cases site investigation reports included a record of the incremental blows and penetrations. These have been entered into the geotechnical database for analysis. The summaries presented for the SPT are derived from over 2,000 tests. The data from these tests were processed in the following stages:		The Standard Penetration Test (SPT) may be regarded as crude, but it is inexpensive and effective. In most cases site investigation reports included a record of the incremental blows and penetrations. These have been entered into the geotechnical database for analysis. The summaries presented for the SPT are derived from over 2,000 tests. The data from these tests were processed in the following stages:

Ajhil: /* Standard Penetration Test (SPT) results */

2021-08-06T09:52:00Z

Standard Penetration Test (SPT) results

← Older revision		Revision as of 10:52, 6 August 2021
Line 1,395:		Line 1,395:
	The Standard Penetrometer Test (SPT) is a long-established method of in-situ geotechnical testing. This dynamic method employs a falling weight to drive a split-sampler and cutting shoe (or solid 60° cone in the case of coarse soils or soft rock) 300 mm into the ground from a position 150 mm below the base of a borehole; the initial 150 mm being the 'seating’ drive. The use of the test is described in British Standard 5930 (1999)<ref name="BS5930 1999">British Standards: BS 5930. 1981; 1999. Code of practice for site investigations. ''British Standards Institution'', BS5930. </ref> and the methodology in British Standard 1377: Part 9: Clause 3.3 (1990)<ref name="BS1377 1990"></ref>. There has been much discussion concerning the test method, test apparatus, and test interpretation (Stroud & Butler, 1975<ref name="Stroud 1975">STROUD, M A, and BUTLER, F J. 1975. The standard penetration test and the engineering properties of glacial materials. ''Proc. Symp. on the Behaviour of Glacial Materials''. Univ. of Birmingham, pp.124–135.</ref>; Stroud, 1989<ref name="Stroud 1989">STROUD, M A. 1989. The standard penetration test — its application and interpretation. pp.29–49 ''In: Proceedings of the Symposium on Penetration Testing in the UK''. University of Birmingham. (London: Thomas Telford.) </ref>). International variations in practice have been a feature of its use.		The Standard Penetrometer Test (SPT) is a long-established method of in-situ geotechnical testing. This dynamic method employs a falling weight to drive a split-sampler and cutting shoe (or solid 60° cone in the case of coarse soils or soft rock) 300 mm into the ground from a position 150 mm below the base of a borehole; the initial 150 mm being the 'seating’ drive. The use of the test is described in British Standard 5930 (1999)<ref name="BS5930 1999">British Standards: BS 5930. 1981; 1999. Code of practice for site investigations. ''British Standards Institution'', BS5930. </ref> and the methodology in British Standard 1377: Part 9: Clause 3.3 (1990)<ref name="BS1377 1990"></ref>. There has been much discussion concerning the test method, test apparatus, and test interpretation (Stroud & Butler, 1975<ref name="Stroud 1975">STROUD, M A, and BUTLER, F J. 1975. The standard penetration test and the engineering properties of glacial materials. ''Proc. Symp. on the Behaviour of Glacial Materials''. Univ. of Birmingham, pp.124–135.</ref>; Stroud, 1989<ref name="Stroud 1989">STROUD, M A. 1989. The standard penetration test — its application and interpretation. pp.29–49 ''In: Proceedings of the Symposium on Penetration Testing in the UK''. University of Birmingham. (London: Thomas Telford.) </ref>). International variations in practice have been a feature of its use.

	It was recommended (Clayton, 1995<ref name="Clayton 1995">~~Clayton~~, C R I. 1995. The Standard Penetration Test (SPT): Methods and use. ''Construction Industry Research and Information Association (CIRIA) Report'', No. 143.</ref>; British Standard 5930, 1990; International Society for Rock Mechanics, 1988<ref name="International Society for Rock Mechanics 1988">International Society for Soil Mechanics and Foundation Engineering. 1988. International Reference Test Procedure. Proc. ISOPT-1 Standard Penetration Test (SPT). ''International Society for Soil Mechanics and Foundation Engineering'', Vol. 1, pp.3–26. </ref>) that test results be reported in the form of six 75 mm penetration increments; the first two representing the 'seating’ drive and the final four the 'test’ drive, the sum of the latter providing the SPT 'N’ value. This is often not the case in site investigation reports, though it does form part of the Association of Geotechnical Specialists (AGS) format.		It was recommended (Clayton, 1995<ref name="Clayton 1995">CLAYTON, C R I. 1995. The Standard Penetration Test (SPT): Methods and use. ''Construction Industry Research and Information Association (CIRIA) Report'', No. 143.</ref>; British Standard 5930, 1990; International Society for Rock Mechanics, 1988<ref name="International Society for Rock Mechanics 1988">International Society for Soil Mechanics and Foundation Engineering. 1988. International Reference Test Procedure. Proc. ISOPT-1 Standard Penetration Test (SPT). ''International Society for Soil Mechanics and Foundation Engineering'', Vol. 1, pp.3–26. </ref>) that test results be reported in the form of six 75 mm penetration increments; the first two representing the 'seating’ drive and the final four the 'test’ drive, the sum of the latter providing the SPT 'N’ value. This is often not the case in site investigation reports, though it does form part of the Association of Geotechnical Specialists (AGS) format.

	The Standard Penetration Test (SPT) may be regarded as crude, but it is inexpensive and effective. In most cases site investigation reports included a record of the incremental blows and penetrations. These have been entered into the geotechnical database for analysis. The summaries presented for the SPT are derived from over 2,000 tests. The data from these tests were processed in the following stages:		The Standard Penetration Test (SPT) may be regarded as crude, but it is inexpensive and effective. In most cases site investigation reports included a record of the incremental blows and penetrations. These have been entered into the geotechnical database for analysis. The summaries presented for the SPT are derived from over 2,000 tests. The data from these tests were processed in the following stages:

Ajhil: /* Standard Penetration Test (SPT) results */

2021-08-06T09:51:39Z

Standard Penetration Test (SPT) results

← Older revision		Revision as of 10:51, 6 August 2021
Line 1,393:		Line 1,393:

	===Standard Penetration Test (SPT) results===		===Standard Penetration Test (SPT) results===
	The Standard Penetrometer Test (SPT) is a long-established method of in-situ geotechnical testing. This dynamic method employs a falling weight to drive a split-sampler and cutting shoe (or solid 60° cone in the case of coarse soils or soft rock) 300 mm into the ground from a position 150 mm below the base of a borehole; the initial 150 mm being the 'seating’ drive. The use of the test is described in British Standard 5930 (1999)<ref name="BS5930 1999">British Standards: BS 5930. 1981; 1999. Code of practice for site investigations. ''British Standards Institution'', BS5930. </ref> and the methodology in British Standard 1377: Part 9: Clause 3.3 (1990)<ref name="BS1377 1990"></ref>. There has been much discussion concerning the test method, test apparatus, and test interpretation (Stroud & Butler, 1975<ref name="Stroud 1975">STROUD, M A, and BUTLER, F J. 1975. The standard penetration test and the engineering properties of glacial materials. ''Proc. Symp. on the Behaviour of Glacial Materials''. Univ. of Birmingham, pp.124–135.</ref>; Stroud, 1989<ref name="Stroud 1989">~~Stroud~~, M A. 1989. The standard penetration test — its application and interpretation. pp.29–49 ''In: Proceedings of the Symposium on Penetration Testing in the UK''. University of Birmingham. (London: Thomas Telford.) </ref>). International variations in practice have been a feature of its use.		The Standard Penetrometer Test (SPT) is a long-established method of in-situ geotechnical testing. This dynamic method employs a falling weight to drive a split-sampler and cutting shoe (or solid 60° cone in the case of coarse soils or soft rock) 300 mm into the ground from a position 150 mm below the base of a borehole; the initial 150 mm being the 'seating’ drive. The use of the test is described in British Standard 5930 (1999)<ref name="BS5930 1999">British Standards: BS 5930. 1981; 1999. Code of practice for site investigations. ''British Standards Institution'', BS5930. </ref> and the methodology in British Standard 1377: Part 9: Clause 3.3 (1990)<ref name="BS1377 1990"></ref>. There has been much discussion concerning the test method, test apparatus, and test interpretation (Stroud & Butler, 1975<ref name="Stroud 1975">STROUD, M A, and BUTLER, F J. 1975. The standard penetration test and the engineering properties of glacial materials. ''Proc. Symp. on the Behaviour of Glacial Materials''. Univ. of Birmingham, pp.124–135.</ref>; Stroud, 1989<ref name="Stroud 1989">STROUD, M A. 1989. The standard penetration test — its application and interpretation. pp.29–49 ''In: Proceedings of the Symposium on Penetration Testing in the UK''. University of Birmingham. (London: Thomas Telford.) </ref>). International variations in practice have been a feature of its use.

	It was recommended (Clayton, 1995<ref name="Clayton 1995">Clayton, C R I. 1995. The Standard Penetration Test (SPT): Methods and use. ''Construction Industry Research and Information Association (CIRIA) Report'', No. 143.</ref>; British Standard 5930, 1990; International Society for Rock Mechanics, 1988<ref name="International Society for Rock Mechanics 1988">International Society for Soil Mechanics and Foundation Engineering. 1988. International Reference Test Procedure. Proc. ISOPT-1 Standard Penetration Test (SPT). ''International Society for Soil Mechanics and Foundation Engineering'', Vol. 1, pp.3–26. </ref>) that test results be reported in the form of six 75 mm penetration increments; the first two representing the 'seating’ drive and the final four the 'test’ drive, the sum of the latter providing the SPT 'N’ value. This is often not the case in site investigation reports, though it does form part of the Association of Geotechnical Specialists (AGS) format.		It was recommended (Clayton, 1995<ref name="Clayton 1995">Clayton, C R I. 1995. The Standard Penetration Test (SPT): Methods and use. ''Construction Industry Research and Information Association (CIRIA) Report'', No. 143.</ref>; British Standard 5930, 1990; International Society for Rock Mechanics, 1988<ref name="International Society for Rock Mechanics 1988">International Society for Soil Mechanics and Foundation Engineering. 1988. International Reference Test Procedure. Proc. ISOPT-1 Standard Penetration Test (SPT). ''International Society for Soil Mechanics and Foundation Engineering'', Vol. 1, pp.3–26. </ref>) that test results be reported in the form of six 75 mm penetration increments; the first two representing the 'seating’ drive and the final four the 'test’ drive, the sum of the latter providing the SPT 'N’ value. This is often not the case in site investigation reports, though it does form part of the Association of Geotechnical Specialists (AGS) format.

Ajhil: /* Swelling & shrinkage */

2021-08-06T09:51:12Z

Swelling & shrinkage

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	The clay-dominant formations of the Lias Group are generally considered to be of ‘low’ to ‘medium’ shrink/swell potential depending on lithology and mineralogy, while the dominantly sandy formations are ‘low’. This is borne out by the database (see below).		The clay-dominant formations of the Lias Group are generally considered to be of ‘low’ to ‘medium’ shrink/swell potential depending on lithology and mineralogy, while the dominantly sandy formations are ‘low’. This is borne out by the database (see below).

	The Building Research Establishment (BRE) Digest 240 (1993)<ref name="BRE 1993">~~Building Research Establishment~~. 1993. Low-rise buildings on shrinkable clay soils. ''Building Research Establishment'', BRE Digest 240.</ref> gives a scale of susceptibility to volume change (i.e. swelling or shrinkage), or volume change ‘potential’, for over-consolidated clays in terms of a modified plasticity index, Ip' (Table 7.22).		The Building Research Establishment (BRE) Digest 240 (1993)<ref name="BRE 1993">BUILDING RESEARCH ESTABLISHMENT. 1993. Low-rise buildings on shrinkable clay soils. ''Building Research Establishment'', BRE Digest 240.</ref> gives a scale of susceptibility to volume change (i.e. swelling or shrinkage), or volume change ‘potential’, for over-consolidated clays in terms of a modified plasticity index, Ip' (Table 7.22).

	where: I<sub>p</sub>’ (modified plasticity index):		where: I<sub>p</sub>’ (modified plasticity index):

Ajhil: /* Consolidation */

2021-08-06T09:50:39Z

Consolidation

← Older revision		Revision as of 10:50, 6 August 2021
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	An over-consolidated clay is one in which the maximum previous overburden exceeds the present overburden, resulting in a denser, stronger, and less deformable soil.		An over-consolidated clay is one in which the maximum previous overburden exceeds the present overburden, resulting in a denser, stronger, and less deformable soil.

	Clays are often classified or discussed in terms of their degree of consolidation in their natural state, i.e. the natural, geological stress history. The over-consolidation of a clay is an important engineering descriptor, particularly where the degree of over-consolidation is high. Over-consolidation affects undrained shear strength, lateral stress, pore-water response, and allowable bearing pressure and settlement (Borowczyk & Szymanski, 1995<ref name="Borowczyk 1995">~~Borowczyk~~, M, and ~~Szymanski~~, A. 1995. The use of in situ tests for determination of stress history. ''Proceedings of the XI European Conference on Soil Mechanics and Foundation Engineering — The Interplay between Geotechnical Engineering and Engineering Geology'', Copenhagen. Vol. 1, pp.17–22. </ref>). It is not always possible to obtain stress-history information from standard oedometer tests, due to the fact that near-surface disturbance tends to remove the effects of over-consolidation. Disturbance may be caused by natural factors such as weathering and glaciation, whilst man-made factors might include drainage, loading, and excavation.		Clays are often classified or discussed in terms of their degree of consolidation in their natural state, i.e. the natural, geological stress history. The over-consolidation of a clay is an important engineering descriptor, particularly where the degree of over-consolidation is high. Over-consolidation affects undrained shear strength, lateral stress, pore-water response, and allowable bearing pressure and settlement (Borowczyk & Szymanski, 1995<ref name="Borowczyk 1995">BOROWCZYK, M, and SZYMANSKI, A. 1995. The use of in situ tests for determination of stress history. ''Proceedings of the XI European Conference on Soil Mechanics and Foundation Engineering — The Interplay between Geotechnical Engineering and Engineering Geology'', Copenhagen. Vol. 1, pp.17–22. </ref>). It is not always possible to obtain stress-history information from standard oedometer tests, due to the fact that near-surface disturbance tends to remove the effects of over-consolidation. Disturbance may be caused by natural factors such as weathering and glaciation, whilst man-made factors might include drainage, loading, and excavation.

	===Deformability===		===Deformability===

Ajhil: /* General */

2021-08-06T09:49:54Z

General

← Older revision		Revision as of 10:49, 6 August 2021
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	==Geotechnical data==		==Geotechnical data==
	===General===		===General===
	Geotechnical data reported in this section of the report are derived in the main from routine laboratory testing using either British Standards, e.g. British Standards: BS1377, (1990)<ref name="BS1377 1990"></ref>; BS5930 (1999)<ref name="BS5930 1999"></ref>; Head, (1992<ref name="Head 1992">HEAD, K H. 1992; 1998. Manual of Soil Laboratory Testing. (3 vols.) ''Wiley'', 2nd Ed. </ref>, 1998<ref name="Head 1998">~~Head~~, K H. 1998; 1998. Manual of Soil Laboratory Testing. (3 vols.) ''Wiley'', 2nd Ed.</ref>), or recommended British or American procedures, e.g. International Society for Rock Mechanics, ISRM (1981)<ref name="ISRM 1981">INTERNATIONAL SOCIETY FOR ROCK MECHANICS, ISRM. 1981. Rock Characterization Testing and Monitoring: ISRM Suggested Methods. Brown, E T (editor). ''Published for the Commission on Testing Methods, International Society for Rock Mechanics'',. Pergamon Press.</ref>. In general, research data are not included unless stated otherwise. Geotechnical tests on soils and rocks may be broadly sub-divided into ‘index’ and ‘mechanical’ property tests. The term ‘index’ implies a simple, rapid test, the equipment and procedure for which are recognised worldwide (e.g. liquid limit) and which can be repeated in any competent geotechnical laboratory; or a test which measures a fundamental physical property of the material (e.g. particle density). A mechanical property test may measure the behaviour of the material under certain imposed conditions (e.g. a triaxial strength test), and be more complex and time consuming. If conditions are changed the result of the test will be different. Mechanical property tests tend to require carefully prepared ‘undisturbed’ specimens. Index tests, often carried out on ‘disturbed’ or ‘bulk’ samples, tend to be used to generally characterise a deposit and to plan further testing, whereas mechanical property tests may be used for design calculations. For mechanical properties where little or no data are available (e.g. shrink/swell, permeability, durability), index tests are often used as a guide if relationships have been established elsewhere.		Geotechnical data reported in this section of the report are derived in the main from routine laboratory testing using either British Standards, e.g. British Standards: BS1377, (1990)<ref name="BS1377 1990"></ref>; BS5930 (1999)<ref name="BS5930 1999"></ref>; Head, (1992<ref name="Head 1992">HEAD, K H. 1992; 1998. Manual of Soil Laboratory Testing. (3 vols.) ''Wiley'', 2nd Ed. </ref>, 1998<ref name="Head 1998">HEAD, K H. 1998; 1998. Manual of Soil Laboratory Testing. (3 vols.) ''Wiley'', 2nd Ed.</ref>), or recommended British or American procedures, e.g. International Society for Rock Mechanics, ISRM (1981)<ref name="ISRM 1981">INTERNATIONAL SOCIETY FOR ROCK MECHANICS, ISRM. 1981. Rock Characterization Testing and Monitoring: ISRM Suggested Methods. Brown, E T (editor). ''Published for the Commission on Testing Methods, International Society for Rock Mechanics'',. Pergamon Press.</ref>. In general, research data are not included unless stated otherwise. Geotechnical tests on soils and rocks may be broadly sub-divided into ‘index’ and ‘mechanical’ property tests. The term ‘index’ implies a simple, rapid test, the equipment and procedure for which are recognised worldwide (e.g. liquid limit) and which can be repeated in any competent geotechnical laboratory; or a test which measures a fundamental physical property of the material (e.g. particle density). A mechanical property test may measure the behaviour of the material under certain imposed conditions (e.g. a triaxial strength test), and be more complex and time consuming. If conditions are changed the result of the test will be different. Mechanical property tests tend to require carefully prepared ‘undisturbed’ specimens. Index tests, often carried out on ‘disturbed’ or ‘bulk’ samples, tend to be used to generally characterise a deposit and to plan further testing, whereas mechanical property tests may be used for design calculations. For mechanical properties where little or no data are available (e.g. shrink/swell, permeability, durability), index tests are often used as a guide if relationships have been established elsewhere.

	===Density and water content===		===Density and water content===

Ajhil at 09:48, 6 August 2021

2021-08-06T09:48:15Z

Show changes

Ajhil at 10:08, 29 November 2019

2019-11-29T10:08:53Z

← Older revision		Revision as of 11:08, 29 November 2019
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	{\| class="wikitable"		{\| class="wikitable"
	<span id="Table 7.17"></span>		<span id="Table 7.17"></span>
	\|+ Table 7.17    Summary of BGS oedometer test data (Nelder & Jones, 2004<ref name="Nelder 2004">Nelder, L M, and Jones, L D. 2004. Determination of the swelling and shrinkage properties of the Lias Clay: Oedometer consolidation testing. ''British Geological Survey'', Internal Report No. IR/04/137.</ref>).		\|+ Table 7.17    Summary of BGS oedometer test data (Nelder & Jones, 2004<ref name="Nelder 2004"></ref>).
	\|- style="vertical-align:top;"		\|- style="vertical-align:top;"
	\| style="background-color: #dcdcdc;" \| '''Sample Site'''		\| style="background-color: #dcdcdc;" \| '''Sample Site'''

Ajhil: /* Consolidation */

2019-11-29T10:08:07Z

Consolidation

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	The ''rate'' at which the consolidation process takes place is characterised by the coefficient of consolidation, c<sub>v</sub> (m<sup>2</sup>/yr), and the amount of consolidation by the coefficient of volume compressibility, m<sub>v</sub> (m<sup>2</sup>/MN). Consolidation data derived from the oedometer test on undisturbed specimens are used in the calculation of likely foundation settlement, and may also provide information on the stress history, geological history, state of disturbance, permeability, and elastic moduli of clay soils.		The ''rate'' at which the consolidation process takes place is characterised by the coefficient of consolidation, c<sub>v</sub> (m<sup>2</sup>/yr), and the amount of consolidation by the coefficient of volume compressibility, m<sub>v</sub> (m<sup>2</sup>/MN). Consolidation data derived from the oedometer test on undisturbed specimens are used in the calculation of likely foundation settlement, and may also provide information on the stress history, geological history, state of disturbance, permeability, and elastic moduli of clay soils.

	The consolidation data selected for inclusion in the database are confined to oedometer tests where loading increments are doubled, as recommended in British Standards: BS1377 (1990)<ref name="BS1377 1990"></ref>. The stress range is 25 to 3,200 kPa, but with only a small proportion of tests reaching 3,200 kPa, this range is inadequate to characterise the Lias Group materials fully, but adequate for most engineering purposes. There are a total of 284 consolidation data points in the database. Statistical analyses of the coefficients of volume compressibility, mv, and coefficient of consolidation, c<sub>v</sub>, at specific stresses are shown in Appendix B. A summary of the data for specific applied stresses is shown in Table 7.15. The overall median values for cv range from 1.24 to 14.79 m<sup>2</sup>/yr. A plot of medians by Formation is shown in Figure 7.11. This reveals almost uninterrupted decreases in c<sub>v</sub> with stress increase for all Formations except the Dyrham Formation. The Dyrham Formation curve stands apart from the others with significantly higher overall values of c<sub>v</sub>, and a pattern of decreasing c<sub>v</sub> from 50 to 200 kPa but increasing c<sub>v</sub> from 200 to 3,200 kPa. Above 100 kPa, the Blue Lias, Charmouth Mudstone, Scunthorpe Mudstone, and Whitby Mudstone Formations are very closely grouped. The results place the Lias Group in the ‘medium’ cv class, typical of medium plasticity soils, with the exception of the Dyrham which is placed in the ‘high’ category, typical of low plasticity, more permeable soils (e.g. silts) (Lambe & Whitman, 1979<ref name="Lambe 1979">Lambe, T W, and Whitman, R V. 1979. Soil mechanics, SI version. ''John Wiley & Sons'' .</ref>).		The consolidation data selected for inclusion in the database are confined to oedometer tests where loading increments are doubled, as recommended in British Standards: BS1377 (1990)<ref name="BS1377 1990"></ref>. The stress range is 25 to 3,200 kPa, but with only a small proportion of tests reaching 3,200 kPa, this range is inadequate to characterise the Lias Group materials fully, but adequate for most engineering purposes. There are a total of 284 consolidation data points in the database. Statistical analyses of the coefficients of volume compressibility, mv, and coefficient of consolidation, c<sub>v</sub>, at specific stresses are shown in Appendix B. A summary of the data for specific applied stresses is shown in Table 7.15. The overall median values for cv range from 1.24 to 14.79 m<sup>2</sup>/yr. A plot of medians by Formation is shown in Figure 7.11. This reveals almost uninterrupted decreases in c<sub>v</sub> with stress increase for all Formations except the Dyrham Formation. The Dyrham Formation curve stands apart from the others with significantly higher overall values of c<sub>v</sub>, and a pattern of decreasing c<sub>v</sub> from 50 to 200 kPa but increasing c<sub>v</sub> from 200 to 3,200 kPa. Above 100 kPa, the Blue Lias, Charmouth Mudstone, Scunthorpe Mudstone, and Whitby Mudstone Formations are very closely grouped. The results place the Lias Group in the ‘medium’ cv class, typical of medium plasticity soils, with the exception of the Dyrham which is placed in the ‘high’ category, typical of low plasticity, more permeable soils (e.g. silts) (Lambe & Whitman, 1979<ref name="Lambe 1979">Lambe, T W, and Whitman, R V. 1979. Soil mechanics, SI version. ''John Wiley & Sons''.</ref>).

	<center>		<center>
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	(''note:'' Figures 7.11 and 7.12 do not represent individual test curves, but are simply a visual representation of the statistics at each stress increment). Initial void ratio medians for Formations, from the oedometer consolidation test, range from 0.52 to 0.63.		(''note:'' Figures 7.11 and 7.12 do not represent individual test curves, but are simply a visual representation of the statistics at each stress increment). Initial void ratio medians for Formations, from the oedometer consolidation test, range from 0.52 to 0.63.

	A total of 11 oedometer consolidation tests were carried out at BGS on samples of Lias Group clays undertaken as part of an assessment of shrink/swell geohazards (Nelder & Jones, 2004<ref name="Nelder 2004">Nelder, L M, and Jones, L D. 2004. Determination of the swelling and shrinkage properties of the Lias Clay: Oedometer consolidation testing. ''British Geological Survey'', Internal Report No. IR/04/137</ref>). The oedometer results, along with matching plasticity results, are summarised in Table 7.17. Plots of voids ratio vs. stress and coefficient of volume compressibility vs. stress are given in Figures 7.13 and 7.14, respectively. These data show a wide variety of behaviour, apparently unrelated to formation, with some samples having very high voids ratios and coefficients of volume compressibility at low applied stresses compared with the medians shown in Figure 7.12. This may be due to fissuring and softening caused by stress-relief, despite the use of carefully hand-prepared ‘undisturbed’ tube samples. It may be considered, however, that the use of such preparation methods has captured the true behaviour of weathered Lias Group mudstones. The oedometer results do not appear to relate to plasticity in any straightforward manner. A plot of compression index (the change in voids ratio for one log cycle of pressure change), C<sub>c</sub>, vs. liquid limit, w<sub>L</sub>, for some Lias Group formations is shown in Figure 7.15 (BGS data). Also shown are Skempton’s C<sub>c</sub> vs. w<sub>L</sub> relationships for undisturbed and remoulded soils, where C<sub>c</sub> = 0.009 (w<sub>L</sub>-10) is representative of undisturbed and C<sub>c</sub>’ = 0.007 (w<sub>L</sub>-10) of remoulded soils. The data do not conform to the Skempton relationship, though this has been found elsewhere with indurated mudrocks (Hobbs et al, 1998<ref name="Hobbs 1998">Hobbs, P R N, Hallam, J R, Forster, A, Entwisle, D C, Jones, L D, Cripps, A C, Northmore, K J, Self, S J, and Meakin, J L. 1998. Engineering geology of British rocks and soils: Mercia Mudstone (1998) by ''BGS Technical Report'' No. WN/98/4.</ref>). There are too few data with which to establish such a relationship, should it exist, for the Lias Group.		A total of 11 oedometer consolidation tests were carried out at BGS on samples of Lias Group clays undertaken as part of an assessment of shrink/swell geohazards (Nelder & Jones, 2004<ref name="Nelder 2004">Nelder, L M, and Jones, L D. 2004. Determination of the swelling and shrinkage properties of the Lias Clay: Oedometer consolidation testing. ''British Geological Survey'', Internal Report No. IR/04/137</ref>). The oedometer results, along with matching plasticity results, are summarised in Table 7.17. Plots of voids ratio vs. stress and coefficient of volume compressibility vs. stress are given in Figures 7.13 and 7.14, respectively. These data show a wide variety of behaviour, apparently unrelated to formation, with some samples having very high voids ratios and coefficients of volume compressibility at low applied stresses compared with the medians shown in Figure 7.12. This may be due to fissuring and softening caused by stress-relief, despite the use of carefully hand-prepared ‘undisturbed’ tube samples. It may be considered, however, that the use of such preparation methods has captured the true behaviour of weathered Lias Group mudstones. The oedometer results do not appear to relate to plasticity in any straightforward manner. A plot of compression index (the change in voids ratio for one log cycle of pressure change), C<sub>c</sub>, vs. liquid limit, w<sub>L</sub>, for some Lias Group formations is shown in Figure 7.15 (BGS data). Also shown are Skempton’s C<sub>c</sub> vs. w<sub>L</sub> relationships for undisturbed and remoulded soils, where C<sub>c</sub> = 0.009 (w<sub>L</sub>-10) is representative of undisturbed and C<sub>c</sub>’ = 0.007 (w<sub>L</sub>-10) of remoulded soils. The data do not conform to the Skempton relationship, though this has been found elsewhere with indurated mudrocks (Hobbs et al, 1998<ref name="Hobbs 1998"></ref>). There are too few data with which to establish such a relationship, should it exist, for the Lias Group.

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Ajhil at 10:05, 29 November 2019

2019-11-29T10:05:27Z

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	It is difficult to give typical or average values of strength for the Lias Group, or individual Formations and Members within it, because of the variability of lithology, fabric, structure, and cementation and the post-depositional processes of weathering and consolidation it has undergone. This results in variable depth profiles for intact strength on a scale of metres or centimetres, whether these are determined in-situ or in the laboratory. It should be borne in mind that the great majority of data within the Lias Group database are from ‘routine’ engineering investigations where samples are taken at relatively shallow depths, either from trial pits or from shallow drilling; over 75% of the triaxial strength data are derived from sample depths less than 10 m. At depths greater than 20 m the absence of weathering and other stress-relief factors means that the strength of the rock mass tends to be much greater than is represented here in the database. In some cases one or even two orders of magnitude difference may be anticipated, depending on the precise nature of the strength test (Haydon & Hobbs, 1977<ref name="Haydon 1977">Haydon, R E V, and Hobbs, N B. 1977. The effect of uplift pressures on the performance of a heavy foundation on layered rock. ''Proc. Conf. Rock Engineering'', Newcastle, pp.457–472. </ref>).		It is difficult to give typical or average values of strength for the Lias Group, or individual Formations and Members within it, because of the variability of lithology, fabric, structure, and cementation and the post-depositional processes of weathering and consolidation it has undergone. This results in variable depth profiles for intact strength on a scale of metres or centimetres, whether these are determined in-situ or in the laboratory. It should be borne in mind that the great majority of data within the Lias Group database are from ‘routine’ engineering investigations where samples are taken at relatively shallow depths, either from trial pits or from shallow drilling; over 75% of the triaxial strength data are derived from sample depths less than 10 m. At depths greater than 20 m the absence of weathering and other stress-relief factors means that the strength of the rock mass tends to be much greater than is represented here in the database. In some cases one or even two orders of magnitude difference may be anticipated, depending on the precise nature of the strength test (Haydon & Hobbs, 1977<ref name="Haydon 1977">Haydon, R E V, and Hobbs, N B. 1977. The effect of uplift pressures on the performance of a heavy foundation on layered rock. ''Proc. Conf. Rock Engineering'', Newcastle, pp.457–472. </ref>).

	Undrained (total) triaxial strength data are reported in site investigations either with the assumption that the friction angle, Φ, is zero, or that it has a positive value, despite this being contrary to the principles of the test (Head, 1992<ref name="Head 1992"></ref>; 1998<ref name="Head 1998">~~Head, K H. 1992; 1998. Manual of Soil Laboratory Testing. (3 vols.) ''Wiley'', 2nd Ed.~~ </ref>). Undrained strength data containing a positive friction angle have been omitted from the database. A total of 2,965 results were obtained for c<sub>u</sub>, and 204 for c' and Φ'. A summary of triaxial test median values for these strength parameters is given in Table 7.12.		Undrained (total) triaxial strength data are reported in site investigations either with the assumption that the friction angle, Φ, is zero, or that it has a positive value, despite this being contrary to the principles of the test (Head, 1992<ref name="Head 1992"></ref>; 1998<ref name="Head 1998"></ref>). Undrained strength data containing a positive friction angle have been omitted from the database. A total of 2,965 results were obtained for c<sub>u</sub>, and 204 for c' and Φ'. A summary of triaxial test median values for these strength parameters is given in Table 7.12.

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