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Spent oil shale use in earthwork construction
Engineering Geology 60 (2001) 285±294
www.elsevier.nl/locate/enggeo
Spent oil shale use in earthwork construction M.G. Winter* TRL Limited, Heriot-Watt Research Park, Riccarton, Edinburgh, EH14 4AP, UK Accepted for publication 8 March 2000
Abstract Spent oil shale (or blaes) is a potentially valuable engineering material and is present in large quantities in the West Lothian area of Scotland. It can be used successfully as general ®ll or capping layer. However, due to its high quality it may be more suited to use as selected granular ®ll or sub-base. In particular, cement stabilisation will reduce frost susceptibility and may be a particularly appropriate outlet for spent oil shale for use as sub-base. However, an increase in control and testing may be required, having an effect on the cost of using such materials. Conditions under which spent oil shale should not be used are also identi®ed. q 2001 TRL. Published by Elsevier Science B.V. All rights reserved. Keywords: Spent oil shale; Earthwork construction; Granular ®ll
1. Introduction The oil shale industry in the West Lothian area of Central Scotland was founded on James Young's invention of a process for obtaining oil from bituminous coal. The industry began in 1851 and reached its peak in 1913, before closure of the last oil shale mine in 1962. The legacy of this industry is an estimated 100 million tonnes of processed, or spent, oil shale stored in around 30 tips, locally known as bings. Some of the bings have been landscaped and integrated into the surrounding environment as distinctive visual features and, in one case, a nature reserve has been created. Nonetheless a great deal of spent oil shale remains available for reuse in construction works to the bene®t of the areas surrounding the bings. The potential uses of spent oil shale (or blaes) in road construction include general ®ll, selected granular ®ll, capping and sub-base. The Speci®cations for * Tel.: 144-131-449-3377; fax: 144-131-449-3111. E-mail address: [email protected] (M.G. Winter).
these materials are given in the Manual of Contract Documents for Highway Works (MCHW 1). The chemical and physical properties of spent oil shale are described and each potential application is examined in this context and that of the speci®cation. Conditions under which spent oil shale should not be used are also identi®ed. Broad conclusions are drawn within the environmental and economic contexts.
2. The oil shale industry The oil shale industry in Scotland was founded on James `Paraf®n' Young's invention of a process for obtaining oil from bituminous coal. This was achieved by a two-stage process involving low temperature distillation followed by further re®nement of the oil by distillation and chemical treatment (British Patent No. 13292). The industry began in 1851 and reached its peak output in 1913 when 3.3 million tonnes of oil shale was extracted, producing an estimated 73
0013-7952/01/$ - see front matter q 2001 TRL. Published by Elsevier Science B.V. All rights reserved. PII: S 0013-795 2(00)00109-5
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M.G. Winter / Engineering Geology 60 (2001) 285±294
Fig. 1. Location map of spent oil shale bings.
million gallons of crude oil and naptha. The industry declined rapidly after the First World War and in 1938 less than half the quantity of oil shale was mined compared to the peak. Despite a brief recovery, during the Second World War, the last Scottish oil shale was mined at Bathgate in May 1962. Kerr (1994) provides an excellent reference on this subject. The oil shale exists in a layer around 900 m thick and forms part of the Carboniferous sandstone series. It lies below the coal and limestone beds that were worked in Lothian and Lanarkshire, but above the
volcanics that form, for example, Arthur's Seat in Edinburgh. Accessible shales with recoverable amounts of oil were found in West Lothian, parts of Midlothian, Lanarkshire and Fife. The unprocessed shale consisted of tough, ®negrained, thinly laminated material and was generally brown or black in colour. It had a rubber-like consistency and was identi®ed by miners by its ability to be pared with a knife and to leave a brown streak when rubbed. The spent oil shale, together with materials
M.G. Winter / Engineering Geology 60 (2001) 285±294
287
Fig. 2. Five Sisters spent oil shale bing, near West Calder, West Lothian.
considered unsuitable for processing, was deposited in spoil heaps, or bings, on land adjacent to the mines and re®neries. The locations of the bings are illustrated in Fig. 1 and the Five Sisters bing, near West Calder, is pictured in Fig. 2. In 1962 it was estimated that between 100 and 150 million tonnes of such material was stored in 30 bings (Burns, 1978). More recent estimates indicate that around 100 million tonnes of spent oil shale occupy an area of 395 hectares of land around Livingston and Bathgate, about 20 km to the west of Edinburgh (Whitbread et al., 1991; Sherwood, 1994).
3. Chemical and physical properties 3.1. Chemical properties Studies indicate that spent oil shale can vary in colour from pink, red and yellow to dark blue (Lake et al.,1966; Burns, 1978). The typical chemical composition of spent oil shale is given in Table 1 (data for burnt colliery spoil is given for comparison). The range of water soluble sulphate contents for spent oil shale has been reported as between 2.2%(SO3) and 2.8%(SO3), with one value
Table 1 Typical chemical compositions of spent oil shale and burnt colliery spoil Chemical component
SiO2 Al2O3 FE2O3 CaO MgO Na2O K2 O SO3 Loss on ignition (%)
Composition (%) Spent oil shale (Burns, 1978)
Burnt colliery spoil (Sherwood and Ryley, 1970)
48.5 25.2 12.1 5.3 2.2 Not recorded Not recorded 3.2 3
45±60 21±31 4±13 0.5±6 1±3 0.2±0.6 2±3.5 0.1±5 2±6
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3.2. Physical properties
of 0.7% (Burns, 1978), and is similar to the range for burnt colliery spoil (Sherwood, 1994). There appears to be an ambiguity in the standard (Anon, 1975) used to determine the values of sulphate content. after some study and debate it appears most likely that the values quoted by Burns (1978) should be reported in units of g(SO3)/l. More recent work indicates that sulphate contents may be lower (Winter and Butler, 1999), although still at a level to cause some concern. Consequently, sulphates may cause problems by migrating from the shale and reacting with lime, concrete, cement bound or other cementitious materials (MCHW 1). Problems are also likely to arise if spent oil shale is placed in contact with metallic objects (Winter and Butler, 1999). Because the shale was heated to extract the oil, spontaneous combustion is clearly not a problem. Neither is the presence of sulphides as these will have been driven off or converted to sulphates during the extraction process (Sherwood, 1994).
Fine
CLAY 100
Medium SILT
Coarse
Considerable variations are commonly found in the physical properties of spent oil shales, particularly the grading. However, Burns (1978) noted that the particle size distributions for such materials were generally within the grading limits for Type 2 (Fig. 3) granular sub-base materials (Speci®cation for Road and Bridge Works, 1976) and were very close to the requirements for Type 1 granular sub-base materials. (These limits are essentially the same as those in MCHW 1.) Burns (1978) reported the results of standard 2.5 kg rammer compaction tests. These indicated maximum dry densities in the range from 1.30 to 1.44 Mg/m 3 and optimum moisture contents in the range 22± 34%. The relatively high optimum moisture contents and correspondingly low maximum dry densities were probably due to the porous nature of the material. This is supported by the high values of water absorption (10±21%) and the low particle densities for the size range from 2.4 to 37.5 mm (2.06±2.42 Mg/m 3).
Fine
Medium SAND
Coarse
Fine
Medium Coarse COBBLES GRAVEL
Type A Type B
Percentage passing (%)
80
Type C Type D Type E
60
Grading Limits for Type 2 Sub-base (MCHW 1) 40
20
0
0.0001
0.001
0.01
0.1 Sieve size (mm)
1
Fig. 3. Particle size distributions of samples of spent oil shale (after Burns, 1978).
10
100
M.G. Winter / Engineering Geology 60 (2001) 285±294 Fine
CLAY 100
Medium SILT
Coarse
Fine
Medium SAND
Coarse
289 Fine
Medium Coarse COBBLES GRAVEL
Before compaction After standard compaction 80
Percentage passing (%)
After heavy compaction
60
40
20
0
0.0001
0.001
0.01
0.1 Sieve size (mm)
1
10
100
Fig. 4. Typical effect of compaction on the grading of spent oil shale (after Burns, 1978).
Particle densities for sizes smaller than 2.4 mm were between 2.58 and 2.76 Mg/m 3. The degree of crushing, or fragmentation, that will occur during the compaction of a granular material generally depends upon the original particle size distribution, the crushing strength of the grains, and the stress level applied. Essentially, if a brittle particle is subjected to a stress in excess of its ultimate strength it will break. The stress may place the particle in tension, compression, ¯exure, shear or torsion. In addition, a particle may be worn away by another particle: that is, subjected to attrition. Burns (1978) observed that spent oil shale was subject to crushing as a result of the compaction process (Fig. 4). While fragmentation during compaction is often viewed as a problem, crushing may confer bene®ts to the compacted mass. Small particles resulting from crushing may ®ll voids and thus produce higher densities and lower air voids than would otherwise be the case. This will, in turn, tend to produce a more stable compacted mass. The fragmentation of earthwork materials is discussed in more detail by Winter (1998).
Most spent oil shales are frost susceptible and therefore should not be placed within 450 mm of the road surface. However, the addition of cement reduces the frost susceptibility. Burns (1978) observed that the addition of 5% cement reduced the voids content and, thus, the frost induced heave to acceptable levels for the materials tested. However, he did note that larger proportions of cement might be required for materials from some spent oil shale sources to reduce heave to acceptable levels.
4. Use of spent oil shale 4.1. Historical use Spent oil shale bings may contain both spent oil shale and material excavated from non-oil bearing areas. The heating of oil shale produces a stable granular material that can be used in place of natural aggregates. The optimum use of spent oil shale is as a selected granular ®ll or as an unbound granular subbase although it could be used as general ®ll.
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M.G. Winter / Engineering Geology 60 (2001) 285±294
Nevertheless, Burns (1978) estimated that some 20±25 million tonnes of spent oil shale had been used in Central Scotland as general ®ll since the early 1960s, principally on the M8, M9 and M90 motorways. It has also been used in other bulk ®ll applications such as the Edinburgh airport runway, where some 200,000 tonnes were placed. More recently some 15,000 m 3 were place as general ®ll during the construction of the underpass at the M8/ M9 Newbridge interchange. Small quantities of spent oil shale have also been used as general ®ll on other recent road construction projects in Central Scotland. Stabilising spent oil shale with cement on a pre-mixed basis has proved commercially viable and Burns estimated that some 0.5±1.0 million tonnes had been so used, including as sub-base on the M9 motorway. 4.2. General ®ll The assessment of acceptability for general ®ll should be by conventional means. For a granular material such as spent oil shale this is generally by control of the moisture content within set limits of the optimum moisture content (see MCHW 1, Table 6/1). However, given that spent oil shale is generally acceptable for use as selected ®ll it may be uneconomic to use these materials as general ®ll. 4.3. Selected granular ®ll Spent oil shale is susceptible to crushing during compaction (Fig. 4). However, crushing may yield higher densities and lower air voids than would otherwise be the case, thus tending to produce a more stable compacted mass. Indeed, this indicates one barrier to the use of spent oil shale (and burnt colliery spoil) as selected granular ®ll. Previous speci®cations have relaxed the 10% ®nes value required for well burnt non-plastic shale sub-bases (Speci®cation for Road and Bridge Works, 1976; Burns, 1978) but the current Speci®cation (MCHW 1) retains a requirement for a minimum 10% ®nes value of 50 kN. Such a requirement is unlikely to be met by many spent oil shales and Dawson (1989) described the 10% ®nes value as too severe a test of the ability of well-graded aggregates to withstand compaction stresses. There is a strong argument for reducing the 10% ®nes value requirement for spent oil shale, provided that the
compacted material is within the particle size distribution limits de®ned in the speci®cation. 4.4. Capping layer The Speci®cation (MCHW 1) allows spent oil shale to be used as granular capping, provided that the grading and other speci®cation requirements are met. However, as for selected granular ®lls, the 10% ®nes value requirement (30 kN in this case) is unlikely to be met. Similar arguments may be applied to relaxing the 10% ®nes value as are made above for selected granular ®ll. While spent oil shale may be stabilised to form a capping layer there would generally be little reason for doing so as it would be suitable for use in an unbound form (Sherwood, 1994). The only exception to this would be if the capping layer were within 450 mm of the completed road surface as many spent oil shales are highly frost susceptible and thus cannot be in such a location. The addition of 5% or more cement has been shown to reduce the frost susceptibility to acceptable levels (Burns, 1978). Frost susceptibility is related to voids content and the use of cement reduces the voids content while having the added bene®t of increasing the inter-particle strength. For this reason, many sub-bases constructed from spent oil shale have been stabilised with cement. Such a treatment will be suitable only for materials with low sulphate contents (HA74 Ð DMRB 4.1.6) when ordinary portland cements are used. However, the use of sulphate resisting cements may prove effective with higher sulphate materials. To ensure that the material is not susceptible to heave as a result of the reactions between sulphates and the cement it would be prudent to use the durability test given in the Speci®cation (MCHW 1, Clause 1036) for CBM1. However, as the frequency of testing may have to be increased, such a process may become uneconomical. The use of sulphate resisting cements may prove effective with higher sulphate materials. Comprehensive warnings have been given on the damage caused by mixing high sulphate materials with cement and lime (Perry et al., 1996a,b). 4.5. Sub-base Fig. 3 shows spent oil shale can be obtained to satisfy the grading requirements of granular
M.G. Winter / Engineering Geology 60 (2001) 285±294
291
Earthworks No
Will use be environmentally beneficial ?
Reject and seek alternative No
No
Yes
Landscape and non-structural uses
Will waste material be cheaper than other material ? Yes
Do quantified environmental benefits outweigh extra costs ?
Yes
Is material likely to suffer spontaneous combustion when compacted ?
No
Is material frozen ?
Pursue further use
Embankments and other structural fill
Reject for use in roadworks
Yes
Consider use in landscaping
Reject or allow to thaw
Yes
No Does material meet plasticity requirements?
No
Yes No Does material meet moisture content requirements ?
Allow to dry
Yes Does material contain excess sulphates ?
Yes
Will material be used within 450mm of concrete ?
Yes
No No Does material meet specification requirements in other respects ?
No
Yes
Use in embankments and structural fill
Fig. 5. Determining the potential use of waste materials in earthworks construction (after Anon, 1985; Sherwood, 1994).
sub-base materials and can therefore satisfy the more relaxed criteria for selected granular materials. Wellburnt colliery spoil is mentioned by name in the Speci®cation (MCHW 1) for many selected granular ®ll applications. However, Clauses 803 and 804 of the Speci®cation (MCHW 1), which refer to granular subbase, allow ªwell burnt non-plastic shaleº which embraces both burnt colliery spoil and spent oil shale. The clauses for selected granular ®ll could usefully be phrased in the same manner rather than speci®cally requiring burnt colliery spoil (Sherwood, 1994), effectively excluding spent oil shale. Similarly,
where burnt colliery spoil is excluded then it would be prudent to also exclude spent oil shale by the use of the phrase ªwell burnt non-plastic shaleº. Burns (1978) noted that in the Speci®cation for Road and Bridge Works (1976) sub-base materials, with the exception of well burnt non-plastic shales, were required to have a minimum 10% ®nes value of 50 kN. This exception speci®cally acknowledged that crushing could occur with this material with no apparent structural disbene®t to the completed subbase. Under the current Speci®cation (MCHW 1) well-burnt non-plastic shales are speci®cally included
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M.G. Winter / Engineering Geology 60 (2001) 285±294
in the allowable materials but the exception to the minimum 10% ®nes value of 50 kN has been removed. Sherwood (1995a,b) notes that although many burnt colliery spoils, and by implication spent oil shales, would be suitable for such a use it is unlikely that many would achieve a 10% ®nes value of 50 kN. Further, it is quite possible that a more stable material may result as voids are ®lled with the smaller particles created by crushing. Similar arguments may be applied to relaxing the 10% ®nes value as are made above for selected granular ®ll and capping layer. 4.6. Other considerations Visual inspection of spent oil shale at the tip is required to ensure that the material delivered to site does not vary too frequently. It is important that all design and speci®cation tests should be carried out on the material in the crushed, post-compaction state, not on the excavated or delivered material. If spent oil shale is to be placed within 500 mm of metallic items, lime, concrete, cement bound or other cementitious materials then the limits in the Speci®cation (MCHW 1, Clauses 601.13 and 601.14) apply. It seems unlikely that it could be used in close proximity to such materials given the high sulphate content of many spent oil shales. Care is also required if spent oil shale is to be stabilised using cement. For lower sulphate materials it may be possible to use ordinary Portland cement. However, for higher sulphate materials sulphate resisting cements may be required. Doubts also remain as to the potential reactions between spent oil shale and polymeric reinforcing materials. Notwithstanding the above comments on frost susceptibility and the interaction with cementitious products, the durability of spent oil shales is unlikely to pose a problem. However, it is nonetheless important to ensure that compaction is suf®cient to minimise the air voids of the earthworks and that the requirements of MCHW 1 (Clause 602.15) are followed to ensure that water ingress does not cause a long-term durability problem. 5. Discussion The transport of waste materials, such as spent oil
shale, to site incurs a cost for haulage. If a waste material is not available within an economic haulage distance of the site then it may be rejected on economic grounds. It is generally accepted that the maximum economic haulage distance for the import of waste materials will depend on a number of factors, including the following: ² the location and nature of the site; ² the location and nature of the waste material source; ² the method of transport; ² the relative costs of the waste material and its alternative. However, if the waste material is located within economic haulage of the site then its use should be considered and the factors to be taken into account are summarised in Fig. 5. The advantages of using waste materials are: ² removal of waste tips; ² avoidance of borrow pits and consequent savings in the ®nite sources of natural aggregates; and ² avoidance of liability for land®ll tax (where appropriate). It should, however, be noted that it is seldom possible to remove all of a tip due to the mix of materials contained therein. Indeed, planning permission is generally required to remove material from an old tip due to the possibility of aggravating the existing dereliction of an area. In some cases, landscaping a tip to sympathetically blend into the local area may be a more environmentally bene®cial solution than seeking engineering uses for the materials contained therein (Sherwood, 1994). The disadvantages of using waste materials are: ² increased haulage costs; ² disturbance caused by haulage; and ² greater variability of waste materials. Increased haulage costs are almost certain to be a factor in the substitution of waste materials for sitewon bulk ®ll and, for some materials, haulage costs may increase if waste materials are used. This will however depend upon the relative locations of the
M.G. Winter / Engineering Geology 60 (2001) 285±294
waste materials and borrow-pits or quarries from which the selected ®lls would otherwise be obtained. If haulage costs are increased by the use of waste ®lls then the disturbance caused by haulage will also increase and environmental disbene®ts will accrue if public roads are used. These disbene®ts will include congestion, noise, pollution, dust and deposition of the material along the haulage route. Such disbene®ts are, with the exception of congestion, dif®cult to price and are frequently ignored by engineers. Inspection of waste materials, such as spent oil shale, at the tip is one means of managing their potentially greater variability compared to conventional materials. Clearly a blend between economic and environmental bene®ts must be achieved if waste materials are to be successfully used in road construction. Without an economic bene®t contractors will not be encouraged to use waste materials. If some economic bene®t exists then it is important that environmental bene®ts can be demonstrated by their use. Such bene®ts might include savings in the use of ®nite natural aggregate resources. Designers should identify sources of waste materials and allow contractors to select on an economic basis, within the prevailing environmental legislation (HA44 Ð DMRB 4.1.1). 6. Summary The crushing of particles during compaction is often viewed as a problem. However, crushing may confer bene®ts to the compacted mass. Small particles resulting from crushing may ®ll voids and thus produce higher densities and lower air voids than would otherwise be the case. This will, in turn, tend to produce a more stable compacted mass. Spent oil shale can be used successfully as general ®ll. However, due to its high quality as aggregates it is more suited to use as selected granular ®ll. In particular, given its frost susceptibility, stabilisation as sub-base seems a particularly appropriate outlet for this material. However, it would be prudent to use the chemical durability test given in the Speci®cation (MCHW 1, Clause 1036) for CBM1 to ensure that the material is not susceptible to heave as a result of the reactions between sulphates and the cement. Spent oil shale can be obtained to satisfy the grad-
293
ing requirements of granular sub-base materials and can therefore satisfy the more relaxed criteria for selected granular materials. The relevant clause of the Speci®cation for granular sub-base refers to ªwell burnt non-plastic shaleº which embraces both spent oil shale and burnt colliery spoil. The clauses for selected granular ®ll refer speci®cally to well-burnt colliery spoil whether including or excluding such materials from use. In either case spent oil shale is not covered, effectively disallowing its use where it could be used and allowing its use where it should not be used. The minimum 10% ®nes value requirement of 50 kN for granular sub-base materials is severe. In previous speci®cations this requirement was waived for burnt non-plastic shales, such as spent oil shale. although limited crushing during compaction will tend to produce a more stable compacted mass many such materials will be deemed unsuitable on the basis of the 10% ®nes value. The minimum 10% ®nes value of 30 kN required for some classes of capping layer also seems severe. Spent oil shales generally have high sulphate contents. Consequently, these materials are unlikely to be suitable for use close to concrete structures or metallic items. There also remain doubts as to the potential reactions between spent oil shales with high sulphate contents and polymeric reinforcing materials. Clearly a blend between economic and environmental bene®ts must be achieved if waste materials are to be successfully used in road construction. Without an economic bene®t contractors will not be encouraged to use waste materials. Designers should identify sources of waste materials and allow contractors to select on an economic basis, within the prevailing environmental legislation. If some economic bene®t exists then it is important that environmental bene®ts can be demonstrated by their use. Such bene®ts might include savings in the use of ®nite natural aggregate resources. Acknowledgements The author is grateful to R.A. Snowdon (TRL) for helpful discussions and suggestions. Dr J. Perry, Dr G.D. Matheson and P. McMillan variously performed
294
M.G. Winter / Engineering Geology 60 (2001) 285±294
the technical and quality audits for this report; the author is grateful for their helpful and constructive suggestions. The work described in this paper forms part of a Scottish Of®ce Development Department research programme and the paper is published by permission of the Scottish Of®ce and the Chief Executive of TRL Limited q TRL Limited 2001. This report has been produced by the TRL Limited, under a contract placed by the Scottish Of®ce and the Department of the Environment, Transport and the Regions. any views expressed in it are not necessarily those of either Department. References Anon, 1975. Methods of Test for Sols for Civil Engineering Purposes, BS1377. British Standards Institution, London. Anon, 1985. Guide to the Use of Industrial By-Products and Waste Materials in Building and Civil Engineering, BS6543. British Standards Institution, London. Burns, J., 1978. The Use of Waste and Low-Grade Materials in Road Construction: 6. Spent Oil Shale. TRRL Laboratory Report LR 818. Transport Research Laboratory, Crowthorne. Dawson, A.R., 1989. The Degradation of Furnace Bottom Ash under Compaction. Unbound Aggregates in Roads: UNBAR 3, Butterworths, London, 169±174. HA 44 Ð Earthworks: Design and Preparation of Contract Documents (DMRB 4.1.1). Design Manual for Roads and Bridges. The Stationery Of®ce, London. HA 74 Ð Design and Construction of Lime Stabilised Capping Layers (DMRB 4.1.6). Design Manual for Roads and Bridges. The Stationery Of®ce, London. Kerr, D., 1994. Shale Oil Scotland: The World's Pioneering Oil Industry. Scotch Publishing, Edinburgh. Lake, J., Fraser, C.K., Burns, J., 1966. Investigation of the physical
and chemical properties of spent oil shale. Roads and Road Construction 44 (522), 155±159. Manual of Contract Documents for Highway Works (MCHW 1). Speci®cation for Highway Works (December 1991, reprinted August 1993 and August 1994 with amendments), vol. 1. The Stationery Of®ce. London. Perry, J., MacNeil, D.J., Wilson, P.E., 1996a. The Uses of Lime in Ground Investigation: a Review of Work Undertaken at the Transport Research Laboratory. Lime Stabilisation. Thomas Telford, London. Perry, J., Snowdon, R.A., Wilson, P.E., 1996b. Site Investigation for Lime Stabilisation of Highway Works. Advances in Site Investigation Practice. Thomas Telford, London, 85±96. Sherwood, P.T., 1994. The Use of Waste Materials in Fill and Capping Layers. TRL Contractor Report CR 353. Transport Research Laboratory, Crowthorne. Sherwood, P.T., 1995a. The Use of Waste and Recycled Materials in Roads. Proceedings, Institution of Civil Engineers, 111(2). Thomas Telford, London, 116±124. Sherwood, P.T., 1995b. Alternative Materials in Road Construction: a Guide to the Use of Waste, Recycled Materials and ByProducts. Thomas Telford, London. Sherwood, P.T., Ryley, M.D., 1970. The Effect of Sulphates In Colliery Shale on its Use for Roadmaking. TRRL Laboratory Report LR 324. Transport Research Laboratory, Crowthorne. Speci®cation for Road and Bridge Works, 1976. Fifth Edition. Department of Transport, Scottish Development Department, Welsh Of®ce, Department of the Environment for Northern Ireland. The Stationery Of®ce. London. Whitbread, M., Marsey, A., Tannel, C., 1991. Occurrence and the Utilisation of Mineral and Construction Wastes. The Stationery Of®ce, London (Department of the Environment). Winter, M.G., 1998. The Determination of the Acceptability of Selected Fragmenting Materials for Earthworks Compaction. TRL Report 308. Transport Research Laboratory, Crowthorne. Winter, M.G., Butler, A.M., 1999. Stainless steel corrosion in spent oil shale. Ground Engineering, September, 28. (Associated Discussion December 1999, 7 and January 2000, 6.)
www.elsevier.nl/locate/enggeo
Spent oil shale use in earthwork construction M.G. Winter* TRL Limited, Heriot-Watt Research Park, Riccarton, Edinburgh, EH14 4AP, UK Accepted for publication 8 March 2000
Abstract Spent oil shale (or blaes) is a potentially valuable engineering material and is present in large quantities in the West Lothian area of Scotland. It can be used successfully as general ®ll or capping layer. However, due to its high quality it may be more suited to use as selected granular ®ll or sub-base. In particular, cement stabilisation will reduce frost susceptibility and may be a particularly appropriate outlet for spent oil shale for use as sub-base. However, an increase in control and testing may be required, having an effect on the cost of using such materials. Conditions under which spent oil shale should not be used are also identi®ed. q 2001 TRL. Published by Elsevier Science B.V. All rights reserved. Keywords: Spent oil shale; Earthwork construction; Granular ®ll
1. Introduction The oil shale industry in the West Lothian area of Central Scotland was founded on James Young's invention of a process for obtaining oil from bituminous coal. The industry began in 1851 and reached its peak in 1913, before closure of the last oil shale mine in 1962. The legacy of this industry is an estimated 100 million tonnes of processed, or spent, oil shale stored in around 30 tips, locally known as bings. Some of the bings have been landscaped and integrated into the surrounding environment as distinctive visual features and, in one case, a nature reserve has been created. Nonetheless a great deal of spent oil shale remains available for reuse in construction works to the bene®t of the areas surrounding the bings. The potential uses of spent oil shale (or blaes) in road construction include general ®ll, selected granular ®ll, capping and sub-base. The Speci®cations for * Tel.: 144-131-449-3377; fax: 144-131-449-3111. E-mail address: [email protected] (M.G. Winter).
these materials are given in the Manual of Contract Documents for Highway Works (MCHW 1). The chemical and physical properties of spent oil shale are described and each potential application is examined in this context and that of the speci®cation. Conditions under which spent oil shale should not be used are also identi®ed. Broad conclusions are drawn within the environmental and economic contexts.
2. The oil shale industry The oil shale industry in Scotland was founded on James `Paraf®n' Young's invention of a process for obtaining oil from bituminous coal. This was achieved by a two-stage process involving low temperature distillation followed by further re®nement of the oil by distillation and chemical treatment (British Patent No. 13292). The industry began in 1851 and reached its peak output in 1913 when 3.3 million tonnes of oil shale was extracted, producing an estimated 73
0013-7952/01/$ - see front matter q 2001 TRL. Published by Elsevier Science B.V. All rights reserved. PII: S 0013-795 2(00)00109-5
286
M.G. Winter / Engineering Geology 60 (2001) 285±294
Fig. 1. Location map of spent oil shale bings.
million gallons of crude oil and naptha. The industry declined rapidly after the First World War and in 1938 less than half the quantity of oil shale was mined compared to the peak. Despite a brief recovery, during the Second World War, the last Scottish oil shale was mined at Bathgate in May 1962. Kerr (1994) provides an excellent reference on this subject. The oil shale exists in a layer around 900 m thick and forms part of the Carboniferous sandstone series. It lies below the coal and limestone beds that were worked in Lothian and Lanarkshire, but above the
volcanics that form, for example, Arthur's Seat in Edinburgh. Accessible shales with recoverable amounts of oil were found in West Lothian, parts of Midlothian, Lanarkshire and Fife. The unprocessed shale consisted of tough, ®negrained, thinly laminated material and was generally brown or black in colour. It had a rubber-like consistency and was identi®ed by miners by its ability to be pared with a knife and to leave a brown streak when rubbed. The spent oil shale, together with materials
M.G. Winter / Engineering Geology 60 (2001) 285±294
287
Fig. 2. Five Sisters spent oil shale bing, near West Calder, West Lothian.
considered unsuitable for processing, was deposited in spoil heaps, or bings, on land adjacent to the mines and re®neries. The locations of the bings are illustrated in Fig. 1 and the Five Sisters bing, near West Calder, is pictured in Fig. 2. In 1962 it was estimated that between 100 and 150 million tonnes of such material was stored in 30 bings (Burns, 1978). More recent estimates indicate that around 100 million tonnes of spent oil shale occupy an area of 395 hectares of land around Livingston and Bathgate, about 20 km to the west of Edinburgh (Whitbread et al., 1991; Sherwood, 1994).
3. Chemical and physical properties 3.1. Chemical properties Studies indicate that spent oil shale can vary in colour from pink, red and yellow to dark blue (Lake et al.,1966; Burns, 1978). The typical chemical composition of spent oil shale is given in Table 1 (data for burnt colliery spoil is given for comparison). The range of water soluble sulphate contents for spent oil shale has been reported as between 2.2%(SO3) and 2.8%(SO3), with one value
Table 1 Typical chemical compositions of spent oil shale and burnt colliery spoil Chemical component
SiO2 Al2O3 FE2O3 CaO MgO Na2O K2 O SO3 Loss on ignition (%)
Composition (%) Spent oil shale (Burns, 1978)
Burnt colliery spoil (Sherwood and Ryley, 1970)
48.5 25.2 12.1 5.3 2.2 Not recorded Not recorded 3.2 3
45±60 21±31 4±13 0.5±6 1±3 0.2±0.6 2±3.5 0.1±5 2±6
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M.G. Winter / Engineering Geology 60 (2001) 285±294
3.2. Physical properties
of 0.7% (Burns, 1978), and is similar to the range for burnt colliery spoil (Sherwood, 1994). There appears to be an ambiguity in the standard (Anon, 1975) used to determine the values of sulphate content. after some study and debate it appears most likely that the values quoted by Burns (1978) should be reported in units of g(SO3)/l. More recent work indicates that sulphate contents may be lower (Winter and Butler, 1999), although still at a level to cause some concern. Consequently, sulphates may cause problems by migrating from the shale and reacting with lime, concrete, cement bound or other cementitious materials (MCHW 1). Problems are also likely to arise if spent oil shale is placed in contact with metallic objects (Winter and Butler, 1999). Because the shale was heated to extract the oil, spontaneous combustion is clearly not a problem. Neither is the presence of sulphides as these will have been driven off or converted to sulphates during the extraction process (Sherwood, 1994).
Fine
CLAY 100
Medium SILT
Coarse
Considerable variations are commonly found in the physical properties of spent oil shales, particularly the grading. However, Burns (1978) noted that the particle size distributions for such materials were generally within the grading limits for Type 2 (Fig. 3) granular sub-base materials (Speci®cation for Road and Bridge Works, 1976) and were very close to the requirements for Type 1 granular sub-base materials. (These limits are essentially the same as those in MCHW 1.) Burns (1978) reported the results of standard 2.5 kg rammer compaction tests. These indicated maximum dry densities in the range from 1.30 to 1.44 Mg/m 3 and optimum moisture contents in the range 22± 34%. The relatively high optimum moisture contents and correspondingly low maximum dry densities were probably due to the porous nature of the material. This is supported by the high values of water absorption (10±21%) and the low particle densities for the size range from 2.4 to 37.5 mm (2.06±2.42 Mg/m 3).
Fine
Medium SAND
Coarse
Fine
Medium Coarse COBBLES GRAVEL
Type A Type B
Percentage passing (%)
80
Type C Type D Type E
60
Grading Limits for Type 2 Sub-base (MCHW 1) 40
20
0
0.0001
0.001
0.01
0.1 Sieve size (mm)
1
Fig. 3. Particle size distributions of samples of spent oil shale (after Burns, 1978).
10
100
M.G. Winter / Engineering Geology 60 (2001) 285±294 Fine
CLAY 100
Medium SILT
Coarse
Fine
Medium SAND
Coarse
289 Fine
Medium Coarse COBBLES GRAVEL
Before compaction After standard compaction 80
Percentage passing (%)
After heavy compaction
60
40
20
0
0.0001
0.001
0.01
0.1 Sieve size (mm)
1
10
100
Fig. 4. Typical effect of compaction on the grading of spent oil shale (after Burns, 1978).
Particle densities for sizes smaller than 2.4 mm were between 2.58 and 2.76 Mg/m 3. The degree of crushing, or fragmentation, that will occur during the compaction of a granular material generally depends upon the original particle size distribution, the crushing strength of the grains, and the stress level applied. Essentially, if a brittle particle is subjected to a stress in excess of its ultimate strength it will break. The stress may place the particle in tension, compression, ¯exure, shear or torsion. In addition, a particle may be worn away by another particle: that is, subjected to attrition. Burns (1978) observed that spent oil shale was subject to crushing as a result of the compaction process (Fig. 4). While fragmentation during compaction is often viewed as a problem, crushing may confer bene®ts to the compacted mass. Small particles resulting from crushing may ®ll voids and thus produce higher densities and lower air voids than would otherwise be the case. This will, in turn, tend to produce a more stable compacted mass. The fragmentation of earthwork materials is discussed in more detail by Winter (1998).
Most spent oil shales are frost susceptible and therefore should not be placed within 450 mm of the road surface. However, the addition of cement reduces the frost susceptibility. Burns (1978) observed that the addition of 5% cement reduced the voids content and, thus, the frost induced heave to acceptable levels for the materials tested. However, he did note that larger proportions of cement might be required for materials from some spent oil shale sources to reduce heave to acceptable levels.
4. Use of spent oil shale 4.1. Historical use Spent oil shale bings may contain both spent oil shale and material excavated from non-oil bearing areas. The heating of oil shale produces a stable granular material that can be used in place of natural aggregates. The optimum use of spent oil shale is as a selected granular ®ll or as an unbound granular subbase although it could be used as general ®ll.
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M.G. Winter / Engineering Geology 60 (2001) 285±294
Nevertheless, Burns (1978) estimated that some 20±25 million tonnes of spent oil shale had been used in Central Scotland as general ®ll since the early 1960s, principally on the M8, M9 and M90 motorways. It has also been used in other bulk ®ll applications such as the Edinburgh airport runway, where some 200,000 tonnes were placed. More recently some 15,000 m 3 were place as general ®ll during the construction of the underpass at the M8/ M9 Newbridge interchange. Small quantities of spent oil shale have also been used as general ®ll on other recent road construction projects in Central Scotland. Stabilising spent oil shale with cement on a pre-mixed basis has proved commercially viable and Burns estimated that some 0.5±1.0 million tonnes had been so used, including as sub-base on the M9 motorway. 4.2. General ®ll The assessment of acceptability for general ®ll should be by conventional means. For a granular material such as spent oil shale this is generally by control of the moisture content within set limits of the optimum moisture content (see MCHW 1, Table 6/1). However, given that spent oil shale is generally acceptable for use as selected ®ll it may be uneconomic to use these materials as general ®ll. 4.3. Selected granular ®ll Spent oil shale is susceptible to crushing during compaction (Fig. 4). However, crushing may yield higher densities and lower air voids than would otherwise be the case, thus tending to produce a more stable compacted mass. Indeed, this indicates one barrier to the use of spent oil shale (and burnt colliery spoil) as selected granular ®ll. Previous speci®cations have relaxed the 10% ®nes value required for well burnt non-plastic shale sub-bases (Speci®cation for Road and Bridge Works, 1976; Burns, 1978) but the current Speci®cation (MCHW 1) retains a requirement for a minimum 10% ®nes value of 50 kN. Such a requirement is unlikely to be met by many spent oil shales and Dawson (1989) described the 10% ®nes value as too severe a test of the ability of well-graded aggregates to withstand compaction stresses. There is a strong argument for reducing the 10% ®nes value requirement for spent oil shale, provided that the
compacted material is within the particle size distribution limits de®ned in the speci®cation. 4.4. Capping layer The Speci®cation (MCHW 1) allows spent oil shale to be used as granular capping, provided that the grading and other speci®cation requirements are met. However, as for selected granular ®lls, the 10% ®nes value requirement (30 kN in this case) is unlikely to be met. Similar arguments may be applied to relaxing the 10% ®nes value as are made above for selected granular ®ll. While spent oil shale may be stabilised to form a capping layer there would generally be little reason for doing so as it would be suitable for use in an unbound form (Sherwood, 1994). The only exception to this would be if the capping layer were within 450 mm of the completed road surface as many spent oil shales are highly frost susceptible and thus cannot be in such a location. The addition of 5% or more cement has been shown to reduce the frost susceptibility to acceptable levels (Burns, 1978). Frost susceptibility is related to voids content and the use of cement reduces the voids content while having the added bene®t of increasing the inter-particle strength. For this reason, many sub-bases constructed from spent oil shale have been stabilised with cement. Such a treatment will be suitable only for materials with low sulphate contents (HA74 Ð DMRB 4.1.6) when ordinary portland cements are used. However, the use of sulphate resisting cements may prove effective with higher sulphate materials. To ensure that the material is not susceptible to heave as a result of the reactions between sulphates and the cement it would be prudent to use the durability test given in the Speci®cation (MCHW 1, Clause 1036) for CBM1. However, as the frequency of testing may have to be increased, such a process may become uneconomical. The use of sulphate resisting cements may prove effective with higher sulphate materials. Comprehensive warnings have been given on the damage caused by mixing high sulphate materials with cement and lime (Perry et al., 1996a,b). 4.5. Sub-base Fig. 3 shows spent oil shale can be obtained to satisfy the grading requirements of granular
M.G. Winter / Engineering Geology 60 (2001) 285±294
291
Earthworks No
Will use be environmentally beneficial ?
Reject and seek alternative No
No
Yes
Landscape and non-structural uses
Will waste material be cheaper than other material ? Yes
Do quantified environmental benefits outweigh extra costs ?
Yes
Is material likely to suffer spontaneous combustion when compacted ?
No
Is material frozen ?
Pursue further use
Embankments and other structural fill
Reject for use in roadworks
Yes
Consider use in landscaping
Reject or allow to thaw
Yes
No Does material meet plasticity requirements?
No
Yes No Does material meet moisture content requirements ?
Allow to dry
Yes Does material contain excess sulphates ?
Yes
Will material be used within 450mm of concrete ?
Yes
No No Does material meet specification requirements in other respects ?
No
Yes
Use in embankments and structural fill
Fig. 5. Determining the potential use of waste materials in earthworks construction (after Anon, 1985; Sherwood, 1994).
sub-base materials and can therefore satisfy the more relaxed criteria for selected granular materials. Wellburnt colliery spoil is mentioned by name in the Speci®cation (MCHW 1) for many selected granular ®ll applications. However, Clauses 803 and 804 of the Speci®cation (MCHW 1), which refer to granular subbase, allow ªwell burnt non-plastic shaleº which embraces both burnt colliery spoil and spent oil shale. The clauses for selected granular ®ll could usefully be phrased in the same manner rather than speci®cally requiring burnt colliery spoil (Sherwood, 1994), effectively excluding spent oil shale. Similarly,
where burnt colliery spoil is excluded then it would be prudent to also exclude spent oil shale by the use of the phrase ªwell burnt non-plastic shaleº. Burns (1978) noted that in the Speci®cation for Road and Bridge Works (1976) sub-base materials, with the exception of well burnt non-plastic shales, were required to have a minimum 10% ®nes value of 50 kN. This exception speci®cally acknowledged that crushing could occur with this material with no apparent structural disbene®t to the completed subbase. Under the current Speci®cation (MCHW 1) well-burnt non-plastic shales are speci®cally included
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M.G. Winter / Engineering Geology 60 (2001) 285±294
in the allowable materials but the exception to the minimum 10% ®nes value of 50 kN has been removed. Sherwood (1995a,b) notes that although many burnt colliery spoils, and by implication spent oil shales, would be suitable for such a use it is unlikely that many would achieve a 10% ®nes value of 50 kN. Further, it is quite possible that a more stable material may result as voids are ®lled with the smaller particles created by crushing. Similar arguments may be applied to relaxing the 10% ®nes value as are made above for selected granular ®ll and capping layer. 4.6. Other considerations Visual inspection of spent oil shale at the tip is required to ensure that the material delivered to site does not vary too frequently. It is important that all design and speci®cation tests should be carried out on the material in the crushed, post-compaction state, not on the excavated or delivered material. If spent oil shale is to be placed within 500 mm of metallic items, lime, concrete, cement bound or other cementitious materials then the limits in the Speci®cation (MCHW 1, Clauses 601.13 and 601.14) apply. It seems unlikely that it could be used in close proximity to such materials given the high sulphate content of many spent oil shales. Care is also required if spent oil shale is to be stabilised using cement. For lower sulphate materials it may be possible to use ordinary Portland cement. However, for higher sulphate materials sulphate resisting cements may be required. Doubts also remain as to the potential reactions between spent oil shale and polymeric reinforcing materials. Notwithstanding the above comments on frost susceptibility and the interaction with cementitious products, the durability of spent oil shales is unlikely to pose a problem. However, it is nonetheless important to ensure that compaction is suf®cient to minimise the air voids of the earthworks and that the requirements of MCHW 1 (Clause 602.15) are followed to ensure that water ingress does not cause a long-term durability problem. 5. Discussion The transport of waste materials, such as spent oil
shale, to site incurs a cost for haulage. If a waste material is not available within an economic haulage distance of the site then it may be rejected on economic grounds. It is generally accepted that the maximum economic haulage distance for the import of waste materials will depend on a number of factors, including the following: ² the location and nature of the site; ² the location and nature of the waste material source; ² the method of transport; ² the relative costs of the waste material and its alternative. However, if the waste material is located within economic haulage of the site then its use should be considered and the factors to be taken into account are summarised in Fig. 5. The advantages of using waste materials are: ² removal of waste tips; ² avoidance of borrow pits and consequent savings in the ®nite sources of natural aggregates; and ² avoidance of liability for land®ll tax (where appropriate). It should, however, be noted that it is seldom possible to remove all of a tip due to the mix of materials contained therein. Indeed, planning permission is generally required to remove material from an old tip due to the possibility of aggravating the existing dereliction of an area. In some cases, landscaping a tip to sympathetically blend into the local area may be a more environmentally bene®cial solution than seeking engineering uses for the materials contained therein (Sherwood, 1994). The disadvantages of using waste materials are: ² increased haulage costs; ² disturbance caused by haulage; and ² greater variability of waste materials. Increased haulage costs are almost certain to be a factor in the substitution of waste materials for sitewon bulk ®ll and, for some materials, haulage costs may increase if waste materials are used. This will however depend upon the relative locations of the
M.G. Winter / Engineering Geology 60 (2001) 285±294
waste materials and borrow-pits or quarries from which the selected ®lls would otherwise be obtained. If haulage costs are increased by the use of waste ®lls then the disturbance caused by haulage will also increase and environmental disbene®ts will accrue if public roads are used. These disbene®ts will include congestion, noise, pollution, dust and deposition of the material along the haulage route. Such disbene®ts are, with the exception of congestion, dif®cult to price and are frequently ignored by engineers. Inspection of waste materials, such as spent oil shale, at the tip is one means of managing their potentially greater variability compared to conventional materials. Clearly a blend between economic and environmental bene®ts must be achieved if waste materials are to be successfully used in road construction. Without an economic bene®t contractors will not be encouraged to use waste materials. If some economic bene®t exists then it is important that environmental bene®ts can be demonstrated by their use. Such bene®ts might include savings in the use of ®nite natural aggregate resources. Designers should identify sources of waste materials and allow contractors to select on an economic basis, within the prevailing environmental legislation (HA44 Ð DMRB 4.1.1). 6. Summary The crushing of particles during compaction is often viewed as a problem. However, crushing may confer bene®ts to the compacted mass. Small particles resulting from crushing may ®ll voids and thus produce higher densities and lower air voids than would otherwise be the case. This will, in turn, tend to produce a more stable compacted mass. Spent oil shale can be used successfully as general ®ll. However, due to its high quality as aggregates it is more suited to use as selected granular ®ll. In particular, given its frost susceptibility, stabilisation as sub-base seems a particularly appropriate outlet for this material. However, it would be prudent to use the chemical durability test given in the Speci®cation (MCHW 1, Clause 1036) for CBM1 to ensure that the material is not susceptible to heave as a result of the reactions between sulphates and the cement. Spent oil shale can be obtained to satisfy the grad-
293
ing requirements of granular sub-base materials and can therefore satisfy the more relaxed criteria for selected granular materials. The relevant clause of the Speci®cation for granular sub-base refers to ªwell burnt non-plastic shaleº which embraces both spent oil shale and burnt colliery spoil. The clauses for selected granular ®ll refer speci®cally to well-burnt colliery spoil whether including or excluding such materials from use. In either case spent oil shale is not covered, effectively disallowing its use where it could be used and allowing its use where it should not be used. The minimum 10% ®nes value requirement of 50 kN for granular sub-base materials is severe. In previous speci®cations this requirement was waived for burnt non-plastic shales, such as spent oil shale. although limited crushing during compaction will tend to produce a more stable compacted mass many such materials will be deemed unsuitable on the basis of the 10% ®nes value. The minimum 10% ®nes value of 30 kN required for some classes of capping layer also seems severe. Spent oil shales generally have high sulphate contents. Consequently, these materials are unlikely to be suitable for use close to concrete structures or metallic items. There also remain doubts as to the potential reactions between spent oil shales with high sulphate contents and polymeric reinforcing materials. Clearly a blend between economic and environmental bene®ts must be achieved if waste materials are to be successfully used in road construction. Without an economic bene®t contractors will not be encouraged to use waste materials. Designers should identify sources of waste materials and allow contractors to select on an economic basis, within the prevailing environmental legislation. If some economic bene®t exists then it is important that environmental bene®ts can be demonstrated by their use. Such bene®ts might include savings in the use of ®nite natural aggregate resources. Acknowledgements The author is grateful to R.A. Snowdon (TRL) for helpful discussions and suggestions. Dr J. Perry, Dr G.D. Matheson and P. McMillan variously performed
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M.G. Winter / Engineering Geology 60 (2001) 285±294
the technical and quality audits for this report; the author is grateful for their helpful and constructive suggestions. The work described in this paper forms part of a Scottish Of®ce Development Department research programme and the paper is published by permission of the Scottish Of®ce and the Chief Executive of TRL Limited q TRL Limited 2001. This report has been produced by the TRL Limited, under a contract placed by the Scottish Of®ce and the Department of the Environment, Transport and the Regions. any views expressed in it are not necessarily those of either Department. References Anon, 1975. Methods of Test for Sols for Civil Engineering Purposes, BS1377. British Standards Institution, London. Anon, 1985. Guide to the Use of Industrial By-Products and Waste Materials in Building and Civil Engineering, BS6543. British Standards Institution, London. Burns, J., 1978. The Use of Waste and Low-Grade Materials in Road Construction: 6. Spent Oil Shale. TRRL Laboratory Report LR 818. Transport Research Laboratory, Crowthorne. Dawson, A.R., 1989. The Degradation of Furnace Bottom Ash under Compaction. Unbound Aggregates in Roads: UNBAR 3, Butterworths, London, 169±174. HA 44 Ð Earthworks: Design and Preparation of Contract Documents (DMRB 4.1.1). Design Manual for Roads and Bridges. The Stationery Of®ce, London. HA 74 Ð Design and Construction of Lime Stabilised Capping Layers (DMRB 4.1.6). Design Manual for Roads and Bridges. The Stationery Of®ce, London. Kerr, D., 1994. Shale Oil Scotland: The World's Pioneering Oil Industry. Scotch Publishing, Edinburgh. Lake, J., Fraser, C.K., Burns, J., 1966. Investigation of the physical
and chemical properties of spent oil shale. Roads and Road Construction 44 (522), 155±159. Manual of Contract Documents for Highway Works (MCHW 1). Speci®cation for Highway Works (December 1991, reprinted August 1993 and August 1994 with amendments), vol. 1. The Stationery Of®ce. London. Perry, J., MacNeil, D.J., Wilson, P.E., 1996a. The Uses of Lime in Ground Investigation: a Review of Work Undertaken at the Transport Research Laboratory. Lime Stabilisation. Thomas Telford, London. Perry, J., Snowdon, R.A., Wilson, P.E., 1996b. Site Investigation for Lime Stabilisation of Highway Works. Advances in Site Investigation Practice. Thomas Telford, London, 85±96. Sherwood, P.T., 1994. The Use of Waste Materials in Fill and Capping Layers. TRL Contractor Report CR 353. Transport Research Laboratory, Crowthorne. Sherwood, P.T., 1995a. The Use of Waste and Recycled Materials in Roads. Proceedings, Institution of Civil Engineers, 111(2). Thomas Telford, London, 116±124. Sherwood, P.T., 1995b. Alternative Materials in Road Construction: a Guide to the Use of Waste, Recycled Materials and ByProducts. Thomas Telford, London. Sherwood, P.T., Ryley, M.D., 1970. The Effect of Sulphates In Colliery Shale on its Use for Roadmaking. TRRL Laboratory Report LR 324. Transport Research Laboratory, Crowthorne. Speci®cation for Road and Bridge Works, 1976. Fifth Edition. Department of Transport, Scottish Development Department, Welsh Of®ce, Department of the Environment for Northern Ireland. The Stationery Of®ce. London. Whitbread, M., Marsey, A., Tannel, C., 1991. Occurrence and the Utilisation of Mineral and Construction Wastes. The Stationery Of®ce, London (Department of the Environment). Winter, M.G., 1998. The Determination of the Acceptability of Selected Fragmenting Materials for Earthworks Compaction. TRL Report 308. Transport Research Laboratory, Crowthorne. Winter, M.G., Butler, A.M., 1999. Stainless steel corrosion in spent oil shale. Ground Engineering, September, 28. (Associated Discussion December 1999, 7 and January 2000, 6.)