7.6.5 Compliance testing

The Designer should select the appropriate form of compliance testing for the earthworks. The selection of material properties should consider the feasibility of performing compliance testing relative to the selected acceptability criteria and the constraints imposed by the contract and construction operations.

Relationship testing should be used to determine the correlation between compliance tests that will be used to control the earthworks (such as MCV) and the fundamental soil properties upon which the earthworks design is based (such as undrained shear strength). An illustration of the relationship test concept is provided at Figure 11. The relationship testing should be used to determine the acceptability limits for the chosen compliance tests. The correlation testing should be carried out during the ground investigation phase but may also be required during the construction phase to address natural variation of materials encountered.

Designers should maintain awareness of developing technologies for in-situ and laboratory testing.

Figure 9 Determination of acceptability limits for coarse soils using relationship testing data
Determination of acceptability limits for coarse soils using relationship testing data

Key

  • 1 Saturation line (0% air voids)
  • 2 X% air voids
  • MC Moisture content (%)
  • DD Dry density (kg/m3)
  • OMC Optimum moisture content
  • LAL Lower acceptability limit
  • UAL Upper acceptability limit

NOTE The indicated UAL and LAL will generally allow compaction to achieve at least the indicated percentage of maximum dry density.

Figure 10 Determination of acceptability limits for fine soils using relationship testing data
Determination of acceptability limits for fine soils using relationship testing data

Key

  • 1 Saturation line (0% air voids)
  • 2 X% air voids
  • MC Moisture content (%)
  • DD Dry density (kg/m3)
  • OMC Optimum moisture content
  • LAL Lower acceptability limit
  • UAL Upper acceptability limit
Figure 11 Example of relationship testing
Example of relationship testing

Key

  • MC Moisture content (%)
  • DD Dry density (kg/m3)
  • γcn Undrained shear strength (kN/m2)
  • CBR California bearing ratio
  • MCV Moisture condition value
  • 1 Zero air voids (particle density = 2,64 Mg/m3)
  • 2 2,5 kg rammer compaction test

Based on Reeves et al [41].

COMMENTARY ON 7.6.5

On most civil engineering projects, the rate of earthworks construction is usually a critical activity. Related to this is the need for rapid turnaround of the results from compliance testing linked to the contract specification.

Delays in this process increase the volume of material placed and compacted for which compliance is unproven. When assessing the appropriate form of compliance testing for an earthworks project the designer should be aware of these testing limitations.

Material failing to conform to the specification might require remedial treatment. In the worst case, this can entail excavation of the non-conforming material and its disposal off site. This is wasteful of material and site resources, including plant, fuel, labour and time. The site control and testing procedures should be devised to minimize this risk.

Tests such as the undrained triaxial test, optimum moisture content and Atterberg Limits are not generally appropriate for routine earthworks control, either in the equipment required by a site laboratory or in the time/personnel resource required.

Available rapid methods for determining suitability of cohesive materials include the hand shear vane and the moisture condition value (MCV) test. Both can be carried out in situ and provide immediate results. If in-situ density is required as a control mechanism, the nuclear density gauge is proven technology that may be used.

Additionally, there are several techniques which provide a quick assessment of CBR values; these include the Dynamic Cone Penetrometer and the MEXE cone penetrometer.

7.6.6 Use of potentially contaminated, site-won fill

The earthworks designer should carefully consider the implications of potential contamination in site-won fill. Expert advice should be sought in relation to potentially contaminative previous land uses, regulatory requirements and testing regimes. See also SHW [1] Clause 601.

The earthworks designer should refer to EA guidelines that are current at the time of the design in order to remain aware of current legislation. It is advisable to discuss proposals for use of these fills with the EA (and HSE if an occupational health problem is suspected) at as early a stage as possible. The earthworks designer should avoid the temptation to overspecify the requirements; in general terms if the fill meets the contract terms and is acceptable to the EA then the contractor should consider using it. It may often be appropriate to obtain input by a waste management/human health risk assessment specialist to assess the suitability of the material for reuse.

A sampling and testing plan, comprehensive in both location of sample points and determinands analysed should be prepared to assess the source of material. Recommendations have been published (e.g. BS EN 14899) and have been incorporated by EA in their guidance; it is, however, strongly recommended to seek the advice and assistance of a contaminated land specialist in this.

NOTE Alongside the chemical nature of the material, the earthworks designer will commonly need to consider physical re-processing methods that will be necessary in order to ensure that fill materials will meet the physical requirements of suitable fill (e.g. screening to remove oversize particles).

Designers should be aware that the chemical characteristics of some materials might limit the applications for use.

7.6.7 Stabilized and modified materials

Designers should consider the use of stabilized or modified materials to maximize the use of site-won materials, and should make use of published guidance such as HA 74/07 [43].

COMMENTARY ON 7.6.7

The use of lime for treating cohesive materials and enabling them to be used on site has been established within the UK for a considerable time as has the use of cement to treat granular materials. More recently a two stage process of using lime followed by cement on cohesive materials has been developed – details are provided in the SHW [1].

The two main applications within cohesive soils are:

  • modification/improvement which is a process to render unacceptable bulk fills acceptable and simply uses lime;
  • stabilization which is used for higher quality uses such as capping/ subbase material or for slope repairs and uses lime together with additional binders such as cement, ggbs, pfa etc. in order to prevent potential swelling effects owing to high sulfur contents.

There is an extensive suite of European standards which have been developed over the past few years [see BS EN 13286 (all parts) and BS EN 14227 (all parts)].

Britpave (http://www.britpave.org.uk/) provide extensive guidance on procedures and considerations that can be undertaken if the option for stabilization is considered. Additional information on the performance, materials, mixture design, construction and control testing of hydraulically bound mixtures for pavements is available from the Concrete Centre [www.concretecentre.com/publications].

7.6.8 Use of secondary aggregates and recycled materials

Published guidance (see commentary) should be followed on the use of secondary aggregates and recycled material. Data on compaction, durability and environmental aspects, such as leaching, should be sought from potential suppliers before confirming use in design. The designer should seek to minimize overall environmental and economic impact. However, there can be instances where primary aggregates carry the least cost, both in environmental impact and commercial economy.

COMMENTARY ON 7.6.8

Government policy encourages the use of these materials; this is captured in SHW [1], where recycled aggregate is specifically permitted in Table 6/1 for many Class 6 materials.

Although, in general use, the term "recycled aggregate" is used to cover all non-primary material, there are differences between recycled and secondary aggregates. The former have been recovered from previously used material (e.g. crushed concrete and masonry), the latter are by-products of an industrial process (e.g. PFA, china clay stent). Whilst different in origin, both types are covered by legislation to control the process of recovery (and licensing of this by EA) and taxation.

WRAP (Waste and Resources Action Programme) provide information on recycling on their webpages (http://www.wrap.org.uk/), which includes Aggregain (http://www.aggregain.org.uk), specifically for recycled aggregate in construction. This includes a directory of suppliers with distance from a defined location.

NISP (National Industrial Symbiosis Programme) http://www.nisp.org.uk/ exists to create symbiotic links between businesses to reduce waste by keeping material in the chain of utility.

Examples of practical research initiatives that have resulted in guidance notes for designers in order to promote certain recycled materials (e.g. Winter et al [15]), or options in particular settings (e.g. Brampton et al [44]).

In addition, there are a number of materials exchange initiatives, business and publicly funded, with a presence on the internet. As this is a fluid marketplace, the designer is encouraged to search for themselves.

BS 6031:2009 Code of practice for earthworks