Section 2: Design and management of earthworks

5 Planning of earthworks

Planning of earthworks

5.1 Introduction

Clause 5 is provided as a brief summary of some of the issues that should be considered when planning an earthworks project; it is not intended to be a complete list and is provided only as guidance. The person applying the code should remain cognisant of the current and applicable statutory requirements that apply to all civil engineering projects.

5.2 Sustainable development

Earthworks should be designed with sustainability in mind. For the purpose of this standard sustainable development is taken to mean: "an enduring, balanced approach to economic activity, environmental responsibility and social progress" (BS 8900:2006).

COMMENTARY ON 5.2

In future projects, evaluation of options will increasingly be required to consider construction cost and whole life cost, but also include an evaluation of the "carbon footprint" of various scheme options. The designer will be expected to calculate the "embodied carbon" present in various designs (this requires consideration of all aspects of an earthwork solution, e.g. import/export of fill materials; plant operations; use of carbon-based geosynthetic materials; soil modification or stabilization, etc.).

This process is intended to prioritize "carbon critical design". To encourage designers to follow this approach, both the Environment Agency (EA) and Highways Agency websites provide "carbon calculators" (based on research undertaken by Bath University) that are suitable for undertaking a basic assessment of earthwork scheme options. It is likely that these calculators will be progressively enhanced as experience is developed in this field.

5.3 Scheme conception

5.3.1 Design strategy

The earthworks team should aim to provide an earthworks design that is feasible, functional, constructible and suitable for the proposed end use. Consideration should be given to land requirements, including all temporary works. The design should be developed to minimize environmental impact during the construction phase, in use and for future maintenance operations.

5.3.2 Consultations

5.3.2.1 General

The consultation process is a necessary part of any earthworks design and should be implemented at an early point following the project's conception.

The earthworks team should identify their environmental, legal and planning obligations at the earliest opportunity to enable them to conceive and develop the project in the most effective way.

The nature of the consultation(s) will depend on the size of the project, and should involve dialogue with both regulatory and community bodies.

5.3.2.2 Regulators

It is important to develop a constructive dialogue with the regulators to ensure that they are aware of what is happening on the project and the reasons behind any design decisions that are made.

COMMENTARY ON 5.3.2.2

Legislation is in place which is enforced by the environmental regulators to protect both the natural environment and residents surrounding sites through the planning process and implementation of project specific environmental management schemes.

Regulators have a diverse range of responsibilities and enforcement powers. Their responsibilities are as follows:

  • Local Authority Noise, air quality, traffic, the planning process and contaminated land
  • Environmental regulators Discharges to land and controlled waters, waste, water abstraction control, nature conservation
  • Nature conservation Designated ecological, geological and organizations geomorphological sites and protected species
  • Heritage bodies Designated archaeological and heritage sites

5.3.2.3 Community relations

Developing effective communication and consultation with the local community is important to minimize the likelihood of nuisance (e.g. noise and vibration, dust, waste etc.) and should be instigated at the earliest opportunity; if members of the community are engaged and kept informed throughout a project they are less likely to complain.

Public consultation is particularly important on larger projects where prolonged periods of disturbance and/or significant changes to the environment or landscape are likely to occur.

Typical liaisons should include:

  • community representatives e.g. town or parish councillors;
  • occupants of sensitive buildings e.g. schools, nursing homes, hospitals, etc.;
  • local residents and/or resident groups;
  • national and local interest groups, e.g. environmental groups, trade associations, etc.

5.4 Environmental considerations

Environmental considerations should be assessed by the designer, who should judge where the balance of importance lies for a given scheme.

NOTE 1 Which aspect takes priority will change from scheme to scheme and with time as legislation and other factors change.

At many sites there are environmental restrictions on the works that will be permitted (SSSI, protected species, etc); at all sites the earthworks should be planned to consider environmental considerations and thus reduce the environmental impact of the scheme.

NOTE 2 There is environmental and planning legislation to be complied with during the development of an earthworks design. This includes, but is not limited to Environmental Assessments, Environmental Statements and Habitat Surveys [12].

Affected parties such as Natural England should be consulted to ascertain environmental requirements during and post construction, including translocation of endangered species and acceptable environmental mitigation works.

The earthworks design team should be aware of the overall environmental objective to minimize environmental impact, which is often summarized by the slogan "rethink, reduce, reuse, recycle", which reflects the priority of each option. These options in the case of earthworks may be applied in various ways including the following:

  • rethink – e.g. consider whether any particular course of action is actually necessary;
  • reduce – e.g. reduce the overall environmental impact, such as reducing the volume of material excavated or the requirement for aggregate;
  • reuse – e.g. reuse all earthworks materials generated on a project whenever possible (within earthworks or landscaping), or use of stabilisation techniques to render materials suitable for reuse;
  • recycle – e.g. recycling of materials between sites such as use of secondary aggregates.

Whenever management of waste materials forms part of an earthwork scheme, input should be obtained from an environmental specialist to address aspects such as waste classification and assessment for hazardous substances; this will necessitate appropriate testing as part of the site investigation (SI). In addition to the requirements of BS EN 1997-2:2007, the SI should consider the following issues that are of particular significance to earthworks.

  • Existing ground and re-use of materials:
    • suitability as construction materials (classification), including "relationship testing" (see 6.1.3);
    • aggressivity of ground (see BRE SD1 [13]);
    • contamination testing sufficient to develop the conceptual model of the site and inform appropriate risk assessment.
  • Modification of marginal materials for use as engineering fills.
  • Enhancement of soils as growing media.

NOTE 3 This standard does not cover the treatment of contaminated materials.

Any materials that might require off-site disposal should be tested to ascertain their classification under relevant requirements, including:

  • waste acceptance criteria;
  • European waste classification; and
  • suitability for re-use off-site (subject to acceptance by EA).

NOTE 4 The above list is a general guide and any assessment has to satisfy the requirements of current UK environmental and waste management legislation (and likely developments in the short term).

The project team should be aware of any changes to relevant legislation, and that industry best practice will change to accommodate regulatory revision. Consultation with relevant regulatory authorities is recommended at the earliest opportunity.

The tax imposed on disposal of waste and the importing of primary aggregate can change; up-to-date information should be obtained from HM Revenue and Customs.

Designers should be aware of the potentially significant commercial impact of designs requiring off-site disposal of waste. Treatment of waste can significantly increase the proportion of material classified as inert, thus reducing the potential cost of disposal. The following treatment methods may be cost-effective depending on the condition of the materials awaiting disposal.

  • physical sorting/screening to separate inert and contaminated materials;
  • pH adjustment to immobilize heavy metals;
  • stabilizing with hydraulic binders;
  • bioremediation;
  • sparging or similar techniques to reduce volatiles;
  • soil washing.

During the design of any investigation, testing should be specified to assist in the selection of a treatment process suitable for dealing with arisings from the site.

NOTE 5 Legislation [14] requires that all waste is pre-treated prior to disposal.

Environmental impacts and impact mitigation that should be considered include the following:

  • habitat loss due to earthworks and opportunities for the creation/improvement of habitat provision;
  • sustainable drainage systems (SUDS; a drainage option to enhance biodiversity, amongst other benefits, as described in 7.5.5);
  • loose tipping (reduced compaction) of sub-soil, which should be practiced, where possible, to promote re-vegetation;
  • geodiversity can be enhanced by retention of exposures in cutting, pre-existing spoils of mineralogical/palaeontological interest as an educational resource (some cuttings are designated as Regionally Important Geological and Geomorphological Sites [RIGS]);
  • plan from an early stage to use local resources (e.g. use of locally available recycled and secondary aggregates) and to avoid unnecessary disposal of materials off site (e.g. inclusion of environmental bunding to avoid disposal of surplus material);

NOTE 6 Planning in this way greatly increases the potential for these options to be successful at detailed design stage.

  • the physical footprint of an earthwork can be modified by design to mitigate adverse impacts of land take; a narrow footprint achieved by using reinforced soil will reduce land take in areas where level ground is required for development; a wide footprint, with gentle batter slopes, may permit agricultural use of the slopes; and
  • potential impact of the earthworks form on future air and noise quality in the immediate area.

NOTE 7 There are opportunities to apply innovation to achieve environmental sustainability objectives, e.g. use of tyre bales (see TRL report PPR080 [15]).

5.5 Environmental impact assessment (EIA)

The process of preparing the EIA for a scheme should be led by suitably experienced environmental specialists who are aware of both the nature of the proposed engineering works and the current legislation covering this area of work. Earthworks professionals should have sufficient understanding of the process to provide input to the EIA and use the completed assessment (see [12]).

BS 6031:2009 Code of practice for earthworks