Guidance

Technical Guidance Note: TGN02

Published 1 July 2021

1. Scope

This guidance note provides the Coal Authority's minimum required standards for Designers seeking engineering appraisal of their design proposals. Any geotechnical or structural elements which, as part of their design, need to consider the potential adverse effects resulting from coal mining legacy, even in its remediated condition, must pass through engineering appraisal. Submissions will only be considered if they are made as part of an existing Coal Authority Permit, or a proposal being considered under pre-application advice.

2. Introduction

The Coal Authority owns the vast majority of unworked coal in Great Britain, as well as former coal mines.In order to manage the Coal Authority's property, it has a formalised Permitting regime to access its property mainly with respect to the development industry. Planning, enabling and construction works continue to be influenced by mining legacy within the coalfield areas and the Coal Authority is committed to ensuring that where these interactions affect design, minimum requirements and expectations are maintained in accordance with relevant published standards, guidance and legal obligations. Engineering appraisal under an associated Coal Authority Permit is the adopted mechanism of achieving this. The proof of acceptance of a design is often a requirement of Insurers, Funders, mortgage providers and the Local Authority including buildings control approval/warranties, NHBC, Land Quality Endorsement, and achieving successful discharge of associated planning conditions.

3. Design appraisal

The engineering appraisal is the evaluation by the Coal Authority of a design proposal to ensure that the identified coal mining legacy risks associated with a development have been adequately considered and addressed. Permission to proceed with associated works following such an engineering appraisal is not an approval, rather an acceptance by the Coal Authority that the Designer has identified the coal mining legacy risks associated with the development and taken reasonable steps to mitigate these risks.

The applicant making the submission is the Designer as defined by the CDM Regulations 2015; in undertaking the appraisal the Coal Authority does not accept any responsibility under those Regulations. When objections or comments are raised through the appraisal process and an alteration, modification or correction is made by the applicant to a design, this position remains unchanged. It is by this process that a resubmitted design may subsequently be deemed acceptable. If acceptance is conditional on other criteria being met, this will be communicated in writing upon issue of the relevant permit or advice.

Notwithstanding the Coal Authority's acceptance (or otherwise) of a design, appropriate statutory approval must be gained under whatever relevant regulatory regime applies. This may include approvals pertaining to the Building Regulations 2010, The Highway Act 1980, the Water Industry Act 1991, Environmental Permitting Regulations, etc.

4. Disclaimer on Design Appraisal

Acceptance by the Coal Authority of a design merely signifies that coal-mining legacy risks may be suitably mitigated and addressed. This shall be determined to the best of the Coal Authority's ability based on the reports received, and information provided, during the appraisal process. It is not a guarantee that no damage relating to a coal-mining legacy risk will occur as a consequence of the works undertaken by the Permit Holder. Notwithstanding the Coal Authority's acceptance of a design, the Coal Authority does not accept any liability or responsibility whatsoever for damage which may result from any coal-mining legacy risk, where the Designer or other third party was able to suitably mitigate such a risk, or where the nature or extent of the risk was not within the Coal Authority's knowledge. All such risk remains with the Designer and the Permit Holder.

5. Requirements

An engineering appraisal is required for any permanent structural or geotechnical element which is designed to mitigate against the adverse effects of mining legacy.

Typically these include, but are not limited to:

• reinforced concrete capping-slabs spanning former mine entries
• walls, plugs and barrier solutions to remediate mine entries
• geogrids, reinforced concrete beams/slabs and other foundations designed to protect against a loss of ground support
• piles, foundations, sub-structures, superstructures or ground improvement techniques where the design must take account of former mine workings or mine entries

Sometimes solutions might include a combination of these methods, or consider only the residual effects.

Where foreseeable, an existing Coal Authority Permit may include Conditions (detailed on the certificate itself) requiring a design be submitted and accepted through engineering appraisal. The design being appraised must in this case be within the agreed scope of works defined on the Permit Certificate.

6. Submission

All submitted design packages should be as a minimum requirement checked and signed by the Competent Person, a structural, civil or geotechnical engineer with proven experience in the type of design proposed.

They may be typed or hand written provided they:

• are clear, legible and accurate
• all pages are titled, numbered and signed
• include a design rationale explaining all methods of analysis, adopted standards, assumptions, adopted actions (loads) and any specific requirements, conditions or controls
• present the design within the context of the proposed development layout, planning application status or relevant planning condition
• use standard defined notation and provide in-text references to the relevant standards, drawings, specific report extracts or references from which information and guidance is derived
• contain labelled, relevant up-to-date and matching sketches, cross-sections and construction drawings
• make reference to the any relevant Coal Authority Permit reference number, and
• include a schedule confirming all items submitted

The design submission must contain all information used in the structural/geotechnical design including, geotechnical investigation/Interpretative report, remedial validation reporting, site survey information/proposed development layout, and where appropriate Coal Mining Risk Assessments and monitoring results etc. Only relevant information or extracts should be provided.

The design analysis may be done manually or by the use of computer software. Analysis calculations done by software must, by presented evidence, have been checked and validated by the Designers Competent Person. Design calculations should be completed in accordance with the relevant Design Standards, for example, BS EN 1992 (Eurocode 2) or BS 8110 for reinforced concrete. The location of each structural component being designed must be shown in construction drawings and/or sketches including or along with the specification of the proposed materials, for example, relevant BBA certificates, manufacturer's product cards etc. The design must take into account the practical issues relating to construction and health and safety issues.

7. Rejection

Failure to meet the above requirements risks design packages being rejected pending redrafting and resubmission.

To help applicants avoid this, some of the common reasons for rejection are:

• generic designs not reflecting site-specific requirements or conditions
• designs not compliant with CIRIA C758D or National Planning Policy Framework (NPPF), for mine shafts specific attention is drawn to section 14.7.6 of the CIRIA document
• missing information the design is reliant upon;
• absence of necessary design checks against failure in shear or bearing capacity
• drawings and specifications not matching accompanying calculations
• designs not considering the latest development layout or adjacent buildings, foundations or infrastructure

If any construction works are undertaken without obtaining a Coal Authority permit, enforcement action either by way of an injunction to stop works or a claim for damages may be issued. Permits constitute a non-transferrable legal contract which is specific to the named parties and the defined scope of works.

8. Costs

The financial cost of engineering appraisals remains part of the Permit application fee unless it is a redesign (see Section 9 below). No separate charges are currently levied for instances where structural precautions form part of the remedial design. If a new Designer is appointed, this must be communicated by the Permit Holder (Client). The associated costs will be payable again by the Permit Holder (Client).

Fees for pre-application advice are levied at cost-recovery rates and will be specific to each individual submission, prices being quoted at the time of enquiry and where appropriate include engineering appraisal costs.

9. Redesign (withdrawal of design)

Designers may submit and later withdraw a design as a result of a multitude of reasons, for example, costs, buildability, programme or a change in layout or brief. If the later resubmission requires the engineering appraisal essentially be repeated then the Coal Authority reserves the right to charge the applicant the same corresponding permit or pre-application advice fee, to cover the expense of undertaking the appraisal again. The same applies to resubmissions which have not formally been withdrawn but constitute the same level of re-assessment.

10. Retention of existing protection measures

In some scenarios it may be beneficial for a developer to consider the re-use of existing permanent protective measures. In such circumstances it will be necessary for the Permit Holder to validate that re-use to the satisfaction of the Coal Authority by engineering appraisal.

When considering the case of the re-use of a reinforced capping slab over a former mine shaft, some points of consideration would include:

• the present condition of the capping slab and its predicted design life
• proof by investigation and/or records detailing its construction
• a design back-analysis that demonstrates its suitability for retention, given the proposed land use and ground conditions, engineering properties, etc.

11. Pre-application advice

The Coal Authority operates a pre-application advice service aimed at developers and their advisors working within Development High Risk Areas. Consultants managing sites that are impacted by mining legacy are encouraged to take early advantage of this process, which provides the Coal Authority's response. While the appraisal of proposed engineering solutions can in principle occur at later stages of the development process, it is advisable that pre-application advice is sought before any planning application has been submitted, so that where appropriate development layouts can be amended to minimise risks, and related guidance on supporting documentation can also be provided. Outcomes can vary, from an outline design being accepted 'in principle' or the agreement of a fully detailed design, as circumstances allow. In the context of planning applications engineering appraisal does not guarantee that planning permission will be granted since the Coal Authority is only a statutory consultee.

12. References

Coal Authority (2012) Policy for Building over or within the influencing distance of a Mine Entry.

Health and Safety Executive (2015) Managing health and safety in construction, Construction (Design and Management) Regulations 2015, Guidance of Regulations L153. HSE Books.

East Ayrshire Council (2016) BSP3: Minimum requirements when submitting Structural Calculations for Building Warrant Applications.

CIRIA C758D (2019) Abandoned Mine Workings Manual Ed. Parry D and Chiverrell C, 546pp. ISBN 978-0-86017-765-4.

13. Further information

Institution of Structural Engineers (2015) Guidance on the submission of structural calculations to Building Control. Business Practice and Regulatory Control Committee. The Structural Engineer February 2015.

Coal Authority Risk based approach to development management, Guidance for developers.

Coal Authority "Exemptions List" for the Risk Based Approach to Development Management.

Ministry of Housing, Communities and Local Government (2019) National Planning Policy Framework. Updated 19th February 2019.

Coal Authority Interactive Map Viewer. (Freely available online mining information with national coverage)

Online guidance with respect to making a permit application, undertaking a Coal Mine Risk Assessments or seeking Pre-application advice.