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CROSS Safety Report

Adjacent excavations in Australia

Report ID: 360 Published: 1 July 2013 Region: CROSS-UK

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Overview

In parts of Australia, says a reporter, deep excavations in clay and sandy materials have caused damage to adjacent property and to existing buildings founded on high level footings.

Key Learning Outcomes

For the construction team:

  • Having a competent temporary works designer/adviser in place to supply an engineered solution can ensure all excavations are carefully considered and planned

  • Verification of temporary works erection by a competent person who can oversee and coordinate the whole process can also ensure the works are installed correctly

For civil and structural design engineers:

  • The condition and stability of adjoining structures should be determined to make sure that the methodology of deep excavations does not endanger the stability of adjoining property

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In parts of Australia, says a reporter, deep excavations in clay and sandy materials have caused damage to adjacent property and to existing buildings founded on high level footings. Additional regulations have been introduced, but these difficulties continue. There have been cases, says the reporter, where building owners have been involved in civil actions against developers or builders to try to recover the costs of rectification to their damaged property.

This is a potential risk for structural and geotechnical engineers and builders. Under the Australian regime, when a local Building Surveyor consents to a new project there are standard regulations intended to reduce the risk of damage to adjacent buildings, and there are also legal obligations under various statutes.

However, continues the reporter, reliance is placed on the builder to repair any obvious and immediate damage. This is an unsatisfactory situation when the consequences of any damage can include latent defects which may not become apparent for many years.

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This is an example where different customs, practices, regulations and legal principles may apply in different regions. In general, however any redevelopment next to an existing building needs to take into consideration the implications on the adjoining structure. A potential major implication always relates to foundations where overloading existing foundations or causing settlement during construction or in the longer term are potential issues.

These may be related to serviceability as well as to potential collapse but in every type of scheme it is incumbent upon the structural engineer to consider the wider consequences of the design. Proving that adjacent excavations are or are not the reason for distress to adjacent properties is easier if there is site monitoring of movements during and after the works. 

In the UK, regulations in the form of the CDM (Construction Design and Management) Regulations and the Party Wall Act are there to ensure that consequential risk is mitigated to a satisfactory level. In particular The Party Wall Act 1996 provides a framework for preventing and resolving disputes in relation to party walls, boundary walls and excavations near neighbouring buildings.

Particular problems associated with protection work in Australia are considered to be as follows:

  • Some engineers give inadequate attention to the protection of adjacent properties in their design. This should commence with comprehensive geotechnical investigations of next door conditions and include recommendations on how to eliminate long term effects due to the proposed construction.
  • Some builders with or without the connivance of other parties may not comply with the design documents and take ‘short cuts’ to reduce costs or gain a time advantage
  • There is sometimes inadequate supervision of builders work with regard to protective works
  • The legal framework for situations where the protection works are found to be inadequate are often cumbersome, expensive and time consuming. The reimbursements of costs incurred in engaging engineers, architects and legal representatives can become points of contention.
  • There can be problems associated with insurance

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