Suppose a client has retained a technical report prepared several years ago. Is it always necessary to carry out all engineering surveys again?
The short answer is: not always. However, this cannot be determined solely by looking at the date of the report.
There is no single validity period applicable to all types of engineering surveys. Different types of surveys and individual parameters are subject to different validity periods.
For example:
- an engineering topographic plan is generally considered valid for no more than two years, provided that the relevance of the information shown on it has been confirmed;
- for most engineering-geological survey results, the validity period is up to five years for undeveloped areas and up to two years for developed areas;
- hydrological data are generally used subject to a validity period of up to two years, while meteorological data may be used for up to five years;
- for engineering and environmental survey data, the applicable periods vary depending on the parameter being investigated and the level of development of the territory.
However, compliance with the applicable validity period alone is not sufficient.
It is also necessary to verify:
- whether the boundaries of the survey area remain the same;
- whether development, topography, utility networks or anthropogenic impacts have changed;
- whether the location and parameters of the proposed facilities remain unchanged;
- whether the design loads, foundation types or foundation depths have changed;
- whether the scope of field and laboratory investigations is sufficient;
- whether the available materials comply with current regulatory requirements.
For example, the results of engineering-geological surveys carried out in previous years may be used without additional investigations only if the applicable regulatory time limits are observed, engineering-geological conditions have not changed, and there have been no significant changes to the design solutions.
Following the review, three options are possible.
- Use the previous results if they correspond to the current project, remain relevant and are sufficient to support the design solutions.
- Use them together with new data if the existing materials remain useful but require verification or additional investigations. In this case, the scope of new work may be reduced, provided that this approach is properly justified in the engineering survey programme.
- Carry out new engineering surveys if the territory or the project has changed, the applicable regulatory periods have expired, or the previous data are insufficient.
It is important to understand:
A positive expert review obtained on the basis of an old technical report does not make that report valid indefinitely. However, even materials that can no longer be used directly may still help to understand the site conditions and define the scope of new investigations more accurately.
Recommendation: assess the suitability of previous survey materials before starting the design process. The selected approach should be justified in the engineering survey programme and agreed with both the client and the designer.
This is more cost-effective and reliable than discovering during the expert review that part of the required data is missing.
I have compiled a decision tree in the accompanying cards to help with the initial assessment.
