Quality in Construction

The Importance of Site Investigation before Construction

The Importance of Site Investigation before Construction

In recent years Malta saw a shift towards commissioning a site investigation before a project actually commences. This shift was driven partially by the fact that in the recent past there were a number of accidents which involved third parties that might have easily been avoided with a proper site investigation and proper guidance by professionals that can properly interpret the investigation document and relate the findings to what there is on site.

The main purpose of a site investigation is to properly identify issues that are relevant to the site in question and to understand better the specific ground conditions that will ultimately affect the development being proposed. Thus, this investigation inherently gives a better understanding to the architect and the engineers responsible for the new construction and guide them towards the right choices that would enable safe and economic constructions. In a very broad sense, the ground investigation is understood to include not only the underlying rock or soil, but also the ground water regime or any other underlying conditions that might be relevant. A site investigation on the other hand will give a broad understanding of the construction methods used for neighbouring buildings so that decisions on the way forward on how to construct the building in question can be taken.

The need to carry out a site investigation

The characterization of the ground conditions whether it is a greenfield site or a site that has already been developed will include geotechnical, geo-environmental and structural issues. The investigation of all these will result in an economic, cost-effective design without a lot of site disruptions that may develop if these issues are not studied beforehand. The investigation should allow for a comprehensive risk assessment of the conditions of the site to be made. The risks to be identified may include risks related to health, engineering, financial and regulatory which may all arise from unforeseen ground conditions and liabilities.

The main objectives of a Site Investigation

The main objectives of a site investigation are the following:

1 To determine the suitability of the site and the surroundings to the project being proposed and to try and understand better the engineering challenges at hand.

2. To obtain all the necessary design parameters to be able to do the necessary geotechnical and structural design.

3. To understand better the potential ground and ground water conditions that would affect the construction. To also get a better understanding of how the neighbouring buildings are constructed and how this might affect the construction of the structure being proposed.

4. To understand better if there is any risk of contamination in the ground and if there is to understand what kind of contamination one is dealing with. This does not only have an environmental effect but also an effect on the kind of materials chosen for the project.

5. To understand if there are any materials present on site that can actually be used in the project itself.

6. To understand better how the proposed design affects the adjacent structures and possibly the ground water.

Data present in a Site Investigation

A site investigation is classified as the gathering of information about the proposed location of the project. The process of the site investigation can be categorized in the following areas:

1. Desk Study – This should be done every time and before any intrusive site investigation is made. During this stage research on the site is done to gain as much information as possible both from a geotechnical and a historical point of view. A desk study draws together existing information from a variety of sources to form an initial appraisal of possible ground conditions. The desk studies must consider past uses and the current status of the site. This should include the gathering of information on neighbouring structures that might be affected by the proposed development. Records of previous SI would be useful information. Other useful information may include data of services such as electricity, water, sewers, network systems etc. Records of neighbouring structures may also be included in the site investigation. Here one can thus understand better the benefits of having a centralized information library including architectural and structural details and calculations of all the developments that are constructed. In this way the data for the desk study is readily available to other engineers and architects. This would reduce the need for assumptions and thus would reduce the chance of mistakes being made.

2. Walk-over Survey – This can give a very good insight into the ground condition problems and contamination issues. Such site visits usually also give rise to contributions being made by neighbors and other residents that also have their value to help structure other investigations that in all will help get a clear picture of the site conditions. The combination of the desk study and the walk-over survey is a cost effective first stage of the investigation as it provides a strong basis for a structured and more informative further investigation by other intrusive means. In other words, it is always better to understand beforehand where it is better to do the intrusive investigation than just investigating in the blind. Like that there is more guarantee that the intrusive investigation is more meaningful.

3. Site Investigation Planning – There are two aspects to the site investigation, the geological structure and character of the site and the testing of the soil/rock both in the laboratory or in situ. When planning a site investigation, the following points should be considered. The succession of strata over the whole site should be known. If there are any questions regarding this, the site investigation should be designed in such a way to address this issue. The homogeneity of the strata of rock or soil across the site should be understood in the process and if there are any localized variations these should be found and understood well as these might have an adverse effect on the structure erected. Ideally the flow of water across the site if this is present should be understood as this might affect the general stability and integrity of the structure.

4. Ground Investigation – There are two principal ways to investigate the ground conditions – the trial pits and boreholes. There are also the geophysical techniques such as the seismic surveys that are becoming lately popular on larger projects locally. Trial pits are ideal if the information required is at a shallow depth as these provide more extensive information, then boreholes in general. These are also good to detect services. The trial pit can be done either by hand or by a hydraulic excavator. A trial pit log should be made following investigation by trial pit. This should include the orientation and size of the pit, detailed sketches of faces, depth scale, water level and water seepage if any. Weather and time of sampling should also be