Photography can be used as an investigatory tool where images of the site in a previous use are available and also as a record of the investigations carried out in terms of the condition of the site at the time and of the materials encountered within the investigation. These two different uses of photography within a ground investigation are complementary, and it is important that the investigation strategy includes obtaining a comprehensive record of the site before, during and after the investigation.
H.2 Remote sensed images
No desk study is complete without a full review of the available remote sensed images, whether these are aerial photographs or satellite images. These images can be photographs in the visible spectrum from archives or specially flown (see Clause 14), false colour images where sensing has been made in other parts of the spectrum, or processed results from other sensors such as radar. The uses to which these different types of images can be put are summarized in Section 2.
H.3 Site photographs
H.3.1 Historical photographs
An important element of the desk study is to identify any photographic records that show previous uses of the site. This is likely to be particularly important if those previous uses are potentially contaminative, they can also indicate the position of previous structures and also in case there are any indications of ground instability on the site, either due to mass movements or due to man's activities.
H.3.2 The site before the investigation
As part of the desk study and during the walk-over reconnaissance survey, it is essential to build a photographic record of the site and its environs including features of particular interest on and around the site. The features worth recording might include existing structures and any signs of distress, indications of mass movement, anticipated or unexplained spoil heaps, any indications of drainage such as boggy areas, any circular features.
It is useful if all photographs taken on the walk over include a date record; in addition a plan of the site showing the position and direction of the camera for each image are useful.
H.3.3 The site during the investigation
Photographs of the site before it is disrupted by any ground investigation activities are always useful. An additional photographic record can then usefully be compiled to show the damage to the site and the completion of restoration activities; this photographic record is useful in sorting out disputes with the contractor and the landowner.
In addition, photographs of where on the site particular investigation positions, including any monitoring installations, were constructed or tests carried out can be useful in later interpretation of findings.
It is useful if all photographs include the date and a record of where and why the picture was taken.
H.4 Photographs of recovered materials
A photographic record of the materials recovered during the investigation is often a contractual requirement; even if it is not, the inclusion of such a record is to be recommended. All photographs of recovered materials normally include a project reference, investigation point reference number, depth information, date, scale and colour chart.
The photographic records could include:
- looking down into trial pits at the in-situ materials;
- spoil excavated from the trial pits;
- any other exposures created in making access for plant and equipment;
- all cores recovered, whether of soil, rock or other materials;
- all samples that are split for detailed logging; and
- laboratory test specimens before and after test.
Photographs of cores are to be taken as soon as possible after extraction from the ground and before description, sampling and testing.
The following are good points to adhere to when taking photographs.
- A graduated scale running parallel to the core axis for the full length of the core box is included in photographs.
- The core fills at least 50% of the photograph frame and care is taken to ensure that the core is in sharp focus with good even lighting (this might require some form of artificial lighting).
- Cores of soil (rotary or extruded tube samples) usually show little on the outside, and so photographs can be taken once the cores have been split. Further photographs after allowing the samples to air dry might also reveal useful information on soil structure.
- In addition to routine photography of all cores and split samples, photographs are also be taken of any atypical features.
- All photographs of the materials encountered include relevant project reference information, the number of the hole and sample, the date, an international photographic colour chart to allow correction of the colours subsequently if necessary and a scale bar.
H.5 Contractual requirements
The requirements for photographs to be taken during the investigation and to be included within the GIR are to be set out in the contract documents at the time of tender. These can be based on the UK specification for ground investigation , which has useful clauses to cover this activity.