Notes on field reconnaissance
Field reconnaissance is carried out once the factual information for the site and its environs has been compiled and preliminary proposals for any ground investigation prepared. Additional information on the geology and hydrogeology, potential construction and access constraints for ground investigation might be revealed by the field reconnaissance. The following are some key points to consider when undertaking the field reconnaissance.
- a) Traverse the whole area, preferably on foot.
- b) Set out the proposed location of work on plans, where appropriate.
- c) Observe and record differences and omissions on plans and maps; for example, boundaries, buildings, roads and transmission lines.
- d) Inspect and record details of existing structures.
- e) Observe and record obstructions; for example, transmission lines, ancient monuments, trees subject to preservation orders, manhole covers, gas and water pipes, electricity cables, sewers.
- f) Check access, including the probable effects of investigation plant and construction traffic and heavy construction loads on existing roads, bridges and services.
- g) Check and note water levels, direction and rate of flow in rivers, streams and canals, and also flood levels and tidal and other fluctuations, where relevant.
- h) Observe and record adjacent property and the likelihood of its being affected by the proposed works and any activities that might have led to contamination of the site under investigation.
- i) Observe and record mine or quarry workings, old workings, old structures, and any other features that might be relevant.
- j) Observe and record any obvious immediate hazards to public health and safety (including to trespassers) or the environment.
- k) Observe and record any areas of discoloured soil, polluted water, distressed vegetation or significant odours.
- l) Observe and record any evidence of gas production or underground combustion.
- m) Tree types and locations if site underlain by fine soils.
E.2 Ground information
The following steps can be followed when gathering ground information.
- a) Observe the ground morphology and associated features to provide information on the geomorphology of the site and surrounding area. Study and record surface features, on-site and nearby, preferably in conjunction with Ordnance Survey mapping, geological maps and remote sensed images, and note the following:
- 1) type and variability of surface conditions;
- 2) comparison of surface lands and topography with previous map records to check for presence of fill, erosion or cuttings;
- 3) steps in surface, which might indicate geological faults or shatter zones. In mining areas, steps in the ground are probably the result of mining subsidence. Other evidence of mining subsidence should be looked for:
- compression and tensile damage in brickwork, buildings and roads; structures out of plumb; interference with drainage patterns;
- 4) mounds and hummocks in more or less flat country which frequently indicate former glacial conditions; for example, till and glacial gravel. Similarly, hollows and depressions, locally water-filled, could also indicate former glacial conditions;
- 5) broken and terraced ground on hill slopes, which might be due to landslips; small steps and inclined tree trunks can be evidence of creep;
- 6) crater-like holes in chalk or limestone country, which usually indicate swallow holes filled with soft material; and
- 7) low-lying flat areas in hill country, which might be sites of former lakes and could indicate the presence of soft silty soils and peat.
- b) Assess and record details of ground conditions in any exposures in quarries, cuttings and escarpments, on-site and nearby.
- c) Assess and record, where relevant, ground water level or levels (often different from water course and lake levels), positions of wells and springs, and occurrence of artesian flow.
- d) Study and note the nature of vegetation in relation to the soil type and to the wetness of the soil (all indications require confirmation by further investigation). Unusual green patches, rushes (e.g. Juncus sp.), willow trees (Salix sp.), alder (Alnus glutinosa) and black poplar (Populus nigra) usually indicate wet ground conditions.
- e) Study embankments, buildings and other structures in the vicinity having a settlement history, in particular, looking for cracks in walls, subsiding floors, and other structural defects.
E.3 Field reconnaissance for ground investigation
The following steps can be followed when carrying out field reconnaissance. Referenced photographs can form part of the subsequent record.
- a) Inspect and record location and conditions of access to working sites.
- b) Observe and record obstructions, such as overhead or underground pipes and cables, boundary fences and trenches, trees and other vegetation clearance requirements.
- c) Locate and record areas for depot, offices, sample storage, field laboratories.
- d) Ascertain and record ownership of working sites, where appropriate.
- e) Consider liability to pay compensation for damage caused.
- f) Locate a suitable water supply where applicable and record location and estimated flow.
- g) Locate a suitable means of disposing of solids and liquid arising from the investigation.
- h) Record particulars of lodgings and local labour, as appropriate.
- i) Record particulars of local telephone including mobile phone reception, employment, transport and other services.
- j) Note the surface conditions at each exploratory hole and the particular reinstatement requirements (e.g. breaking out of pavement and replacement).
- k) Record details of post investigation access to instrumentation and any requirements to protect the instrument (e.g. fencing).