Archaeology Survey Techniques Quiz

Site and Soil Investigations

• Site investigation is crucial for foundation design and construction.
• Typical information sources and survey techniques are needed.
• Understanding soil properties relevant to foundations and ground movements is essential.
• The effects of groundwater movement and control methods should be appreciated.

Types of Site Investigation

• Desk study involves collecting existing information, maps, service drawings, aerial photographs, and information from public bodies.
• Site reconnaissance is a walk-over survey to visually inspect the site, including topography and location features.
• Ground and soil investigations include site investigations, on-site tests, and laboratory work.
• Performance appraisal involves feasibility studies, environmental audits, and risk assessments.

Objectives of Site Investigations

• Determining site conditions within the region of influence of a proposed building.
• Determining the engineering properties of soils and rocks that affect foundation design and construction.

Inadequate Site Investigation

• Leads to additional payment and time claims from contractors.
• Insufficient information can result in the presence of groundwater or insufficient information for the design of temporary works.

Potential Hazards & Associated Risks

• High water table/low-lying land: Flooding, toxic material transport.
• Mining: Ground movement, ground gases, shrinkage/heave.
• Peat: Changes in volume due to moisture content, methane/carbon dioxide production.
• Infill/made ground: Tipping, gas release, settlement.
• Low bearing capacity ground: Settlement, tilt problems.
• Former buildings/structures: Settlement, impact on new structures.
• Adjacent buildings: Effect on existing structures, stability.
• Drains: Contamination, flooding, waterlogging, interruption of land drainage systems.
• Sulfates in ground/groundwater: Expansive reaction.
• Contamination: Chemical attack on concrete, potential hazards from chemicals.
• Solution features in chalk/limestone: Settlement, cavities, ground movement.
• Unstable ground/landslip: Ground movement.
• Seas/lakes/rivers: Erosion.

Desk Study

• Ordnance survey maps (historical+modern), grid reference.
• Rights of way.
• Geological maps (subsoil types, radon risk).
• Site history (greenfield/brownfield).
• Previous planning applications/approvals.
• Current planning applications.
• Development restrictions/conservation orders.
• Utilities (location of services).
• Wayleaves.
• Aerial photographs.
• Ecology factors (protected wildlife).
• Proximity of landfills (methane risk).
• Flood risk and history.
• Underground mining/subsidence history.
• Restrictions from deeds of land.
• Archaeological findings.

Sources of Information

Public Domain

• British Geological Survey (maps, information).
• Ordnance Survey.
• Environmental Agency.
• Coastal erosion/landfill sites/water extraction details.
• Local Authority (building control, environmental health, legal searches, previous investigations).
• County records, libraries, museums, local history.
• Utility companies.
• Coal Authority (mining reports).
• Soil survey maps.

Private Domain

• Local residents.
• Site vendor.
• Nearby sites.
• Projects of similar sites (in-house information).

Information Identified

• Location, accessibility, and space.
• Subsoil nature.
• Extent of difficult ground conditions.
• Filled/contaminated ground.
• Mining shafts/tunnels.
• Ponds, watercourses, groundwater level, and risk of flooding.
• Utility services.
• Previous vegetation.
• Landslip.
• Natural aggressive chemicals, harmful gases, and landfill gases.
• Foundations of adjacent buildings.

Walk-Over Survey

• Checking site boundaries against deeds.
• Identifying potential hazards (e.g., hazardous waste tipping).
• Assessing condition of existing structures.
• Assessing ground slope/contours.
• Identifying invasive vegetation (e.g., Japanese Knotweed).
• Confirming Tree Preservation Orders.
• Assessing adjacent structures/property.

Information to be Collected

• Location & accessibility.
• Potential hazards.
• Site size/shape/level.
• Tree position/species/size/condition.
• Existing building/utility locations.
• Signs of groundwater/flooding.

Topography

• Changes in slope.
• Valley bottoms/depressions.
• Overburden on slopes.
• Excavations.
• Signs of landslip/tilting.
• Signs of subsidence.
• Imported soil details, especially if odorous or hot in nature.

Soils and rocks

• Basic ground type.
• Evidence of compressible soil (peat, silt etc).
• Cracking/stickiness.
• Change in soil conditions (clay to chalk or soil to rock).

Surface water and vegetation

• Presence/level of the water table
• Evidence of flooding (reeds, water-loving plants).
• Springs, ponds, rivers.

Structural information

• Damage to structures (cracking).
• Evidence of movement (tilting, distortion).
• Structures/services below ground level.

Local information

• Local knowledge of site activities (mining, tipping), history/past usages.
• Place names/street names that may give clues.

Initial Assessment Results

• Desk study and walk-over survey results must be recorded and evaluated.
• Site plans (dates, previous/current uses, proposed layout).
• Site geology (maps, previous investigations, laboratory reports/test results).
• Photographs (including aerial).
• List of sources consulted and copies of information obtained.

Site Survey & Ground Investigation

• Digital measured survey (including ground levels).
• Location of ground investigations.

Purpose of Site Survey and Ground Investigation

• Identifying subsoil types, properties and depths.
• Determining water table levels.
• Obtaining subsoil samples for identification, classification and ascertaining properties.
• Assessing subsoil strata depths.
• Enabling design and construction of foundations.
• Identifying geological fault lines and water table levels.

Soil Sampling

• Sample extraction at intersections of a grid pattern (10-20m²).
• Representative samples in areas outside those directly impacted by the project.

Soil Investigation Methods

• Trial pits, Boreholes. -Appropriate for low rise buildings. -Appropriate foundations up to 3m, 30m, and > 30m respectively.

Soil Analysis

• Sieve Analysis: Laboratory test determining soil particle size via sieving.
• Soil particle size and distribution.

Site Soil Testing Techniques

• Tests for bearing capacity, density, shear strength.
• Methods avoid disturbing the soil under test.
• Referenced in BS 1377.

Compression Test

• Measures compression strength of cohesive soil (e.g., clay).
• Soil samples are loaded until shear or bulging occurs.

Combined Stress Exerted on Subsoil

• Foundations exert stress overlapping and increasing force in close proximity.
• Angle of maximum shear is 45 degrees.

Borehole Depths

• Depth of borehole depends on type of foundation -Pad/raft, Strip, and Friction Pile foundations require different borehole depths.

Water Table

• Precipitation seeps downwards to form the water table.
• Water table level is determined using instruments such as piezometers.

Problems from Ground Water

• Groundwater can flow into excavations, leading to the need for timbering.
• High water table leads to flooding and/or high humidity in buildings post-construction.

Recommendations

• Obtain sufficient site information & ground information for design & construction.
• Balance investigation costs against risks in both design and construction.
• Seek professional advice (e.g., geotechnical engineer or environmental specialist).