Ground Investigation

Rotary Drilled Boreholes

Boreholes formed by rotary drilling equipment are normally used when rock or hard or ground is anticipated. Rotary techniques are used to drill through rock / solid geology.  There are two types or rotary borehole frequently used on ground investigation projects, rotary open holes and rotary cored holes.  Rotary open hole holes are drilled where rapid progress is required on projects such as mining investigations when the structural details of the rock is not necessarily important but we are more interested in the presence of voids that could indicate shallow mine workings. Rotary cored holes are drilled when structural details of the underlying rock are required.  Generally used in applications such as when a proposed development has heavy loadings, require deep foundations or when the site is underlain by shallow bedrock.

Dynamic Sampling & Dynamic Probing

Dynamic sampling rigs are a very useful tool for quick shallow unconsolidated ground investigations. Our rigs are rubber tracked, low ground pressure self-propelled units so they can access any site where shallow soft soil sampling is required.  They are ideal for a ground investigation which requires chemical sampling, installing ground gas and ground water monitoring wells for subsequent environmental monitoring, and for in-situ geotechnical testing of the shallow underlying soils. However they are restricted to shallow depths.

Cable Percussive Boreholes

Also referred to as “cable tool” or “shell & auger” these tripod rigs can reach significant depths but are limited to drilling through soils or weak weathered rock.  Cable percussion boreholes are used where ground conditions may be variable and when information is required at depths greater than around 6.00mbgl from the ground investigation.

Trial Pitting

Machine dug trial can often provide the most practical and economical method of site investigation and assessment. Often used to obtain samples and engineering logs of shallow strata and can be important when dealing with variable ground conditions.

Soil and Rock Logging

Our geotechnical engineers have extensive experience in the logging of soil and rock to BS 5930-2015, BS EN ISO 14688-1 2002 and BS EN ISO 14688-2 2002 along with relevant CIRIA guidance.

Factual and Interpretative Reporting

Factual reports are written by our highly qualified and experienced team of Geotechnical and Geo-environmental engineers and cover every aspect of the site investigation, including:

• Purpose and scope of the investigation
• Accounts of all field and laboratory work
• Exploratory hole records (trial pits, window sample holes and boreholes), including grid co-ordinates and levels
• Any in-situ test results
• Any laboratory test results
• Any instrumentation and monitoring results
• Site plans include locations of any exploratory holes
• The provision of data in various formats

Technical advice can be provided from our Geo-technical team who are highly qualified experts in a wide range of fields including engineering geology and foundation design so well qualified to offer solutions to geotechnical problems connected with:

• Adequate load bearing for shallow and deep foundations
• Settlement estimations
• Slope instability/stability
• Causes of failure
• Ground improvement solutions

Interpretative Reporting

Technical advice can be provided from our Geo-technical team who are highly qualified experts in a wide range of fields including engineering geology and foundation design so well qualified to offer solutions to geotechnical problems connected with:

• Adequate load bearing for shallow and deep foundations
• Settlement estimations
• Slope instability/stability
• Causes of failure
• Ground improvement solutions

Geomorphological Mapping

Geomorphological mapping techniques are used to identify surface features and landforms which can provide a good indication of geological processes occurring on a site. The mapping is often used on sites with slope stability problems. Geotechnical engineers can use the geomorphological map to target areas for potential ground investigation and monitoring and also to assist in producing a ground model and to aid subsequent design.

Earthworks Examinations and Inspections

Central Alliance have experience undertaking earthworks examinations and inspections. We have particular expertise in rail geotechnics and in the identification slope stability problems on earthworks.

Scan Line Surveys

Understanding the spacing and size of discontinuities in a rock mass is extremely important in the prediction of rock behaviour. The characteristics of discontinuities in rock faces can be estimated using scan line surveys. Central Alliance are able to provide experienced engineering geologists with an understanding of rock mechanics to carry out such surveys.

Subsurface Laser Scanning

Subsurface laser scanning can provide accurate survey information about voids and cavities below the surface, including those that cannot be accessed readily or safely by a surveyor.
Using remote 3D laser scanning and sonar technology we can accurately capture geo-referenced survey data to provide information about the size, shape and position of a void or cavity. Our range of subsurface laser scanning services include:

• DTH (Down The Hole) scanning of voids and cavities located in boreholes
• Deep manholes
• Shafts

Subsurface Sonar Survey

• Dry and submerged cavities (using subsurface sonar systems)
• ROV inspections
• CCTV high definition photography/video of shafts and voids ​