Left : Soil resistivity testing configuration with a 4-electrode Wenner array.
Soil resistivity testing measures the capacity of the ground to pass an electrical current. This property utilises the electrical power industry for assessing the design requirements of earthing systems. SUMO provides soil resistivity testing services to assist in the design and installation of power generation plant, substations and engineering infrastructure.
Standard soil resistivity testing procedure involves four equidistant electrodes set-out in a fixed configuration array. This is illustrated in the diagram below. A low-frequency electrical current runs across the outer electrodes and the voltage measured between the inner potential electrodes. The resulting soil resistance reading is then converted by standard equations into a resistivity reading. This represents the average resistivity of the ground between the potential electrodes. Depth readings from electrical soundings use an expanding electrode array centred on the same point. The depth penetration achieved increases in direct proportion to the electrode spacing of the array.
Above : Soil resistivity test equipment configuration and current paths.
Soil Resistivity Testing & Earthing Design
Earthing systems provide a safe outlet between an electrical circuit and the ground. The systems are for the dissipation of electrical faults, grounding lightning strikes and maintaining the correct operation of electrical equipment. Their design requires detailed knowledge of the resistivity of the ground in the site area. This measures depth at locations around the site, using an expanding Wenner array, standard BS EN 50522. This is called soil resistivity or earth resistance testing.
The correct measurement of soil resistivity is particularly important in high resistivity ground. Specifically where electrical currents do not dissipate readily. In such ground conditions achieving a good earth can be problematic. Information on ground resistivity is required in much greater depths for the successful installation of an earthing system.
Inversion software removes the effects of electrode geometry from the data set and produces a model of the resistivity layers at the test location. Correlation with background geological data interactively refines the model and ensures it relates to actual ground conditions on the site.
Above : Earth rod testing by the fall of potential method.
Earth System Testing
Soil resistivity equipment is also used on new earthing installations, to verify the system has sufficient capacity to dissipate fault related current and lightning strikes. This is known as earth-rod testing. The method measures the electrical resistance of an earth rod once it has been emplaced in-position in the ground.
An adapted testing procedure termed the Fall-of-Potential (standard IEEE 81), uses two electrodes and a resistivity meter all connected to the installed earth rod. The current electrode is inserted in a fixed position, outside the direct influence of the earthing rod. Readings are then taken with the potential electrode spaced at set intervals in between the earth rod and the current electrode. The results are plotted graphically to determine the resistance of the earth rod. This will also gage if the earthing system requires additional earth rods.
Soil Corrosivity Testing
In addition to normal earthing applications, SUMO also carries out soil corrosivity testing. This assists the design and installation of pipelines and buried steel structures. Knowledge of soil corrosivity is critical for cathodic protection measures and coatings. This will also predict the effective lifetime of an underground storage tank (UST). Factors such as soil composition, moisture content, pore water chemistry, pH and redox potential all effect the soil resistivity. This is a principal diagnostic factor.
The corrosivity test uses a standard Wenner array based on BS 1377 and BS EN 50522. This is to measure the resistivity along specific sections of a new pipeline route. Readings are usually taken where lithologies change. As well as at special situations such as fault zones and infilled channels. Surveys take readings down to pipeline depth at each test location. Longer arrays are required near water courses and at cross-overs where the pipeline needs to be embedded to a greater depth. The resultant resistivity data is converted into corrosivity factors and integrated into the design of effective protection measures.
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How accurate is SUMO's underground utility survey and what types of utilities can it locate?Using cutting-edge technologies like electro-magnetics, signal induced threading, and Ground-Penetrating Radar (GPR), our underground utility surveys accurately detect a wide array of buried utilities including metal and plastic pipes, drainage systems, electricity cables, telecoms, and fiber optic cables. The methodology ensures high accuracy without the need for invasive trial holes.
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What is the turnaround time for obtaining results with SUMO's Underground Utility Detection service?SUMO’s service is built for rapid response. Contractors can receive immediate results onsite. Our equipment provides real-time information, and once we leave the site, the detected utilities are visibly marked on the ground surface for quick reference.
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Does SUMO provide detailed mapping of the detected utilities for permanent records or construction purposes?Absolutely, SUMO not only marks the detected utilities on-site but also offers high-quality, color-coded survey drawings. These drawings can include topographic features and a comprehensive record of the utility detection survey, ensuring it meets the client’s needs for future reference or pre-construction design works.
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Topographical and Geophysical surveyIn addition to mapping out utilities, our experience team can accurately survey the land, creating topographical drawings for use. With our state-of-the-art aerial technology, nothing is missed.
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What additional information can be included in the underground utility mapping service provided by SUMO?In addition to topographic features, SUMO’s mapping service can include fixed surface utility features such as inspection chambers, valve boxes, and telegraph poles. It can also incorporate key topographic details like building lines, fence lines, kerb lines, street furniture, street names, building names, and house numbers, facilitating easy site location.
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Does the utility mapping service by SUMO include standard referencing and compatibility with existing survey data?Yes, SUMO ensures the utility mapping references the ordnance survey grid and level datum as standard. Additionally, the drawings can be supplied to a specified grid and level datum and can overlay an existing topographical survey, making it a versatile and adaptable service for various project needs.
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What sets SUMO Services apart from other survey providers?SUMO stands out due to our impeccable level of service with nationwide coverage, state-of-the-art equipment, and our commitment to delivering top-quality, detailed colour-coded survey drawings in both hard and electronic formats.
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How do I request a survey quotation from SUMO Services?Requesting a quotation is easy. Just click on the "Request a Survey Quotation" button on this page, and our team will get in touch with you promptly.
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Can I book a SUMO Survey online?Yes, you can! Simply click on the "Book a SUMO Survey" button on this page, and you can schedule your survey with us at your convenience.
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What type of survey is suitable for my project or site?Our experienced team will work with you to determine the most appropriate survey for your specific needs. Contact us, and we'll assist you in making the right choice.
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Can I obtain both digital and hard copies of survey drawings?Absolutely. We offer the convenience of electronic copies for digital use and hard copies for your records. Just let us know your preference.
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Do you provide custom survey solutions for unique projects?Yes, we understand that every project is unique. Our team is highly adaptable and can tailor our surveying services to meet your specific requirements.
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How do I get in touch with SUMO Services for further questions?For any additional questions or inquiries, feel free to contact us through the contact form, and our dedicated team will assist you promptly.
Case Studies
We think you may be interested in reading our clients case studies.
Resistivity Imaging
Archaeological & Geophysical Surveys
Survey Methodologies
Detailed Magnetic Survey
Soil Self-Potential
Electrical Resistivity Tomography (ERT)
Soil Thermal-Resistivity Testing
Electromagnetic Ground Conductivity
Electromagnetic Location (EML)
Ground Penetrating Radar (GPR)
