Investigation into the Properties and Behaviour of Liquid Soil (LS) Technology

Completed

Other Cross-Cutting Technologies or Research
Other Power and Storage Technologies(Electricity transmission and distribution)

Applied Research and Development

ENGINEERING AND TECHNOLOGY (Electrical and Electronic Engineering)
ENVIRONMENTAL SCIENCES (Earth Systems and Environmental Sciences)

Not Cross-cutting

Project Contact
National Grid Electricity Transmission

Network Innovation Allowance

Ofgem

01 September 2018

01 July 2019

ENA months

£128,000

Power

London

Network Innovation Allowance

Project Contact, National Grid Electricity Transmission

The project will consist of a literature review to identify any alternative flowable type backfills for potential use in an HV environment and an investigation into the specific properties and behaviours of this type of backfill to assess the suitability of flowable type backfill materials for use on the UK transmission system. Tests will also be undertaken to gain an understanding of the possibility of any potentially harmful ingredients from the backfill material leaking (leaching) into the surrounding environment, and an assessment of the propensity for long term shrinkage of the LS. This project will investigate the properties and behaviours of the LS product to determine whether it could be suitable for use on the National Grid HV system. The study will take the following approach to meet the project objectives:1. A literature review will be carried out to identify any alternative temporarily flowable backfills with potential for use in an HV environment which might have similar properties and benefits that could be assessed using the same methods2. Investigation into thermal-hydraulic transport through LS when formed from a variety of soil samples3. Investigation to understand moisture migration in a variety of LS samples 4. Basic soil mechanics and concrete tests will be used to determine the fundamental properties of the material and to gain familiarity with its use. 5. Investigation into the coupled thermal-hydraulic behaviour of LS when formed from poorly-graded, coarse sand, which is likely to provide the most onerous test of its performance.6. A demonstration to show the extent to which experimental results can be modelled numerically and the potential to model design scenarios (case studies) to explore the suitability of various metrics (including the 50°C isotherm) in predicting the merit of using a LS backfill material 7. Investigation into the propensity for leaching of the proprietary ingredients of LS using the Toxicity Characteristic Leaching Procedure (TCLP).8. An assessment of the propensity for long-term shrinkage of LS, especially at the soil-cable interface by deduction from the results of the basic soil testing. 1. To identify any flowable type backfill materials available with potential for use on the UK transmission system.2. To gain an understanding of the basic properties of flowable type backfills, specifically LS, when formed from a variety of indigenous materials, to assess the suitability of this type of backfill material for deployment on the UK transmission system.

Cement Bound Sand (CBS) is a standard backfill material which is frequently used to reinstate excavations associated with laying underground high voltage transmission cables. However, this backfill is unsuitable when higher ratings are required as it cannot adequately dissipate the additional heat generated by the conductor. As we seek to increase the amount of undergrounding and capacity of our transmission infrastructure, this is likely to become of increasing importance. Liquid Soil (LS) has been identified as a potential alternative to CBS as it claims to have a relatively low Thermal Resistivity (TR), which would allow the heat to dissipate quickly through the material and enable higher rated cables. LS is formed by using excavated native soil which is then processed together with additives, which allows it to become temporarily flowable. This means that once prepared it can be poured into the trench and around the Gas Insulated Lines (GIL) or cable. The material adheres closely to the cable or GIL and sets hard without the risk of air gaps forming, thus removing the need for the backfill material to be compacted. However, LS has not yet been used in the UK. In order to deploy this backfill on the High Voltage (HV) transmission system we need to understand the material properties of the LS and in particular how it behaves under certain conditions in terms of moisture retention and the consequent impact on TR.The project will consist of a literature review to identify any alternative flowable type backfills for potential use in an HV environment and an investigation into the specific properties and behaviours of this type of backfill to assess the suitability of flowable type backfill materials for use on the UK transmission system. Tests will also be undertaken to gain an understanding of the possibility of any potentially harmful ingredients from the backfill material leaking (leaching) into the surrounding environment, and an assessment of the propensity for long term shrinkage of the LS.

02/12/22