The Millennium Challenge Corporation (MCC) Nepal Electricity Transmission Project (ETP) is a major energy infrastructure programme that includes the construction of three new 400 kV indoor gas-insulated substations (GIS) at Ratmate in Belkotgadhi Municipality, Nuwakot District; New Damauli in Tanahun District; and New Butwal at Bhumahi in Nawalparasi West District. The transmission lines will also interconnect with existing Nepal Electricity Authority substations at Lapsiphedi in Bhaktapur District and New Hetauda in Makawanpur District.

IES Nepal was sub-contracted by CEMAT Consultant Pvt. Ltd. to carry out pavement investigation works along the access roads serving each of the three new GIS substation sites. The investigations provide the subgrade characterisation data — bearing capacity, material classification and compaction properties — required for the structural design of all-weather access roads capable of supporting heavy equipment movement during substation construction and long-term operational maintenance.

Field work was conducted across three provinces (Bagmati, Gandaki and Lumbini) spanning both hilly and Terai terrain conditions in December 2020 and January 2021, with laboratory analysis and reporting completed within the two-month contract period.

What We Did

Test pitting and CBR sampling — 6 dry & 4 soaked tests per location

Excavated test pits along the access road alignments at each of the three substation locations to expose the subgrade material and collect undisturbed and bulk samples for California Bearing Ratio (CBR) testing. Ten CBR tests were conducted per location — six dry condition tests and four soaked condition tests — to characterise the subgrade bearing capacity under both ambient and worst-case saturated conditions relevant to monsoon performance.

Dynamic Cone Penetrometer (DCP) testing — subgrade strength profiling

Carried out in-situ Dynamic Cone Penetrometer (DCP) tests on subgrade material at each access road location to measure penetration resistance with depth, providing a continuous in-situ strength profile of the subgrade layer. DCP results were used alongside CBR data to confirm subgrade strength consistency and identify any weak or compressible zones requiring special treatment in the road design.

Laboratory testing — sieve analysis, Atterberg limits & MDD (6 sets)

Performed a full laboratory testing programme on subgrade samples collected from each location comprising: Sieve Analysis for particle size distribution and soil classification; Atterberg Limit Tests (Liquid Limit and Plastic Limit) to determine plasticity and classify fine-grained material behaviour; and Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) tests using the Proctor compaction method — six complete test sets in total across the three substation access road locations.

Data analysis and pavement investigation report

Compiled and analysed all field and laboratory test results to characterise the subgrade material properties at each of the three access road locations — Ratmate (Nuwakot), New Damauli (Tanahun) and New Butwal (Nawalparasi West). Prepared the pavement investigation report presenting CBR design values, DCP strength profiles, soil classification, compaction parameters and engineering recommendations for the structural design of each access road, submitted to CEMAT Consultant for incorporation into the MCC ETP detailed design package.

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