Six soil parameters (moisture content, pH, resistivity, oxidation-reduction potential, chloride and sulfate) of 23 samples were analyzed using standard methods for their corrosive nature towards the buried galvanized-steel and cast-iron pipes used to supply drinking water in three areas (Tikathali, Imadol- KA and Imadol-KHA) of Lalitpur district of Kathmandu Valley. Amounts of these six soil parameters in the collected 23 samples were found to be of 11–37% moisture content, 6.1–8.4 pH, 0.3330 x 104– 4.7620 x104 Ohm.cm resistivity, 317–553 mV (SHE) oxidation-reduction potential, 14–75 ppm chloride and 56–176 ppm sulfate contents. These findings indicated that most of soil samples collected from the study areas of Lalitpur district of Nepal are found to be mildly corrosive and less corrosive nature of soils on the buried galvanized-steel and cast-iron pipes used for the supply of drinking water. The use of non-conducting materials like gravel/sand around the buried-pipes, before burying them in the study areas seems to be effective to control such corrosion and to increase life time of the pipes.

The catastrophe failures of the underground water pipelines, made by Fe-alloys have been largely reported in Nepal, mostly due to the unwanted electrochemical interactions in the interfacial regions between the aggressive soils and external pipe surfaces. To cope with such pipe corrosion, this study was put forward a novel probabilistic approach for the proximate analysis of the corrosive grade of soils to the pipes with the improvement of the previously practiced ASTM, AWWA, and NACE classifying methods. In this non-deterministic approach, four corrosive groups were firstly classified based on the quantitative data of 6 soil properties, which were further classified into ten sub-corrosion groups by considering the sum of the cumulative point of each soil sample. The proximate soil analysis of twenty-four samples of the Sanagaun-Imadol (SNG-IDL) and Kantipur (KNT) housing areas of Lalitpur metropolitan (Kathmandu Valley) was performed to evaluate their corrosion conditions and to draw a corrosive soil mapping. The results of such proximate analysis under the probabilistic approach disclosed that ~ 92% of the total 24 soils of the study areas belonged to five specific sub-corrosion groups, which are considered the members of two corrosion groups, i.e., less and mildly corrosion groups.

The facts of early non-performance of iron-based underground water pipes of the Kathmandu Valley (Nepal) are mostly due to the corrosive nature of the surrounding soil factors. A comparatively high percentage of the damage to the water pipelines in Nepal is anticipated, compared with the data reported in the developed countries. For the reasons, the quantitative data analysis of six kinds of the corrosive soil factors (i.e., moisture-holding capacity, pH, electrochemical resistivity, redox potential, Cl−, and SO4 2− ions) of 15 specimens, sampled from the Manohara Town Planning (MTP) area, was carried out using a novel probabilistic model, which is based on the internationally accepted standards (i.e., ASTM, NACE, AASTHO) with some modifications. The corrosivity of each soil factor was categorized into four corrosive groups (CGs) based on the conventionally applied classification methods. The experimentally obtained data of the soil factors were then used for proximate analysis using a new non-deterministic (probabilistic) model to classify the corrosive sub-groups (CSGs) of the soil specimens. This model would be a meritorious method to assess the soil corrosion condition of any area of the country, where the engineers and technologists could be applied pertinent methods or materials for the buried-pipe works in the future.