Determination of Rippability Classes Through Classical and Geophysical Methods in New Forest Road Excavations, and Their Evaluation in Terms of Cost and Progress Payments

Accurately determining soil classes in forest road constructions holds paramount importance in mitigating inconsistencies and disputes in cost and progress payments during and after construction. This study aims to explore the potential of geophysical methods (seismic refraction tomography – SRT, active multichannel analysis of surface waves – A-MASW, electrical resistivity tomography – ERT, and ground-penetrating radar-GPR) in determining the rippability classifications of geological units to be excavated in new forest road constructions, as well as vertical stratification and lateral lithological facies boundaries. This study also conducts a comparative analysis between the cost and progress payment values obtained through classical methods. The study area encompasses six new forest road alignments identified within the Trabzon Regional Directorate of Forestry investment program in Türkiye. For assessing the reliability and validity of the measurements, the Cronbach's alpha test was employed. The equality of the measured variable variances across groups was determined using the Levene's test, and to determine the source of differences among groups subsequent to the measurements, the Dunnett's test from multiple comparison tests was utilized. The study revealed disparities between the excavation volumes/class ratios/approximate costs calculated based on soil classes in new forest roads by the forestry administration, the excavation volumes/class ratios/approximate costs realized upon construction completion, and the excavation volumes/class ratios/approximate costs calculated within the scope of this study. The results obtained demonstrated that the combined utilization of SRT, ERT, and A-MASW methods enhanced the reliability of soil characterization and rippability classification when determining rock rippability characteristics in forest road constructions. In this context, it is considered that the additional cost incurred by geophysical engineering measurements can be justifiably met, given the potential benefits, which include more rational planning of investment budgets and cost analyses in new forest road constructions, as well as the facilitation of savings in time, labor, and capital. Furthermore, these measurements are anticipated to contribute to the resolution of potential disagreements between contractors and forestry administrations.