Geotechnical and Geophysical Investigations with Pga Estimation of the Kathmandu Fun Park Project, Thankot, Kathmandu, Nepal

Abstract

This work focuses on the study of the foundation characteristics by geotechnical and geophysical investigations with PGA estimation of the Kathmandu Fun Park Project (KFPP) located in Thankot area, Kathmandu. To obtain information on subsurface material, velocity distribution and soil thickness seismic refraction survey was conducted using a 24 channel seismograph system by Oyo. Other soil properties were studied by in-situ Direct Cone Penetration Test (DCPT) and laboratory test of samples. The problem of ground shaking in the case of large earthquake near the Kathmandu valley is assessed in terms of synthetic peak ground acceleration (PGA) due to the lack of observed data. The present study provides tools for estimating geotechnical parameters from seismic wave velocity in the area where soil test are difficult to conduct. Fewer amounts of observed data and unavailability of instruments for undisturbed sampling have somehow affected this research work. Manual picking of travel time data from waveforms has affected the subsequent processing and interpretation of seismic refraction data. The study area comprises of colluvium deposits, mainly washout with high clay content. The high moisture content, low unconfined compressive strength and low bearing capacity of the soil are noteworthy. A modeled equation relating the P-wave velocity and porosity for the Lesser Himalayan colluvium soil has been established together with the material velocity. Similarly, the PGA distribution due to 1934 Taplejung, 1988 Udayapur and other two hypothetical earthquakes shows the PGA may exceed 150 gal for earthquakes greater than magnitude 8. However, the result shows the PGA hardly reach 15 gal for small but strong earthquakes. Moreover, the geotechnical parameters, specially moisture content, unconfined compressive strength, friction angle and porosity, show reasonably good correlation with seismic P-wave velocity. The single field measurement (i.e. seismic P-wave velocity) can serve the best for estimating other geotechnical parameters.