The Investigation of Traffic and Near-Field Earthquake Loads Effects on the Nailed and Braced Excavations

Abstract

Considering the statistical and probabilistic characteristics of construction conditions, the investigation of dynamic overloads' effects on the urban excavation wall is of great importance. In the present study, the performance of nailed and braced excavations under two vibrational dynamic excitations, traffic and near-field earthquake loads, have been investigated in four regions of Ahvaz. Critical boreholes with the lowest static bearing capacity have been selected by analyzing the layers' strength parameters in each region. Numerical models have been designed to limit the seismic waves' reflection at the excavation boundaries with 20 x 100 meters and with absorbing walls. Also, the damping ratio was assumed to be 2%. A harmonic wave at different speeds has simulated the excitation caused by the traffic passage. Resonant frequencies due to traffic induced vibration have been recorded in the speed range of 56 to 72 km/hr. Due to the traffic load, the bracing and the nailing systems showed less vertical and lateral displacements, respectively. Moreover, the excavations have been analyzed under ten acceleration with compatible near field characteristics of the Ahwaz plan acceleration (0.25g). The Kiyanpars region showed the highest vertical displacement difference between the two systems in the range of 0.032 m to 0.006 m. Due to earthquake loads, the bracing system showed less vertical displacement. The error of the analytical models' results in vertical displacement was 10% and 26% and in lateral displacement was 5% and 20% less than a nailed excavation located in the Kiyanpars region under traffic passage.