EXPERIMENTAL AND NUMERICAL SIMULATION FOR SHALLOW AND DEEP FOUNDATIONS IN LAYERED SOIL SUBJECTED TO EARTHQUAKE LOADING

Abstract

ABSTRACT Governorate of Diyala (Baqubah City, Iraq) is considered an affected area by seismic activity, and this is due to geological characterization, which is located along the earthquake line that runs between the Arab and Iranian plates. It is critical to investigate two different foundation systems (soil-raft and soil-pile system) on the given soil conditions of Baquba soil properties under real earthquake records. Especially after the Halabja earthquake in 2017, near the Iranian-Iraqi border. The 3-D seismic behavior of piles and raft foundations is experimentally and numerically investigated in this study using the finite element program PLAXIS3D v20.Twenty models are performed to highlight the vertical settlement, horizontal displacement, bending moment, and pore water pressure under El-Centro, Halabja, and Ali-Gharbi earthquakes. A raft model of a fourstorey building was simulated with (18.5x18.5 m) dimensions and different thicknesses (0.8,1,1.2,1.4,and1.6m), and change the raft with a pile foundation with different diameters(0.5,0.7,1m) and length 19m. An experimental model was developed using shaking table to analyze a verification case similar to the domain problem of raft foundation under the Halabja earthquake. It found the numerical analytical results to the experimental results are extremely well matched, in the term that the maximum settlement obtained numerically is more than the experimental work is about 8%. The results raft foundation showed the vertical settlement decreases as the thickness increases from 0.8m to1.6m, and the percentage of reduction VIII ranged between 5% at 1.4m to 17% at 1m, (7% to8%) at 1.6m, and (19% to21%) at 1.4m, while the horizontal displacement with the percentage of reduction is about 39.49%, 43%, and 45.17% under the El-Centro, Halabja, and Ali AL-Gharbi earthquakes, respectively. The maximum bending moment distribution at the raft foundation under the different earthquakes appeared the same behavior with the change of thickness and decreases about 87% with an increase the thickness to 1.4m and 85% at 1.6m. From the pile foundation simulation, it observed the vertical settlement and horizontal displacement similar to the edge, exterior, and interior piles which means the diameter of the pile did not affect the displacements. On the other hand, the percentage difference in the maximum settlement ranged between (0.5-3)% under the Halabja and the Ali Al-Gharbi earthquakes. While the lateral displacement increase with the direction of the earthquake from the right to the left side of the pile-soil system. The maximum bending moment along pile foundations occurred at a depth of 10m of the interior pile has the largest diameter of the group model with a range between (40-59)% more than the corner, and exterior piles for all earthquakes applied. In general, the highest values of the settlement and displacements were under the Halabja earthquake with a percentage increase of (85-89)% and 44% over the El- Centro and Ali Al-Gharbi earthquakes, respectively. while under Ail Al- Gharbi increase of (73-80)% over the El-Centro earthquake. Finally, In the case of comparison between the overall response of raft and groups pile subjected to the same load and factor safety under the El-Centro earthquake, it is clear the settlement with in the rate of 18% and horizontal displacement with68% for raft foundation more than pile foundation.