Stability analysis of low-rise building on isolated footings affected by liquefaction-induced settlement during earthquakes: a plaxis 3D study across varied magnitudes/ Mariniell G. Marcos, Jade Allyson P. Pelayo, and Hannah Grace D. Piamonte .--

Thesis (undergraduate)

College of Engineering .-- Bachelor of Science in Civil Engineering: Technological University of the Philippines, 2023.

Includes bibliography:

Due to its location in the Pacific Ring of Fire, the Philippines has always anticipated
potential destructive earthquakes that could severely damage important structures like
schools. The City of Manila is highly susceptible to liquefaction, making any structures
built on its soil vulnerable to liquefaction-induced settlement brought on by earthquake
loads. This study employs to analyze and showcase the variance in settlement of the

underlying soil and foundation of a low-rise school structure in the highly liquefaction-
prone soil of Manila under various earthquake loads. It does this by using the FEM

software, PLAXIS 3D. The methodology is divided into two distinct categories: empirical
analysis using manual calculation and numerical analysis using software. By considering
the foundation weight, structural loads, and all three loads—including the various
earthquake loads—the FEM analysis is used to calculate the settlement of soil and
foundation. The empirical analysis is used for the settlement using the three loads used in
PLAXIS 3D and the differential settlement and angular rotation, which was used to
evaluate the stability of the structure using Preene's stability criteria. In the evaluation using
Preene's stability criteria, the angular rotation of 1/300 and differential settlement of less
than 2 cm falls only under the slight risk criteria, which implies that the damage in the
building will only be limited to cracks of 1 mm in maximum width and no significant
structural damage. The PLAXIS 3D results show that the foundation's self-weight
settlement is 5.472 mm and that the maximum total displacement in the foundation results
from the structure's gradual consolidation over time—is 22.25 mm when the point load
from the structure's dead load is applied. The different earthquake loads were added using
the same model of the soil foundation and structure under the point load from the structure's

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dead load and the extracted time and acceleration data in cm/sec2 from the SeismoSignal
time-acceleration input of the earthquake event data. The maximum total displacement
along the foundation due to earthquake data with magnitudes of 5.1, 6.5, and 7.0 is 22.28
mm, 22.37 mm, and 22.38 mm, respectively. In comparison to the empirical analysis using
manual computation, show the differential settlments for the magnitudes 5.1, 6.5, and 7.0
earthquakes to be differential settlement of 21.170 mm, 21.186 mm, and 21.287
respectively. The angular rotation based on the manual computation using differential
settlement is 8.019x10-4, 8.025x10-4, and 8.063x10-4 listed respectively for the three
earthquake magnitudes mentioned above. The findings, derived from both empirical
analysis and the Finite Element Method, showed that the settlement values as well as
angular distortions do not exceed 1/500, which, following Preene's (2000) building damage
criteria, falls into the slight risk category which suggests the possibility of superficial
damage with no significant effect to the structural integrity of the building.