Finite Element Analysis of a Deep Excavation: A Case Study

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Bilimleri Enstitüsü, İnşaat Mühendisliği, Türkiye

Tezin Onay Tarihi: 2019

Tezin Dili: İngilizce

Öğrenci: TUĞÇE AKTAŞ ENGİN

Danışman: Erdal Çokça

Özet:

FINITE ELEMENT ANALYSIS OF A DEEP EXCAVATION: A CASE STUDY

Aktaş Engin, Tuğçe

Master of Science, Civil Engineering

Supervisor: Prof. Dr. Erdal Çokça

Co-Supervisor: ... ...

[Defense Date], [#] pages

The optimum use of safety and economy in deep excavation design is possible with the selection of the appropriate system, and modelling of the selected system and soil properties properly. Therefore, soil parameters selection has a crucial effect in deep excavation analyses. The realistic estimation of the displacements with the finite element software is only possible by using the realistic deformation values during analyses. However, in hard clays which undisturbed sampling is very difficult, displacements calculated with laboratory deformation modulus parameters may be higher than the measured values. Objective of this study is to determine the constant that shows linear relationship between SPT-N and deformation modulus parameter of Ankara clay by using three constitutive soil model of Plaxis-2D, namely Mohr-Coulomb (MC), hardening soil model (HS) and hardening soil model with small strain stiffness (HSsmall). For this purpose, a back analysis of a 25.0m deep excavation was performed by using an inclinometer measurement result. To be more precise in numerical analysis, instead of using the idealized soil profile the soil is divided into layers according to SPT-N distances. Additionally, each displacement measured by the inclinometer along the depth is compared with the analysis results to minimize the margin of error. In case trial-error method is used in the study, time loss and the possibility of not reaching the correct result were taken into consideration; therefore, the analysis was done by writing the Python code. As a result of analyzes, the soil models were compared with each other and it is concluded that displacements curves obtained from the MC model could not converge on the real displacements. HSsmall model results are closest to real displacements. Moreover, displacement curves obtained from HS and HSsmall models are very close to each other, and the linear correlation formula is determined as E50ref=780xN60.

Keywords: deep excavation, Ankara clay, back analysis, finite element method, constitutive soil model