Geotechnics on Berk Demir

Diaphragm Wall Intervention

Tue, 19 May 2026 00:00:00 +0000

Memories from 2007 back in Durban, building a 2010 World Cup Stadium; we hit a problem with the diaphragm wall excavation, when the grabber got stuck in the bedrock about -20m down. So we sent commercial divers down through the bentonite slurry to fix a new steel cable to the grabber so we could retrieve it and keep the project going. Those boys were hardcore.

Paper on Nordhavnstunnel

Wed, 28 Aug 2024 00:00:00 +0000

Demir et. al. 2024 — Nordhavnstunnel.pdf

Hardening Soil Model

Fri, 16 Dec 2022 00:00:00 +0000

During 2019 Plaxis User Meeting in İstanbul, I have presented a detailed discussion on Hardening Soil Model. The presentation was really welcomed by the audience and in fact, later on, I have been invited to two other companies for the same presentation. This short post will be a summary of that presentation. Hardening Soil model (will be called HS from now on) was presented in an excellent conference for 10th year of Plaxis in a paper called The hardening soil model: Formulation and Verification by Schanz, Vermeer and Bonnier. However, HS is tightly bonded to previous studies on the literature such as Lade, Tatsuoka and Ishihara, Cam-Clay model, Kondner and Zelasko, Jardine, Duncan and Chang, Al Tabbaa, Simson et. al.

Hoek Brown Model

Fri, 16 Dec 2022 00:00:00 +0000

I have just published a new tool and this post will detail the methods that are being used in this tool. What it does: Performs Hoek-Brown analyses for rock and recommends additional parameters based on the inputs.

https://berkdemir-bd-hoek-brown-bd-hoek-brown-vsh6i6.streamlit.app/

Theory

Introduction

The Hoek-Brown material model is the most widely used rock mechanic model due to its simplicity and ease-of-use in continuum based numerical models such as finite element or finite difference models. Hoek-Brown model is published in Hoek & Brown (1980) and after that, it is constantly updated. Latest update was published in 2019.

Modulus of Subgrade Reaction

Fri, 16 Dec 2022 00:00:00 +0000

Introduction

By now, everything should have been settled about modulus of subgrade reaction. We all know some typical statements about it:

It depends on the soil properties
It depends on the foundation size
It depends on loading type, temperature, bitcoin prices and others.

However, let’s think about a weathered rock with E=500 MPa and a foundation to be built on top of this rock with 20 x 50 m dimensions. You can say it depends on many factors as much as you like, everybody has a rough idea already: 100,000 kN/m3. So, if you are a fancy engineer and dare to make some calculations, you can find much lower values. Will they believe you or will they think that you are being too conservative (if lowering the subgrade reaction means being conservative)? Let’s start with simple terms. The equation that everybody knows and nobody wants to use: $$ K=\frac{q}{s} $$ So, the subgrade reaction is equal to a spring stiffness distributed under the foundation. If you divide the pressure by the settlement, you will find the subgrade reaction, amount of deformation for unit pressure. If we think about how we calculate settlement (how it depends on many factors), we can see actually how complex this modulus is.

MR Data from Tatone et. al. (2022)

Fri, 04 Feb 2022 00:00:00 +0000

A new paper from Tatone et. al. is published here. Using the data of the authors, following violin graph is drawn to estimate Modulus Ratio (MR = E / UCS) of the different rocks. Update: Aly Abdelaziz has proposed an update on the code and graph. Thanks to him, it looks better now. Code and data are in the Github Gist.

# Data from Tatone, B. S., Abdelaziz, A., & Grasselli, G. (2022). Novel Mechanical Classification Method of Rock Based on the Uniaxial Compressive Strength and Brazilian Disc Strength. Rock Mechanics and Rock Engineering, 1-5.
import pandas as pd
import seaborn as sns

# Rock Category
rock_type = {"Sedimentary": ["SL", "SSh", "SS", "SC"],
 "Metamorphic": ["MG", "MS", "MQ", "MM"],
 "Igneous": ["IG", "IF", "ID"]}

ordered_box_list = []
for i, v in rock_type.items():
 ordered_box_list += v

df = pd.read_csv("data.csv")

df = df[df.E != "-"]
df = df.astype({"E": float, "UCS": float})

df["MR"] = df["E"] / df["UCS"] * 1000

sns.set(rc={"figure.figsize": (20, 8.27), "figure.dpi": 300})

ax = sns.violinplot(x="Type", y="MR", data=df, order=ordered_box_list)
ax.set_ylim(0)

The data.csv file can be saved from here or from Gist. [[Notion/Quick Note/BDEM (1)/Blog Posts/_assets/data.csv]]

Hoek-Brown Parameters Database

Fri, 12 Mar 2021 00:00:00 +0000

If you will use Hoek-Brown in your Python code, you may want to recommend some constants based on rock type. There is a widely used table in literature by Hoek and others that we use to select Modulus Ratio and material constant (mi) in the absence of high quality laboratory tests. I have done the manual labour, don’t write it all again. A dictionary called RockDict is given in the following Gist. Rock types are given as keys of dict and a sub-dictionary with: