Comparative Study of Mohr-Coulomb Soil Model And Hardening Soil Model on Slope Stability Above Soft Soil
Using Plaxis Application
M. Abshar Habib, Helmy Darjanto
Program Study Civil Engineering, Faculty of Engineering, Narotama University Surabaya, Indonesia.
habibabshar@gmail.com, helmy.darjanto@narotama.ac.id
Abstract
Slope is a land surface that is sloping and forms a certain angle to a horizontal plane. Slopes can cause natural disasters, namely landslides, which according to BNPD in 2020 the number of natural disasters due to landslides reached 573 cases, most of which occurred due to increased pore water. This results in a decrease in the shear strength of the soil and the internal shear angle which in turn causes landslides. Slope stability is based on the concept of limit plastic equilibrium. The purpose of the stability analysis is to determine the safety factor of the potential landslide field. In slope stability soil modeling can affect the stability of the slope. In this analysis, two soil models are used, namely the Mohr-Coulomb and hardening soil models as a comparison material to find the results of the safety factor in slope stability. By using the finite element method, namely the PLAXIS program, to find the results of the analysis of the two soil models, in which the results of the analysis found that soil modeling using the hardening soil model obtained a better safety factor than soil modeling using Mohr-Coulomb.
Keywords :
Hardening Soil Model, Mohr-coulomb, Plaxis, Slope stability
1. Introduction
Landslides are one of the disasters that often occur on natural and artificial slopes. According to BNPD data, in 2020 the number of natural disasters due to landslides reached 573 cases. Landslides that occur on slopes mostly occur during the rainy season. It occurs due to the increase in pore water on the slopes. This results in a decrease in the shear strength of the soil and the internal shear angle which in turn causes landslides.
Slope stability analysis has a very important role in the planning of a civil construction. Unstable slopes cause many problems to the surrounding environment. To determine the stability of the slope is determined by calculating the magnitude of the factor of safety.
In calculating the safety factor, there are several things that need to be taken into account, such as ground water level, soft soil or not, land prone areas to move or not. To find this out, a laboratory test was carried out first to determine the safety factor of the slope.
To make it easier to determine the safety factor on the slope. Soil modeling can be an option to be able to find more accurate soil data, so that the calculation of the slope stability factor of safety can be obtained with results that are in accordance with the existing soil conditions.
In determining the safety factor on the slopes, the finite element method is used to analyze the stability of the slopes using the hardening soil model and the Mohr-Coulomb model. The disimilar application of the finite element method used is Plaxis.
2. Methodology
The data used in this study are secondary data obtained from textbooks, journals, scientific articles, literature reviews of comparative Mohr-Coulomb soil modeling and hardening soil models on slope stability. by taking the data of the land. The steps or research design in this study are as follows according to the flow chart in Figure 1 1. Collecting secondary data (soil parameters) from journals.
2. Entering soil data using the Plaxis V8.6 . application 3. Trial and error before doing the analysis.
4. Slope stability analysis on hardening soil modeling and Mohr-Coulomb soil modeling using Plaxis application.
5. Comparing the results of the safety factor.
Figure 1. Flowchart of Research Method
3. Result and Discussion
3.1. ResultThe data used in this final project uses secondary data from an international journal entitled Stiffness and strength parameters for hardening soil model of soft and stiff Bangkok clays, which was written by Chanaton Surarak.
The following data is used to perform slope analysis using Mohr-Coulomb soil modeling and hardening soil model on soft soil using the PLAXIS application:
Table 1. Soil Parameters 1 (Chanaton et al, 2012).
Type sat unsat Kx Ky E50 Eoed EUR C
Soft Clay 15 16 0.001 0.001 4831 5813 14439 5 27 0
Stif Clay 15 16 0.001 0.001 9618 11104 28854 5 27 0
For data embankment (soil embankment) using data from the PLAXIS 2D Tutorial Manual CONNECT Edition V20. The following data is used for Embankment (soil embankment).
Table 2. Soil Parameters 2 (Plaxis Manual, 2019).
Type sat unsat Kx Ky E50 Eoed EUR C
Embankment 19 16 3,499 3,499 2.5*104 2.5*104 7.5*104 1 30 0
1. Slope analysis using hardening soil model
The following is an image of the slope modeling using the Hardening Soil Model.
Figure 2. Slope with Hardening Soil Model.
The analysis process using Plaxis on the hardening soil model has 8 phases, namely:
a. The first phase is to calculate the gravity loading with -Mweight = 1.
b. The second phase is to provide the first embankment with a 5-day period.
c. The third phase is consolidation of the first embankment with a span of 200 days.
Mulai
Pengumpulan Data Sekunder:
Data Tanah dari studi litertur
Lereng dengan pemodelan Mohr-Coulomb
Lereng dengan pemodelan Hardening Soil Model Memasukan data tanah dengan aplikasi
PLAXIS V 8.6
Kesimpulan Studi Literatur
Selesai Hasil Perbandingan Hasil Faktor
Keamanan Analisis faktor keamanan stabiltas
lereng
Trial and error
Yes
No
g. The seventh phase is to calculate the slope stability safety factor for the second embankment.
h. The eighth phase is to calculate the slope stability safety factor at the last consolidation.
The results of running the Plaxis 2D program can be seen from the following figure:
Figure 3. Calculation Stages in Plaxis 2D Program With Hardening Soil Model (Plaxis Input).
After analyzed. Then the safety factor is obtained, namely:
Figure 4. Stages of Calculation of Safety Factor in the First Pile (Input Plaxis).
Figure 5. Stages of Calculation of the Safety Factor in the Second Pile (Input Plaxis).
Figure 6. Stages of Calculation of Safety Factor in the Last Consolidation (Plaxis Input).
In soil modeling using the hardening soil model, the slope safety factors are:
a. 1.4302 on the first heap b. 1.4997 on the second pile
c. 1.9863 on the last consolidation on the second heap
With the safety factor in all phases above 1.3 in the hardening soil model, the slope stability is satisfactory.
2. Slope analysis using mohr-coulomb model
The following is an image of the slope using Mohr-Coulomb modeling.
Figure 6. Slope with Mohr-Coulomb Soil Modeling (Input Plaxis).
The analysis process using Plaxis on Mohr-Coulomb soil capitalization is exactly the same as the analysis of the hardening soil model, which has 8 phases, namely:
a. The first phase is to calculate the gravity loading with -Mweight = 1.
b. The second phase is to provide the first embankment with a 5-day period.
c. The third phase is consolidation of the first embankment with a span of 200 days.
d. The fourth phase is to provide the next embankment with the same time span as the first embankment, which is 5 days.
e. The fifth phase is to carry out the final soil consolidation with a minimum pore pressure of 1 kN/m2.
f. The sixth phase is to calculate the slope stability safety factor for the first embankment.
g. The seventh phase is to calculate the slope stability safety factor for the second embankment.
h. The eighth phase is to calculate the slope stability safety factor at the last consolidation.
i. The results of running the Plaxis 2D program can be seen from the following figure:
After being analyzed. Then the safety factor is obtained, namely:
Figure 8. Stages of Calculation of the Safety Factor in the First Pile (Plaxis Input).
Figure 9. Stages of Calculation of the Safety Factor in the Second Pile (Input Plaxis).
Figure 10. Stages of Calculation of Safety Factor in the Last Consolidation (Plaxis Input).
In soil modeling using Mohr-Coulmb, the slope safety factors are:
a. 1.1144 on the first heap b. 1.3979 on the second pile
c. 1.7195 on the last consolidation on the second pile
With the safety factor in the first embankment phase which is less than 1.3, the stability of the slope using Mohr-Coulomb soil modeling is doubtful. However, for the second embankment and final consolidation the safety value is more than 1.3 which means that the slope stability in that phase is satisfactory.
3.2. Discussion
1. Comparison of Results on Hardening Soil Model and Mohr-Coulomb.
After analyzing the two soil models, namely the hardening soil model and the Mohr-Coulomb model. The results of the second factor of safety have been found where the results of the safety factor in the two models are different, the following table shows the results of the safety factor in the two soil models:
Table 3 Factor Safety.
Phase First Heap Second Heap Final Consolidation
HSM 1.4302 1.4997 1.9863
MC 1.1144 1.3979 1.7195
In the results of the safety factor in the two soil models, there are significant differences. The most significant is in the first embankment where the factor of safety in the Mohr-Coulomb model is less than 1.3, which means that the slope stability is not in a steady state or the slope is prone to landslides. However, in the modeling of the hardening soil model, the safety factor number is more than 1.3, which means that the slope stability is in a steady state or there will be no landslides.
The following is a graph of the results of the two models:
Figure 11. Graph of Safety Factors
4. Conclussion
The conclusions obtained from the work of this final project are
1. The influence of modeling on slope stability can be seen in the safety factor, following the safety factors in the hardening soil model:
a. 1.4302 on the first heap b. 1.4997 on the second pile
c. 1.9863 on the last consolidation on the second heap
With the safety factor in all phases above 1.3 in the hardening soil model, the slope stability is satisfactory.
Then the following is the safety factor in the Mohr-Coulomb modeling:
a. 1.1144 on the first heap b. 1.3979 on the second pile
c. 1.7195 on the last consolidation on the second pile
With the safety factor in the first embankment phase which is less than 1.3, the stability of the slope using Mohr-Coulomb soil modeling is doubtful. However, for the second embankment and final consolidation the safety value is more than 1.3 which means that the slope stability in that phase is satisfactory.
2. When viewed from the existing safety factors, the hardening soil model is more suitable for use in slope stability analysis, because in all phases there is no result less than 1.3.
5. Suggestion
1. The data used is real from the state of a project 2. In further research, the above load can be used
0 0,5 1 1,5 2 2,5
SF 1 SF 2 SF 3
Safety factor
HSM MC
References
Bowless, JE, 1977, Foundation Analysis and Design, McGraw-Hill Kogakusha, Ltd., Tokyo, Japan.
Brinkgreve, RBJ, Manual Plaxis 2D – Version 8, AA Balkema Publisher, Netherlands Craig, RF, 1989, Soil Mechanics, Erlangga Publishers, Jakarta.
Hardiyatmo, Hary Christady, 2003, Soil Mechanics I. Gadja Mada University Press, Yogyakarta.
Das, Braja M., 1993, Soil Mechanics (Principles of Geotechnical Engineering) Volume 1, Erlangga, Jakarta.
Das, Braja M., 1993, Soil Mechanics (Principles of Geotechnical Engineering) Volume 2, Erlangga, Jakarta.
Das, Braja M., 2011, Principles of Foundation Engineering 7th Edition, Cengage Learning, Stamford.
Surarak, Chanaton, Suched Likitlersuang and Dariusz Wanatowsk. 2012.
Stiffness and strength parameters for hardening soil model of soft and stiff Bangkok clays. Soil and foundations, 52(4):682–697
