3RD SEM ppt

1. ANALYSIS OF LIQUEFACTION INDUCED SETTLEMENT BY
USING FINITE ELEMENT METHOD (ABAQUS)
Minar Islam
M.Tech in Civil Engineering
(Specialization: Geotechnical Engineering)
Reg. No.: 320419018
Under the Guidance of
Prof. Ashis Kumar Bera

2. OUTLINE
 Introduction
 Methods of settlement analysis
 Parameters to be considered
 Review of Literature
 Plan Of Work
 Progress of Work
 References

3. INTRODUCTION
• Soil liquefaction can occur when the strength and stiffness of soil are
reduced by changes in the stress condition, and the settlement of
structures can be affected by this phenomenon following an
earthquake.
• The settlement and lateral spreading of saturated soil deposits are
the major geotechnical hazards following liquefaction during
earthquakes.
• For design and insurance purposes it is therefore necessary to be
able to estimate the magnitude of these settlements.

4. Parameters to be considered for studying the Liquefaction induced
settlement
Time duration of acceleration
 Viscosity
 Moist unit weight of soil
 Foundation width
Foundation length
 Surcharge from structure Sawicki and Mierczynski
(2009)

5. LITERATURE REVIEW
AUTHOR/S FINDINGS CONCLUSION
Hadi Shahir, Ali Pak (2010)
They studied the dynamic response
of shallow foundations on liquefied
soils using a 3D fully coupled
dynamic analysis
It became possible to capture the
main aspects of the dynamic
response of footings on liquefied
sub soils by employing a well-
calibrated critical state two
surface plasticity model.
Karamitros et al.(2013)
• They presented a simplified
analytical methodology for the
computation of the seismic
settlements of strip and rectangle
footings resting on liquefiable soil
with a clay crust
• Liquefaction-induced settlements
are correlated to the seismic
excitation characteristics and the
post-shaking degraded static
factor of safety. Liquefaction-
induced settlements decrease
drastically with increasing
thickness and undrained shear
strength of the clay crust.

6. LITERATURE REVIEW
AUTHOR/S FINDINGS CONCLUSION
Ishihara and Yoshimine(1992)
They established a family of curves
on the basis of a bulk of information
on the response of saturated sands
obtained by using the simple shear
test apparatus.
By summing up all the volume
changes contributed by each sand
layer, it becomes possible to
estimate the settlement of the
ground surface due to shaking of an
earthquake.
Dimitriadi et al (2017) They considered a case where the
non-liquefiable crust is not natural,
but it has been artificially created by
ground improvement, and focuses
upon the effect of the size (thickness
and width) of the improved area on
the seismic settlement and the
degraded post-seismic bearing
capacity of the foundation.
Predictions of the proposed
methodology are in good agreement
with the few available empirical
guidelines, regarding the
recommended volume of the
improved ground.

7. PLAN OF WORK
Total work plan divided into three series -
• Series –I Foundation + Soil (One type)
• Series-II Foundation + 2 layer Soil ( Upper layer is Natural Clay Crust)
• Series-III Foundation + 2 layer Soil(Artificially improved Crust top layer)

8. PROGRESS OF WORK
Assumptions:
 The soil behaves like a perfectly plastic material followed by linear elastic behavior.
 Soil obeys the Mohr-Coulomb failure criterion.
 The botom of the model is restricted in X-Y direction (Acceleration and displacement is allowed in Z
Direction) and Two vertical edges of the model restricted in X direction and other two opposite side
restricted in Z direction.
 Soil layer is assumed to be fully saturated with G.W.T at G.L.
 Friction contact is used in the Interaction module.
 The nature of loading is static loading plus dynamic loading.

9. Geometric Modeling
Numerical modelling and analysis has been carried out for in cohesionless (sand) soil with Dr= 5%.In this present
study the geometry of the (Soil – footing) system has been considered as a 3D model. For avoiding errors due to
dynamic load full model is prepared for FE simulation. As using symmetry and part of the model, there might be
errors in boundary conditions.
Fig 2 : Shallow Foundation Fig 3:Toyura Sand Layer (Dr = 50 %)

10. Material Properties
 Material Properties of Soil:
Poisson ratio – 0.3. Other properties are:
 Material Property of Shallow Foundation
Density (kN/m3) 25
Young’s Modulus, E (kPa) 30x106
0.25
Dr (%) e
𝞺
(kg/m3)
E(kPa)
𝟇
(degree)
K(m/s2)
50 0.80 1879 50 x 104 35
2.2 e -5

11. Assembly
It is necessary to assemble all the material
constitutive behaviour, geometry and the
boundary condition for FE analysis. This
operation has been done using the assembly
module in ABAQUS environment.
Figure 4 Assembly of Model

12. Analysis Procedure, Step and Interaction
 ABAQUS provides various analysis procedure such as
geostatic, static general, Dynamic analysis etc. The present
analysis has been carried out in four consecutive steps. The
first step has been used as a geostatic stress analysis(gravity).
The second step has been is steady state soil step for
hydostatic stress.The third step has been is static analysis .
The fourth step is the dynamic analysis step. In this step a
bottom acceleration is applied in the form of sin wave.
 In FE analysis it is also necessary to provide proper
interaction property to maintain the continuity of the solution.
In the present analysis all the interacting surfaces are fused
together using the surface to surface contact.
Figure 5 Loading condition

13. Mesh Generation
In order to perform the finite element
calculations, the geometry have been divided into
elements. A composition of finite elements is
called a finite element mesh.
Mess Details
Total number of nodes: 5247
Total number of elements: 4180
100 linear hexahedral elements of type C3D8R
4080 linear hexahedral elements of type C3D8P
Figure 6 Meshing of Soil Figure 7 Meshing of Foundation
Nodes: 242
Elements - 100

14. Deformed Shape of Model
Pile
Figure 8 Deformed shape of model
Soil
Shallow Foundation

15. Results and Discussion
 Geometry study:
In this study, the pressure of 10 kN/m2 is applied on a shallow foundation of (6m x 6m x 0.1 m)embedded into soil
mass cross-section of the soil mass (20 x 6 x 7).The GWT is at G.L. The acceleration load is varied to observe the
change in settlement and also to find out whether liquefaction is occurring or not. The Settlement and an effective
stress decreasing ratio (ESDR) versus time are used in the numerical analysis.
In this study, soil is assumed to behave like a liquid when ESDR equals 0.8, which is the timing that the large
settlement of soil is discovered -(Lu and Peng 2020).

16. Results
Based on the results obtained from ABAQUS analysis by applying acceleration of 228.9 gal at the bottom of soil layer for 0.35
sec, 0.5 sec, 2sec and 3.5 sec the displacement vs time curves are plotted and presented herein.
Acceleration
time (sec)
0.35 0.5 2 3.5
Settlement
(cm)
0.78 0.795 0.81 3.4

17. Contd….
By polynomial forecasting in excel that is by extrapolating the values of the above table the settlement of shallow foundation for
acceleration time of 35 sec is found to 25.68 cm.
Fig 10: Displacement curve for 35 sec
earthquake

18. Contd….
Fig 11: Settlement curve for 35 sec
earthquake in LIQCA (Peng 2020)
Shallow Foundation(6m x 6m)
DR(%) Experimental ALID ABAQUS Variation
50 25.54 cm 29.36 cm 25.68 cm 3.93 %
Comparision chart for settlement in 35 sec earthquake
of acceleration 228 gal,0.8 Hz frequency

19. Verifications
1.For Validation the following empirical formula given by
(Hadi Shahir, Ali Pak- 2010) is used-
2. Another Equation Given By Sawicki and Mierczynski (2009)
where is the maximum thickness of liquefaction in m and
q,net is net bearing pressure in kPa.

20. REFERENCES
• Shahir H, Pak A. “Estimating liquefaction-induced settlement of shallow foundations by numerical approach.
Comput Geotech “2010;37(3):267–79..
• Dashti S, Bray JD. “Numerical simulation of building response on liquefiable sand”. J. Geotech. Geoenviron. Eng.,
ASCE 2013;139(8):1235–49
• Karimi Z, Darshti S. “Seismic performance of shallow-founded structures on liquefiable ground: validation of
numerical simulations using centrifuge experiments”. J Geotech Geoenviron Eng 2016;142(6).
• Karimi Z, Darshti S. “Numerical and centrifuge modeling of seismic soil-foundation interaction on liquefiable
ground”. J Geotech Geoenviron Eng 2016;142(1).
• Chih-Wei Lu a, Min-Chien Chu b,*, Louis Ge b, Kai-Siang Peng c “Estimation of settlement after soil liquefaction for
structures built on shallow foundations.”
• Tsukamoto Y, Ishihara K. “Analysis on settlement of soil deposits following liquefaction during earthquakes”. Soils
Found 2010;44(3):399–411. [7]
• Elgamal A, Lu J, Yang Z. “Liquefaction-induced settlement of shallow foundations and remediation: 3D numerical
simulation”. J Earthquake Eng 2005;9(1):17–45.