2. CONTENT:-
INTRODUCTION
ABOUT TOPIC
LITERATURE REVIEW
SUMMARY OF LITERATURE REVIEW
RESEARCH GAP
OBJECTIVE
PROBLEM DEFINITION
STATIC ANALYSIS
DYNAMIC ANALYSIS
CONCLUSION
3. INTRODUCTION:-
The first known effect of liquefaction was reported on 1 November 1755 Libson Earthquake, also
known as Great Libson Earthquake. On India's 52nd Republic Day, 26 January 2001, a severe
earthquake with a magnitude of 7.7 struck the Bhuj district of Gujarat, killing over 20,000 people
and damaging structures, bridges, highways, and ports, among other things. Heavy shaking
resulted in Liquefaction in the sandy soil of Rann of Kachchh leading to massive destruction. The
death toll during each earthquake was horrifying.
Therefore, to reduce the risk of liquefaction-induced hazards, the scientific community realized
more study is to be needed to sidestep life-threatening results from the earthquake in liquefaction-
prone areas to ensure the safety of buildings and structures.
4. SIGNIFICANCE:-
Earthquake Engineering: Liquefaction can occur during earthquakes when water-saturated granular soils temporarily
lose their strength and behave like liquids. This phenomenon can lead to ground failures, such as landslides and
foundation settlements, causing immense damage to infrastructure. Understanding liquefaction helps engineers design
buildings and structures that can withstand seismic forces.
Infrastructure Design: Knowledge of liquefaction potential is vital for designing critical infrastructure such as
bridges, dams, and levees. Engineers use this information to ensure that these structures can withstand liquefaction-
induced ground deformations during seismic events, preventing catastrophic failures.
Urban Planning: In earthquake-prone regions, urban planners need to consider liquefaction susceptibility when
designing new developments. Studying liquefaction helps in identifying safe areas for construction and can influence
zoning regulations and building codes to mitigate potential risks.
Risk Assessment and Management: Understanding liquefaction hazards allows for the assessment and management
of risks associated with earthquakes. This knowledge helps in identifying vulnerable areas, prioritizing retrofitting
efforts, and planning emergency response strategies.
5. ABOUT TOPIC:-
Liquefaction:-
Liquefaction happens when a loose, saturated sandy soil loses its strength due to rapid dynamic loading. Rate of
loading is too rapid that undrained condition developed and excess pore pressure builds up. Consequently, effective
vertical stress reduced to zero due to increase in the EPP and shear strength becomes zero in case of loose saturated
cohesionless soil. In this case, soil behaves as a viscous fluid causing the sinking of heavy structures and light
structure floats.
Strength of cohesionless soil is a function of effective stress and friction angle.
Su=σ’vtan ϕ
For the dynamic loading, strength of cohesionless soil is given by
Sdyn = (σ’v - Uexcess) tan (ϕ dyn)
During liquefaction, Shear strength becomes equal to excess pore water pressure.
σ’v = Uexcess
6. FACTORS AFFECTING LIQUEFACTION:-
Type of soil- Soils with high silt and clay content are less susceptible to liquefaction compared to sandy soils.
Soil Density- Loose soils have higher porosity and are more susceptible to liquefaction.
Presence of seismic waves- the presence of seismic waves induces cyclic loading and changes in pore water pressure,
reducing effective stress and soil strength.
Location of drainage- During seismic events, water in saturated soils generates excess pore pressure, reducing soil
strength. Adequate drainage systems prevent the buildup of excess pore pressure, maintaining soil stability.
Historical Environment- Soils that have experienced previous cycles of loading and unloading are more susceptible to
liquefaction.
Natural Factors:
• Vegetation: Plant roots can bind soil particles, reducing liquefaction susceptibility.
• Organic Content: Soils with higher organic content tend to have better structure and are less prone to liquefaction.
7. Consequences of Liquefaction:-
Bearing Capacity:-
The foundation of the building is constructed as per the safe bearing capacity of the soil.
During Liquefaction, the soil loses all of its strength. As a result, there may be tilting and
settlement of the structure. Differential settlement leads to cracks in the structure.
Lateral Spread:-
Lateral Spreading is the movement of soil that may occur because of translation, rotation, or
flow. It can be described as the finite movement of the soil layer horizontally in the lateral
direction. Lateral spreading is most common on a modest slope of 0.3% to 5%.The lateral
spreading has had the greatest impact on buildings, pipelines, roads, and railway lines.
8. Oscillation of Ground:-
It occurs when the soil below the flat layer of the ground surface liquefies, which
causes oscillation of the top layer in the form of ground waves. It occurs due to
inertial force applied to the soil layer above or in the liquefied zone. One can
observe ground oscillation as a moving surface ground wave goes along with the
opening and closing of cracks.
Sand Boil:-
Sand Boil is when sand and water expel from the ground during an earthquake
because of liquefaction of the sub-surface soil layer. The soil around this undergoes
excessive settlement. Soil erupts in the form of volcanos hence also called Sand
Volcano.
9. Settlement:-
During the earthquake, Liquefaction in soil results in further consolidation of the
liquefied soil; this results in an excessive settlement in the ground. Various
incidents have been recorded for ground surface settlements during liquefaction,
causing tilting of buildings and cracks to the structures during differential
settlement
Floating:-
During Liquefaction, soil behaves as viscous fluid, and structures seem to float
over the liquefied soil. It is a phenomenon in which any submerged body starts
floating because of its lower unit weight. Tunnels, sewer lines, pipelines, and
manholes are the structures that suffer floatation during an earthquake because of
Liquefaction as they have a lower unit weight than surrounding soil.
10. LITERATURE REVIEW:-
P.K. Robertson and C.E. Fear (1995) carried out "Liquefaction of Sands and Its Evaluation,"
which focuses on the phenomenon of liquefaction in sandy soils, particularly during seismic
events, and provides insights into the methods and approaches used for its evaluation. The
authors present a comprehensive overview of the factors contributing to liquefaction,
including factors related to soil properties, seismic loading characteristics, and groundwater
conditions. Widely recognized Standard Penetration Test (SPT) and the Cone Penetration Test
(CPT), and their correlations to estimate liquefaction potential are discussed. The paper also
examines the use of liquefaction triggering curves, which relate cyclic stress ratios and fines
content to the likelihood of liquefaction occurrence.
11. CONTINUED:-
H.B. Seed and I.M. Idriss (1971) carried out "A Simplified Procedure for Evaluating Soil
Liquefaction Potential". The paper addresses the challenges associated with accurately
assessing soil liquefaction potential and proposes a simplified procedure to estimate the
liquefaction susceptibility of soils. The procedure involves determining the cyclic stress
ratio (CSR) and comparing it with an empirical chart to assess the likelihood of liquefaction.
The authors provide clear instructions on how to calculate the CSR using seismic
information, soil properties, and effective stress considerations.
12. CONTINUED:-
A. Tsegaye(2010) carried out "Plaxis Liquefaction Model" a significant contribution to the field
of geotechnical engineering, specifically addressing the simulation of soil liquefaction behaviour
using the Plaxis software. The paper delves into the specific constitutive model implemented
within the Plaxis software to simulate soil liquefaction. This model captures the changes in soil
behaviour due to pore water pressure increase, shear strength reduction, and other factors
associated with liquefaction. The author discusses the process of calibrating the Plaxis
Liquefaction Model using laboratory test data and case histories of liquefaction events. This
calibration involves adjusting various model parameters to match observed behaviour and
achieve accurate predictions.
13. CONTINUED:-
M.H. Beaty and P.M. Byrne(1998) carried out "An Effective Stress Model for
Predicting Liquefaction Behaviour of Sand”. It proposes an effective stress-based
model for predicting the onset of liquefaction. The model is based on the principles
of effective stress, which considers both total stress and pore water pressure effects
on soil behaviour. The authors discuss the significance of using effective stress to
capture the soil's response more accurately
14. CONTINUED:-
T.L. Youd and I.M. Idriss (2001) carried out "Liquefaction Resistance of Soils:
Summary Report from the 1996 NCEER and 1998 NCEER/NSF Workshops on
Evaluation of Liquefaction Resistance of Soils "with primary objective to consolidate
and present the key outcomes of the workshops held in 1996 and 1998, which focused
on assessing the liquefaction resistance of soils during seismic events. Challenges and
complexities associated with predicting and evaluating soil liquefaction susceptibility
are discussed. They provide an overview of the various factors influencing liquefaction,
such as soil characteristics, groundwater conditions, and seismic loading.
15. SUMMARY OF LITERATURE REVIEW:-
Discussion on Standard Penetration Test (SPT) and Cone Penetration Test (CPT)
correlations for estimating liquefaction potential.
Introduction of the Mohr–Coulomb model to understand soil response to seismic
events and predict liquefaction potential.
Parameters of the UBC3D-PLM material model were calculated using
mathematical relations given by Beaty and Byrne.
Description of the vibro-replacement technique to prevent liquefaction.
16. RESEARCH GAP:-
There has been very few studies done on 3D models for shallow
footing.
Further research is needed to compare the influence of
prefabricated drains, stone columns, and sand drains for
liquefaction mitigation.
17. OBJECTIVE:-
Behavioural analysis of bearing capacity of shallow foundation under
liquefaction condition.
To study the effects of liquefaction on effective stress and excess pore
water pressure in the soil.
21. FOOTING PROPERTIES:-
RCC SQUARE FOOTING
Parameters Values
Material model Linear elastic
Grade M25
Width 2m
Depth below EGL 1.5m
Modulus of Elasticity E 25000000 kN/m2
Unit Weight γ 25 kN/m3
Poisson’s Ratio μ 0.15
Analysis type Non-porous
29. BEARING CAPACITY(IS-6403(1981)):-
The net safe bearing capacity of the soil was determined by considering the general shear failure condition and
calculated according to IS: 6403 code. From the equation given in the code, the net ultimate bearing capacity of the
soil was calculated:-
where c is cohesion; Nc, Nq, Nc are bearing capacity factors; Sc, Sq, Sγ are shape factors; dc, dq, dc are depth factors;
ic, iq, iγ are inclination factors; q is an effective surcharge at foundation base level; B is footing width; γ is soil bulk
unit weight; and W’ is water table correction factor.
30. CALCULATIONS:-
B=2m, γ=14.5kN/m2
Wt. avg. c=1, Wt. avg. φ =24.6
Nc=20.72, Nq=10.66, Nγ=10.88 (depends on φ)
Sc=1.3, Sq=1.2, Sγ=0.8 (Square footing)
dc=1.234, dq=1.117, dγ=1.117 (depends on depth)
ic=iq=iγ=1, (depends on angle of loading w.r.t. vertical)
W’=0.5 (depends on depth of W.T. from E.G.L.)
qu=123.53 kPa
31. RESULTS:-
The soil was found liquefiable from 2.3 to 6m depth. Thus, liquefaction
mitigation is required for the project site.
NUMERICALLY ANALYTICALLY
BEARING CAPACITY(kPa) 116 123.53
After assessing the bearing capacity numerically and analytically it can be concluded that the
present ground condition is not safe for construction and requires ground improvement for
strength enhancement.
32. LIQUEFACTION POTENTIAL(IS-1893(part-1)):-
The soil layer having FS less than 1 was considered as critically liquefaction prone, FS value between 1 and
1.1 was considered as moderately liquefaction prone and the FS value greater than 1 was considered
liquefaction resistant and safe.
36. UBC3D-PLM MODEL :-
Parameters Value
Drainage Condition Undrained (A)
Peak Friction Angle (φ’
p) 26.6
Friction angle at constant volume(φ’
cv) 26
Effective cohesion (C’) 0
Elastic Bulk Modulus (ke
B) 552.006
Elastic Shear Modulus (ke
G) 788.58
Plastic Bulk Modulus (kp
G ) 185.166
Power for stress dependency of ke
G(ne) 0.5
Power of stress dependency of ke
B(me) 0.5
Power of stress dependency of kp
G (np) 0.4
Corrected SPT No.(N1)60 9
Failure Ratio(Rf) 0.79
43. EXCESS PORE PRESSURE vs DYNAMIC
TIME CURVE:-
-300
-250
-200
-150
-100
-50
0
50
100
0 5 10 15 20 25 30 35 40 45
EXCESS
PORE
PRESSURE
(
kN/
m
2
)
DYNAMIC TIME( s )
1 m in Liquefiable layer 2 m in lquefiable layer 3 m in liquefiable layer
44. VERTICAL EFFECTIVE STRESS VS
DYNAMIC TIME CURVE :-
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
0 5 10 15 20 25 30 35 40 45
EFFECTIVE
VERTICAL
STRESS
(kN/m
2
)
DYNAMIC TIME (s)
At 1m in liquefiable layer at 2m in liquefiable layer At 3m in liquefiable layer
45. SETTLEMENT-TIME HISTORIES IN
HORIZONTAL DIRECTION (X-AXIS) :-
-0.04
-0.035
-0.03
-0.025
-0.02
-0.015
-0.01
-0.005
0
0.005
0 5 10 15 20 25 30 35 40 45
U
X
DISPLACEMENT
(
m
)
DYNAMIC TIME (s)
Ground surface Below Footing Liquefiable layer
46. SETTLEMENT-TIME HISTORIES IN
HORIZONTAL DIRECTION (Y-AXIS) :-
-0.0035
-0.003
-0.0025
-0.002
-0.0015
-0.001
-0.0005
0
0.0005
0.001
0 5 10 15 20 25 30 35 40 45
U
Y
DISPLACEMENT
(
m
)
DYNAMIC TIME( s )
Ground surface Below Footing Liquefiable layer
47. SETTLEMENT-TIME HISTORIES IN
VERTICAL DIRECTION (Z-AXIS) :-
-0.09
-0.08
-0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0 5 10 15 20 25 30 35 40 45
U
Z
DISPLACEMENT
(m)
DYNAMIC TIME( s )
Ground Surface Below Footing Liquefiable layer
48. ACCELERATION-TIME HISTORIES IN
HORIZONTAL DIRECTION (X-AXIS):-
-1.5
-1
-0.5
0
0.5
1
1.5
0 5 10 15 20 25 30 35 40 45
A
X
(
m/s
2
)
DYNAMIC TIME( s )
Ground surface Below footing Liquefiable layer
49. METHODS TO MITIGATE
LIQUEFACTION:-
Prefabricated Vertical Drains (PVD): Installing vertical drains to accelerate the
dissipation of pore water and increase the effective stress in the soil.
Soil Replacement: Completely removing liquefiable soil and replacing it with non-
liquefiable fill material.
Vibro-Replacement: Using a vibrating probe to displace and densify surrounding
soil, creating stone columns.
Base Isolation: Designing structures with flexible bearings that can absorb seismic
energy and prevent it from reaching the building's superstructure.
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IS -6403(1981)
IS-1893 (part-1)
IS-1904(1986)
