National Conference on Recent Advances in Mechanical Engineering (NCRAME 2017)
ISBN: 978-93-86256-89-8
Assessment of Liquefaction Potential of Chandigarh City Joseph T.M.1, Nitish Puri2 and Ashwani Jain3
1 2
M.Tech Student, Department of Civil Engineering, NIT Kurukshetra, Kurukshetra, Haryana–136119, India INSPIRE Fellow, Department of Civil Engineering, NIT Kurukshetra, Kurukshetra, Haryana–136119, India 3 Professor, Department of Civil Engineering, NIT Kurukshetra, Kurukshetra, Haryana–136119, India E-mail:
[email protected],
[email protected],
[email protected]
Keywords: Liquefaction, PGA, Chandigarh, SPT N-Value
I.
classified as non-liquefiable. A layer may also liquefy during an earthquake, even for FOS > 1.0. A FOS of 1.2 at a particular depth is considered as the threshold value for the layer to be categorized as non-liquefiable. Although FOS shows the liquefaction potential of a soil layer at a particular depth in the subsurface, it does not show the degree of liquefaction faction severity at a liquefaction-prone liquefaction site. Hence, liquefaction iquefaction potential index (LPI) is evaluated at each borehole location from the obtained factors of safety to predict the potential of liquefaction to cause damage at the surface level at the site. The results of the study can be used for safe designing of structures in the city of Chandigarh.
G in AL PR p t o ES art co S o r p y, W in p R fu rin I T ll, t T E on or N a sa PE ny ve R r et an M ri y IS ev c S I al on O sy t e N s nt of t e of th m, th e is co pd py f, rig ht -h ol de r
Abstract—Liquefaction of soils, the most devastating after effect of an earthquake, is a phenomenon in which the strength and stiffness of a soil are reduced by an earthquake shaking or another rapid loading. For the assessment of liquefaction potential, borehole data has been collected from different organizations including government and private undertaking. The semi-empirical method proposed by Idriss and Boulanger has been used for the assessment of liquefaction potential. A total of 100 boreholes for 41 sites covering entire city of Chandigarh have been analyzed. PGA values calculated by carrying out seismic hazard analysis and site response analysis have been used to calculate cyclic stress ratios (CSR).
II. LIQUEFACTION
INTRODUCTION
w ith
ou
EX
tt he
It
is
IL
LE
Chandigarh city is the first planned city and a Union territory of India which serves as the capital of the S States tates of Punjab and Haryana. It is located near the foot hills of Shivalik valik range covers an area of 114 km2 with cartographic coordinates of 30.74°N N and 76.79 76.79°E. Liquefaction of soils, the most devastating after effect of an earthquake, is a phenomenon in which the strength and stiffness of a soil are reduced by earthquake shaking or another rapid loading. It iss manifested in the form of sand boils and mud spouts at the ground surface formed by seepage of water, or in some cases by the development of quicksand condition. Buildings may sink substantially into the ground or tilt excessively; lightweight structures and foundations may get displace laterally causing structural failures. Loose, poorly graded soil is more susceptible to liquefaction in comparison with dense, well graded soil. Liquefaction of soil is a function of soil condition with the effect of Peak Ground Acceleration (PGA) being an inevitable factor. Bulk density values have been calculated using SPT N values, from the empirical correlations. After site response analysis, using amplification factor and rock PGA, soil PGA for all the sites has been calculated and used for the assessment of liquefaction potential. Cyclic resistance ratio (CRR) of the soil which implies the resistance of soils towards liquefaction and Cyclic stress ratio (CSR) which implies the cyclic stress induced by the earthquake have been calculated. Its ratio implies the factor of safety (FOS). A soil layer with FOS < 1 is generally classified as liquefiable and with FOS > 1 is
A. Definition
Liquefaction is the phenomena when there is a loss of strength due to dynamic loading, in saturated and cohesionless soils because of increased pore water pressures and hence reduced effective stresses. Liquefaction occurs in loose saturated soils; saturated soils are the soils in which space (pores) between individual particles is completely filled with water. This water exerts a pressure on the soil particles, this pressure is termed as pore water pressure. The pore water pressure is however relatively low before the occurrence of an earthquake. But earthquake shaking can cause the pore water pressure to increase to the point at which the soil particles can readily move with respect to one another. Although earthquakes often trigger this increase in pore water pressure, but activities such as blasting can also cause an increase in pore water pressure. When liquefaction occurs, the strength of the soil and the ability of a soil deposit to support the construction above it decreases. Soil liquefaction can also exert a higher pressure on retaining walls, which can cause them to slide or tilt. This movement can cause the destruction of structures on the ground surface and settlement of the retained soil. B. Causes It is required to recognize the conditions that exist in a soil deposit before an earthquake in order to identify liquefaction. The soil is basically an assemblage of many
350
Joseph T.M., Nitish Puri and Ashwani Jain
soil particles which stay in contact with many neighboring soils. The contact forces produced by the weight of the overlying particles holds individual soil particle in its place and provide strength. The occurrence of liquefaction is the result of rapid load application and break down of the loose and saturated sand and the loosely-packed individual soil particles try to move into a denser configuration. However, there is not enough time for the pore-water of the soil to be squeezed out in the case of an earthquake. Instead, the water is trapped and prevents the soil particles from moving closer together. Thus, there is an increase in water pressure which reduces the contact forces between the individual soil particles causing softening and weakening of soil deposit. In extreme conditions, the soil particles may lose contact with each other due to the increased pore-water pressure. In such cases, the soil will have very little strength and will behave more like a liquid than a solid.
ratio (CRR). Liquefaction potential index (LPI) is a singlevalued parameter to evaluate regional liquefaction potential. LPI at a site is computed by integrating the factors of safety (FOS) along the soil column up to 20 m depth. A weighting function is added to give more weight to the layers closer to the ground surface. The liquefaction potential index (LPI) quanti ity of liquefaction and predicts surface manifestations of liquefaction, liquefaction damage or failure potential of a liquefactionprone area.
III. ASSESSMENT OF LIQUEFACTION POTENTIAL
w ith
ou
EX
tt he
It
is
IL
LE
G in AL PR p t o ES art co S o r p y, W in p R fu rin I T ll, t T E on or N a sa PE ny ve R
Assessment of liquefaction susceptibility provides a preliminary idea of the resistance of soils to liquefaction. It can range from not susceptible, to highly susceptible. A detailed assessment of liquefaction hazard can be carried out by estimating liquefaction potential. The liquefaction potential of any given soil deposit is determined by a combination of the soil properties, environmental tal factors and characteristics of the earthquake to which it may be subjected. A number of methods have been developed to help design engineer in the evaluation of liquefaction potential of cohesionless soil deposits based on data obtained from the laboratory tory test results, field performance of sand deposits or by geological and geomorphological criteria [1].. Both laboratory investigations and observations of field performances have shown that the liquefaction potential of a soil deposit to earthquake motions ns depends on properties of the soil and characteristics of the earthquake involved. In the prese present study, Idriss & Boulanger [2] approach based on SPT Nvalue has been used for evaluation of liquefaction potential at the sites. Liquefaction potential refers to the probability that soil will actually liquefy at a given site and therefore depends not only on the liquefaction susceptibility of soil but also the level of seismic activity in the region. For example, very loose clean sand may be highly susceptible to liquefaction, however, if it exists in a region of negligible seismicity, then its liquefaction potential will be low. In contrast, a denser soil may have a lower susceptibility, however, a higher liquefaction potential because it is situated in an area of very strong seismic activity. The use of in situ testing is the dominant approach in common engineering practice for quantitative assessment of liquefaction potential. Evaluation of liquefaction resistance of soils requires the calculation of seismic demand on a soil layer, expressed in terms of cyclic stress ratio (CSR) and the capacity of the soil to resist liquefaction, expressed in terms of cyclic resistance
Fig. 1: Location of Bore Holes
Liquefaction potential assessment has been done using Semi-empirical procedure developed by Idriss and Boulanger, key components of which are as follows: 1. Groundwater table: The soil must be below GWT. The liquefaction analysis could also be performed if it is anticipated that the groundwater table will rise in future, and thus the soil will eventually be below the groundwater table. 2. Cyclic stress ratio (CSR): Determine CSR that will be induced by the earthquake. 3. Cyclic resistance ratio (CRR): By using the standard penetration resistance test data, the CRR of the in-situ soil is determined. 4. Liquefaction Potential Index (LPI): Determine LPI from the obtained FOS, gives the severity towards liquefaction. For the present study, the water table has been considered at the ground surface which is the most extreme severe condition for the liquefaction. Bulk density values have been calculated using SPT N values, from the empirical correlations developed by Prasad et al. [3]. PGA values for rock sites have been obtained from deterministic seismic hazard analysis carried out by Siddhardha et al. [4]. Using the amplification factors determined for Chandigarh city by Joseph et al. [5], the PGA values calculated for rock sites have been modified
Assessment of Liquefaction Potential…
for soil sites. The PGA values for soil sites have been used for the assessment of liquefaction potential. LPI has been calculated by using the procedures developed by Luna and Frost [6]. The liquefication severity corresponding to LPI has been explained in Table 1. TABLE 1: LIQUEFACTION SEVERITY LPI Severity 0 None 0–5 Minor 5–15 Moderate >15 Major
10.3 11.2 13.2 13.9 16.2 16.8 19.2 24 25
CI ML-CI CI SP CI ML-CI CI CI SM
36 33 27 32 25 24 34 30 39
0.4781 0.4813 0.4872 0.5247 0.4803 0.48 0.4499 0.4353 0.452
1.2119 0.6741 0.3206 0.5614 0.2443 0.2281 0.347 0.2314 0.4312
351
2.5349 1.4007 0.658 1.0701 0.5087 0.475 0.7714 0.5315 0.9539
TABLE 4. SUMMARY OF LIQUEFACTION ANALYSIS OF SECTOR 17 IS Symbol SPT N Value CI 7 CL 6 SM 9 CI 15 CL-ML 21 ML 30 SP 30 SP 30 SP 39
CSR 0.5691 0.57 0.6682 0.5398 0.5216 0.5001 0.5544 0.5484 0.5073
CRR 0.1399 0.1318 0.1619 0.2333 0.3207 0.694 1.3759 0.749 1.965
FOS LPI 0.2457 5.274 0.2312 0.2423 0.4322 0.6149 1.3877 2.4815 1.3659 3.873
TT E N on or s a PE ny ave R r et an M ri y IS ev c S I al on O sy t e N s nt of t e of th m, th e is co pd py f, rig ht -h ol de r
Liquefaction potential assessment has been carried out for the all the sites. Using the LPI values obtained from all the sites, a hazard map has been plotted. Sites showing none, minor, moderate and major susceptibility to liquefaction are located at Sectors 11, 15, 17 and 50 respectively. Detailed analysis of these sites has been reported in Table 2-5. Summary of results for all the 41 sites has been reported in Table 6.
Depth 0.5 2.2 3 3.75 5 5.4 6 8.4 12
OF L IQUEFACTION ANALYSIS OF SECTOR 50 TABLE 5. SUMMARY OF Depth IS Symbol SPT N value CSR CRR FOS LPI 1 CI 19 0.4712 0.3095 0.6569 27.844 2 SP 6 0.6115 0.116 0.1896 3 SP 10 0.5845 0.1279 0.2189 4 SP 24 0.5154 0.4931 0.9569 5 SP 28 0.4987 0.4116 0.8254 6 SP 23 0.5154 0.3356 0.6511 7 SP 24 0.5093 0.385 0.756 8 SP 20 0.5231 0.215 0.4109 9 SP 12 0.5589 0.1755 0.314
TABLE 6. SUMMARY OF LIQUEFACTION ANALYSIS OF ALL SITES SITES
w ith
Community Centre, Village Sarangpur Ext of Govt. School, Mauli Jagram Govt. High School, Manimajra Govt. High School, Maloya
Fig. 2: Liquefaction Hazard Map of Chandigarh City
TABLE 2. SUMMARY OF LIQUEFACTION ANALYSIS OF SECTOR 11 Depth 1 2 3 4 5 6 7 8
IS Symbol ML CL-ML ML ML ML SP SP SP
SPT N value 22 34 34 33 27 32 34 36
CSR 0.5436 0.5145 0.5130 0.5134 0.5248 0.5658 0.5561 0.5466
CRR 0.4275 4.4037 2.7542 1.8352 0.5443 0.7388 1.8823 1.9533
FOS LPI 0.7863 0 8.5588 5.3687 3.5745 1.0372 1.3058 3.3847 3.5734
TABLE 3. SUMMARY OF LIQUEFACTION ANALYSIS OF SECTOR 15 Depth 3 3.4 4.8 6 6.5
IS Symbol SPT N value ML 11 CI 21 SM 18 SP 26 CI 20
CSR 0.5546 0.5263 0.6125 0.5723 0.5227
CRR 0.1839 0.3754 0.3055 0.7181 0.3020
FOS LPI 0.3316 0.5485 0.7133 0.4987 1.2548 0.5779
Govt. High School, Village Kaimbwala Govt. Primary School, Manimajra Govt. building for UT offices at Jan Marg, Sector 9 Sector 10 3 Storey Block-C, Sector 11 Additional block in Govt. College for boys, Sector 11 Sector 15 Sector 17
Maximum No. of LPI Sever Depth (m) Boreholes ity 9 2 6.908 Mode rate 6 3 22.87 Major 9 10
4 3
9
2
8
4
15
3
12 9
1 2
8
4
20 12
1 1
Govt. Model Senior Secondary School, Sector18 Judge Houses, Sector 24
9
2
9
4
New Judge House, Sector 24
9
3
ITI/Centre of Excellence, Sector 28 Sector 31 Doctor's Hostel in Govt. medical college, Sector 32
9
2
15 9
1 3
16.98 Major 6.391 Mode rate 42.20 Major 6 20.81 Major 11.02 7 0 26.27 5 0
Mode rate None Major None
0.549 Minor 5.274 Mode rate 21.04 Major 3 46.81 Major 1 26.85 Major 6 22.76 Major 4 2.179 Minor 17.27 Major 8
352
Joseph T.M., Nitish Puri and Ashwani Jain
Sector 33
21.5
1
Sector 35 Community Centre, Sector 37
13 7.4
1 3
Sector 38
16
1
Govt. High School, Sector 38 west Type V houses for Govt. Employees, Sector 39 Auditorium in G.C.G, Sector 42 Gymnasium hall in G.C.G, Sector 42 Dr. Ambedkar Institute of HM and C&N, Sector 42D Type II houses, Sector 42C
9
2
9
2
9
2
9
4
9.559 Mode rate 21.51 Major
9
2
18.21 Major
9
3
9
2
9
3
17.70 7 32.99 9 14.73 2 28.97 4 25.55 3 6.517
9
Govt. School, Sector 45, Burail
9
Hostel, Govt. college, Sector 46 Govt. Senior Secondary School, Sector 47 Sector 48 Govt. High School, Sector 50B
9
25 9
Sector 52 Sector 54
20 14
Govt. High School, Sector 54A
9
3 3
1 5 1 1
3
13.4
1
LE
15
is
Type II houses in C.A.P, Dhanas
3
IL
Sector 56
4
9
IV. CONCLUSION
tt he
It
Major Major
ou
ACKNOWLEDGMENT We acknowledge the help from UT Secretariat Chandigarh and Geotech Engineering Services (Mohali) by providing sufficient data for the study. REFERENCES
Mode rate Major
[1]
Major
[2]
Mode rate 4.489 Minor
[3]
4
4.806 27.84 4 0.133 5.799
Minor Major
Minor Mode rate 22.92 Major 5 8.801 Mode rate 27.69 Major 7
Based on the assessment carried out for 41 sites sites, it has been observed that only 2 sites have shown no
w ith
susceptibility towards liquefaction. For the rest of the sites, 6 have minor susceptibility, 13 have moderate susceptibility and 20 have major susceptibility towards liquefaction. It can be observed from the liquefaction hazard map that a high degree of liquefaction hazard is likely to occur at many sites in the city during a severe seismic event. The hazard map will help the structural designers and city planners to check the vulnerability of the area against liquefaction. It can also be used effectively for seismic safety plans and in the seismic hazard mitigation programs.
G in AL PR p t o ES art co S o r p y, W in p R fu rin I T ll, t T E on or N a sa PE ny ve R r et an M ri y IS ev c S I al on O sy t e N s nt of t e of th m, th e is co pd py f, rig ht -h ol de r
Type II houses, Sector 43
Mode rate Minor Mode rate Mode rate 13.26 Mode 2 rate 34.05 Major
EX
Dr. Ambedkar Institute of HM and C&N, Sector 42D Type II houses, Sector 43
11.23 9 2.055 14.35 1 8.673
[4]
[5]
[6]
N. Puri. and A. Jain, ““Preliminary Preliminary investigation for screening of liquefiable areas in i the he state of Haryana, India India”, ISET Journal of Earthquake Technology, vol. 51, pp. 19-34, 19 January 2017. I.M. Idriss,. And R.W. Boulanger, “Semi “Semi- empirical procedures for evaluating liquefaction potential during earthquakes”, Soil Dynamics and Earthquake Engineering, vol. 26, pp. 115- 130, 2006. H.D. Prasad, N. Puri. and A. Jain, “Prediction of in-place density of soil using S SPT N-Value”, Conference on Numerical modeling in Geomechanics (CONMIG-2017), IIT Roorkee, Uttarakhand, India, March 2017. Siddhardha, T.M. Joseph, N. Puri. and A. Jain, “Deterministic seismic hazard analysis of Chandigarh City”, 6th Indian Young Geotechnical Engineers Conference (6IYGEC), NIT Trichy, Tamil Nadu, India, March 2017. T.M. Joseph, Siddhardha, N. Puri. and A. Jain, “Assessment of site response and liquefaction potential of some sites in Chandigarh City”, 6th Indian Young Geotechnical Engineers Conference (6IYGEC), NIT Trichy, Tamil Nadu, India, March 2017. R. Luna and J. D. Frost, “Spatial liquefaction analysis system”, J. Comput. Civil Eng., vol. 12, pp. 48–56, 1998.
