Assessment of soil liquefaction beneath the National Capital Region of Delhi: implications for earthquake-resilient structures

Abstract

Delhi is the capital of India and is located in seismic zone IV as per the Indian Standards which could generate an intensity of ground motion up to VIII on the MMI scale. Concerning the fast-growing population and its demand for an easy life and livelihood, infrastructure is expanding very fast in the National Capital Region (NCR) of Delhi constructing low-rise to medium-rise buildings to skyscrapers with or without building bylaws resulting in uncountable loss of lives and socio-economic losses when a catastrophic earthquake struck. Failure of subsurface soil columns due to liquefaction is the most common phenomenon after and during an earthquake resulting in foundation failure and tilting of the structures, and huge damages occurred. About 75% of the total area of NCR Delhi is falling under water-saturated and very loose alluvium deposits located under seismic intensity VIII on the MMI scale. Therefore, a detailed liquefaction study of the in situ Yamuna River soils is conducted by laboratory analysis to countermeasure the liquefaction potential hazard of the NCR of Delhi. Here, an attempt has been made to measure the soil liquefaction characteristics of the Yamuna River soil (YRS) of the National Capital Region of Delhi using state-of-the-art cyclic triaxial testing (CTT). In this study, a total 4 undisturbed samples (UDS 3, UDS 4, UDS 5, and UDS 9) are collected from the different depths from three different boreholes (BH 4, BH 9, and BH 13) along the flood plain of YRS in the north-eastern part of Delhi. Each UD sampler is 0.45 m in length and is collected from the respective boreholes as per the available Indian Standard Code under the project of seismic microzonation of NCT Delhi. UDSs 5 and 9 are collected from the same borehole BH 13 at different depths below ground level. The sieve analysis shows that UDS 3, UDS 4, UDS 5, and UDS 9 are ML, SM, SW-SM, and ML that are depths ranging between 9.0–9.45 m; 12.0–12.45 m; 15.0–15.45 m, and 27.0–27.45 m respectively. The excess pore water pressure, axial strain, deviator stress, and double-amplitude axial strain (DA) are obtained through stress-controlled and strain-controlled CTT measurements. The stress-controlled CTT is applied for UDS 3 and UDS 4 and strain-controlled CTT is applied for UDS 5 & UDS 9 at given confining pressure of 106 kPa and frequency at 1 Hz yielded the value of excess pore water pressure ratio. It is noted that the double-amplitude (DA) axial strain at 5–6% can liquefy the soils at a higher number of cyclic loading (~ 140th cycles) for cyclic stress ratio (CSR) lying between 0.1 and 0.2 of YRS. It is also observed that the same samples of SM and ML can get liquefied at 15th cycles of loadings with CSR values of about 0.3 and 0.27, respectively, which is equivalent to an earthquake loading of moment magnitude (Mw7.5) of the Yamuna River soil (YRS). The hysteresis curves yielded by the strain-control show that damping is increasing from low to high strain measure of YRS. Therefore, site-specific soil laboratory analysis for laboratory measurements is important to anticipate the area of liquefiable hazard areas along the flood plain of the Yamuna River of Delhi to prepare earthquake-resilient structures of the NCR of Delhi.