Liquefaction and post-liquefaction resistance of sand reinforced with recycled geofibre

Highlights

• Effects of geofibres on post-liquefaction resistance, via cyclic triaxial test followed by monotonic shearing, were assessed.

• Adding geofibres significantly improved both liquefaction and post-liquefaction resistances of clean sand.

• Experimental results show that the initial shear modulus of liquefied specimen significantly increased by adding geofibres.

Abstract

The present study provides an insight into the effect of recycled carpet fibre on the mechanical response of clean sand as backfill material subjected to monotonic loading and cyclic loading as well as post-liquefaction resistance of both unreinforced and carpet fibre reinforced soils. To achieve these goals, a series of multi-stage soil element tests under cyclic loading event resulting in liquefaction followed by undrained monotonic shearing without excess pore water pressure dissipation as well as a series of monotonic undrained shear test is conducted. All the specimens are isotropically consolidated under a constant effective confining stress of 100 kPa by considering the effect of cyclic stress ratio and carpet fibre content ranging from 0.25% to 0.75%. The obtained results revealed the efficiency of carpet fibre inclusion in increasing the secant shear modulus and ductility of clean sand under monotonic shearing without previous loading history. The impact of carpet fibre inclusion on the trend of cyclic excess pore water pressure generation and cyclic stiffness degradation was minimal. However, adding carpet fibre significantly improved both liquefaction and post-liquefaction resistances of clean sand. The liquefaction resistance of clean sand, at a constant 15 loading cycles, improved by 26.3% when the soil was reinforced with 0.75% recycled carpet fibre. In addition, the initial shear modulus of the liquefied specimen significantly increased by adding recycled carpet fibre.

Introduction

Previous earthquake events have revealed the susceptibility of backfill materials to liquefaction and significant damages to the structures embedded or built in these types of soils. Over the years, many researchers have tried to evaluate the performance of backfill materials subjected to seismic loading and assess the mitigation techniques such as grouting, and reinforcing with geosynthetics to minimise the post-liquefaction impacts resulting in loss of bearing capacity, lateral spreading and excessive settlement (Pillai and Salgado, 1994; Orense et al., 2008; Wotherspoon et al., 2012; Festugato et al., 2013; Kang et al., 2013; Papathanassiou et al., 2016; Suazo et al., 2016, 2017; Shen et al., 2018). For instance, during the 2011 earthquake off the Pacific coast of Tohoku, the lifelines facilities such as buried pipeline and sewages manholes were floated due to soil liquefaction and decreasing uplift resistance of soil (Otsubo et al., 2016).

Previous studies have shown improvements in the physical and mechanical proprieties of soil by the inclusion of geosynthetic and bio-based fibres (Yetimoglu and Salbas, 2003; Punthutaecha et al., 2006; Consoli et al., 2010; Tang et al., 2010; Yoo and Lee, 2012; Fatahi et al., 2013a; Fatahi et al., 2013b; Hamidi and Hooresfand, 2013; Mirmohammad Sadeghi and Hassan Beigi, 2014; Chen et al., 2015; Yoo, 2015; Kumar and Gupta, 2016; Debnath and Dey, 2017; Festugato et al., 2017; King et al., 2017a, b; Yoo, 2018; Yoo and Abbas, 2020). Consoli et al. (2010) and Hamidi and Hooresfand (2013) showed that increasing the unconfined compression strength and ductility behaviour of cemented sand by adding fibre. Fatahi et al. (2013a and b) showed the efficiency of polypropylene and recycled carpet fibres on reducing shrinkage of kaolinite and bentonite clays treated by cement whiles maximum shear wave velocity decreased by the inclusion of carpet fibres. Yetimoglu and Salbas (2003) using direct shear test showed that the effect of polypropylene fibre reinforcement on peak shear strength and initial stiffness of dense sand with the relative density of 70% was negligible. Punthutaecha et al. (2006) showed the efficiency of polypropylene and hydrophilic nylon fibre in reducing swelling and shrinkage of sulphate rich expansive soils. Mirmohammad Sadeghi and Hassan Beigi (2014) studied the effect of polypropylene fibre on the dynamic behaviour of clayey sand and showed an increase in shear modulus. Chen et al. (2015) studied the effect of polypropylene and polymer textile bags on the mechanical response of cemented clay on unconfined compressive strength and ductility of the reinforced soil. Kumar and Gupta (2016) using unconfined compression test and split tensile tests showed an increase in UCS, STS, and ductility of clay reinforced with pond ash, rice husk ash and polypropylene fibres.

The beneficial effects of geosynthetics such as geotextile and monofilament fibres on increasing liquefaction resistance and dynamic characteristics of different types of soils ranging from clayey to gravelly soils have been experimentally shown by many researchers (X.Bao et al.; Krishnaswamy and Isaac, 1994; Krishnaswamy and Thomas Isaac, 1995; Yetimoglu and Salbas, 2003; Altun et al., 2008; Geng et al., 2017; Ye et al., 2017; Ghadr et al., 2020). Liu et al. (2011), using ring-shear test showed that the effect of randomly distributed fibre on loose soil under monotonic undrained shearing was minor while the monotonic behaviour of medium to dense fibre-reinforced soil improved significantly. Moayed and Alibolandi (2018) using cyclic triaxial test showed an improvement in liquefaction resistance and dynamic characteristics of pond ash reinforced with geotextiles. Zhang and Russell (2020) using a series of drained and undrained compression test, showed the effectiveness of Loksand fibre on improving the behaviour of loose sand reinforced with Loksand fibre. Chegenizadeh et al. (2018) using stress-controlled triaxial testing studied the liquefaction resistance of low plasticity silt reinforced with continuous bulk filament by considering different parameters including relative density, fibre content and length, and effective confining stress. The obtained results revealed an increase of liquefaction resistance with increasing fibre content and length, relative density and effective confining stress. Noorzad and Fardad Amini (2014) using cyclic triaxial tests showed increasing liquefaction resistance and shear modulus of loose to medium dense sand reinforced with randomly distributed polypropylene fibres. Diambra et al. (2010) using undrained and drained monotonic shearing tests studied the effect of oil palm empty fruit bunch fibres on shear strength of silty soil. The obtained results showed that adding and increasing fibre content increased the peak shear strength, ductility, liquefaction resistance and shear modulus. In addition, the results reported by Diambra et al. (2010) revealed that the effects of added monofilament fibres in medium dense sand were more pronounced than loose sand. The results also showed that the volume dilation decreased by increasing the fibre content, while the fibre inclusion increased the positive excess pore water pressure generation during undrained shearing. Ghadr et al. (2020) using cyclic triaxial testing observed an increase in liquefaction resistance of silty sand by inclusion and increasing thermoplastic polymeric micro-synthetic.

The previous studies showed that the susceptible soils to liquefaction, ranging from loose saturated silty to sandy soils, can also liquefy and lose strength due to excess pore water pressure generation under static loading such as slight vibration due to construction activities, local erosion, and more importantly overloading imposed by additional fill (Lade, 1993). Previous case histories also showed several loose sandy slopes, embankment foundation and tailings dam failures due to static liquefaction phenomena (Olson et al., 2000; Davies and Martin, 2002; Sadrekarimi, 2020; Sadrekarimi and Riveros, 2020).

Most previous studies have attempted to show the beneficial effects of soil reinforcement on mechanical characteristics of backfill material under static and dynamic loadings, while the post-liquefaction resistance of soil reinforced with fibre has gained no attention. In addition, many researchers well studied the liquefaction and post-liquefaction resistances of unreinforced sand (Sitharam et al., 2009, 2013; Soroush and Soltani-Jigheh, 2009; Wang et al., 2013, 2015a, 2015b; Yazdi and Moss, 2016; Noorzad and Shakeri, 2017; Rouholamin et al., 2017), while assessing the effect of monofilament fibre inclusion on liquefaction of clean sand remains unclear.

This research aims to present the effectiveness of recycled carpet fibre reinforced sand as backfill material by assessing the post-liquefaction resistance of the liquefied specimen without excess pore water pressure dissipation after liquefaction by considering different fibre contents including 0%, 0.25%, 0.5% and 0.75%. A series of multi-stage soil element tests capturing stress-controlled undrained cyclic loading events at a frequency of 1 Hz leading to liquefaction were conducted under three different cyclic deviatoric stresses. The post-liquefaction resistance of the liquefied specimens was studied using undrained monotonic shearing without allowing dissipation of the generated excess pore water pressure during cyclic loading events. In addition, a series of undrained monotonic shear tests were conducted to assess the susceptibility of specimens to static liquefaction.