# Effect of Micropiles on Clean Sand Liquefaction Risk Based on CPT and SPT
## 1 Introduction  
Liquefaction can occur by cyclic seismic loadings and causes an unexpected decrease in soil strength properties. Undrained saturated or moderately saturated sandy soils in areas with a high risk of earthquakes are prone to liquefaction. Such soils commonly exist in coastal regions with water levels close to the ground surface. During liquefaction, the pore water pressure peaks, and the effective stress of the soil is quickly reduced to almost zero. These abrupt changes in the soil stress properties result in massive destruction of the built environment, such as overturning of buildings. Since liquefaction happens suddenly and unexpectedly during seismic-based ground motion, the response time for building residents to get to safety is very short, which can cause considerable death tolls in large magnitude quakes. For instance, liquefaction was the main reason for the destruction of the buildings in 1964 Nigata, 2010 Canterbury, and 2011 Christchurch [1; 2; 3]. As a more recent example, liquefaction was the major cause of damages in the 2018 Central Sulawesi, Indonesia, earthquake [4]. In the past, traditional soil improvement techniques have been developed to increase soils' effective stress such as soil dynamic and vibro compaction [5] permanent dewatering [6], blast densification [7; 8], deep soil mixing [9; 10], and post-liquefaction dissipation of pore pressure [11], along with the gravelvertical drain method [12]. The stone column stabilization technique is also used for decreasing liquefaction potential [13; 14]. The combined soil stabilization with vertical columns (CSV) method has gained a reputation for liquefaction control. The CSV method is preferred over the stone column method in residential projects due to economic considerations [15]. Presently, environmentally friendly approaches have been developed to mitigate the risk of liquefaction. The aim of such approaches, which are known as passive soil stabilization methods, is to cause minimum disruption to the soil during the geotechnical practices of strengthening the soil against liquefaction. In the passive soil stabilization method, biological soil remediation, such as biogas and bioccmentation, and cementitious composite [16] have made considerable advances. As an innovative environment-friendly approach, the use of recycled materials, such as tire chips and fiber-reinforced material, are used to enhance the structural capacity of pile foundations [17; 18]. Such a recyclable material is also useful to reduce the risk of liquefaction. Tire shreds (chips) absorb seismic vibration and decrease pore water pressure, which in respect reinforces the soil against liquefaction [19]. Using the jet grouting method for soil stabilization is a preferable method to decrease liquefaction potential by improving the shear strength of the soil. This method is constantly developing and has received wide attention over the years [20]. The jet grouting method enhances the mechanical properties of the soil using slurry grout that includes a mixture of Portland cement and water. The grouted material is applied to the soil using high-pressure jets, which penetrate through the soil by collapsing its existing structure. As a result, the soil is mixed and reinforced with the cement grout material. The high-pressure grouting also leads to filling the available cracks or cavities in the soil [21]. The stiffness and strength properties of the grouted materials are important factors in controlling the soil deformation during earthquakes. The reinforced soil, with high-strength grouted material, has an enhanced capacity against overturning under seismic loads. Micropiles have gained attention widely in the geotechnical applications for settlement control, and improvement of the bearing capacity of soil [22]. The structural capacity of the micropile elements, along with their soil reinforcement capability, are significant factors in the design and construction of many projects following the Federal Highway Administration (FHWA-NHI) guideline [23].