## 1 Introduction  
Groundwater tables adjacent to water bodies such as rivers, estuaries, and near the shore affect underground construction, and countermeasures against groundwater flows are necessary. Steel sheet piling, slurry trench walls, cast-in-place pile, soil-cement wall, etc., are widely used to cut off the groundwater table, and then a working space is excavated within the cutoff walls [1]. A seepage is induced into the working space due to the head differential. Although cutoff walls are installed into bedrock, the walls do not ensure perfect prevention of water intrusion into the working space due to the uncertainty of cutoff walls [2]. Therefore, a foundation system is constructed while working space is temporarily ensured by pumping water out (Figure 0(a)). After the completion of sub- and super-structure construction, the pump is removed, and excavated space is backfilled. The groundwater table rises until the equilibrium state is reached, and the system is subjected to buoyancy and uplifting force. This process finally results in the tensile force of the foundation system [3] (Figure 0(b)). The pullout capacity of a pile is dependent on the length of the pile and interfacial bonding capacity between pile and ground [4]. When a hard layer or bedrock exists, a deep foundation system has various limitations. For example, in the case of a bored pile, it is difficult to assure the design length of the pile with deep penetration due to the high penetration resistance of the hard layer. For a driven pile, noise during construction causes civil complaints [5]. In this situation, a micropile can be an effective alternative to the deep foundation system. A micropile has a small diameter (typically less than 300 mm) consisting of a reinforcing bar and grouting [6]. The micropile is classified as a non-displacement pile because of its small diameter and boring installation method [7]. A steel bar is inserted into a borehole, and the borehole is grouted, bonding the reinforcing bar and surrounding soils. The bonding strength between micropile and soil differ according to the types of grouting (e.g., level of pressure during grouting). Due to grouting, the unit bearing and pullout capacity of the micropile are considerably higher than those of conventional piles [8,9]. The unit price of a micropile is much lower than for conventional systems, as relatively small-scale equipment is used during micropile construction. For example, using 2017 market prices in South Korea (based on a personal communication from an engineering company in South Korea), the rental fee for construction equipment is approximately USD 90,000 per month for cast-in-place pile construction (e.g., drilling machine, crane, oscillator, casing, power pack, and water supply truck), while USD 26,000 is required for micropile construction (e.g., crawler drill, air compressor, grouting mixer, crane, water supply truck, pork lift, and generator). Therefore, a micropile is an attractive alternative where bedrock exists at shallow depth and the foundation system is subjected to the uplifting force due to groundwater. To install a micropile, a centralizer and a reinforcing bar are inserted into a borehole, and cement grout is poured into the borehole through a tremie pipe. At this stage, the micropile is classified into four types (Type \(A\), \(B\), \(C\), and \(D\)) according to the filling methods of the cement grout as presented by [PERSON] and [PERSON] [10]. The simplest method is Type \(A\), which uses gravitational grouting. The grouting is applied after boring with no pressure. The gravitational fill technique is generally used when the micropile is located on a rock or the design load is not significantly high [11]. For the Type \(B\) method, gravitational grouting is first placed into the casing, and pressure grouting (typically at 1 MPa) is applied during the withdrawal of casing or auger. The Type \(C\) method is similar to Type \(B\), but pressure grouting greater than 1 MPa is applied from the head of the reinforcing pipe.