## 2 Materials and Methods
### Experimental Investigation
#### 2.3.2 Test Setup and Loading Procedure  
A 1 g small-scale laboratory test is carried out to test the suitability of the numerical model. The experiments were conducted on helical piles having an H/D ratio of 8.75 and 6. In addition, the spacing ratio S/D is varied as 3.75, 1.875, and 1.25 for helical piles having a number of helical plates of 2, 3, and 4, respectively. Other details are mentioned in Table 1. According to [PERSON] et al. [9], by keeping the diameter of the test tank at approximately six times the anchor diameter, boundary effects could be eliminated completely for uplift loading. Considering the elimination of boundary effects, a test tank dimension of 1 m \(\times\) 1 m \(\times\) 1 m is used. The soft clay bed is prepared following the procedure adopted by [PERSON] and [PERSON] [24]. All tests were carried out on a soil bed with a water content of 39%, corresponding to a consistency index of \(I_{c}\) ((LL \(-\) water content)/(LL \(-\)\(I_{p}\))) of 50%. The undrained shear strength (\(c_{u}\)) of the prepared soft clay bed is measured at various depths after each test by using vane shear test apparatus by collecting random samples, and the value is found to be an average of 7.5 kN/m\({}^{3}\). The soil taken from the field is kneaded thoroughly and soaked by adding water to the soil mixing tank. The kneaded soil is covered with polythene sheets in order to avoid evaporation and loss of moisture content. The wet soil with higher water content makes the filling job easy and is placed in layers of 50 mm thick. Initially, each layer is manually placed by hand packing and then pressed with a template to remove the entrapped air. Because of the high water content, a legitimately homogeneous soft clay bed could be formed. The homogeneity of the prepared clay bed is confirmed by testing a few random samples to determine water content, unit weight, and undrained shear strength at different levels while placing the sample after the test. The average test results show a water content of 39 \(\pm\) 3%, a unit weight of 17 \(\pm\) 0.5 kN/m\({}^{3}\), and an undrained shear strength of 7.5 \(\pm\) 0.3 kN/m\({}^{3}\). Once the clay bed has been prepared, the helical pile is installed in place by screwing it slowly into the remolded clay bed with sufficient downward force until it reaches the required embedded depth. It is necessary to drive the pile in such a way that its rate of advancement is equal to or greater than the pitch of the helical plate (which is 8 mm per rotation) [40]. Random samples were taken from the test tank and tested in triaxial testing assembly. It is found that the sample takes a time interval of 24-36 h for 95% equilibration of pore pressures. Thus, the setup is left for three days before testing the helical pile. During the process, the clay bed is covered with polythene sheets in order to reduce the loss of moisture content. The loading method is carried out in accordance with AC 358: Acceptance Criteria for helical pile foundation systems and devices [41]. The procedure E: constant rate of uplift test, as specified in ASTM D3689-07 [42], is used for the uplift test. The uplift load is measured using a 20 kN capacity load cell that is mounted with the ram attached to the static pullout test apparatus. A constant uplift rate of about 1 mm/min is applied and the pullout is carried out until the pile withdrawal reaches 15% of the anchor diameter or until the pile withdrawal stops, whichever occurs first. The ultimate lateral capacity of helical pile is found by adopting the loading procedure followed by [PERSON] et al. [13]. The lateral load is imposed by adding cast iron weights over a load hanger attached to the free end of the pile using steel wire. Observations of lateral displacement were made until there was no further increase in lateral deflection in response to the applied force. In both cases, the displacement is measured using a set of Hottinger Baldwin Messtechnik (HBM) made displacement transducers (WA-200 mm) and an average value is taken.