20 HORIZONTAL MOVEMENT OF PILE FOUNDATION DUE TO COMBINED LOADS *Sumiyati Gunawan 1 , Niken Silmi Surjandari 2 , Bambang Setiawan 3 and Yusep Muslih Purwana 4 1 Department of Civil Engineering, Sebelas Maret Surakarta University, Indonesia; 2,3,4 Department of Civil Engineering, Sebelas Maret Surakarta University, Indonesia *Corresponding Author, received: 07 June. 2021, Revised: 17 Feb. 2022, Accepted: 27 March 2022 ABSTRACT: The vertical loads of a structure are usually carried by pile foundations, but horizontal loads are dominant in some other structures. It is, however, necessary to note that combined loads are seldomly analyzed in simultaneity even though they work simultaneously on-site. This means the horizontal movement added due to the combined loads is not usually considered in construction. Therefore, this research was conducted to investigate and analyze the effect of combined loads at horizontal movement on a single pile and group pile foundations. The process was in three stages. The first was an analysis conducted through 2D-FEM Plaxis2D8.6, the second was an experimental test in the laboratory, and the third involved the analysis through 3D-FEM Plaxis3D Foundation1.1 for validation using soil data and loading test on several projects. The results showed the horizontal movement increased significantly up to the moment it averagely collapsed after reaching ((Pu.D)/(Hu. L.E)=2.5x10 -6 ) for a single pile and ((Pu.D)/(Hu.L.E)=0.745x10 -6 ) for group pile. This increment needs to be considered in the construction process and the additional horizontal movement due to the combined load also needs to be considered after the limits have been reached. Keywords: Vertical-horizontal loads; Single-pile; Group-pile; Horizontal-movement 1. INTRODUCTION The vertical loads of a structure are usually carried by pile foundations but the dominant loads in some other structures are horizontal. This makes it very important to calculate the horizontal loads in pile foundations [1]. It is important to note that combined loads are seldomly analyzed in simultaneity. This involves calculating the vertical load first to determine the vertical carrying capacity and vertical movement followed by the determination of the horizontal load to evaluate the horizontal bearing capacity and horizontal movement. Meanwhile, the two loads work simultaneously on-site [2]. These loading tests are, however, not usually conducted simultaneously in Indonesia and this leads to non-consideration of the additional horizontal movement due to the combined loads in the construction process as required by the ASTM D3966-07 [3]. Previous studies have reported the reduction of horizontal movement in pile foundation under combined loads due to vertical loads [4] while horizontal loading was discovered not to be causing any vertical movement but can increase the movement in combined loads [5]. A study also showed horizontal bearing reduced as the embedded part of the pile was decreased while the horizontal movement also reduced with an increase in the vertical load on the pile head [6]. Moreover, a three-dimensional finite element analysis was conducted to determine the influence of combined vertical and horizontal loads on homogeneous clay and sandy soils. The results showed a significant increase in the effect of vertical load on the horizontal bearing capacity in sandy soil and a slight decrease in clay soil, but a substantial influence was recorded for sandy soils, even for piles with 30D in length, and a less significant impact was found with clay soils for piles above 15D in length [7]. Another test conducted on poorly graded sand with the pile and loading varied also showed an increase in the horizontal bearing capacity as the vertical load was increased [8]. A numerical study analysis of pile- soil interactions subjected to vertical and horizontal loads simultaneously using LPILE, a finite element (FE) model with Abaqus/Cae and SAP 2000, also showed an increase in vertical load caused the induced bending moment and horizontal movement to reduce and this subsequently increased its capacity to withstand horizontal forces [9]. Another research also discovered that the influence of vertical loads on horizontal bearing capacity pile increased significantly in sandy soils but less significantly in loamy soils [10]. Vertical loads were also reported to have less effect on horizontal resistance in sandy soil, but the progression was observed to be increasing as the soil density increased [11,12]. Moreover, the influence of vertical load on horizontal bearing capacity significantly increased in sandy soils and slightly in clay soils while the square-shaped pile was found to have the ability to withstand 1.3 times more load than the round pile [13]. The numerical analysis International Journal of GEOMATE, May, 2022, Vol.22, Issue 93, pp.20-27 ISSN: 2186-2982 (P), 2186-2990 (O), Japan, DOI: https://doi.org/10.21660/2022.93.j2227 Geotechnique, Construction Materials and Environment