Lateral Performance for Long Pile Subjected to Simultaneous Axial and Lateral Loads in Dense Sand: An Experimental Study

The present study focus on the investigation ofthe response of single pile when subjected to both axial and lateral loads simultaneously in dense sand. To study this issue, laboratory model was locally improved to examine the piles under this kind of loading. The dense sand provided using raining technique. The slenderness ratio of the tested pile is ( L/D=45). On the other hand, the vertical and horizontal loads are divided into 5 stages to assess the influence of load intensities on the lateral pile response. It can be concluded that the lateral pile response is affected by changing the load intensities

In fact, piles foundationare structural member which made from timber, steel, or concrete, used to support the structures and to transfer the loadsto the deep layers of soil that have adequate bearing capacity to support the structures. Always piles were subjected to vertical loadswhich result from the weight of the structures and to lateral loads result from wave, wind or earth quake especially when the piles used in the offshore structures. Actuality, piles are subjected to both vertical and lateral loads in the same time, so it is important to know the response and the behavior of piles in such cases especially when the studies are limited in such way.
A number of pervious study takes into account the effect of pure lateral load on piles, these studies were early reported by (Broms 1964, Reese et al. 1974, and continuously improved until present (Awad 1999 Based on the menstioned study it can be shown that the study about the pile behavior under combined loads is limited, therefore this study included experimental tests for lateral pile performance with the effect of the presence of the vertical load in the same time in dense sand.

Sand
The sand used in the present study was brought from Karbalaa governorate, Iraq. The laboratory tests were conducted on it to explain its physical properties according to the ASTM specification. Figure (

2.2Pile
The pile used in the present study was made of steel material with diameter (D) of 1.5cm, wall thickness (t) 0.1 cm, and slenderness ratio (L/D) of 45.

Model Tank
The model tank that used in the present study was locally manufactured with dimensions of (100cmx 100cm x 100cm) to prevent any interface between the effective zones of the piles used, and also to prevent the frictionbetween the container wall and the soil used which may affect the obtained test results.
The laboratory model was made from steel plate of thickness equal to 4mm. All the sides of themodel tank were fixed together via a number of screws as shown in the figure below. Figure 2 show the laboratory testing model that included all equipment's and the location for each part.

Experimental Work
In the current study the pile used were subjected to both vertical and lateral loads. At initial stage the strain gauges were fixed at the pile side figure (3) to measure the lateral deflection of pile inside the soil. After that the pile model was placed in the laboratory model in the required depth by using steel mesh which fixed above the sides of model tank, the soil used (sand) was placed in the same tank from a required height (0.6m) for obtaining the required placement density in the test via using the raining technique. The lateral load was applying on the pile by using a wire which attached by the cap of the pile from one direction and from the other it is related to the loading base via frictionless pulley. The lateral deflection of pile above the soil surface was measured by two dial gauges above the soil surface fixed at the pile cap and the lateral 112 deflection along the pile inside the soil was measured by using the strain gauges.

Figure 3: The location of the strain gauges at the pile side
The amount of lateral load that used in the current study is equal to 20% of the allowable vertical load of the pile used and applies infive increments on pile. In each increment the lateral displacement was measured by using two dial gauges (sensitivity of 0.01 mm) which fixed on the pile cap and by strain gauges fixed along the pile. Vertical load is apply on the pile with the appliedof lateralload in five stages (0%, 20%, 40%, 60%, 80%, 100% from the allowable vertical load).

4.Test Results and Discussion
The load-displacement curves were plotted for the pile used as shown in figure 4to explain the effect of the presence of the vertical load on the lateral response of pile.The lateral deflection of pile was measured by using dial gauge which is fixed on the pile head and for the embedded length of pile, the lateral deflection was measured by using strain gauges fixed at the pile side in the direction of load. From figure 4 it can be shown that when the vertical load is between 20% and 60% from the allowable vertical load, the lateral capacity of pile increases about 15.8% and 1.2% respectively, this is possibly due to the increase of pile stiffness due to increase of axial load. While, when the applied the vertical load more than 80% from the allowable vertical load, the lateral capacity of pile decreases to reach about 33.8%. This is possibly due to increases the effect of p-delta phenomena.  its amount it is 20 and 60% from the allowable vertical load of pile. From the test results it can be shown that when the vertical loads applied on the pile is 20% and 60% from the allowable load then the lateral capacity of pile increases about 15.8% and 1.2% respectively and when the vertical load applied on the pile are 40%, 80%, and 100%, then the lateral capacity of pile decreases. The location of the flexural point is 156.25mm from the soil surface.