The researchers conducted tests on single piles and a pile cap with two piles to see how the pile cap affects the horizontal bearing behavior of a pile foundation. They found that the pile cap significantly increases the foundation's ability to resist horizontal loads and deformation. The pile cap with two piles had a much higher horizontal load capacity compared to single piles, showing an increase of 264% in critical load and 238% in ultimate load. This means that using a pile cap can make the foundation stronger and more stable against horizontal forces.