Pore Water Pressure Behavior in Granular Subbase under Pavement Pumping

Pavement pumping can significantly reduce the overall strength of pavements, even rigid or flexible pavements. The fine contents in the subbase material underneath the pavement slabs move up to the pavement surface through the cracks in the slabs due to pumping, resulting in the erosion of the subbase and decreased structural support. Pumping occurs when water that has accumulated underneath a slab is pressurized when the slab deflects under traffic loading. Therefore, the pore water pressure behavior in the granular subbase is an essential factor in clarifying the pumping mechanism. Model tests were conducted in this study to observe the pore water pressure behavior under various conditions. The model was a small-sized circular road simulator, consisting of a transparent cylindrical soil chamber made of acrylic, a transparent slab, and a rotational wheel loader. The slab had a single artificial joint in the radial direction simulating a pavement crack. The soil chamber had manometers equipped on the side wall to measure the pore water pressure in the ground. The experimental results showed that the excess pore water pressure generated under the load was greater at the leave slab side than at the approach slab side. It was also observed that the excess pore water pressure was larger in the case of a slower traveling speed, which implies that the larger slab deflection under slower loading resulted in larger excess pore water pressure.