Piezometers are installed into a buried stratum of compressible clay to monitor excess pore water pressures during the placement of earth fill in an area where construction of a new highway is taking...

Piezometers are installed into a buried stratum of compressible clay to monitor excess pore water pressures during the placement of earth fill in an area where construction of a new highway is taking place. The top of the buried clay layer and the area groundwater table are at a depth of 10 m below the natural ground surface. Initially, the water level reading in the piezometers is at a depth of 10 m. When a 5-m thickness of soil fill is placed over the area, the water level reading in the piezometers rises to an elevation 9 m above the top of the clay layer. What is the stress increase at the level of the clay layer in kPa (i.e., what is the excess pore water pressure that develops)?