You are tasked to supervise a construction work for laying a water pipe. You see some site workers excavate a nearly vertical trench of approximately 2.5m depth as shown in the Figure Q4 below. The site workers tell you that this is a clay soil, so don't worry, the trench won't collapse. From soil investigation, the soil undrained shear strength s = 15 kPa and soil unit weight y = 17.5 kN/m. Should you be concerned? Substantiate your answer. H = 2.5m water pipe Figure Q4