Analysis of hollow area beneath concrete slab of seawall by means of ground penetration radar

Seawall is an important public facility which can protect areas of human habitation from the destructive aspects of tides or waves. Maintenance and monitoring of seawall structures plays an essential role in public safety and prevention of flooding of areas behind the seawall. The presence of hollow area beneath the concrete slab of riverside slope can result in the settlement and distortion of face slab. It has been one of the most important factors seriously influencing the safety of seawall body. Here, GPR survey for hollow areas beneath the concrete slab of the seawall of Qiantang River has been implemented. The bottom of concrete slab and top of the soil layer can be clearly identified from GPR profile. The gap between these two interfaces is regarded as the hollow area beneath the concrete slab. Also, time slice obtained from grid survey lines. Excavation data at some points demonstrated that the height determination error for the hollow areas from GPR profile is less than 10%. Also, the distribution of the hollow area determined by GPR is consistent with the real information revealed by excavation on site.