Checking distribution of post grouting at bottom of long piles by ultrasonic CT

According to the theoretical analysis,it was possible to check distribution of post grouting at the bottom of piles by ultrasonic CT.The testing check was done at first.Several technological difficulties in checking process were solved,such as the reliability and stability of instruction system,ultrasonic sign identify and correction,criterion for identifying different materials in the checking profile and its speed distribution figure.Since the materials in checked profile form several boundaries and lead complex reflection from refraction,the key in test checking was to identify arrive time correctly and build right criterion to link sonic wave velocity with materials.The results approved that the grouting at the bottom of piles could form a ball-liked end.The final shape of pile end after grouting depended on both ratio of cement grouting to sand and pressure and speed.The enlarged part at pile bottom increased the frictional resistance around piles and the bearing capacity at pile bottom,which effectively improved the bearing capacity of pile foundation.The results,together with those by bearing capacity tests,supported the decision of applying the post grouting technology.In a practical engineering at fundament of constructing Yangtze River Bridge in Nantong city,Jiangsu Province,it was observed at checking profile that the post grouting flowed along center coarse sand layers and a no bar concrete layer was formed.The shape of enforced region was satisfactory.