Knowledge24
Civil/Environmental
Hi
When SPT is carried out in deep boreholes, say 60m, it would include 40 rods each assumed 1.5m. The hammer strikes tend to buckle the 60m rod length and therefore some of the energy will be lost although the rod length rebounds as an elastic material (and the confinement in the borehole does not allow to have a buckle failure anyway). Therefore if the reading is for example 45 blows, it could have been less if some of the energy had not been lost in the rod assembly. Is there any correction for it. I am aware of correction for overburden but this aspect is more related to energy loss. Although we do a correction on rod length for N60, but the correction factor is 1 for longer rod lengths - almost on the contrary to the above phenomenon. I wonder if someone gives me a clue to understand if I am missing an item.Thank you.
When SPT is carried out in deep boreholes, say 60m, it would include 40 rods each assumed 1.5m. The hammer strikes tend to buckle the 60m rod length and therefore some of the energy will be lost although the rod length rebounds as an elastic material (and the confinement in the borehole does not allow to have a buckle failure anyway). Therefore if the reading is for example 45 blows, it could have been less if some of the energy had not been lost in the rod assembly. Is there any correction for it. I am aware of correction for overburden but this aspect is more related to energy loss. Although we do a correction on rod length for N60, but the correction factor is 1 for longer rod lengths - almost on the contrary to the above phenomenon. I wonder if someone gives me a clue to understand if I am missing an item.Thank you.
