大型動的コーン貫入試験における打撃効率と打撃孔傾斜角

抄録

Heavy Dynamic Cone Penetration Test (H-DCPT) was carried out to study penetration mechanism by measuring impact acceleration and force during blows of the hammer at the top and bottom of the driving rod. First, the driving efficiency was estimated from measured acceleration and force. Then, the number of blows, N_d, was corrected based on the driving efficiency and comparably studied with the conventional correction based on torque. The driving efficiency at the top of the driving rod was constantly approximately 80%, while they at the bottom of the driving rod differed in kinds of soil, almost 80% in sandy soil and ranged from 5 to 10% in clayey soil. These were concluded from measurements; the driving energy was dissipated significantly affected by skin friction of the driving rod, particularly in clayey soil. The N_dE, which is the number of blows corrected by the driving efficiency at the bottom, was well agreed with the SPT-N value. However, the conventional N_d was excessive compared to the SPT-N value, particularly in clayey soil. In addition, the verticality of the driving hole was surveyed. The inclined angle of the driving hole was measured by using a cone installed 2-axis inclinometer. The measurements revealed that the driving hole was not always drilled vertically, inclined angle changed in complexity depending on kinds of soil or ground hardness, and had sometimes a sizable horizontal displacement.