Automatic Digital Monitor for Standard Penetration Test in Ground Investigation in Hong Kong

Abstract

This paper introduces the automatic SPT monitor, an in-situ digital device for automatic monitoring and recording of the standard penetration test (SPT) in ground investigation in Hong Kong. The SPT monitor has a SPT Tip-depth monitor and a SPT N-value monitor. The SPT tip-depth monitor checks and records the depth of the split spoon sampler during this inserting or retrieving from the borehole. The SPT N-value monitor checks and records both the shock axial force in drill rod and the shock axial penetration of the split spoon sampler in borehole induced by each of the hammer blowing in real time series. It can produce a test report for the N-value (N) and other factual data according to a given specification in real time and digital format. The device is portable and can be non-destructively mounted onto existing SPT apparatus. It can be used in normal ground conditions (i.e. 1≤N≤200), extreme hard (i.e. N>200) or extreme soft (i.e. 0<N<1) ground conditions. The most weak and/or soft soil seam thinner than 75 mm to 300 mm can be detected from the monitored and recorded shock force and shock penetration per hammer blow.