Abstract
A permanent test facility was constructed to investigate energy transfer and rod length effects in the Standard Penetration Test (SPT). It is designed to be simpler than past experiments, to gather data more quickly and conveniently. Three closed (watertight) cased boreholes at depths of 6, 15, and 30 m were installed at MARL Technologies in Edmonton. The facility is designed to perform SPTs at the bottom of the boreholes within a removable chamber built to mimic the blow counts (N values) encountered in dense sand, N=50 to 60. Previous researchers have investigated aspects of the SPT with a 30 m drill string supported by a tower, while others have done this below ground in natural soils. The advantage of the current setup is that permanent casings now exist. Testing with different hammers can be done in the future, and various factors can be evaluated, such as accelerometer type and mounting method, rod type, joint tightness.
In September 2020, SPT testing was done at each of these depths with energy measurement devices from Northwoods Instruments and Pile Dynamics Inc. for comparison. The eSPT (Patent #2998280) auto hammer from MARL Technologies was used to measure the hammer drop height and impact velocity for all blows. The hammer efficiencies measured by the stress wave energy devices were statistically equivalent to the efficiency based only on the eSPT's impact velocity measurements. This finding is important because using a device like the SPT Analyzer requires expertise and sensitive equipment, whereas measuring impact velocity is simpler and more reliable.