In the year of 2012 the NARO announced an in-situ ground survey machine, the Nippon Screw Weight System (NSWS), designed to overcome problems with the standard penetration test.
The NSWS was developed with the specific aim to encounter the recent weather abnormalities and natural hazard, saving human lives. The creator of NSWS, Kozo Okita, was the member of 311 earthquake disaster committee of the Japanese Geotechnical Society. The society released a report in June, 2012 proposing to Japanese government a use of NSWS to investigate the 3.11 aftermath.
It is compact, weighs 120 kg, and highly-mobile because the wheels are attached, suited to measure the ground in the crowded residential areas. It costs about only half of what used to cost with the conventional SPT test and triaxial compression test. The NARO has released the cost index table.
Features for detecting weak spots:
- It can measure very soft zones, converted N-value of zero in the ground that had been considered difficult.
- It has 1.08 cm interval, far finer than SPT
- SPT conducts the test every 50 cm, and 30 cm interval out of 50 cm is tested so the rest, 20 cm, is not measured; that means 40% of an entire hole is unknown. NSWS does not suffer from such a limitation.
- NSWS can penetrate the ground diagonally.
- NSWS can cut soft gravels.
Features for conducting in-situ shear test and sampling at a different hole:
- In-situ shear test capability, the result of the joint research with NARO and Okita-Ko Co.,Ltd
Features for conducting Stability Analysis:
- NSWS can prepare converted N-value, density, in-situ shear data for Stability Analysis.
- Since NSWS enables multi-point surveying due to its diagonal penetration capability and high-mobility. The multiple spots on the weak layers can be analyzed.