Micro-cone penetrometer for more concise subsurface layer detection

As the disturbance zone and measurement of soil properties are affected by the size of the penetrometer, a more local value may be measured by a smaller penetrometer. An ultra small Micro-Cone penetrometer with a 5 mm outer diameter is designed and manufactured to characterize soil properties with minimum disturbance during penetration tests. The tip resistance is measured by using strain gages attached near the Micro-Cone (MC) tip. A friction sleeve is adopted to effectively remove the skin friction from the tip resistance. Design concerns include the installation of strain gages, circuits, operating temperature, input voltage, penetration systems, penetration rate, sampling rate, and calibration. Application tests show that the air-clay interface, and the soil layers that consist of clay and sand are closely detected by the MC penetrometer. The cone tip resistances measured by the MC and the miniature cone with a 16 mm outer diameter are similar in clay. The strength change in sand after multiple liquefactions is clearly identified. This study shows that, with a relatively high resolution, the MC penetrometer may effectively detect the soil interface and yield the reasonable cone tip resistance.