Piezoresistive <scp>SWCNT</scp> /Epoxy Pressure Sensors Enabling Ultrawide‐Range and Stable Geotechnical Stress Monitoring

ABSTRACT Reliable measurement of earth pressure is essential for the safe operation of geotechnical structures; however, most carbon‐nanotube‐based piezoresistive sensors are limited by low mechanical rigidity and narrow operating ranges. This study presents a high‐stiffness single‐walled carbon nanotube (SWCNT)/epoxy piezoresistive sensor for wide‐range geotechnical pressure monitoring, achieved through the combined use of a rigid epoxy matrix, an optimized CNT conductive network near the percolation threshold, and tailored circular diaphragm geometry. A homogeneous SWCNT network is formed via ultrasonic–magnetic co‐dispersion at a low loading (~0.10 wt.%), enabling stable and repeatable electromechanical responses under compression. The sensor exhibits an ultrawide pressure range up to 3000 kPa with piecewise linear behavior, maintaining high sensitivity (0.75 kPa −1 below 100 kPa) and stable response at higher pressures (0.010 kPa −1 up to 3000 kPa). Key performance metrics include fast response/recovery (133/140 ms), excellent cyclic stability over 10,000 cycles, and negligible resistance drift under sustained loading. Finite element simulations indicate that structural geometry significantly influences stress transfer efficiency, with an intermediate diameter‐to‐thickness ratio (~4) providing optimal uniform stress distribution and maximizing sensitivity, whereas hollow or ribbed configurations induce localized strain and reduce overall resistance response. Soil‐embedding tests across multiple soil types confirm reliable performance under realistic geotechnical conditions, with low noise, strong resistance to particle disturbance, and good agreement with theoretical stress distributions.