Method for measuring the membrane penetration of triaxial specimens based on an external circular array of laser displacement sensors

In triaxial tests, membrane penetration is an important factor influencing the accuracy of volume change and pore pressure measurement. To measure and evaluate the membrane penetration of specimens made of gravelly sandy soils, a method using a newly developed measurement system based on an external circular array of laser displacement sensors is proposed in this paper. A series of experimental studies were conducted on the effects of several factors on membrane penetration. The result shows that there is a linear correlation between the unit membrane compliance and the effective confining pressure on a semilog plot. In addition, as the gravel content increases, the membrane penetration increases, but this trend weakens with increasing relative density. Notably, when the characteristic particle size is the same, the membrane penetration will be greater for more broadly graded soils. Moreover, the error caused by the thickness of the membrane increases as the diameter-to-thickness ratio decreases.