Isotropic triaxial compression tests were conducted on five different, fairly uniform sands, with mean grain sizes between 2.8 and 0.105 mm, to determine the effects of effective confining pressure, mean grain size, and relative density on unit membrane penetration. Volume changes due to membrane penetration were determined using sand specimens with identical void ratios and height to diameter ratios but with different sizes, surface areas, and volumes. A semiempirical exponential relationship with respect to effective mean stress was used to model unit membrane penetration, and the results were compared with some other models proposed in the literature. A posttesting correction procedure was formulated to calculate pore-pressure accumulation in monotonic and cyclic tests, taking into consideration coupling between membrane compliance and pore-pressure accumulation. The procedure developed is based on membrane flexibility and soil compressibility expressed as semiempirical exponential relationships with respect to effective mean stress. The applicability of the model is shown based on undrained monotonic and cyclic tests and with respect to some methods proposed in the literature.