New Method for Internal Pore-Water Pressure Measurements

The triaxial test is the most common procedure performed in a geotechnical laboratory to investigate the mechanical behavior of soils. However, often only global pore-water pressure (pwp) is measured at the bottom of specimen during conventional triaxial tests, which cannot detect the variation in internal pwp values to represent the true effective stress path adjacent to the failure surface. Here, a modified triaxial testing apparatus capable of measuring internal pwp within the soil using a filterless rigid piezometer (FRP) is outlined. To validate the effectiveness and capability of this novel test method, a series of consolidated undrained tests were conducted on saturated loose and dense sand. The FRP measurements provide a reliable pwp response, especially at pressures above 400 kPa where the FRPs have a faster response than the base transducer. Moreover, the internal pwp measured by FRPs during the initiation of shearing in loose sand can capture the rapid development of excess pwp before liquefaction or failure. The results also show that there are increases of 25 % in average peak strength of the loose specimen and 8 % in average residual strength of the dense specimen with internal pwp measurement, respectively, compared with only global pwp measurement because of the FRP installation. However, FRP installation appears to have no apparent effect on average peak strength of the dense specimen and average residual strength of the loose specimen. The new triaxial testing method can be applied to study the response and distribution of pwp at specific zones within the soil.