Cavitation in high-capacity tensiometers: effect of water reservoir surface roughness

Abstract

High-capacity tensiometers (HCTs) are sensors made to measure negative pore water pressure (suction) directly. In this paper, a new approach is proposed to expand the range and duration of suction measurements for a newly designed HCT. A new technique is employed to reduce significantly the roughness of the diaphragm’s surface on the water reservoir side in order to minimise the possibility of gas nuclei development and the subsequent early cavitation at the water–diaphragm interface. The procedures employed for the design, fabrication, saturation and calibration of the new tensiometers are explained in detail. Furthermore, the performance of the developed HCTs is examined based on a series of experiments carried out on a number of unsaturated clay specimens. An improvement in maximum sustainable suction in the range of 120–150% of their nominal capacity was obtained from different surface treatment methods. Moreover, the results show an improvement of up to 177% for the long-term stability of measurements, compared to the developed ordinary HCTs with untreated diaphragms.

Creep and consolidation of a stiff clay under saturated and unsaturated conditions

“…Saturated tests were carried out in conventional oedometer cells, whereas unsaturated tests were carried out in suction-monitored oedometer cells equipped with two high-capacity tensiometers (HCTs) for monitoring suction evolutions (Bagheri et al 2018). The special design of the oedometer loading cap allows for replacement of a cavitated HCT without any disturbance to the specimen and interruption in measurement of deformations.…”

“…The compression curves were finally obtained based on the final settlement values. For unsaturated MSL tests, prior to each experiment, the HCTs were saturated and preconditioned following the procedure explained by Bagheri et al (2018). In order to ensure ultimate contact between the specimen and the HCTs, the ceramic disks of the tensiometers were covered with soil paste, and a small vertical stress was also applied to the specimen.…”

Rate Dependency and Stress Relaxation of Unsaturated Clays

“…1 presents a schematic diagram of the apparatus. Two HCTs, accommodated at the mid-height of the specimen, allowed for continuous measurement of pore-water pressure (suction) evolutions throughout the experiments (see Bagheri et al 2018 for more information about the design characteristics of the HCTs). A set of two MS-CRS tests were carried out on unsaturated specimens, having an initial suction of s0 ≅ 701 kPa (initial water content of w0 = 33%).…”

“…Before commencing each experiment, the preparation of the cell was carried out according to the procedure described in Bagheri et al (2019). The HCTs were also preconditioned (see Bagheri et al (2018) for more details). All tests were performed in a temperature-controlled laboratory environment to avoid the influence of temperature fluctuations on the output data.…”

Geological and Geotechnical Characteristics of London Clay from the Isle of Sheppey

“…A series of drained constant rate of strain (CRS) compression-relaxation tests was performed on reconstituted Sheppey LC using an innovative CRS oedometer cell (Bagheri et al 2020) equipped with two high-capacity tensiometers (Bagheri et al 2018) for monitoring pore-water pressure evolutions, in order to evaluate the rate-dependent and stress-relaxation responses. Specimens of different initial water contents (and hence different initial suction s 0 ) were loaded to a certain stress level (r 0 = 3450 kPa), then allowed for stress relaxation at zero rate of axial displacement for a minimum time period of 210 h. Table 5 outlines the details of these tests and Fig.…”