In this paper, the one-dimensional (1D) time-dependent behaviour of natural and reconstituted London Clay samples under saturated and unsaturated conditions is studied. For this purpose, a set of 1D consolidation tests including multi-staged loading (MSL) oedometer tests and single-staged loading (SSL) long-term oedometer creep tests were carried out on saturated and unsaturated specimens. Conventional oedometer cells were used for tests on saturated specimens, whereas a newly designed unsaturated oedometer cell, equipped with two high-capacity tensiometers (HCTs) for suction measurements, was used for unsaturated tests. The tests results revealed stress dependency and suction dependency of primary and secondary consolidation responses of the soil samples. Furthermore, counter to formerly acknowledged suggestions of independency of the slope of normal consolidation line to suction changes, it was observed that an increase in suction results in a decrease of the slope of compression curve (Cc) and the creep index (Cαe) values and an increase in yield vertical net stress (σp). Moreover, the Cαe/Cc ratio for London Clay was found to be stress- and suction-dependent, unlike the previously suggested hypotheses.

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.

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7Research into the thermo-hydro-mechanical (THM) behavior of unsaturated soils and the effect 8 of strain rate on their mechanical responses requires employment of advanced laboratory 9 testing systems and procedures as well as protocols of correcting the measured data in order to 10 account for errors associated with complex test conditions and apparatus calibrations. This 11 paper presents design and calibration of an innovative constant-rate-of-strain (CRS) oedometer 12 cell for characterization of the THM behavior of soils under combined non-isothermal and 13 unsaturated conditions. The advanced oedometer cell enables for simultaneous control of 14 temperature, suction, and stress state within the soil specimens. Temperatures of 20 to 200° C 15 is applied through a tubular heating element placed at the base of the soil specimen. Suction is 16 controlled using axis-translation technique, and measured using both axis-translation and two 17 high-capacity tensiometers (HCTs) accommodated on the periphery of the specimen. The18 1

The paper describes a series of experimental testing on natural stiff London clay samples retrieved from the New Hook Farm in the Isle of Sheppey, UK. The experimental program includes determination of macroscopic and microscopic properties, chemical compositions, Atterberg limits, permeability, and compressibility parameters in both intact and reconstituted states. The paper integrates the earlier studies, the new findings, and the commercial investigation results with the aim to extend the current knowledge of the geological and geotechnical characteristics of this stiff clay from the east of the London basin. Some comparisons are also made with shallow depth London clay from Heathrow Terminal 5 site.