Indirect Measurement of Soils in-situ Horizontal Stress from Matric Suction Measurements: Developing a New Tensiometer-Paper

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The paper presents a high-suction tensiometer designed to estimate in-situ horizontal effective stress from matric suction in recovered soil samples. When a saturated, undisturbed sample retains its in-situ effective stress after sampling, its negative pore-water pressure is expected to approximate the in-situ mean effective stress. Combined with vertical effective stress estimated from overlying soil layers, this can be used to infer horizontal stress.<br /><br />The tensiometer was designed for use in triaxial equipment or as a site-laboratory index test, with a target suction capacity of 1.5 MPa. Its calibration was checked through isotropic unloading tests on kaolin. Results indicate that, for well-saturated specimens, measurements can achieve an average error of about 1%. The authors also developed portable equipment and a procedure for testing samples in minutes.<br /><br />Tests on 15 offshore soil samples from European and US sites found that measured suction was generally higher than the estimated in-situ mean effective stress. This suggests that some samples may have been disturbed or that estimates based on triaxial saturation-stage stress were unreliable. The results also indicate that suction measurements should be made soon after sample recovery to limit suction loss.<br /><br />The study concludes that the tensiometer can reliably estimate horizontal stress in good-quality samples that retain their effective stress. However, further research is needed to establish how suction measurements can quantify sample quality.

Keywords

high-suction tensiometer

matric suction

horizontal effective stress

in-situ stress

soil samples

pore-water pressure

triaxial equipment

kaolin calibration

sample disturbance

offshore soil testing