Physics-based and data-driven modeling for stability evaluation of buried structures in natural clays

This study presents a hybrid framework to predict stability solutions of buried structures under active trapdoor conditions in natural clays with anisotropy and heterogeneity by combining physics-based and data-driven modeling.Finite-element limit analysis(FELA)with a newly developed anisotropic undrained shear(AUS)failure criterion is used to identify the underlying active failure mechanisms as well as to develop a numerical(physics-based)database of stability numbers for both planar and circular trapdoors.Practical considerations are given for natural clays to three linearly increasing shear strengths in compression,extension,and direct simple shear in the AUS material model.The obtained numerical solutions are compared and validated with published solutions in the literature.A multivariate adaptive regression splines(MARS)algorithm is further utilized to learn the numerical solutions to act as fast FELA data-driven surrogates for stability evaluation.The current MARS-based modeling provides both relative importance index and accurate design equations that can be used with confidence by practitioners.

Effect of Sample Disturbance on Unconfined Compression Strength of Natural Marine Clays

Quantitatively correcting the unconfined compressive strength for sample disturbance is an important research project in the practice of ocean engineering and geotechnical engineering. In this study, the specimens of undisturbed natural marine clay obtained from the same depth at the same site were deliberately disturbed to different levels. Then, the specimens with different extents of sample disturbance were trimmed for both oedometer tests and unconfined compression tests. The degree of sample disturbance SD is obtained from the oedometer test data. The relationship between the unconfined compressive strength q u and SD is studied for investigating the effect of sample disturbance on q u. It is found that the value of q u decreases linearly with the increase in SD. Then, a simple method of correcting q u for sample disturbance is proposed. Its validity is also verified through analysis of the existing published data.

Pre-Failure Behavior of Deep-Situated Osaka Clay

Great interest has been aroused on deeply-situated Osaka clay since Kobe Earthquake in 1994. In this paper is presented the analysis on the results of a series of lab tests on Osaka clay situated from 100 m to 1500 m under the ground. The wave velocity method, bender element method, LDT and the formula derived by the authors are used, focus is put on the pre-failure mechanical behavior of the clay. The analysis shows that, (i) pore-pressure coefficient B is less than 1.0, (ii) the relationship between shear modulus and Poisson's ratio is not in agreement with that reported before, (iii) the modulus measured with LDT is still less than that measured with bender element method, and (iv) there are two threshold strains, within which the clay can be considered as elastic, and both of them are larger than that reported before.