A frozen soil sampling technique for granular soils and thermal modeling

This study uses a new sampling approach to allow undisturbed sampling without damaging the natural conditions of granular soils, thanks to the artificial ground freezing (AGF) method via a double-independent closed-circulation mechanism, over a 48-h period at − 15 °C. The mechanical properties, textural characteristics, and freezing-thawing observations of three types of granular soils are investigated. The temperature distribution around freezing pipes, the shape of the frost line, and the degree of ice saturation were observed through a thermal simulation by a two-dimensional finite element analysis software, Plaxis 2D. The unconfined compressive strength and strain values of molded and cored specimens are compared. The coring samples are about 2.56 times stronger than the molded ones, depending on the method of soil sampling procedure in the same type of soil. The well-graded sandy samples (SW) achieve up to 1.05 and 2.95 MPa of force values in the molded and coring samples, respectively. Moreover, according to the types of soils, in the SW specimens, 1.57- and 1.39-fold strength values are obtained for poorly graded sand (SP) and well-graded gravel (GW) samples in the molded artificially frozen sampling process, respectively, as well as 1.17- and 1.09-fold strength increments in the coring frozen sampling process within the same order. The results of thermal module simulation nearly match those obtained using laboratory-based tests. The efficiency of the proposed sampling approach has been proven to represent actual on-site behavior. Besides, the strength results are perfect in this method with respect to traditional sampling methods.