The complex problem of squeezing tunnels in clay-rich rocks has led to support design problems in many civil engineering tunnels. The laboratory investigation of clay-rich squeezing rocks has been limited due to the difficulties encountered in obtaining regularly-shaped homogenous and isotropic specimens of such rocks. Preparing's, yet representative, mudstone specimens in the laboratory for physical model studies can overcome this challenge. In the study presented in this paper, synthetic mudstone was prepared by mixing "Goldart" clay as the main ingredient, type I/II cement as the binding agent, and water in defined proportions. During the mixing process, admixtures such as high range water reducer and accelerator were added to increase the workability and decrease the set time of the mix, respectively. Uniaxial compression tests and triaxial tests are conducted on the laboratory prepared 51 mm diameter and 102 mm long cylindrical specimen to determine strength, modulus, Poisson's ratio and plastic properties. The strain-rate sensitivity to strength and the modulus of the synthetic mudstone was determined by conducting triaxial tests at different strain-rates and confining pressure equal to 1 MPa. Three unconfined compressive creep tests were conducted at different stress levels to determine the creep properties of the synthetic mudstone specimens. Based on experimental observations, an empirical correlation was developed to describe the performance of the synthetic mudstone as an engineering material. The synthetic mudstone was found to be homogenous, isotropic, and reproducible, and its properties were similar to natural mudstone.


Squeezing ground conditions exhibit large time-dependent deformation that often can lead to support design problems in large diameter tunnels (Bonini, 2007). Squeezing ground conditions are often associated with the presence of clay minerals in geomaterials (Terzaghi, 1946). The engineering behavior of clay-rich rocks can be very complex and has many factors, such as mineralogy, depositional characteristics, weathering, and age. For soft rocks such as mudstone, it is often difficult to obtain continuous and homogenous regular-shaped specimens from the field to study these problems (Johnston and Choi, 1986). Hence, laboratory-prepared synthetic specimens of clay-rich rocks would be useful in physical model studies.

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