The swelling behavior of weak rocks in open and underground excavations in addition to mineralogy, lithology, and physical characteristics is affected by different confining conditions due to surrounding rock mass presence and support system rigidity and is also affected by periodic water content changes because of climatic conditions. The effect of important parameters on swelling behavior of mudstone samples taken from south west of Iran is investigated in this paper. The mudstone sample with high montmorillonite content showed more swelling potential. The reduction of swelling strain due to axial confinement (which reflects the confinement posed by support systems) is also quantified. It was observed that swelling behavior of mudstone samples are increased with periodic water content changes. Finally, the controlling methods of swelling grounds are reviewed and effect of chem.


The swelling potential of rocks including clay minerals is a complex problem. In an excavation without any support system, swelling rock moves inside and causes problems associated with reduced cross sectional area. When excavation is reinforced by support systems, swelling will usually cause considerable damages to the support system. The pressure from swelling rocks to the support system and lining of underground openings has been the focus in recent years. Mudstone, as a fine-grained sedimentary rock, is composed mostly of clay minerals that absorb moisture and swell [1]. Most often this phenomenon causes problems when encountered in constructions and mining excavations. ISRM [2, 3] and Madsen [4] have proposed some procedures for determining the swelling potential of swellable rock. Some researchers have tried to find a relation between the swelling potential of a weak rock and its mineralogy, lithology and physical characteristics. Among important contributions are the work of Shakoor and Sarman [5] and Huang et al. [6]. Shakoor and Sarman performed some free and confined swelling tests on mudstone samples gathered across the United States for determining the maximum swelling strain and pressure [5]. They calculated the maximum volumetric increase of samples according to unconfined compressive strength, second-cycle slake durability index, absorption, void-ratio, liquid limit and plasticity index parameters. Huang et al. [6] performed free and confined swelling tests on shale samples. They recorded the swelling strain and swelling pressure versus time and proposed some equations for predicting the maximum swelling strain and maximum swelling pressure, separately, with regards to the relative moisture humidity, the testing temperature and the moisture activity index of the shale samples.

Sample characterization and testdetails

The ISRM commission on swelling rock has proposed special tests to predict swelling potential of swelling rocks [2, 3]. In this research, three methods for swelling potential tests are used which are briefly described in the followings. Mudstone cores for experimental 248 study were obtained from drilled holes at Masjed-Soleiman Underground Hydro Electric Power Plant (UHEPP). Core sampling was carried out using a conventional rotary core barrel of 100 mm inside diameter. Cores were sealed with waxed cloth to prevent any loss of moisture.

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