The swelling behavior of marls is a complex phenomenon. In saturated state, these materials present considerable volume changes resulting in swelling and mobilizing high swelling pressures. The behavior of swelling in rocks is controlled by numerous factors acting jointly and resulting in an effect whose main agent is frequently hard to identify. The design of tunnels in swelled grounds is a difficult task. Some problems are generally met for characterization and testing marls and for prediction the response of tunnel excavation and support loading. In this research we investigate the swelling behavior of marls and analyze the effect of their physical and mechanical properties on swelling considering to a case study. Our studied samples are red and green marls that are taken from Kohrang III water conveyance tunnel project, located in Chaharmahal Province in Iran (fig. 1). Physical and mechanical properties of these rocks were determined of some laboratory tests on samples which were derived from horizontal boreholes in digged parts of the tunnel. Our results showed the role of texture, structure and mineralogy in swelling potential in marls. The comparison between these two kinds of marls indicates that the major factor in swelling of marls is their hydration. Unloading has no impact on their swelling in comparison with their mineralogical composition and the type of clay minerals. Also the results indicate that red marls are more compacted with higher resistance. Finally experimental results confirme.
Most fine grained sedimentary rocks (marl) can be included in weak rocks group, which are widely distributed on ground surface and represent about 60% of sedimentary basin stratigraphy columns. The main components of these rocks are clay minerals with variable mineralogy. After clays the abundant minerals are quartz, calcite, and in minor proportions, pyrite and organic matters . Among these rocks, swelling occurs commonly in materials composed mainly of clay minerals having expansive lattices, e.g., montmorillonite, illite, kaolinite and interstratified clay minerals. These materials, in general, have high liquidity limits and high plasticity [1, 5]. Marl's uniquely behavior is known to change under dry and wet conditions. In spite of its high strength in dry state, in saturated state, its resistance will drop considerably (reportedly by as much as 85%) and also exhibits collapsible, dispersive, swelling and low slake durability behavior when exposed to water . Really, the effect of water on clay stone and marl is very important. In mines and tunnels that are excavated in clayey rocks, depend on type of clay minerals, water and humidity have straight effect on rate of excavation, because any phenomena has special problems in works. Swelling degree in marls depends on type of clay minerals too. Swelling decreases the resistance of marls and causes support destruction and sometime loss of life and property. Because of intricacy of the marls behavior, we decided to choose one of the digged segments in Kohrang III water conveyance tunnel that is located in marl formations.