To investigate the static and dynamic characteristics of rubber–sand composite soil (RS soil) reinforced with cement, a series of triaxial compression tests and resonant column tests was performed by considering the influence of rubber content (10%, 20%, 30%, 40%, and 50%), cement content (0, 1.5, 2.5, 3.5 and 4.0 g/100 mL), and effective consolidation confining pressure (50, 100, and 150 kPa). Compared with the RS soil, the addition of cement significantly improved the shear strength of a cement–rubber–sand composite soil (RCS soil), based on an undrained shear test. The increase in cement content not only makes the elastic modulus and cohesion of the RCS soil increase but also reduces the internal friction angle of the RCS soil. With the increase in rubber content, the failure of the RCS soil samples changes from strain-softening to hardening, and the prediction equation of the initial elastic modulus of the RCS soil is given herein when the recommended cement content is 3.5 g/100 mL. The effects of rubber content, cement content, and effective confining pressure on the dynamic shear modulus and damping ratio of the RCS soil were studied via the resonant column test. The test results show that the increase in rubber content slows down the modulus attenuation of the RCS soil, but increases its damping ratio. The test results also show that the increase in cement content makes the bonding force between particles greater so that the modulus attenuation of the RCS soil becomes slower and the damping ratio is reduced. At the same time, according to the change rule of the maximum dynamic shear modulus of the RCS soil with the rubber content, when the recommended cement content is 3.5 g/100 mL, an empirical formula and recommended value of the shear modulus Gmax of the RCS soil are proposed.
The construction of the tunnels of Metro Line 4 and Gulou Station in central Nanjing poses a potential threat to the nearby historic building, Gulou Tower, due to the relatively small spacing and the deteriorated structure behaviors. Two aspects are important for the protection of Gulou Tower: (i) reducing the soil movement caused by the tunnel–station construction and (ii) increasing the total stiffness of this sensitive building. This research first presents the main features of two tunnels and the triple-arch tunnel as the connection between the two tunnels and Gulou Station. The details of the excavation means and construction procedures of the tunnels, together with the engineering measures that tend to reduce soil disturbance during tunnel excavation, are presented. Meanwhile, to improve the overall stiffness of Gulou Tower, additional support for the masonry terrace and the upper timber structure is also discussed. Moreover, the construction procedures of the tunnels and the station that could influence the settlement development of Gulou Tower are also suggested. The measured ground settlement and structure displacement are found to be limited to the allowable values, indicating that the aforementioned protective measures are adequate to protect hybrid timber–masonry historical structures nearby tunneling.
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