Possibility of using torvane shear testing device for soil conditioning optimization

Determining the optimum amount of soil conditioning agents and the behavior of excavated soil + foaming agent mixture during excavation process play an important role in the design and management of EPB TBM tunneling. Although there are some means of defining optimum soil conditioning parameters, there is still a requirement for new and effective methods. This study aims to analyze the possibility of using a torvane shear testing device as a means of soil conditioning optimization. The soil samples used in the experimental studies were obtained from shaft excavations of Zeytinburnu Ayvali 2 Wastewater Tunnel and Mahmutbey-Mecidiyeköy Metro Tunnel located in Istanbul and industrial kaolinite was also used for soil conditioning experiments. The natural water content, specific gravity, size distribution and consistency limits of the soil samples were determined. An anticlay foaming agent was used in the tests. Classical soil conditioning tests including mixing (with power consumption and sticking amount measurements), cone penetrometer, and vane shear (torvane type) tests suggested in this study were performed on the mixture of soil and foaming agent at natural water contents. Foam concentration of 3% and foam expansion ratio of 16 were kept constant and foam injection ratio was varied. The laboratory studies indicated that optimum conditioning parameters and consistency of conditioned soils could be determined by torvane shear testing. There were strong relationships between the results of classical testing methods and the torvane shear device. Using torvane shear testing for soil conditioning purpose would provide an inexpensive and easy method to measure the shear strength of conditioned soils. Additional studies would increase reliability of this method by testing different fine-grained soils at different soil conditioning parameters.