ABSTRACT
Warsaw Metro Line 2 eastern extension is developed to improve the transportation system of the Polish capital, reducing the distance between residential areas and city center. Tunnel alignment is under-passing residential areas composed by old buildings, boring through clean gravelly fine sand. The lack of fines and the groundwater in the soil, may cause difficulties in the management of the earth pressure. Soil conditioning has been a key parameter for the successful control of the pressure in the bulk chamber. Injecting small quantities of high performances polymer, has been fundamental to obtain a suitable conditioned soil, able to be managed with the screw conveyor. Another key aspect has been the use of a specific mix design of the A component of the two-components backfill grout, with the correct dosage of accelerator, and modified injection parameters, achieving the reduction of the volume loss due to the gap between soil and lining.
