The railway track was built about 150 years ago and was made of coarse rock, an embankment with an average height of 13.0 m and a base width of about 30.0 m. Under the embankment, work was carried out to lay a gas pipeline, for which a tunnel with a diameter of 0 was dug through the base of the embankment, 65 m. During the work, subsidence of the ballast layer was found. Tunneling was suspended pending re-ballast and site safety. According to the geological survey report, the embankment was built of homogeneous stone material, most likely stones of irregular shape, 5-20 cm in size, without fine aggregate. This structure is characterized by a significant void content. Based on experience gained from a similar site on the Zagreb-Rijeka line, the approximate porosity ratio is 35% at the top and 30% at the bottom of the structure. The most likely cause of subsidence was the failure of the pipeline channel due to vibrations associated with the excavation. After removing the protective pipe, it was decided to cement the area affected by subsidence. The attempt failed because the voids between the stones were too large to hold the concrete. Meanwhile, settlement of the embankment continued (about 5 cm per week), and to compensate for the deformations, the ballast layer was poured many times, and at short intervals with the help of new stones.
Through accurate analysis, the most affected areas of the tunnel excavation site were identified, where URETEK injection was proposed. The main goal was to stabilize the initial situation and prevent future deformations.
For this object, the patented URETEK DEEP INJECTIONS technology was chosen - the method of deep injection. This technology made it possible to reduce the number and size of voids in the embankment, filling the space between the particles of the ballast layer, significantly increasing the strength. This was achieved by injecting a rapidly expanding polymer composition at high expansion pressure. Accurate studies have identified the areas most susceptible to stress where injection points were concentrated. Injection pipes with a diameter of 12 mm were installed in specially drilled wells in the embankment. To accurately distribute the injections, the tubes were placed in each well of different lengths.
The movement of trains during the repair and restoration work on this section was not closed, however, for safety reasons, the speed of the train was reduced to 20 km / h. Overall, the entire operation took about 15 working days, including drilling and fluid injection operations.