Shield tunneling technology has a long history in my country, but there are still two forms of through seam and staggered seam assembly in the domestic segment assembly. Among them, through seam assembly is favored by many construction units due to its advantages of easy assembly and construction and high construction efficiency. Therefore, many subway projects in Shanghai have adopted this assembly method. The shield tunnel lining is assembled in the shield tail of the shield machine, and is the main stress structure of the shield tunnel. In the axial direction of the lining tunnel, the longitudinal through seam formed when the assembly seams between the ring segments are not separated is the through seam joint form.
Today, we will talk about the effect of shield tail sealant that is easily overlooked when assembling through seams, which is the filling effect in the joints of the segments. With the development of Shanghai subway tunnels, the depth of shield construction is getting deeper and deeper, and the impact of confined water will also increase. During construction, it is often easy to see water in the joints of segments, and groundwater will The joints along the longitudinal direction of the segment intrude, and because the joints are assembled through the joints, the longitudinal joints are continuous before and after, making it easier for groundwater to continue to affect each ring along the straight channel. The staggered joint assembly will reduce the direct channel effect of groundwater infiltration due to the staggered joints. Therefore, when assembling through joints, it is even more necessary for the shield tail sealant to be filled and left in the gaps of the longitudinal joints of the segments to prevent the continuous infiltration of groundwater.
Before starting, we require that the shield tail sealing grease must be filled after the negative ring is assembled. On the one hand, the sealing cavity can be filled in time to protect the elasticity of the tail brush, and at the same time, the filling state of the grease can be observed on the outer surface of the negative ring. As can be seen from the above figure, when the grease cavity is not full, it is difficult to have residues on the outer surface of the segment, and it is more difficult to effectively fill the seam, which is almost empty. This will not be the best protection for the back tunneling, if the outer surface of each ring segment remains the same. In the following figure, there is grease residue in the seam, and there is also grease residue on the outer surface of the segment, indicating that the grease filling in the sealing cavity is good. At the same time, we observed that the angle state of the tail brush during normal excavation cannot perfectly fill the barrier joints. Therefore, it is necessary to pump the shield tail sealant to fill the concave and convex places such as the longitudinal joints of the concrete segment ring. It is also a test of the filling and flow properties of grease.
For this reason, we also designed and observed the flow and filling performance of the shield tail grease to simulate the flat surface state of the segment. When the shield tail sealant is excavating the shield, the sealing cavity grease will be outside the segment when the shield tail is protruded. There is a layer left on the surface, and the uniformity of this layer greatly affects the wear and gap filling effect of the tail brush, and the uniform flat application also effectively prevents the leakage of the shield tail during construction. We believe that a good grease should have a good and even filling effect on the outer surface of the segment.
Try to compare the residual effect of different types of grease on the outer surface of the cement board at the same speed under the same pressure and injection conditions, and the performance of the grease can also be observed.
It is believed that the two completely different effects in the above picture can also vividly help the construction party to understand the effect of shield tail grease filling in actual construction, and to measure and judge whether the shield tail grease can really be used to prevent water leakage in the longitudinal joints of segment assembly. has an effect.
