| Technical Application of DPS in Tunnel Engineering |
Tunnel diseases and material selection:
1】 DPS deep penetration overall waterproofing: Tunnel construction is a costly and complex engineering project, as well as a long-term facility. Ordinary waterproof layers are prone to aging and have a limited lifespan. Once damaged, they are difficult to repair, and even if repaired, the cost is high. The ordinary waterproof layer is also prone to damage during the construction process. But DPS is different, its lifespan is the same as that of concrete structures, due to a certain thickness of infiltration into the concrete. So, during the construction process, as long as there are no wounds deeper than 10cm on the lining blocks, the waterproof performance will not be affected.
2】 Permanent setting liquid DPS can be used for construction on the back water surface. Similarly, if the project requires DPS, it can also be applied to the inner wall of the first lining as waterproofing for the inner lining, or to the inner wall of the inner lining as anti-corrosion and carbonation prevention for the concrete inner wall. In the construction of composite lining tunnels, DPS can also be directly sprayed on the polished surface of sprayed concrete as a waterproof reinforcement layer for the inner lining, with both inner and outer construction.
3】 Permanent setting liquid DPS water absorbing hydrophilic crystal waterproofing: Tunnel construction is generally underground, and the surrounding geological structures are rich in water. Before the completion of the tunnel, the ventilation of the construction surface is poor, and the humid air causes the waterproof construction surface to always be a damp surface. This requires waterproof materials to be constructed on a damp foundation. DPS is precisely a waterproof material that requires moisture vapor to better penetrate and react. In other words, DPS can be applied on damp surfaces, which most other types of waterproof materials cannot achieve.
4】 The construction of permanent curing liquid DPS is simple, time-saving and labor-saving. In addition, due to the cold spray coating of DPS, the daily workload per capita can reach 1000 square meters or even more, and the high construction efficiency is unmatched by other types of materials, greatly saving high labor costs.
5】 DPS has good acid and alkali resistance and adhesion: Generally, waterproof materials do not have anti-corrosion properties, only self waterproofing, do not protect concrete structures, and have no affinity for penetrating concrete.
The vast majority of tunnels in the world are still constructed as urban railways (subways) and road tunnels (railway tunnels and highway tunnels). Regardless of the purpose of the tunnel, its construction methods are mainly shield tunneling and immersed tube tunneling. For different construction methods, the following focuses on the shield tunneling method and elaborates on the application of DPS reinforced concrete in waterproofing, anti-seepage, and anti-corrosion.
1、 Waterproof characteristics of shield tunneling construction method
There are many ways to classify waterproofing in shield tunneling, including single-layer lining waterproofing and double-layer lining waterproofing according to the lining structure form; According to the composition of the lining, there are lining self waterproofing and lining joint waterproofing; According to the tunnel structure, there are tunnel lining waterproofing and vertical shaft joint waterproofing, and according to the lining material, there are reinforced concrete and cast iron lining waterproofing.
The waterproofing of single-layer lining is closely related to the form, composition, and assembly method of single-layer lining.
The larger the width of the lining ring, the fewer circumferential joints in the tunnel ring within the same mileage, and the lower the probability of water leakage. Similarly, the fewer the segments of the lining ring, the smaller the longitudinal seam of the ring, and the lower the probability of water leakage. Of course, in practical engineering, comprehensive consideration should be given to factors such as the soil layer characteristics, loading conditions, structural characteristics, calculation mode, transportation capacity, and production and assembly of the structure.
（1） 1. Improve the waterproofing and production accuracy of lining segments and blocks: 2. Improve the production accuracy of initial masonry segments and blocks;
3. Add waterproof coating outside the lining, strengthen the anti-seepage and anti-corrosion capabilities of the lining.
（2） Sealing and waterproofing of lining joint surface (joint)
1. The first and main line of defense for lining joints is a sealing gasket (water swelling rubber); 2. Sealing and waterproofing of lining screw holes;
3. Fill the joint groove with sealing waterproof material;
4. Install sealant grooves on the joint surface, and use pipe bolt holes to inject sealant to enhance waterproofing or water retention.
（3） Grouting behind the wall (backfill) of shield tunneling method
Inject grout material with anti mixing function to form a circular unity on the outer wall of the lining ring, forming a "tunnel waterproof barrier". Although it is mainly used to control ground subsidence, it is actually also a defense line for tunnel waterproofing.
（4） The anti-corrosion of metal lining, composite lining of metal and concrete, and metal embedded parts in concrete lining should also be considered together
（5） Double layer lining waterproofing
In addition to the waterproofing of the first lining, the waterproofing of the inner lining must also be considered.
（6） Waterproofing of the joint between vertical shaft and circular tunnel
Based on the waterproof characteristics of the shield tunneling construction method mentioned above, combined with the technical features of concrete DPS, this article focuses on the waterproof function of the lining outside.
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