Ways to restore the sewer collector

Keywords: sewer collector, wear, corrosion, restoration, open method, trenchless method.

Introduction. Diagnostics of the technical condition of wastewater distribution networks and their operation for over 40 years indicate that most of them are in an emergency condition. Today, the experience of operating sewer collectors indicates that it is impossible to ensure their efficiency and sustainable functioning without substantiating the technical and economic indicators of the project for the restoration of emergency areas. The dynamics of emergencies on sewer collectors shows that over the past five years, the number of emergencies on sewage networks laid in the 80s and 90s of the last century is almost 5 times higher than in 2014. Recently, a significant number of accidents have occurred in sewer collectors with a diameter of more than 800 mm. It is also necessary to highlight the components of sewerage collectors operation, as accidents and failures in their operation lead to obvious economic, environmental and social consequences, which is unacceptable in the context of Ukraine's European integration within the framework of European environmental requirements and the European Union Water Framework Directive [1]. Therefore, the issue of substantiating the feasibility of choosing a rational method of carrying out rehabilitation work on sewer collectors by saving material resources is relevant.

Analysis of recent research and publications. Today, there are many tools, models and algorithms that help in choosing the appropriate way to perform sewer rehabilitation works. However, one of the key problems is that a certain method or technique provides an optimal solution for only one section of the sewer collector, while the conditions of work change along the repair route. Paper [2] presents an algorithm for the open method of sewer rehabilitation for underground pipelines for various purposes. Based on operational experience, it has been observed that most real cases of emergencies involve several sections of the collector for scheduled rehabilitation. Although the use of different methods for each individual section is the best solution, it may not be possible when considering the cost, quality and time of rehabilitation in a broader sense. Today, the environmental friendliness of the decisions made in terms of the effectiveness of the sewer rehabilitation method is of great importance.

Paper [3] presents research on the environmental component of the restoration of utility networks using the trenchless method. Based on the developed calculation methodology, the energy consumption and carbon footprint of these methods under similar conditions are compared. It has been established that various trenchless technologies have made it possible to reduce energy consumption and carbon footprint to varying degrees compared to the open method. However, studies have shown that with a small length and depth of excavation, the energy consumption and carbon footprint of the trenchless method can be higher than that of the open-pit method. Due to the growing concern about global warming and greenhouse gases, there is an urgent need to quantify and reduce the environmental impact of the distribution network repair process.

The closed method of repairing sewerage networks avoids the disadvantages of the open method. This is, first of all, a restriction or slight limitation of traffic.  The problem can be solved by overhauling collectors and manholes. At the same time, the use of open methods of pipeline repair is not possible in certain areas due to the need for long-term blocking of traffic flows, destruction of large areas of road surface, damage to green spaces, etc. In such cases, it is not possible to restore worn-out collectors in a “closed” way by pulling pipes made of polymeric materials into the existing collector. The modules were lowered into the existing collector through the starter pits, threaded together and subsequently welded. After the modules were pulled and welded, the inter-pipe space was injected with cement-sand mortar. The last stage involved dismantling steel and wooden supports in the pits, backfilling and landscaping.

Fig. 1. Sequence of technological processes restoration of the sewage collector

Factors that affect the operational durability of sewer collectors. The analysis of accidents on collectors pointed to a number of reasons:

- reduction in the amount of wastewater over the past 20 years by 2-3 times;

- Increased aggressiveness of wastewater. Exceeding the maximum permissible level of ammonium nitrogen by 1.5 times, phosphate - by more than 4 times;

- Reduced flow rate, increased precipitation.

The chemical reaction that occurs in the free space of the pipe creates a highly aggressive environment for concrete structures. During operation (30 years), reinforced concrete collector pipes are completely destroyed due to internal corrosion. The work of Ihor Vyzrystiuk proved that the loss of compressive strength of self-compacting concrete after exposing the samples to the aggressive environment of the sewer mine for three months was 13%, while the loss of strength of conventional heavy concrete is 60-70%. This positions this method of collector restoration as more reliable and resistant to external influences, and saves money on restoration and repair work.

Conclusion.

In case of minor damage to the sewer collector, in the case of networks under road traffic areas, a closed method of collector restoration can be used to “quickly” solve the problem. If there is a need for major repairs of the sewer collector, as well as in order to reduce the cost of works and materials, long-term operation of networks, it is advisable to use an open method of restoring the sewer collector with the preservation of the intact part of the collector with its subsequent reinforcement. 

References:

1.Directive 2000/60/EC of the European Parliament and of the Council establishing a framework for Community action in the field of water policy. URL: http://zakon4.rada.gov.ua.

2.Vykhrystiuk Ihor,  Open Method of Restoration of the Sewage Collector Using Corrosion Resistant Self-Sealing Concrete,  International Journal of Research Publication and Reviews, Vol 5, no 12, pp 5514-5519 December 2024, https://ijrpr.com/uploads/V5ISSUE12/IJRPR36837.pdf

3.Lu H., Matthews J., Iseley T. How does trenchless technology make pipeline construction greener? A comprehensive carbon footprint and energy consumption analysis. Journal of Cleaner Production, 2020. Р.121215.

Author: Martynov Serhii

Doctor of Technical Sciences in Water Supply and Sewerage, Rivne, National University of Water and Environmental Engineering