## 2 Background
### Cured-in-Place Pipe Renewal Technology  
CIPPRT entails inserting a resin-saturated flexible fabric liner into the existing pipeline, inflating, or expanding it to fit the pipe's interior, and hardening the resin through heat sources like hot water, steam, or UV light. This process creates a hard, anti-corrosive, and anti-seepage lining that adheres to the inner wall of the old pipe [4; 18; 23; 33; 34; 35; 36; 37; 38]. Figure 2 depicts the Cured-in-Place renewal process, showing the delivery and insertion of an uncured resin tube into a damaged pipe, inflation with air, curing through thermal or UV methods, trimming of ends, and, finally, the restoring of the pipe, ready for service. The CIPPRT is suitable for pipe diameters ranging from 4 to 120 inches, with installation lengths typically between 1000 and 3000 feet (Table 1) [18]. Two primary techniques for liner installation are inversion and pull-in methods. The pull-in approach demands extra caution to avoid damage while the liner is being pulled through the pipe [18,38]. The curing process predominantly utilizes three heat sources, namely, hot water, steam, and ultraviolet light, all of which must achieve the resin curing point's exothermic temperature. The liner materials are composed of thermoset resin and fabric composites [5,39,40]. The choice of CIPPRT depends on multiple considerations, including available space, the chemical properties of the fluid transported in the pipeline, the number of service connections and manholes, the installation length, renewal goals, and the structural properties of the vinyl ester and epoxy resin systems. Although these systems are particularly effective for sanitary sewers and residential service connections, their use often involves increased costs [33,41,34]. Advantages and Challenges of CIPPRT  
The implementation of CIPPRT in underground infrastructure rehabilitation offers a multitude of benefits that significantly enhance the efficiency and effectiveness of pipeline restoration processes. These advantages can be elucidated as follows [18,23,35,37,35,41,42,33,35,43,44,45,46,47,48,49,50]:  
* CIPPRT installation necessitates minimal excavation, thereby occupying a reduced subterranean footprint and curtailing the duration of construction activities. * CIPPRT lining establishes a seamless interface with the existing pipeline, eliminating the requirement for supplementary grouting procedures, and providing enhanced structural integrity. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Method** & **Diameter (in)** & **Maximum Installation (ft)** & **Liner Material** \\ \hline Inversion Method & 4–108 & 3000 & Thermoset Resin or Fabric Composite \\ Pull-in Method & 4–54 & 500 & Thermoset Resin or Fabric Composite \\ Spray Application & 3–180 & 500 & Epoxy Resin or Cementitious Mortar \\ \hline \hline \end{tabular}
\end{table} 
Table 1: CIPPRT installation method and relevant factors (Adapted from [18]). Figure 2: CIPPRT principle (red arrow for chemical flow, black arrow for process flow, and blue arrow for water flow) (Adapted from [33]). * CIPPRT demonstrates remarkable adaptability to diverse conduit morphologies, accommodating a wide spectrum of cross-sectional configurations encountered in aging infrastructure systems. * A single CIPPRT installation operation can effectively rehabilitate extended pipeline segments, producing a monolithic, joint-free lining. * The smooth interior surface of CIPPRT linings results in a diminished friction coefficient. * CIPPRT materials exhibit superior resistance to corrosive agents and demonstrate exceptional impermeability characteristics. * The host pipe system's composite design utilizes the remaining structural strength of the original pipeline alongside the mechanical characteristics of the CIPPRT liner.