Sewer pipe network systems are an important part of civil infrastructure, and in order to find a good trade-off between maintenance costs and system performance, reliable sewer pipe degradation models are essential. In this paper, we present a large-scale case study in the city of Breda in the Netherlands. Our dataset has information on sewer pipes built since the 1920s and contains information on different covariates. We also have several types of damage, but we focus our attention on infiltrations, surface damage, and cracks. Each damage has an associated severity index ranging from 1 to 5. To account for the characteristics of sewer pipes, we defined 6 cohorts of interest. Two types of discrete-time Markov chains (DTMC), which we called Chain `Multi' and `Single' (where Chain `Multi' contains additional transitions compared to Chain `Single'), are commonly used to model sewer pipe degradation at the pipeline level, and we want to evaluate which suits better our case study. To calibrate the DTMCs, we define an optimization process using Sequential Least-Squares Programming to find the DTMC parameter that best minimizes the root mean weighted square error. Our results show that for our case study, there is no substantial difference between Chain `Multi' and `Single', but the latter has fewer parameters and can be easily trained. Our DTMCs are useful to compare the cohorts via the expected values, e.g., concrete pipes carrying mixed and waste content reach severe levels of surface damage more quickly compared to concrete pipes carrying rainwater, which is a phenomenon typically identified in practice.

翻译：下水道管网系统是土木基础设施的重要组成部分，为在维护成本与系统性能之间寻求良好平衡，可靠的下水道管道退化模型至关重要。本文以荷兰布雷达市为研究对象开展大规模案例研究。我们的数据集包含自1920年代以来建造的下水道管道信息，并涵盖不同协变量的数据。尽管存在多种损伤类型，但本研究聚焦于渗入、表面损伤和裂缝。每种损伤均具有1至5级严重程度指数。为反映下水道管道的特性，我们划分了6个相关类别。两种离散时间马尔可夫链（DTMC）——即"多重"链与"单一"链（"多重"链较"单一"链包含额外转换状态）——常被用于管道级下水道退化建模，我们将评估哪种模型更适用于本案例研究。为校准DTMC，我们基于序列最小二乘规划定义了优化过程，以寻找使均方根加权误差最小化的DTMC参数。结果显示，在本案例中"多重"链与"单一"链并无显著差异，但后者参数更少且易于训练。通过期望值比较不同类别，我们的DTMC模型揭示了典型实践现象：例如，输送混合废水与生活污水的混凝土管道比输送雨水的同类管道更易出现严重表面损伤。