A Maintenance Planning Framework using Online and Offline Deep Reinforcement Learning

Cost-effective asset management is an area of interest across several industries. Specifically, this paper develops a deep reinforcement learning (DRL) solution to automatically determine an optimal rehabilitation policy for continuously deteriorating water pipes. We approach the problem of rehabilitation planning in an online and offline DRL setting. In online DRL, the agent interacts with a simulated environment of multiple pipes with distinct lengths, materials, and failure rate characteristics. We train the agent using deep Q-learning (DQN) to learn an optimal policy with minimal average costs and reduced failure probability. In offline learning, the agent uses static data, e.g., DQN replay data, to learn an optimal policy via a conservative Q-learning algorithm without further interactions with the environment. We demonstrate that DRL-based policies improve over standard preventive, corrective, and greedy planning alternatives. Additionally, learning from the fixed DQN replay dataset in an offline setting further improves the performance. The results warrant that the existing deterioration profiles of water pipes consisting of large and diverse states and action trajectories provide a valuable avenue to learn rehabilitation policies in the offline setting, which can be further fine-tuned using the simulator.Comment: Published Neural Comput & Applic (2023), 12 pages, 8 Figur

Carbon footprint assessment of maintenance and rehabilitation techniques for sewer systems

The research study presented in this paper sets out to improve our understanding of the environmental impacts associated with the maintenance and rehabilitation of conventional gravity sewer systems and, through this, support decision-making processes in sewer system management. The objects assessed are open trench replacement, trenchless renovation, open trench and trenchless spot repair, inspection, and hydraulic cleaning of sewer pipes. Carbon footprint assessment was carried out according to the ISO14067:2018 standard. The life cycle stages considered included raw material extraction, manufacturing processes, maintenance/rehabilitation, and the transportation of materials. The functional unit was defined as: ‘A gravity sewer section with a length of 45 metres and a diameter of 200 to 1500 mm operating in normal conditions over a period of 100 years in the Netherlands’. A sensitivity analysis was included to assess how the results vary as a consequence of changes in the input dimensions. The findings of this study suggest that the main opportunities for reducing the environmental impacts of conventional, open trench pipe replacement lie in the choice of the pipe material and the design of the asphalt pavement that requires reinstatement. Adopting trenchless sewer rehabilitation technologies can significantly reduce the environmental burdens of sewer system rehabilitation.</p

Deterioration modeling of sewer pipes via discrete-time Markov chains: A large-scale case study in the Netherlands

[For the latest version of this repository go to: https://gitlab.utwente.nl/fmt/degradation-models/dtmc_sewer_pipes.git] 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.This research has been partially funded by NWO under the grant PrimaVera (https://primavera-project.com) number NWA.1160.18.238, and has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 101008233

Upper limit to magnetism in LaAlO3/SrTiO3 heterostructures

Using polarized neutron reflectometry (PNR) we measured the neutron spin dependent reflectivity from four LaAlO3/SrTiO3 superlattices. This experiment implies that the upper limit for the magnetization induced by an 11 T magnetic field at 1.7 K is 2 emu/cm3. SQUID magnetometry of the superlattices sporadically finds an enhanced moment, possibly due to experimental artifacts. These observations set important restrictions on theories which imply a strongly enhanced magnetism at the interface between LaAlO3 and SrTiO3