Markus Thewes

Evaluation of Disturbances in Mechanized Tunneling Using Process Simulation

Production in mechanized tunneling frequently encounters disruptions due to sensitive process interdependencies. Reasons can be technical failures, insufficient capacity dimensioning, organizational deficiencies, or sensitive supply chains. These unproductive times could be reduced by an adequately designed project setup including logistical aspects. Therefore, possible disturbances must be identified and analyzed in detail. Based on this investigation, the machine and logistics setup can be changed to cope with unforeseen events. We present a modeling and simulation approach to analyze production and logistic processes of mechanized tunneling processes in a transparent and understandable way. The system is formalized in the modeling standard SysML. Thereby, we consider relevant system elements and process interdependencies to assess the effect of disturbances and to identify bottlenecks. We distinguish three kinds of disruptions: i technical failure of main elements related to the production processes, ii issues resulting from an insufficient supply chain, and iii cascading disturbances. The implementation in a simulation environment and the processing of relevant input data are presented hereupon. The presented approach is then illustrated by means of an application example based on a completed metro project. Three extending simulation studies quantify the impact of the identified disturbance categories.

Simulation-Based Analysis of Integrated Production and Jobsite Logistics in Mechanized Tunneling

The planning of jobsite layouts and logistics management has a major impact on the performance of tunnel construction projects that use tunnel-boring machines (TBMs). Frequently, projects do not reach the highest possible production performance due to undersized logistics processes or insufficient storage capacities. In this paper, a flexible simulation framework for analyzing interactions between production and logistics processes on tunneling jobsites is presented. A formal ontology for logistic elements on a tunneling jobsite is developed using SysML formalism. Based on this formulation, single systems elements combined in process chains are analyzed and their influence on production processes is evaluated. The formal system description identifies process dependencies and resource constraints of the system elements. These formulations are implemented in configurable simulation components for construction equipment, storage spaces, and production materials. Using these components, a jobsite simulation model can be created. The jobsite layout is represented at a high level of detail, with geometric shapes used for estimating storage capacities and movement durations. This approach uses discrete event and system dynamic simulation and applies probability functions to inputs representing production process times. Dynamic simulation can reveal unknown impacts of logistical processes on the continuous advance processes of the TBM. A simulation model for TBMs is integrated to determine the demand for supply processes. A fast and effective comparison between different jobsite layouts and logistics strategies is possible due to flexible components. By analyzing the workload of construction equipment, robust and efficient setups can be developed. A case study illustrates the usefulness of the simulation framework by comparing the performance of three different jobsite setups for a tunneling project.

Advancement simulation of tunnel boring machines

In mechanized tunneling a significant loss of performance resulting from weak spots in the supply chain or unforeseen geological conditions is a frequent and costly problem. Furthermore, disturbances of critical machine components can have such impact on the production that unforeseen modifications become necessary. Due to the sequential character the malfunction of one element might evoke cascading-effects which may result in a complete standstill of the tunneling progress. Transparent evaluation of applicable tunnel boring machine designs is essential in order to improve the productivity, avoid unplanned interruptions and to estimate the project duration in general. In order to meet these defiances, this paper presents a multi-method simulation model to investigate the advancement rate of tunnel boring machines. Process-related disturbances can be considered easily within the presented simulation model. Simulation experiments demonstrate the purposive functionality of the model and visualize the significant influence of technical failure on the overall project performance.

Assessing maintenance strategies for cutting tool replacements in mechanized tunneling using process simulation

In mechanized tunneling, detailed planning with an accurate performance prediction of the tunnel boring machine (TBM) is needed for a successful tunnel project. Undersized logistical components, disturbances of the supply chain, as well as negligence of maintenance schedules reduce the TBM performance and frequently lead to avoidable times of standstill. This paper presents a performance forecast model for mechanized tunneling projects focusing on wear and maintenance processes of the cutting tools. The developed simulation model has been implemented in the simulation environment AnyLogic using the multi-method approach, including agent-based modeling as well as discrete-event and system dynamic simulation. The model can be used to evaluate different maintenance strategies for a tunneling project. Thus, an improved maintenance strategy for reducing the time of standstill can be found.

Uncertainty modeling and simulation of tool wear in mechanized tunneling

The planning of mechanized tunneling projects requires the consideration of complex constraints and project objectives. Process simulation provides a tool to virtually evaluate different concepts in changing environmental conditions. The consideration of uncertain influences is an essential task within the development of a holistic simulation model. Some aspects (e.g. technical disturbances) can be considered by application of a probability function. However, geotechnical constraints feature a fuzzy nature not well suited for a probabilistic approach. The authors present an approach based on Fuzzy Logic to integrate the performance related influence of wear of cutting tools on the advance rate. The approach is described in detail and demonstrated by an artificial example. Simulation experiments were performed to illustrate the influence of wear on the advance rate in the context of disturbances. This innovative approach to consider such an essential performance factor is another step towards a holistic simulation model of mechanized tunneling projects.

Jobsite logistic simulation in mechanized tunneling

Projects in mechanized tunneling frequently do not reach their targeted production performance. Reasons are often related to an undersized or disturbed supply-chain management of the surface jobsite. Due to the sensitive interaction of production and logistic processes, planning and analyzing the supply-chain is a challenging task. Transparent evaluation of chosen logistic strategies or project setups can be achieved by application of process simulation. This paper presents the continued work of a simulation approach to analyze the complex system of mechanized tunneling. Special focus of this publication lies on the internal logistic as a part of the jobsite supply-chain. The generic implementation allows a flexible configuration of jobsite elements to compare possible setups. A case study demonstrates the approach and highlights the sensitive interaction of production and logistic processes under the influence of disturbances. Additionally, improvements to the original setup of the case studys construction equipment can be derived.

Empirical Cutting Tool Wear Prognosis for Hydroshield TBM in Soft Ground

The wear of cutting tools is a major issue in tunneling with Hydroshield TBM in soft ground, because it is a common reason for unplanned downtime. The replacement of cutting tools requires access to the excavation chamber, which is only possible with hyperbaric works or at fixed positions with prearranged grout blocks. In order to improve predictability of the maintenance stops, an empirical prognosis model for the required maintenance stops for changing of cutting tools and the amount of tools was developed. Based on the new Soil Abrasivity Index (SAI), the model helps to estimate distances between maintenance stops and the required amount of cutting tools to be changed. The authors validated the prognosis model based on the original reference projects. The validation lead to an adaption of the prognosis process and individual correction factors in the model itself. The article therefore describes the updated prognosis model.

Simulation of maintenance strategies in mechanized tunneling

Mechanized tunneling is one of the most common methods used for underground constructions for infrastructure systems. Since a tunnel boring machine (TBM) represents a non-redundant single machine system, the efficiency of maintenance work highly impacts the overall project performance. The wear and tear of cutting tools is a critical, but mostly unknown process. To plan the maintenance work of cutting tools efficiently, it is necessary to know the current tool conditions and adapt the planned maintenance strategies to the actual status accordingly. In this paper, an existing theoretical empiric surrogate model to describe cutting tool conditions will be used and implemented as a software component within a process simulation tool that manages TBM steering parameters. Further, different maintenance setups for TBM cutting tools are presented and evaluated. To prove the capability of the presented approach, a case study will show the effects that improved maintenance work can have on project performance.

Consistency Index and Its Correlation with EPB Excavation of Mixed Clay–Sand Soils

The behavioural properties of excavated ground have significant influence on the excavation process performed by an Earth Pressure Balance Machine (EPBM), as they are among the main factors responsible for maintaining the pressure ahead of the face, which affects face stability. Therefore, understanding the characteristics of the excavated material along with its flow behaviour is essential for a successful EPB tunnel drive. In scenarios involving the excavation of fine-grained soils containing clay minerals, the consistency index has been widely used as a guideline to define the ideal state of the excavated material. However, there are certain restrictions for the use of this index, the first of which are the Atterberg limits. These limits become more restrictive when mixed soils are involved. This study presents a brief review of the application of the consistency index and Atterberg limits in order to predict the performance of an EPB excavation. This study presents the results of a laboratory testing campaign with artificially mixed clay–sand soils by using a flow table as a preliminary flow assessment of cohesive soils.