Scheduling And Optimization Of Transportation-type Linear Projects

Linear projects have the essential features of linearity and repeatability and comprise a significant portion of the construction industry. They include transportation projects, such as the construction of railways, roads, and pipelines. Numerous studies have identified various drawbacks associated with the application of the traditional critical path method (CPM) in linear projects. In this context, linear scheduling techniques, which have a series of unique advantages when applied to linear projects, have garnered increasing attention from researchers. Among these, the linear scheduling method (LSM) is the most important.It has been many years since the inception of LSM. However, on account of the benefits of widely used CPM, LSM has not attracted considerable attention from researchers until the last two decades. This has resulted in the view that the LSM theoretical system is not sufficiently mature, which has restricted the application of LSM in scheduling and optimization problems of linear projects. Currently, the main limitations of LSM are expressed in the following two points.1) A clear method of describing the logical relationships among activities within the LSM framework is yet to be proposed. However, the method of describing the logical relationships between activities is the core function that underlies the popularity of traditional methods.2) The three classic constraints in construction project scheduling and optimization fields are logical, resource, and duration constraints. The constraints under the LSM framework currently proposed by researchers are limited to logical and duration constraints, and the two types of constraints are insufficient.The inherent incompleteness of LSM has led to significant limitations in the results of proposed research based on LSM, such as difficulties with optimal rescheduling and the inability to schedule and optimize with constrained resources, multiple resources, or special activities. Moreover, LSM cannot be independently used to solve resource allocation and time-cost tradeoff problems.The objective of this dissertation is to enable LSM to be more effectively used in scheduling and optimization problems of linear projects. To this end, the dissertation focuses on three primary goals:1) To improve and develop core questions on LSM, including the concept of LFloat, a description method of the logical relationships between activities, and the constraint system within the framework of LSM;2) To construct LSM-based scheduling and optimization models; and3) To establish an LSM-based schedule control model and system to verify the optimization model.The core problems of LSM must first be addressed. The LFloat system is proposed to improve and develop LSM. The research confirms the concept of LFloat-2and introduces the concept of LFloat-3, by which the rate float (LFloat-1) is enriched and developed. This dissertation then specifies19evaluation indices for the project scheduling and optimization problem based on LSM. These indices are used to compare and analyze previous LSM-based research outcomes. Next, a description method for the logical relationships between activities is reported within the LSM framework. The description method is reported in24situations; it can be used to describe any time-space relationships between activities. This description method provides a foundation for various LSM-based optimization studies. By actualizing this description, LSM can become a novel planning method that is both independent of the traditional CPM and better suited to linear projects. Finally, an LSM-based constraint system for the scheduling and optimization of linear projects is proposed. This constraint system, comprised of eight types of constraints, is built on the logical constraints between activities.The LSM-based scheduling and optimization model (LSM-SOM) is constructed on the basis of the descriptions of logical relationships and the constrained system. Using the flexibility and practicality of triple construction modes (including LPL-Mode and LPB-Mode) of the constrained system and the setting of decision variables, LSM-SOM covers the optimization capabilities corresponding to the19specified indices. This results in improved practicality and flexibility, such as LSM-SOM realizing scheduling and optimization under the conditions of variable rates, resource constraints, and multiple resources. The proposed triple mode facilitates interaction and integration among different types of optimization. This enables LSM-SOM to account for different optimization objectives while handling a particular type of optimization, which thereby enhances its practicality.By employing the concept of LFloat and different optimization strategies, five derivative models are developed based on LSM-SOM. These include the multi-objective optimization model, critical activity path (CAP)-based two-phase optimization model, and variable-rate optimization model. The introduction of optimization strategies for these derivative models further improves the practicality and flexibility of LSM-SOM and enhances its superiority in providing solutions. Finally, a schedule control model (LPSCM) and schedule control system (LPSCS) are constructed for linear projects based on LSM. This research combines LPSCS with three transportation construction projects employed in classic research and compares the LSM-SOM optimization model with the previous ones. The comparison is conducted through18optimization scenarios under the following two conditions:1) the same data and same constraints as the previous ones are used; and2) the same data and more (or stronger) constraints are used. The analyses of the18optimization results from these scenarios demonstrate the flexibility and practicality of the proposed approach compared to the previous studies as well as the superior solutions given by the proposed model.