Research On Covering Location Of Bilevel Logistics Facilities In A Railway Construction Project

In recent years,the construction of transportation line in China is developing rapidly,especially the high-speed railway construction.With the publication of Medium-term and Long-term Railway Network Plan[27],it is in an important phase of Chinese high-speed railway construction.In the railway construction,the supply and transportation of materials will directly affect the costs and efficiency.The focus of this paper is to find a scientific way to locate logistics nodes and their corresponding supply facilities so that cost is minimized and efficiency is optimized.In railway construction,the demand of materials is along a line,and it is with continuous space demand instead of discrete demand.The demands are always described as discrete points in the previous location models,which is different from the situation in the railway construction.The description of demand line is a new model in this paper.A theoretical model is proposed with continuous space demand along a line.Logistics nodes,railway line(demand),and quarry(supply facility)constitute a three-layer supply chain.This paper involves a bilevel location problem to solve the location problem when the logistics nodes and supply facilities both need to be located A Set Covering Problem model is proposed to minimize the number of logistics nodes and supply facilities with all the railway line demand satisfied.A compared study of two different algorithms is involved in this paper.The two algorithms are Delete Relaxation Algorithm and Greedy Adding Algorithm.The Delete Relaxation Algorithm is based on Voronoi diagram,and it is to find the minimum facility locations and allocation demand of each facility.Greedy Adding Algorithm is based on covering circles with the logistics nodes and supply facilities as centers of circle.The compared study is to check if these algorithms are applicable and to explain which method is better to use in different situations.A realistic case study of Beijing-Shenyang railway construction is involved and the relevant data is collectedto arrive at the solution.When constructing a high-speed railway,concrete is a type of indispensable material,it can be used to produce slab track,sleepers,tunnels,and viaducts.By converting the longitude and latitude of each railway station to coordinates,a fitted railway line is constructed.The concrete demand is higher for the tunnels and viaducts;therefore,the candidate locations of facility are set to be near with tunnels and viaducts.Finally,by involving the two different algorithms into the Beijing-Shenyang high-speed railway case study,it is found that the Greedy Adding Algorithm has better solution compared with Delete Relaxation Algorithm.This solution can be a theoretical reference for the Beijing-Shenyang high speed railway construction and the model can be applied in the continuous space-demand location problem when the demand is along a line.