Risk Control Analysis of Metro Construction Based on Complex System Brittleness Theory Nie TingTing* Postgraduate Institute of architecture and environment, Sichuan University, Chengdu 610500,China;e-mail:[email protected] Xing HuiGe Associate Professor Supported by the National Natural Science Youth Fund (51209156) Institute of architecture and environment, Sichuan University, Chengdu 610500, China; e-mail: [email protected] ABSTRACT Taking the characteristics of the complex system brittleness theory and metro construction into account, the metro construction system was divided into four subsystems: design, technology, environment and management subsystems, so as to analyze the corresponding brittleness risk. This paper made an analysis on the collapse accident which was the typical ground subsidence during the metro construction, and calculated the brittleness degree of various brittleness by means of quantitative analysis on the brittleness in different security level, thus having determined the scope of each grade’s brittle correlation in the safety pre-evaluation for the metro construction. In addition, taking a certain metro project as an example, this paper had verified the complex system brittleness theory by determining the risk level and presenting the evaluation results, and specific measures had also been proposed. Finally, the risk control model for metro construction system had been established, and the risk control strategies for the four subsystems, i.e. design, technology, environment and management subsystems, had also been listed out, which could improve the risk control system of metro construction to a certain extent. KEYWORDS: Construction risk; Metro; Brittleness risk;Complex system; Brittle safety. FOREWORD As one green facility, the metro is very popular because of its diversified advantages. For instance, it is convenient, saving floor space and energy (according to statistics of Minnesota of the United States, the energy in refrigeration and heating can be saved up to 50%+), reducing the pollution, and conducive to the ecological balance of the city [1]. However, in the construction, due to the geological conditions and the unforeseeable risks, the existing building structures around, management technology and other factors, in recent ten years, the domestic construction accidents occur frequently, causing many serious pavement settlements and collapses. - 9797 - Vol. 21 [2016], Bund. 25 9798 The traditional metro construction risk control is mainly based on the qualitative analysis, such as identifying the risk factors by means of Delphi method, check table, reason-result analysis, etc., thus making construction personnel understand the dangers they face. However, as the metro belongs to the underground project, the construction is influenced by various factors, such as hydro-geological conditions, weather conditions and mechanical equipment, etc.. Therefore, the qualitative analysis could not show the loss value and the occurrence of loss when the risk is in face [2]-[5]. Targeting at this problem, the brittleness theory of complex system is employed to analyze the brittleness risk in underground construction as well as the accident factors leading to brittle settlement of pavement combined with the analysis on pavement settlement accidents. Furthermore, the metro construction risk control model has been established according to the brittleness factors for construction and the four subsystems, i.e. the design, technology, environment and management, thus obtaining a valid threshold for the brittle link and determining the safety level of metro construction. In the end, the risk control strategies have been made for the four subsystems, namely, design, technology, environment and management, reducing the brittle connection degree of the risk in metro construction and providing guidance for metro construction so as to reduce the brittleness events, thus then being able to prevent the risk or reduce the risk degree. At present, complex system brittleness theory has been applied in many fields, such as coal mine production [6], power grid system [7], project combination [8], and building construction [9], etc.. COMPLEX SYSTEM BRITTLENESS ANALYSIS Metro is a complex engineering consisting of design, technology, environment and management systems. And the inherent characteristic of complex system is brittleness. Once a system crashes, other subsystems will be interfered, thus leading to the collapse of the whole system. The association between each system is named as the brittleness; when a brittle source is triggered, one or more brittle recipients will be resulted in, the process of which is called the brittle process. The first collapsed subsystem is called the brittle source, for instance, because of the improper supporting structure in the working well, the pit collapse and landslide will result in surface subsidence, during which, the brittle source is the improper supporting structure in working well. In the case of the collapse of one subsystem leading other subsystems to collapse, the other subsystems are called brittle recipients. For instance, the improper ground treatment will result in water or mortar leakage when the shield is lead to tunnel, which may cause sudden inflow of water and sand, resulting into large scale surface subsidence, and even the collapse of the working well, burying the shield machine. During this process, the brittle recipient is the shield. The brittle source corresponds to one or more brittle recipients, the relationship of which is shown in the following Fig.1. Vol. 21 [2016], Bund. 25 9799 Brittle recipient1 Brittle recipient2 …… Brittle source Brittle recipient Brittle source Brittle recipient n One to one relationship One to many relationship Figure 1: The relationship between the brittle source and brittle recipients Complex system brittleness theory Complex system brittleness theory is mainly to study the mechanism of the collapse of complex system, and to prevent the occurrence of brittleness risk. Brittleness risk can be divided into internal and external factors, the former refers to the brittleness factors interaction between the subsystems due to mutual influence, and the latter refers to the brittle factors and brittle events imposed upon the system by the external environment. This current paper mainly analyzes the internal factors of complex system. The brittle structure model of complex system, shown in Fig.2, shows the hierarchy and brittleness relationship in the complex system. The bottom is the brittleness factor, which leads to the security event. Under the influence of the brittle connection, the security event causes the collapse of subsystem, and the whole subsystems make up of the entire brittle system. S uper Complex system structure Subsystem 1 Subsystem m … Security event 1 B Security event 2 … Security event m structure ottom Brittle factor1 Brittle factor2 … Brittle factor m Figure 2: Complex system brittleness structure model Vol. 21 [2016], Bund. 25 9800 Brittle correlation function Risk control of construction projects can be carried out through the evaluation of the safety level from a macro point of view, determining the extent of the brittleness in the important indicators of brittleness, thus providing the basis and ideas for risk control. Brittle correlation H (S) refers to the degree of association between the brittleness indices when the system is in normal operation (without the interference of external factors). The greater degree of brittle relation, the higher the risk of complex system; and the smaller the degree, the more stable the complex system. The brittle correlation function is shown as: H (S) = f (x , x , x ,x ) 1 2 3 4 = (1− x )[w (1− x ) + w (1− x ) + w (1− x )] 1 2 2 3 3 4 4 (1) In the formula (1), H(S) [0,1] ,x respectively indicates the quantitative value of management, w design, technology, environment,∈ i=1,2,3,4; And j means the weights of people, machine and environment in the internal brittleness correlation degree of the complex system, j=2,3,4 and w + w + w =1 2 3 4 During the construction of the metro system, because of its inherent defects such as tough construction environment and complicated construction technology, the brittleness is an inherent property of complex systems, which might make one small trigger of brittle factor result into the collapse of the subsystem, or even domino effect among various brittle factors, security events, and subsystems, thus making the whole complex system collapse. We should first collect specific information about a metro project and determine the unstable brittle factors, which are then detected and strictly controlled. By means of limiting the inspiration of the brittleness factors, effective measures should be adopted to control brittle connection degree or to reduce the influence of the brittleness risk, which plays an important role in controlling metro construction risk. ESTABLISHMENT OF RISK INDEX SYSTEM FOR METRO CONSTRUCTION Project overview The Chengdu Metro Line 4 initiates to integrate the Guanghua Park Station, which is located on the west side of the green belt in the intersection of Guanghua Avenue and Tiaobao Street, and laid out on both sides of the Guanghua Avenue. The station is the underground island type platform station with double deck 11 meters, the total length of which is 481.8m, and the width of standard section 19.9m, the height of standard station 13.13m. The overall terrain of Guanghua Park Station is relatively flat, with intensive