Causes of Delay in the Construction Projects of Subway Tunnel

The constructions of urban infrastructure are an important sector that provides remarkable ingredients for the economic development of modern cities. However, a large number of transportation infrastructure construction projects are delayed; therefore, those projects always exceed their original time and cost estimates. So construction delay has been considered as a recurring problem in the construction projects of urban infrastructure, and it adversely affects the time, cost, safety, and quality of construction. This paper is committed to investigating the time performance of subway tunnel constructions in China to identify the causes of delay based on the questionnaire surveys of 87 tunnel consultants and 91 contractors, and a total of 49 delay causes of tunnel construction are identified one by one in this study. It can be concluded from this study that the six most severe delay causes are national policy for subway tunnel construction, complicated geological conditions, payment delays by owners, award projects to the lowest bid price, shortage of advanced large equipment, and low productivity of laborers. There is a relatively reliable agreement between the tunnel consultants and contractors of 76.3% on the ranking of different delay causes.


Introduction
e constructions of urban infrastructure are one of the best tools through which a country or a region can achieve its economic goals of urban development [1], they have a remarkable effect on the economy of all countries and regions of the world [2]. Because the tunnel constructions are long processes and many parties are involved in the processes such as clients, designers, consultants, contractors, and subcontractors, tunnel constructions are becoming more and more complex [3]. Delay in the construction projects may produce adversarial and mistrust relationships, litigation and arbitration problems, and trepidation feelings among clients, designers, consultants, contractors, and subcontractors [4]. Whether the construction projects are successful or not depend on prime measures including time, cost, safety, and quality, any construction project may not be taken as a success unless it meets these specified requirements, and it is common to see a construction project failing to achieve its original time goal [5]. e delays in infrastructure construction projects became a universal phenomenon around the world.
According to the government work report, it can be known that 13% of gross domestic product (GDP) was contributed by construction projects in China, while only 6-9% of the GDP was contributed by construction projects in many countries and regions. e relatively high proportion of GDP in China shows that the sector of construction projects intensively affects various social, educational, and other sectors. With the substantial success achieved by the construction projects in terms of economic growth, labor output, and employment, these construction projects are partially meeting the local needs of Chinese society. However, more and more construction projects suffer from some problems which may prevent them to achieve their original time, cost, safety, and quality goals in the economy [6]. According to Al-Najjar's work [7], the main problems are as follows: (i) e number of construction projects in comparison with a large number of local workers (ii) Continued increase in material and labor prices (iii) Dependency on government investments to implement construction projects of infrastructure (iv) Complicated geological conditions in different areas In China, the general investigations have indicated that construction project delay is a common phenomenon, but there are no former researches which have carefully investigated the causes of project delay in subway tunnel construction. is paper aims to investigate the most severe delay causes of subway tunnel projects in China. Identifying causes is always the basic work when catching a problem, and then corrections can be done [8], so it is hoped that the studies of this paper may guide further works to improve the performance of the projects especially in the subway tunnel construction.

Literature Review
Construction projects are often faced with delays, and projects finish later than the dates fixed in construction contracts. Analysis of construction delay is usually based on the identification of delay causes since it is a determination of causation, quantification of delay, and assessment of responsibility in its simplest form [9,10]. With the complex and multiparty nature of modern construction projects, it is a daunting task to identify the delay causes [11,12].
Al-Momani studied the causes of delay which were related to the owner, designer, contractors, and consultants in more than 100 public projects in Jordan [13]. Odeh and Battaineh concluded that the top 6 severe causes of construction delay in Jordan were owner's interference, slow decision making, payment delays by owners, improper plans, inadequate experience, and low labor productivity [14]. Assaf and Al-Hejji identified the causes of delay in Saudi Arabia, and it concluded that the most common cause of delay was that the owners change orders [15]. Ahn and Minchin made a comparison between contract types (unit cost, lump sum, and others) which shows the average increase in construction time using innovative contracts was 14.8%, whereas the increase for low bid contract was 30.0%, the average time overruns of bonus contracts was only 1.8% which was shortest among the studied innovative contracting methods [16]. Enshassi and Abu Mosa found that the most important delay cause was employing an unqualified designer to conduct the design and defective design may cause quality accidents [17]. Yang et al. identified the delay causes in various stages of BOTprojects by the opinions of BOT participants, and the study results revealed that the "improper contract planning," "debt problem," and "uncertainty on political issues" were the most significant delay causes [18]. Mahamid et al. studied the delays in road construction projects in Palestine which concluded that the terrible political situation, segmentation, and limited movement between areas are the most severe delay causes [19]. Santoso and Soeng analyzed the delay factors in road construction projects in Cambodia, it concluded that rain and flood were the first two factors, and there was no significant difference between contractors and consultants in assessing the delay factors [20]. Alfakhri et al. proposed a conceptual model of delay factors and used the Statistical Package for Social Sciences (SPSS) software to analyze the level of impact of identified delay categories on the completion of the road construction projects, it concluded that the contractor had the most significant impact on the delay in road projects, and the conversion and transfer of utility services by the competent authorities were the five most significant factor [21]. Bilgin et al. proposed a delay analysis ontology to facilitate the development of databases, information sharing as well as retrieval for delay analysis within construction projects [22,23].
Out of these studies, it can be concluded that the studies about the time delays in subway tunnel construction in developing countries are seldom to see.

Study Objectives
e main study goals of this paper are as follows: (i) To identify the causes of delays in subway tunnel construction projects in China (ii) To identify and rank the severe delay causes according to the viewpoints of a large number of contractors and consultants (iii) To test the agreements between a large number of contractors and consultants on the rank of the severe delay causes

Research Method.
Based on the questionnaire surveys of project participants, the necessary information about project delays is obtained in an effective way. More than 40 delay causes of project delays are generated from related studies together with input, output, and revisions by some construction parties, the list of delay causes are shown in Table 1. e questionnaire surveys are also adopted to estimate the severity of all the delay causes. e studied project participants mainly involve contractors and consultants, the contractors are holding the valid registrations in tunnel specialization within China from the Chinese Contractors Association. e studied project participants do not involve owners because the subway tunnel construction projects are public infrastructure projects which are always funded by the local governments, it means that there is only one owner for each project and so the view of the owner is not collected through a questionnaire survey. e studied contractors and consultants are selected by random sampling from an available list.
e detailed communication information of studied contractors and consultants are obtained from the database of the Chinese Contractors society.
Data are obtained from the questionnaire surveys of contractors and consultants and studied by adopting a severity index. e agreement between the two kinds of parties on the severity rank of the delay causes is also tested. Some suggestions making for reducing the project delays in subway tunnel construction are emphasized in the study results.

Questionnaire Survey.
e questionnaire surveys are divided into two parts. Part one is connected with the integrated information for both the construction companies and responders. e selected contractors and consultants are both requested to respond to the questions about their tunnel construction experience, and they are also further requested to respond to the questions related to their opinions about the causes of project delays according to their tunnel construction experience. Part two contains the detailed list of identified delay causes in subway tunnel construction projects, and the delay causes are in nine kinds of classification in terms of delay (1) In your opinion, what is the occurring probability of each delay causes? e occurring probability ranges from 0.1 to 1 (2) What is the severity degree of each delay causes on subway tunnel construction? e severity is classified into six degrees, which is on a zero to five-point chosen range, as no influence, very low, low, medium, high, and very high

Severity Index.
e severity index is used to rank the suggested delay causes in subway tunnel construction projects. Based on the impact degrees which are chosen by the questionnaire participants, the formula of severity index can be given as follows: where α is the occurring probability of each delay causes; β is the classified degree which ranges between one for no influence and six for very high; n is the number of the participants who respond to the questionnaires; and N is the number of all the participants who receive the questionnaires. erefore, once the classified degree of a cause is one for no influence in all the responses, then the severity index of this cause equals zero, it means that this cause is not a significant one and at the last of rank. Conversely, once the classified degrees of a cause are six for very high influence in all the responses, then the severity index of this cause equals 80-100, it means that this cause is a significant one and at the top of the rank. e correspondence between the possible ranges and impact degrees for the severity index is shown in Table 2. e severity index for each cause can be calculated by formula (1) from the opinions of all the respondents. e average severity index of each classification can be calculated according to the severity index of causes under each classification, the calculation formula is given as follows: where X i is the severity index of cause i under a classification; and m is the number of causes under this classification.

Rank Correlation.
In order to test how well the responsive consultants and contractors agree on the ranking according to the severity index of delay causes, a rank correlation coefficient (0 ≤ r ≤ 1) is adopted to evaluate the rank difference between consultants and contractors. e calculating formula of the rank correlation coefficient can be given as follows: where d is the difference of ranks between consultants and contractors for each delay cause; k is the number of pairs of different ranks. Once the rank correlation coefficient equals one, it means the two ranks are completely reverse. Once the rank correlation coefficient equals zero, it means the two ranks are the same.

Study Results
A total of 100 tunnel consultants and 100 tunnel contractors have received the questionnaires, a total of 87 tunnel consultants and 91 contractors have responded to the question about their opinions on the severity and ranking of 49 delay causes, the response rate by consultants and contractors are both higher than 85%. All the respondents have more than five years of experience in tunnel construction.

Analysis of Delay Rate in Subway Tunnel Construction
Projects. e responses of consultants and contractors about the delay rate in subway tunnel construction projects during the last 5 years are shown in Figures 1 and 2. Figure 1 shows that 68.8% of the responding consultants pointed out that the average durations of their participated tunnel projects are 20%-30% longer than the planned project durations, while 15.6% of them thought that the average durations are 30%-40% longer, while 9.4% of them thought that the average durations are 40%-50% longer, and only 6.3% of them thought that the average durations are 50%-100% longer than the planned project duration. Figure 2 shows that 8.6% of the responding contractors pointed out that the average duration of their participated tunnel projects are 0%-10% longer than the planned project durations, while 68.6% of them thought that the average durations are 20%-30% longer, while 17.1% of them thought that the average durations are 30%-40% longer, and only 5.7% of them thought that the average durations are 40%-50% longer than the planned project duration.

Ranking of Delay Causes.
e causes under each source from different classifications are ranked according to the severity index. According to the view of both consultants and contractors, the severity index is calculated by formula (1).

Range
Impact degrees Very high 4 Advances in Civil Engineering

Cause Ranking from Different Classifications
(1) Causes from the Owner. e severity index and ranking of each delay cause from the owner in the view of consultants and contractors are shown in Table 3. It can be concluded from Table 3 that the severest cause from the owner is the progress payment delay by the owner. It also can be concluded from Table 3 that the cause rankings in the view of consultants are almost similar with the view of contractors, but there is a significant difference in the ranking of "poor communication between the owner and other construction parties" which respectively rank 4 and 7 in the view of consultants and contractors. ere is a span in causes ranking in the combined view of consultants and contractors which ranges from 50.11% to 72.19% which means that each cause from the owner has a medium or high effect on the delay of subway tunnel construction projects.
(2) Causes from the Designer. e severity index and ranking of the 3 delay causes from the designer in the view of consultants and contractors are shown in Table 4. It can be concluded from Table 4 that the severest cause from the designer is late design works. It also can be concluded from Table 4 that the cause rankings in the view of consultants are almost similar with the view of contractors, but there is a small span in causes ranking in the combined view of consultants and contractors which ranges from 41.93% to 55.39% which means that the severities of the causes from the designer are still in the medium level.

(3) Causes from the Contractor.
e severity index and ranking of the 8 delay causes from the contractor in the view of consultants and contractors are shown in Table 5. It can be concluded from Table 5 that the severest cause from the contractor is the ineffective scheduling of projects by the contractor. It also can be concluded from Table 5 that there are little differences between the rankings in the view of consultants and the view of contractors, one of the differences is the cause ranking of "ineffective scheduling of project by the contractor" respectively rank 1 and 2 in the view of consultants and contractors, e.g., there is a span in causes ranking in the combined view of consultants and contractors which ranges from 43.82% to 63.95% which means that the severities of the causes from the contractor are in the levels between medium and high.

(4) Causes from the Consultant.
e severity index and ranking of the 4 delay causes from the consultant in the view of consultants and contractors are shown in Table 6. It can be concluded from Table 6 that the severest cause from the consultant is the delay of inspection by the consultant. It also can be concluded from Table 6 that the cause rankings in the view of consultants are almost similar with the view of contractors, the ranking span of causes according to the combined view ranges from 40.19% to 56.14% which means that all the causes from the consultant have a medium effect on delay of subway tunnel construction projects.  Table 7. It can be concluded from Table 7 that the severest cause from labor is the low productivity of laborers. It also can be concluded from Table 7 that the cause rankings in the view of consultants and the view of contractors are almost similar. ere is a span in causes ranking in the combined view of consultants and contractors which ranges from 47.15% to 69.43% which means that the severities of the causes from labor are in the levels between medium and high.

(6) Causes from Environment.
e severity index and ranking of the 5 delay causes from the environment in the view of consultants and contractors are shown in Table 8. It can be concluded from Table 8 that the severest cause from the environment is complicated geological conditions. It also can be concluded from Table 8 that the cause rankings in the view of consultants and the view of contractors are almost similar. ere is a big span in causes ranking in the combined view of consultants and contractors which ranges from 38.62% to 74.00% which means that the severities of the causes from the environment are in the levels between low and high.
(7) Causes from Equipment and Material. e severity index and ranking of the 7 delay causes from equipment and material in the view of consultants and contractors are shown in Table 9. It can be concluded from Table 9 that the severest cause from equipment and material is the shortage of advanced large equipment. It also can be concluded from        6 Advances in Civil Engineering Table 9 that the cause rankings in the view of consultants are almost similar with the view of contractors, but there are significant differences in the ranking of some causes, e.g., "shortage of advanced large equipment" respectively rank 3 and 1 in the view of consultants and contractors, "shortage in construction material" respectively rank 1 and 2, "serious damage to the equipment" respectively rank 6 and 4, and "material loss in the process of transportation" respectively rank 5 and 7. ere is a span in causes ranking in the combined view of consultants and contractors which ranges from 57.73% to 70.30% which means that all the causes from equipment and material are in the levels between the medium and high effect on delay of subway tunnel construction projects.

(8) Causes from External Factors.
e severity index and ranking of each delay cause from external factors in the view of consultants and contractors are shown in Table 10. It can be concluded from Table 10 that the severest cause from external factors is the national policy for subway tunnel construction, the second severest cause is award the project to lowest bid price, the severity index of both causes are bigger than 70%. It also can be concluded from Table 10 that the cause rankings in the view of consultants are almost similar with the view of contractors, but there is a span in causes ranking according to the combined view of consultants and contractors which ranges from 45.22% to 75.17% which means that each cause from external factors has a medium or high effect on delay of subway tunnel construction projects.

Overall Causes Ranking.
According to the view of consultants, the six most severe causes in subway tunnel construction projects in China are listed in Table 11. It is shown in Table 11 that among the top six delay causes, the first is related to the classification of environment, the second and the fourth are related to the classification of external factors, the third is related to the classification of the owner, and the fifth and sixth are related to the classification of equipment and material.
According to the view of contractors, the six most severe causes in subway tunnel construction projects in China are listed in Table 12. It is shown in Table 12 that among the top six delay causes, the first and the fourth are related to the classification of external factors, the second is related to the classification of environment, the third is related to the classification of the owner, the fifth is related to the classification of equipment, and the sixth is related to the classification of labor. It is also shown that the severity indexes of the top six delay causes are all higher than 70%, the biggest severity index is 76.52%.
According to the combined view of consultants and contractors, the six most severe causes in subway tunnel construction projects in China are listed in Table 13. It is shown in Table 13 that among all the delay causes, the top three causes are respectively related to the classification of external factor, environment, and the owner, the top affecting cause is the national policy for subway tunnel construction and its severity index is 75.17%. e severity indexes, rankings, and related classifications of all the investigated delay causes in subway tunnel construction projects in China are calculated and shown in Tables 11-13. It can be concluded from Tables 11-13 that the severity indexes of five causes are all above 70% according to the view of consultants, contractors, and their combined view, the five causes are national policy for subway tunnel construction, complicated geological conditions, payment delays by owners, award projects to lowest bid price, and shortage of advanced large equipment. It can be concluded that the severity indexes of two causes are less than 40% according to the view of consultants; the two causes are natural disaster and incapable and insufficient inspectors, the severity indexes of two causes are less than 40% according to the view of contractors; the two causes are the natural disaster and poor effect on the drainage system, the severity index of only one cause is than 40% according to the combined view; the cause is the natural disaster. Rankings of the top four causes in the view of consultants are almost similar with the view of contractors, but there is a difference in the ranking of "national policy for subway tunnel construction" which respectively rank 1st and 2nd in the view of consultants and contractors. Rankings of the top six causes according to the contractors' view are the same with the combined view.

Agreement and Disagreement of Severity Index.
e top six delay causes in the agreement between consultants and contractors are listed in Table 14, the difference in the severity index values of those delay causes are lowest, the absolute difference in severity index value are all less than 0.95%. e top six delay causes in disagreement between consultants and contractors are listed in Table 15, the difference in the severity index values of those delay causes are highest than others, the absolute difference in severity index Advances in Civil Engineering 7 value range from 6.84 to 12.04%, there is no huge difference in the severity index values of all the causes between the consultants and contractors. Table 16 lists the severity index difference of six most severe causes between the views of consultants and contractors. It shows the biggest difference value in the severity index of the six most severe causes ranges from 0.76% to 2.71%, the calculated indexes according to the consultants' view are close to the contractors' view.

Classifications Ranking.
All the delay causes can be divided into nine classifications. According to the view of consultants, contractors, and their combined view, the ranking of those classifications which are associated with the degree of severity are all listed in Table 17. Table 17 illustrates that (1) e three most severe classifications of delay in subway tunnel construction projects from the view of consultants are external factor, material, and the owner, while the three most severe classifications of a delay from the view of contractors are equipment, external factor, and material, while most severe classifications of a delay from the combined view are equipment, material, and the owner (2) e least severe classification of delay in subway tunnel construction projects from the consultants' view and combined view are respectively designers and consultants, the least severe classification of a delay from the contractors' view is the same with the consultants' view (3) ere is a short span between the classifications' severity index and the span ranges from 46.59 to 66.41 (3) is adopted to contrast the agreement between consultants and contractors on the severity of the delay causes in subway tunnel projects. According to the overall ranking of all the delay causes in Tables 11-13, the calculated rank correlation coefficient equals 76.3%. It can be concluded from the rank correlation coefficient that the agreement between consultants and contractors is relatively good, so the results of this research are considered to be reliable.

National Policy for Subway Tunnel Construction.
e national policy for subway tunnel construction in China is described as changeable because of the contradictory developing strategy between the rural infrastructure and urban infrastructure, the policy leads to government investment increasing or decreasing. is delay cause has not been discussed in any studied literature.

Complicated Geological Conditions.
Tunneling in the rock layers with complicated geological conditions is very difficult since the surrounding rock of the tunnel will become very loose and incapable of self-consolidating. e time of surrounding rock consolidation is difficult to predict and more variable than other construction procedures.

Payment Delays by Owners.
Because of the high daily expenses involved in the tunneling works, it is very difficult for the contractors to fulfill the high costs without timely progress payment. e tunneling works always delay due to the shortage of cash flow, so payment delays by owners is a critical delay cause in the tunnel construction project especially for those projects with limited construction time.

Award Projects to Lowest Bid Price.
A large number of owners prefer to award their projects to the contractors with lowest bid price, but those contractors always lack capabilities and experience in finishing a qualified project, which may cause a delay in the project completion. Hence, the awarding policy and the postqualification standards must be improved to reduce this problem. peasant laborers lack theoretical basis knowledge and tunnel construction experience, they are not familiar with all kinds of code standards and trends of technological development, which may cause a delay in the project completion. Hence, the continuing education and skills training must be used to improve the productivity of laborers.

Advice to Reduce Overtime in Tunnel
Construction. e advice to reduce and control the delay in subway tunnel construction projects are as follows: (a) To improve the management strategies of construction parties and the skills of laborers, the ministry of construction should conduct some annual training programs in cooperation with the Chinese contractors association.
(b) e local government should take some risk for contractors when owners delay the payments to the contractors because a large number of contracting companies in China are small and lack capital. (c) e local government should modify and improve the construction laws and rules on time to (2) Owners should carefully consider the following advice: (a) Owners should give enough time for contractors to plan, design, and construct tunnel projects, this may be useful in avoiding or reducing time delay.
(b) Owners should pay the progress payment to contractors on time, otherwise, the projects may delay because the contractors cannot afford to finance the construction work. (c) Owners should check the capabilities, experiences, and resources of the suitable bidders before awarding the contracts to them. (d) Owners should confirm the detailed site investigation before the construction phase and avoid the changing of site investigation.   (3) Consultants should give necessary attention to the following advice: (a) Consultants should offer enough information which is necessary for interpreting the construction drawings and laying out the works. (b) Consultants should adopt more suitable ways to evaluate construction works and compromise between high quality and low expenditure.
(4) Contractors should carefully think about the following advice: (a) To improve labor efficiency, contractors should assign a large percentage of trained and skilled laborers in construction projects, especially in large tunnel construction projects. (b) To improve work efficiency, contractors should assign enough advanced equipment and use new materials in large tunnel construction projects [24,25]. (c) To achieve the specified expenditure, time, and quality, contractors should well communicate with owners and consultants.

Conclusion
e delay causes of subway tunnel construction projects in China have been studied by a field survey, the field survey involved 87 consultants and 91 contractors. e 49 delay causes have been identified into 9 categories, the severity indexes and ranks of the delay causes have been discussed according to the view of consultants and contractors. e responses of consultants and contractors about the delay rate in subway tunnel construction projects during the last 5 years show the following: (1) 68.8% of the responding consultants pointed out that the average duration of their participated tunnel projects is 20% to 30% longer than the planned project duration. (2) 85.7% of the responding contractors pointed out that the average duration of their participated tunnel projects is 20% to 40% longer than the planned project duration. (3) Neither contractors nor consultants pointed out any delay rate of more than 100% of the planned project duration.
e conclusions from the statistical analysis of research data are shown as follows: (1) Neither contractors nor consultants indicated any cause with no effect on the delay of subway tunnel construction projects. (2) e severity index of each delay cause is more than 38%. e severity index of each classification ranges from 46.59 to 66.41.
According to the combined view of consultants and contractors, the six most severe delay causes are national policy for subway tunnel construction, complicated geological conditions, payment delays by owners, award projects to lowest bid price, shortage of advanced large equipment, and low productivity of laborers. Conversely, the six least severe delay causes are poor site supervision by the contractor, poor resource management, inappropriate design, poor effect on the drainage system, incapable and insufficient inspectors, and natural disaster.
It also can be concluded from the combined view of consultants and contractors that the three most severe classifications of delay in subway tunnel construction projects are equipment, material, and the owner. e value of the rank correlation coefficient equals 76.3% which illustrates that the agreement on the severity ranking of delay causes is relatively reliable. ese studied results reveal that all the investigated causes have relevance to the delay problems in subway tunnel construction projects in China.

Data Availability
e data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare that there are no conflicts of interest regarding the publication of this paper. Advances in Civil Engineering 13