Time is an index that is easily measured and is remembered frequently by the more involved in the project. Based on the schedule plan, resources are mobilized and coordinated with each other. Therefore, the schedule is a closely binding condition between the parties in the project and is often the source of conflicts during project implementation. Studies on projects’ progress schedules have been interesting in the world and are gradually gaining more attention in Vietnam. It is possible to mention the studies of J. Vijayalaxmi and Umair Khan [ 4] evaluating the factors affecting the time in construction projects. Mohamed SaadBajjou and AnasChafi [ 5] stated that delay is a common problem in construction projects. Jyh-Bin Yang and Shen-Fen Ou [ 6] using SEM model clearly showed the correlation between the main causes of delay in construction investment projects. In another aspect Aftab Hameed Memon, Ismail Abdul Rahman, MohdRazaki Abdullah, Ade Asmi Abdu Azis [ 7] found the relationship between schedule and cost, the causes of increased costs often have a direct impact on progress before affecting costs. RemonF.AzizAsmaaA.Abdel-Hakam [ 8] listed 293 causes of project delay, but only 20 main causes come from contractors and consultants that need attention and improvement. Mahamid [ 9] referred to the main factors affecting the time deviation in construction investment projects such as late payment by owners, and changes in construction laws. Some studies consider time as a blur variable in schedule planning. McCahon [ 10] considers time as triangular blurr numbers. Using blur set theory, the author finds a difference in the expected project completion time and the actual completion time. Ö Ökmen and A Öztaş [ 11] argued that construction activities are carried out under uncertain conditions, so the duration of the works is blur information. Stefan Chanas and Pawel Zielinski [ 12] suggested using a blur critical path in a schedule based on work activities with uncertain information.

In Vietnam, studies on construction projects’ progress schedules have been interesting for researchers. It is to include Le Huy Tai, Tran Van Thong and Dang Cong Thuat, summarizing 31 factors affecting the completion progress of public investment projects in general. The authors show that capital management and progress are issues that strongly affect the ability to complete construction projects using public investment capital. Tran Hoang Tuan pointed out 12 factors affecting the project implementation progress in Can Tho province. Truong Cong Bang [ 13] used a fuzzy set to clarify input information when planning the progress of construction investment projects. Dinh Doan Tu [ 14-16] applied fuzzy set theory to make a project construction schedule, fuzzy numbers used are triangular or trapezoidal fuzzy numbers. Besides, a number of master theses have also studied factors affecting the progress schedules of construction projects, typically applied to different locations by simple research methods such as Nguyen Thi Hoang Lieu [ 17], Ho Chi Luan [ 18], Pham Hoang Khoi [ 19], Tran ThiDien Lam [ 20], Pham Cao Nghia [ 21]. Through the research studied, it can be seen that:

(1) Progress is an important aspect of any type of construction investment project. The relatedstudiestend to show that contractors are the subjects that have the most influence on the progress of construction investment projects with many effective factors.

(2) Causes affecting progress schedules can come from parties inside the project or from outside the project and will increase if the causes affecting the progress are not properly assessed. The main causes affecting the progress schedules of construction investment projects are recorded in Tables 2 and 3.

(3) There has not been any research to thoroughly investigate the factors affecting the progress schedules of construction investment projects using public investment capital in Hanoi. The authors study the factors affecting progress schedules, not to rank the factors, but to find out how these factors affect progress schedules;

(4) With the ability to solve problems without certain information, fuzzy set theory has the ability to describe progress schedules with fluctuations in the execution of construction projects. Sometimes fuzzy set theory helps to collect information on progress schedules more objectively.

F-AHP traditional method (Fuzzy Analytic Hierarchy Process) was developed from AHP (Analytical Hierarchy process) with the integration of fuzzy numbers to effectively deal with the fuzziness of data related to decision making. The F-AHP method has overcome some limitations of the traditional AHP method, so this method is increasingly used by many researchers in practice.

2.2.1. AHP Method

AHP method (Analytical Hierarchy process) is also known as hierarchical analysis. The AHP method is used to solve unstructured problems in economic, social and management science activities. The AHP methodology helps with complex multi-criteria decision-making problems. AHP enables decision makers to bring together the expertise of subject matter experts, combining objective and subjective data within a logical hierarchical framework. AHP helps to classify the relative priority for the options, and the problem occurs based on a scale. This scale is based on the judgment of the decision maker and the importance of those judgments, as well as the consistency in comparing alternatives in the decision-making process. AHP combines both qualitative and quantitative aspects of human thinking. Qualitative through hierarchical arrangement and quantitative through the result set of weights for each hierarchical factor. Three principles when implementing the AHP method: (1) Analyze the decision-making problem (build a hierarchical structure); (2) Comparative evaluation of components (pair comparison of factors); and (3) Aggregate priorities (determine weight matrices).

Fig. (1). Triangle fuzzy number [ 4, 15].

2.2.2. Fuzzy Set Theory

\The important feature of fuzzy set theory is that it proposes to use membership functions and then fuzzy operations to deal with “uncertain” or incomplete information, whose accuracy is only limited. Fuzzy concepts are shown to be very useful and easy to work with in the decision-aid problem [ 22-25]. A fuzzy set is a set whose boundaries are not clear or ambiguous. In a fuzzy set, the membership function is used to represent the membership level of an element. The membership function of a blurr set F over the sum set X denoted µF is determined by: µF: X->[0,1], where µF(t) is the degree of membership of the element t of the set X up a fuzzy set F. A fuzzy number is one whose membership function must satisfy the condition that it is continuous and convex. A fuzzy set is said to be normal if there exists a value 't' such that µF(t)=1. There are many different types of fuzzy numbers, but a triangular fuzzy number (fig. 1) is often applied because of simple calculations and easy data processing.

(1)

In this research, the author uses the F-AHP method with triangular fuzzy numbers for the reason as follows:

- Experts' assessment of the causes affecting progress schedules for construction projects in Hanoi city using linguistic terms will reveal the nature of the problem rather than assigning them to values on a numerical scale. Linguistic phrases will be coded based on triangular fuzzy numbers to ensure objectivity in expert assessment.

- The causes affecting the progress of construction projects in Hanoi city are compared within a logical hierarchical framework. AHP helps to calculate the priority for each cause based on a scale.

- By using F-AHP to some extent, the relationship between the causes is taken into account. The weight of each cause is measured by the relationship of the pairs of causes to each other.

Objective of the paper is to rank and assess the causes affecting the implementation progress of construction projects using public investment capital in Hanoi city. The F-AHP method is applied in the study to take advantages: (1) Rank causes affecting progress schedules based on the relative priority of the causes; (2) Ensure the objectivity of the expert's assessment.

The causes affecting the progress schedules of construction projects using public investment capital in Hanoi are summarized in Table 4.

The survey on process schedules took place in Hanoi City between 2022-2023. After the direct investigation, the data obtained are as follows:

- Total number of surveys distributed: 235 surveys

- Total number of surveys collected: 215 surveys

- Total valid surveys: 205 surveys

Respondent Information:

- Regarding survey participants: Managers accounted for 31% of the votes; Technical staff accounted for 28% of the votes; Support officers and advisors accounted for 26% of the votes.

- Regarding work experience: respondents are mainly those with more than 7 years of work experience, accounting for the highest percentage (56%), those with 5-7 years of work experience accounting for 34%, those with experience from 3-5 years accounts for 10% and no respondents have less than 3 years of experience. The respondents, the majority of which have work experience equivalent to a certificate of type 2 or higher. This shows that the information collected from the survey is objective and has high practical value. With 205 valid votes, the author conducts data processing to prepare for the next analysis steps.

- About the project participants: accounted for 30.24% of the respondents working at the owner, 31.71% of the respondents were from consultants and 38.05% of the respondents were from the private sector contractors. The proportion of parties in the project participating in the survey is quite even, according to the original plan.

(1) Level 1 matrix results comparing level 2 causes Level 1 matrix comparing level 2 causes includes 4 comparative criteria, which are 4 groups of causes that are A1, A2, A3 and A4.

- The result of level 1 matrix fuzzification is shown in Table 5.

Result of level 1 matrix deblurrication is shown in Table 6.

- Level 1 composite matrix is as Table 7.

- Determination of CR rate is as Table 8.

CR = 0,097 < 10% thus ensuring the consistency of the respondents' responses. Weights calculated for admitted grade 1 causes.

(2) The result of the corresponding level 2 matrix comparing the level 3 causes.

The corresponding level 2 matrix comparing level 3 causes includes matrices A1, A2, A3 and A4. Matrix A1 includes 5 comparison criteria: A11, A12, A13, A14 and A15.

- A1 matrix blur results is as Table 9.

- Defuzzification Matrix A1 is shown in Table 10.

- Composite Matrix A1 is as Table 11.

- Determination of CR index is as Table 12.

CR = 0,019 < 10% thus ensuring the consistency of the respondents' responses. Weights calculated for owner-related causes are acknowledged.

(3) A2 matrix results

A2 matrix includes 8 comparison index: A21, A22, A23, A24, A25, A26, A27 and A28.

The result of A2 matrices fuzzification is shown Table 13.

- A2 matrix fuzzification results is as Table 14.

- A2 composite matrix is as Table 15.

- Determination of CR index is shown in Table 16.

CR = 0,082 < 10% thus ensuring the consistency of the respondents' responses. Weighted calculations for recognized contractor-related causes.

(4) A3 matrix results

A3 matrix includes 3 comparison indexes: A31, A32 and A33.

- A3 matrix fuzzification results is as Table 17.

- A3 matrix fuzzification results is 18.

- A3 composite matrix is as Table 19.

- CR index determination is shown Table 20.

CR = 0,066 < 10% thus ensuring the consistency of the respondents' responses. Weights calculated for causes related to the recognized consultant.

(5) A4 matrix results

A4 matrix includes 4 comparison index: A41, A42, A43 and A44.

- A4 matrix fuzzification results is as Table 21.

- A4 matrix defuzzification results is as Table 22.

- A4 composite matrix is as Table 23.

- CRindex determination is shown in Table 24.

CR = 0,020 < 10% thus ensuring the consistency of the respondents' responses. Weights calculated for other causes are assumed.

Looking specifically at the causes related to the owner (Table 4), it is found that the problem of late payment and slow decision-making when there is an unusual incident in the project are the causes that strongly affect the project schedule judgment. These causes have occurred in most of the current slow-moving projects and have become more serious in some projects such as CV1 Harmonized Lake Park project, PhungKhoang Lake Park project, construction project construction of an overpass at the intersection of Chua Boc-Pham Ngoc Thach, the project of building an overpass at the intersection of An Duong-ThanhNien road phase 2. In addition, factors such as the owner's delay in handing over the construction site, the owner's delay in taking over the completed work, and the owner's delay in providing documents to stakeholders also occurred and affected the progress for a period of time short time. There is no lasting effect on the total progress of the project. The weight of these causes has a lower score, respectively 0.11; 0.11; 0.14 (Table 25). The reasons being considered are directly related to the owner's capacity and professionalism in the work. In the face of decision-making issues such as payment decisions, acceptance decisions for main construction tasks or construction phase transitions, decisions on serious construction site incidents, etc., the owner took a long time for consideration. This delay is causing great hindrance to other parties in the project and delaying the project implementation progress.

Construction project implementation phase is the most resource consuming stage. During the bidding process, contractors were required to have working capital for the project. Advance terms for projects using public investment capital are currently kept at 10-15%. With this advance, the contractor can smoothly implement the project's work. But the reality shows that contractors are heavily dependent on payment for completed works from owners. This reason leads to the late payment by the owner, which will make it difficult for the contractor to pay for the subcontractor, pay for labor and procure materials to prepare for the next work. In addition, accounting for over 80% of projects under medium-term capital, the owner's annual capital plan is approved by the subjective agency. The annual funding plan is often delayed due to many objective reasons from the governing body. This also slows down the solvency of the owner. The combination of reasons that caused the owner to delay payment to the project parties upon completion of the work has a high degree of influence on projects’ progress schedules.

Contractor-related causes (Table 5) are more uniform than other groups. This does not represent low-impact contractor causes. It shows that the causes related to the contractor do have not much difference in the level of influence when making a pairwise comparison between the causes. Therefore, contractors participating in the implementation of construction projects using public investment capital in Hanoi need to pay attention to all the reasons under consideration. It is necessary to pay attention to two issues: the contractor's capacity and project's appropriate construction schedule.

Regarding the construction schedule for the implementation of construction projects: The cause “Inappropriate construction schedule” has a higher weight of influence than other causes (Table 26). According to the survey, participants, in projects using public investment capital, contractors in Hanoi have not paid attention to and properly assessed the role of the project's schedule. Before the contractor starts to implement the project, the contractor will submit the total progress to the supervision consultant, project management consultant and the owner for approval. After being approved, the total schedule is the basis for the parties in the project to have an appropriate arrangement of resources and capital. Also based on the total progress, the monthly schedule and the weekly schedule are detailed. However, these schedule plans are often prepared by a technical staff member who is not yet able to cover the project and understand the contractor's ability to provide resources. The timelines for each work item are set based on the subjective judgment of the scheduler. With short-term progress plans by week, by month, delays in implementation are better controlled, but they are far from the total approved progress schedule. The schedule plan does not take into account the downtime in construction and omitting this time leads to the delay in the progress of the whole project.

It should also be added that the schedule plan made by the contractor without the participation of the owner or the consultant leads to the plans of the parties in the project not matching the actual schedule currently building the project. When there is an adjustment or change in the contractor's progress, the other parties are passive and find it difficult to control their progress schedules.

About the contractor's capacity: Along with progress schedules, the contractor needs to have the right supply of resources. Feedback from the respondents said that over 80% of projects are having problems with providing resources that are not consistent with the project implementation schedule. Over 80% of the projects recorded from the survey occurred the situation of materials and materials arriving at the construction site massively but the workers were not ready to accept the job, the construction equipment was slow to be delivered to the construction site, or the condition of the materials was not ready. Material for a job lacks one type, excess of the other leads to insufficient construction conditions, The supply of human resources for the current projects is also a problem. Construction workers in Hanoi are generally assessed as hardworking people, but their compliance with the work plan is not good, and their work discipline is not appreciated. Construction workers in Hanoi and some neighboring provinces are highly dependent on foreign workers and are affected by the agricultural season. During the seasonal season (October-November crop, May-June crop), workers are difficult to find and often, have a serious reduction in the number of workers at construction sites in Hanoi. During off-season, idle labor is easier to attract for construction projects. A summary of construction sector reports [ 1-3] shows that in 2018, there were 176 projects that were delayed for a long time and 276 projects that had to be adjusted to the total schedule. In 2019, 68 projects were delayed for a long time and 394 projects had to adjust the total progress of construction projects. In 2020, there were 113 projects that were delayed for a long time and 82 projects had to adjust the total schedule.

Besides, the price of raw materials fluctuates unpre- dictably, directly affecting the construction of contractors. Many projects use public investment capital in the form of package contracts, leading to high risks for contractors. Faced with risks, some contractors choose to extend the schedule in the hope that the price of materials decreasing. This is also an issue that can be taken foreseen problem and needs to be resolved in public investment projects.

Reviewing the causes related to the consultant found the cause from the design unit “Details in the design documents are not clear or the design details are not suitable with actual construction conditions” weighted more prominently than other causes (effect weight: 0.51) (Table 27). This also reflects the reality of current Hanoi projects. Over 90% of projects are exposed to design risks at the level of cost and schedule interventions. Errors in the design are often discovered during construction, so they are not proactive in adjusting and approving the adjusted design. This result leads to the problem that design documents playing a very important role in construction projects in Hanoi. The selection of a design consultant should be carefully considered by the owner, and at the same time, strict verification and appraisal are carried out to minimize design risks, thereby avoiding negative impacts from design errors on projects’ progress schedules. Reasons “Poor management and expertise in monitoring” and “Sketch and inaccurate geological survey” have lower weights, scores 0.27 and 0.22 (Table 27), respectively.

In the group of other causes, the cause “Unfortunate weather conditions” has a high weighted score (Table 28). In recent years, climate change has been taking place globally. Hanoi is also affected by this situation. The laws of the weather change in an unusual and difficult to control direction. Flooding occurs when there is heavy rain and storms occur more often. The cause of flooding in Hanoi is analyzed largely because the water surface area and agricultural land area are gradually shrinking under the impact of rapid urbanization. In the period 2015 - 2020, the urban natural water surface area will decrease by 203.63 ha. Many ponds and lakes have been leveled to make land fund for urban development and technical infrastructure, the situation of people encroaching on water surface area for business and exploitation. This causes many difficulties for socio-economic development, as well as the construction sector in Hanoi. Low-base constructions are at risk of flooding, especially in the western part of Hanoi including rural areas located in green belts along river routes. From the survey, there are 5 projects that were forced to adjust the design during construction after considering the issues of climate change. Besides, progress plans in most construction investment projects in Hanoi must be adjusted more or less to adapt to climate conditions.

An issue that needs more attention in public investment projects in Hanoi is that the requirement to accelerate progress schedules is always ignored. The parties in the project are more interested in the project implementation process in accordance with the law than in promoting the project progress. The control of state management agencies through legal documents has not been synchronized and the general model has been inconsistent, which has indirectly affected the progress of construction projects. The binding of the parties on the schedule is not tight. In the contract, there is a term to complete the project, but the project progress is not specified in the contract. The regulations on rewards and penalties for delay are not mentioned or are not strong and it is difficult for the parties to handle the causes of delay.