Change is the basic feature of contract performance, and it is also an important content of contract law regulation. Contract changes involved in contract law can be divided into broad sense and narrow sense. In a broad sense, contract change includes the change of contract content and the change of contract subject, while in a narrow sense, contract change only refers to the change of contract content. In principle, contract changes are valid for the future. The rights and obligations that have not been changed continue to be valid, and the debts that have been performed do not lose their legal basis because of the change of the contract.
During the performance of the construction contract, there are also a lot of engineering changes. There are not only traditional engineering changes in the form of engineering change orders, but also engineering changes passively formed by factors such as owner's breach of contract and force majeure. Domestic researchers are usually more accustomed to regard the late stage of project change as the content of project claim. 1994, semple, a foreign engineering management scholar, defined the claim as a very serious destructive engineering change after inspecting 24 controversial engineering projects in western Canada. [1] The change of FIDIC construction contract conditions usually includes the following contents:1) the change of engineering quantity of any work content included in the contract; 2) Changes in the quality or other characteristics of any work content; 3) Changes in elevation, position and/or size of any part of the project; 4) Delete any works except those to be handed over to others; 5) Any additional work, production equipment, materials or services required for the permanent project, including any related completion test, drilling and other testing and exploration work; 6) Changes in project implementation sequence or progress [2].
Because of the influence of engineering change on engineering construction, researchers at home and abroad have carried out a lot of research work on engineering change, and put forward many control methods of engineering change, such as program control, strengthening supervision system, strengthening the management and guidance of decision makers on investment behavior [3]. The American Institute of Building Industry and other institutions have also appointed a number of engineering change managers to quantitatively study the impact of engineering changes on the project and the nature of changes, and put forward many constructive change management methods [4]. However, due to the complexity of engineering changes, there is still a lack of systematic research on controlling engineering changes from technical means, economic means and legal means. Therefore, it is of great practical significance to strengthen the study of change control in construction contracts.
1 Classification and characteristics of engineering changes
1. 1 engineering change classification
According to the specific content of engineering changes, it can be divided into the following five categories: 1) design changes; 2) Construction scheme change; 3) plan change; 4) change of conditions; 5) New projects.
1. 1. 1 design change
Design change refers to the engineering change instructions put forward by different project participants during the performance of the construction contract, and finally released by the design unit in the form of design change or design supplementary documents. Design change contains a wide range of contents, which is the main content of engineering change, accounting for more than 70% of the total engineering change. Common design changes include: design change notice due to design calculation error or graphic error, design supplementary notice due to design omission or insufficient design depth, and design optimization and adjustment at the request of the owner, contractor or supervisor.
1. 1 .2 construction scheme change
The change of construction scheme refers to the process that the contractor proposes to the supervision engineer and the owner to change the original construction measure scheme due to the change of engineering geological conditions, construction environment or construction conditions. The change of construction measures shall be implemented after the approval of the supervision engineer and the owner, otherwise the cost increase and time delay caused by it shall be borne by the contractor. Changes in major construction measures should also seek the opinions of the design unit. During the performance of the construction contract, the change of construction scheme exists in the whole process of construction. If the underground quicksand layer or silt layer appears in the process of excavating the pile hole of manual digging pile, special support measures need to be taken before the construction can continue; In the process of subgrade excavation of highway or municipal road engineering, if underground cultural relics are found, the operation must be stopped and special protective measures must be taken; In the process of building main body construction, the substitution of different specifications and models of materials caused by market reasons and so on.
Conditions change
Condition change refers to the failure of the owner to provide the necessary construction conditions as agreed in the contract, and force majeure occurs during the construction process, resulting in the failure to implement the project as scheduled. If the subsequent construction drawings of the project promised by the owner have not arrived, the project will be stopped halfway, and the temporary construction electricity provided by the owner will be cut off due to the shortage of social power grid, which will lead to the failure of construction production; Heavy rain or landslides caused the project to stop working. Engineering changes caused by the owner's reasons or force majeure are collectively referred to as condition changes.
1. 1 .4 plan change
Plan change refers to the owner's adjustment of the original construction schedule to change the construction sequence and time schedule during the construction process due to instructions from superiors, technical factors or business needs. For example, in the construction of residential projects, according to the sales progress, some houses need to be completed ahead of schedule, while others need to be delivered properly. This change is a typical plan change.
1. 1 .5 new project
The new project refers to the construction process, the industry actively uses the provisional amount to expand the construction scale and increase the construction content other than the original tender bill of quantities.
1 .2 characteristics of engineering change
According to the characteristics revealed by a large number of engineering changes in engineering practice, various common engineering changes can be described from five different levels: controllability, technology, stage, frequency and source, as shown in Table 1.
As can be seen from the table 1, the controllability of design changes and construction scheme changes is strong, while the controllability of other changes is general or weak. From a technical point of view, design changes are highly technical, followed by construction scheme changes, and other changes are weak. From the stage analysis, the general housing construction engineering changes and construction scheme changes are highly controllable, while other changes are generally or weakly controllable. From a technical point of view, design changes are highly technical, followed by construction scheme changes, and other changes are weak. From the stage analysis, the design changes and construction scheme changes of general housing construction projects cover the whole process of project construction, and the rest mainly occur in the construction stage and decoration construction stage of the main project. From the frequency of occurrence, the design change is the highest, the construction drawing change is the second, and the other changes are low. From the source of change, that is, the subject who proposed (or caused) the change, the scope of design change is the widest, and the owner, contractor, supervisor and designer can all propose design change requirements, while the construction scheme change is usually proposed by the contractor, the scheme change and new project are generally proposed by the owner, and the condition change is usually caused by the owner or force majeure.
2 engineering change control procedures and principles
2. 1 engineering change control procedure
From the characteristics of the discussed engineering changes, it can be seen that among the five common types of engineering changes, design changes and construction scheme changes occur frequently and have a great impact on the engineering cost, which is the focus of contract control. With regard to design changes, both the owner and contractor, the supervisor and the designer control the design changes proposed by their respective project managers. Under the current bidding mode of construction project bill of quantities, the reasonable low price method after evaluation is the basic method for owners to select contractors in the project bidding stage. In order to win the bid, the contractor usually only chooses the route with low price, and once winning the bid, the design change becomes an important way for the contractor to adjust the comprehensive unit price of its bill of quantities. Therefore, strengthening the control of the changes proposed by the contractor is the top priority of contract control. The standard control procedure of engineering change proposed by the construction contractor is shown in figure 1.
2 .2 Engineering change control principles
2 .2. 1 double effect principle
Double-effect principle is an engineering change control principle based on efficiency principle and benefit principle.
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