Question

Discuss and explain the operational techniques required for the execution of civil works construction works?

Answer 1

Operational techniques required for the execution of civil works

Construction planning is fundamental in the management and execution of construction projects, it involves many things like

• Choice of technology
• kind of work tasks
• Estimation of the required resources
• Durations for individual tasks
• Identification of any interactions among the various work tasks

A good construction works based on proper planning and budget management. Developing the development plan may be a critical task within the management of construction, albeit the plan isn't written or otherwise formally recorded. In addition to those technical aspects of construction planning, it's going to even be necessary to form organizational decisions about the relationships between project participants and even which organizations to include in a project. For example, the extent to which subcontractors are going to be used on a project is usually determined during construction planning.

Construction planning is mainly based on 2 aspects

1. Cost oriented

In this construction planning is cost or expense oriented. Within this category a distinction is made between costs incurred directly in the performance of an activity and indirectly for the accomplishment of the project.

For example, borrowing expenses for project financing and overhead items are commonly treated as indirect costs where buying materials and labour cost are considered as direct cost

2. Schedule oriented

Scheduling of work activities with respect to time is critical and is emphasized in the planning process. In this case, the planner ensures that the proper precedences among activities are maintained and that efficient scheduling of the available resources prevails.

there are two ways in scheduling program

1. critical path scheduling procedures - By the maintenance of task precedences
2. job shop scheduling procedures - Efficient use of resources over time.

Finally, most complex projects require consideration of both cost and scheduling over time, so that planning, monitoring and record keeping must consider both dimensions. In these cases, the integration of schedule and budget information is a major concern

Choice of Technology and Construction Method

The Choices of appropriate technology and methods for construction are often ill-structured yet critical ingredients in the success of the project. For example, a decision whether to pump or to transport concrete in buckets will directly affect the cost and duration of tasks involved in building construction. A decision between these two alternatives should consider the relative costs, reliabilities, and availability of equipment for the two transport methods. Unfortunately, the exact implications of different methods depend upon numerous considerations for which information may be sketchy during the planning phase, such as the experience and expertise of workers or the particular underground condition at a site.

Real-life examples :

1. A roadway rehabilitation: An example from a roadway rehabilitation project in Pittsburgh, PA can serve to illustrate the importance of good construction planning and the effect of technology choice. In this project, the decks on overpass bridges as well as the pavement on the highway itself were to be replaced. The initial construction plan was to work outward from each end of the overpass bridges while the highway surface was replaced below the bridges. As a result, access of equipment and concrete trucks to the overpass bridges was a considerable problem. However, the highway work could be staged so that each overpass bridge was accessible from below at prescribed times. By pumping concrete up to the overpass bridge deck from the highway below, costs were reduced and the work was accomplished much more quickly.
2. Laser Leveling: An example of technology choice is the use of laser leveling equipment to improve the productivity of excavation and grading. In these systems, laser surveying equipment is erected on a site so that the relative height of mobile equipment is known exactly. This height measurement is accomplished by flashing a rotating laser light on a level plane across the construction site and observing exactly where the light shines on receptors on mobile equipment such as graders. Since laser light does not disperse appreciably, the height at which the laser shines anywhere on the construction site gives an accurate indication of the height of a receptor on a piece of mobile equipment. In turn, the receptor height can be used to measure the height of a blade, excavator bucket or another piece of equipment. Combined with electro-hydraulic control systems mounted on mobile equipment such as bulldozers, graders, and scrapers, the height of excavation and grading blades can be precisely and automatically controlled in these systems. This automation of blade heights has reduced costs in some cases by over 80% and improved quality in the finished product, as measured by the desired amount of excavation or the extent to which a final grade achieves the desired angle. These systems also permit the use of smaller machines and less skilled operators. However, the use of these semi-automated systems requires investments in the laser surveying equipment as well as modification to equipment to permit electronic feedback control units. Still, laser leveling appears to be an excellent technological choice in many instances.

Defining Work Tasks

At the same time that the choice of technology and general method are considered, a parallel step in the planning process is to define the various work tasks that must be accomplished. These work tasks represent the necessary framework to permit scheduling of construction activities, along with estimating the resources required by the individual work tasks, and any necessary precedences or required sequence among the tasks. The terms work "tasks" or "activities" are often used interchangeably in construction plans to refer to specific, defined items of work. In job shop or manufacturing terminology, a project would be called a "job" and an activity called an "operation", but the sense of the terms is equivalent. The scheduling problem is to determine an appropriate set of the activity start time, resource allocations, and completion times that will result in the completion of the project in a timely and efficient fashion. Construction planning is the necessary forerunner to scheduling. In this planning, defining work tasks, technology, and construction method is typically done either simultaneously or in a series of iterations.

The definition of appropriate work tasks can be a laborious and tedious process, yet it represents the necessary information for the application of formal scheduling procedures. Since construction projects can involve thousands of individual work tasks, this definition phase can also be expensive and time-consuming. Fortunately, many tasks may be repeated in different parts of the facility, or past facility construction plans can be used as general models for new projects. For example, the tasks involved in the construction of a building floor may be repeated with only minor differences for each of the floors in the building. Also, standard definitions and nomenclatures for most tasks exist. As a result, the individual planner defining work tasks does not have to approach each facet of the project entirely from scratch.

While repetition of activities in different locations or reproduction of activities from past projects reduces the work involved, there are very few computer aids for the process of defining activities. Databases and information systems can assist in the storage and recall of the activities associated with past projects . For the scheduling process itself, numerous computer programs are available. But for the important task of defining activities, reliance on the skill, judgment and experience of the construction planner is likely to continue.

More formally, an activity is any subdivision of project tasks. The set of activities defined for a project should be comprehensive or completely exhaustive so that all necessary work tasks are included in one or more activities. Typically, each design element in the planned facility will have one or more associated project activities. Execution of activity requires time and resources, including manpower and equipment, as described in the next section. The time required to perform an activity is called the duration of the activity. The beginning and the end of activities are signposts or milestones, indicating the progress of the project. Occasionally, it is useful to define activities that have no duration to mark important events. For example, receipt of equipment on the construction site may be defined as an activity since other activities would depend upon the equipment availability and the project manager might appreciate formal notice of the arrival. Similarly, receipt of regulatory approvals would also be specially marked in the project plan.

The extent of work involved in any one activity can vary tremendously in construction project plans. Indeed, it is common to begin with fairly coarse definitions of activities and then to further sub-divide tasks as the plan becomes better defined. As a result, the definition of activities evolves during the preparation of the plan. A result of this process is a natural hierarchy of activities with large, abstract functional activities repeatedly sub-divided into more and more specific sub-tasks. For example, the problem of placing concrete on site would have sub-activities associated with placing forms, installing reinforcing steel, pouring concrete, finishing the concrete, removing forms and others. Even more specifically, sub-tasks such as removal and cleaning of forms after concrete placement can be defined. Even further, the sub-task "clean concrete forms" could be subdivided into the various operations:

• Transport forms from on-site storage and unload onto the cleaning station.
• Position forms on the cleaning station.
• Wash forms with water.
• Clean concrete debris from the form's surface.
• Coat the form surface with an oil release agent for the next use.
• Unload the form from the cleaning station and transport it to the storage location.

This detailed task breakdown of the activity "clean concrete forms" would not generally be done in standard construction planning, but it is essential in the process of programming or designing a robot to undertake this activity since the various specific tasks must be well defined for a robot implementation.

Defining Precedence Relationships Among Activities

Once work activities have been defined, the relationships among the activities can be specified. Precedence relations between activities signify that the activities must take place in a particular sequence. Numerous natural sequences exist for construction activities due to requirements for structural integrity, regulations, and other technical requirements. For example, design drawings cannot be checked before they are drawn. Diagrammatically, precedence relationships can be illustrated by a network or graph in which the activities are represented by arrows . These arrows are called branches or links in the activity network, while the circles marking the beginning or end of each arrow are called nodes or events. In this figure, links represent particular activities, while the nodes represent milestone events.

More complicated precedence relationships can also be specified. For example, one activity might not be able to start for several days after the completion of another activity. As a common example, concrete might have to cure (or set) for several days before the formwork is removed. This restriction on the removal of forms activity is called a lag between the completion of one activity (i.e., pouring concrete in this case) and the start of another activity (i.e., removing formwork in this case). Many computer-based scheduling programs permit the use of a variety of precedence relationships.

Three mistakes should be avoided in specifying predecessor relationships for construction plans. First, a circle of activity precedences will result in an impossible plan. For example, if activity A precedes activity B, activity B precedes activity C, and activity C precedes activity A, then the project can never be started or completed.

Example : Precedence Definition for Site Preparation and Foundation Work

Suppose that a site preparation and concrete slab foundation construction project consists of nine different activities:

A. Site clearing (of brush and minor debris),
B. Removal of trees,
C. General excavation,
D. Grading general area,
E. Excavation for utility trenches,
F. Placing formwork and reinforcement for concrete,
G. Installing sewer lines,
H. Installing other utilities,
I. Pouring concrete.

Activities A (site clearing) and B (tree removal) do not have preceding activities since they depend on none of the other activities. We assume that activities C (general excavation) and D (general grading) are preceded by activity A (site clearing). It might also be the case that the planner wished to delay any excavation until trees were removed, so that B (tree removal) would be a precedent activity to C (general excavation) and D (general grading). Activities E (trench excavation) and F (concrete preparation) cannot begin until the completion of general excavation and tree removal, since they involve subsequent excavation and trench preparation. Activities G (install lines) and H (install utilities) represent installation in the utility trenches and cannot be attempted until the trenches are prepared, so that activity E (trench excavation) is a preceding activity. We also assume that the utilities should not be installed until grading is completed to avoid equipment conflicts, so activity D (general grading) is also preceding activities G (install sewers) and H (install utilities). Finally, activity I (pour concrete) cannot begin until the sewer line is installed and formwork and reinforcement are ready, so activities F and G are preceding. Other utilities may be routed over the slab foundation, so activity H (install utilities) is not necessarily a preceding activity for activity I (pour concrete). The result of our planning are the immediate precedences shown in Table below.

With this information, the next problem is to represent the activities in a network diagram and to determine all the precedence relationships among the activities. in which the activities appear as branches or links between nodes. The nodes represent milestones of possible beginning and starting times. This representation is called an activity-on-branch diagram.

Node 0 - start of activity

Node 5 - end of all activity

It can also be tabulated as

Estimating Activity Durations

All formal scheduling procedures rely upon estimates of the duration of the various project activities as well as the definitions of the predecessor relationships among tasks. The variability of an activity's duration may also be considered. Formally, the probability distribution of an activity's duration as well as the expected or most likely duration may be used in scheduling. A probability distribution indicates the chance that a particular activity duration will occur. In advance of actually doing a particular task, we cannot be certain exactly how long the task will require.

A straightforward approach to the estimation of activity durations is to keep historical records of particular activities and rely on the average durations from this experience in making new duration estimates. Since the scope of activities are unlikely to be identical between different projects, unit productivity rates are typically employed for this purpose. For example, the duration of an activity Dij such as concrete formwork assembly might be estimated as:

where Aij is the required formwork area to assemble (in square yards), Pij is the average productivity of a standard crew in this task (measured in square yards per hour), and Nij is the number of crews assigned to the task. In some organizations, unit production time, Tij, is defined as the time required to complete a unit of work by a standard crew (measured in hours per square yards) is used as a productivity measure such that Tij is a reciprocal of Pij.

Random factors will also influence productivity rates and make an estimation of activity durations uncertain. For example, a scheduler will typically not know at the time of making the initial schedule how skillful the crew and manager will be that are assigned to a particular project. The productivity of a skilled designer may be many times that of an unskilled engineer. In the absence of specific knowledge, the estimator can only use average values of productivity.

Coding Systems

One objective in many construction planning efforts is to define the plan within the constraints of a universal coding system for identifying activities. Each activity defined for a project would be identified by a pre-defined code specific to that activity. The use of a common nomenclature or identification system is basically motivated by the desire for better integration of organizational efforts and improved information flow. In particular, coding systems are adopted to provide a numbering system to replace verbal descriptions of items. These codes reduce the length or complexity of the information to be recorded. A common coding system within an organization also aids consistency in definitions and categories between projects and among the various parties involved in a project. Common coding systems also aid in the retrieval of historical records of cost, productivity and duration on particular activities. Finally, electronic data storage and retrieval operations are much more efficient with standard coding systems.