Detail of the Permanent Facilities for the Scottish Parliament construction site, no temporary facilities are shown

Parliament building under construction

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The construction village therefore starts to grow almost as soon as the contractor charged with the construction works takes possession of the site and the layout of the TF must be planned and executed in such a way that conflicts requiring relocation of the facilities is avoided. Sadeghpour et al (2004) demonstrate, convincingly, that “site layout planning is often ignored in the planning phase of construction projects”. With the cost of providing temporary facilities being as high as 1.8% of the total contract price the benefits of good quality planning can be summarized as follows,

• Travel time can be minimised, this can be operatives travelling to their place of work from the welfare facilities or as specialised as reducing the travelling and waiting time of large earth moving equipment around a site.

•  The interaction between TF and permanent facilities is defined at an early stage and layout changes (which can be common on construction projects due to the variability of ground conditions) can be dealt with as part of a variable planning system. Ma (2004) points out that space conflicts can be resolved by adjusting the construction schedule and layout planning should never be seen as a fixed 2D activity rather that it should be a dynamic activity across the whole 3D site.

• Chaotic sites are best avoided in order to ensure site safety and productive working.

There are currently three schools of thought of how to deal with the task of Construction Village layout design and Scheduling.

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Computer aided drafting and design software is universally used in the modern construction industry, a typical modelling screen is shown on the right figure.

Just as the permanent facilities can be modelled using bespoke and/or off the shelf software it has become clear that the relationships between the TF and the permanent facilities can be analysed using a variety of newly developed algorithms. Any construction village can therefore be modelled as a set of interrelated objects. The main components of such a system consist of Site Objects (SO), Construction Objects (CO) and Constraint Objects (Con.O). Examples of each type could include the following,

A Computer Aided Draft

·       SO – any fixed object on the site whose location is used to fix the location of other objects due to some interrelationship with that object. Existing buildings, structures, power lines would all fall into this category.

·        CO – these are normally defined as object that are movable but occupy some space on the site. Temporary Facilities such as site accommodation, storage space, workrooms, plant rooms and even parking facilities may be defined as CO. It is important to note that the efficient layout of these CO is the objective function of any site planning process.

·        Con.O – The relationships between the SO and CO are modelled using constraint rules. When the objective function is minimised and the Con.O is/are satisfied then an optimum solution has been reached. These rules however, are dependent upon the skills and experience of the planning engineers who contribute to the knowledge base of the software. As a method of overcoming bias, weighting is applied to the relationship, specifically those dealing with locating rules, again based on the experience of planning engineers. The knowledge base should be modelled in a dynamic way that allows continual expansion and modification of the weighting rules based on developing experience of successful projects. Constraints can exist between a CO and a SO or between CO. Sadeghpour et al (2004) gives a simple example of a constraint existing between the distance to the parking area from the site offices in a construction village. This is an example of a CO-CO constraint and the intention of the model proposed by Sadeghpour et al (2004) is that planning engineers will be able to use the modelling system to avoid inefficient, and potentially dangerous, site layouts. 

The application of this modelling system to the concept of a construction village is clearly demonstrated with the numerical analysis presented by Sadeghpour et al (2004) which examines the placing of four forms of TF, namely temporary offices, reinforcement store, concrete batching plant and a general store. Four different layouts were analysed using an objective function minimising algorithm and high levels of agreement were found with the work of other authors in the field but for one new (previously unanalysed) layout a superior layout was proposed having the best (i.e. lowest) objective function.

The objective function presented is the weighted travelling distance expressed as,

 Where X_i and Y_i are the coordinates of the centroid of the j th construction object and W_ij is the weight of the closeness relationship between the i th and j th objects.

The advantages of a well defined CAD modelling system are that flexible support can be provided for planners to develop a wide range of objects for use on construction sites. Feedback is continuous and models can be updated and refined as model libraries expand but this is dependent on a rigorous regime for recording project progress and efficiency. Planning engineers will therefore be able to bring their expertise to bear in the initial development phase of the modelling system and also have an input into the ongoing development of the modelling system. Simple geometric examples of site layouts can be quickly produced and analysed facilitating the development of the final layout of the construction village.

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Traditional construction site planning systems suffer from the fact that site planning, including the layout of the construction village, is essentially a three dimensional (3-D) process. As the 1990’s progressed digital computing power increased to such an extent that dynamic linkage of the work schedule with the site planning process finally became feasible and true 4-D planning systems were commercially available. These applications can be used in a predictive manner allowing many of the problems inherent in construction village layout planning to be investigated taking into account the changes necessary in the village as the contracted works proceed. The algorithms used to manage layout of the temporary facilities can be integrated with 4-D planning software to achieve a management layout and control package that will analyse and control the three main phases of any construction contract: 

1. Groundworks and Foundation construction.

2. Superstructure construction and

3. Internal fitting out work.

One limitation of existing 4-D planning processes is that the situation whereby the temporary facilities are located inside that, not yet complete final structure, are difficult to model and manage but nonetheless this approach often yields the optimum solution to construction village layout problems especially in inner city commercial developments. The ability of 4-D planning systems to adjust the construction schedule (ideally within the total floats of the individual activities) to alleviate construction conflicts is therefore crucial.

The conflicts are clearly shown on such charts and these conflicts may be space related, resource related (or some combination of the two) and because the site layout is not treated as some entity that is fixed in space and time it is possible to apply a range of modern tools to analyse the problems i.e.

1.       Artificial neural networks

2.       Expert systems

3.       Genetic algorithms

4.       Hybrid intelligence

Ma et al (2005) describe the key benefits of 4-D modelling systems succinctly and may be paraphrased as follows,

·         Space utilisation inside multi storey buildings is enabled and the efficiency of projects is greatly enhanced.

·         Schedule data is provided at much greater speeds than was previously available.

·         Consistency between schedules and 3-D models are implicitly achieved by ensuring that data exchange between the scheduling and CAD libraries is bidirectional.

The main difficulties that are apparent in 4-D modelling software is that dynamic allocation of site plant is not yet achievable and there is, as yet, no industry standard for data exchange between software. It would seem that both problems are not insurmountable as satellite tracking becomes ever more affordable and accurate whilst the dominance of AutoCAD continues unabated current research is ongoing investigating potential interfacing of these existing tools.

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Most construction projects still rely heavily on paper based communication of technical material in the form of working drawings.

Planning staff of the construction contractor may be required to interpret this information and then, assuming unlimited resources (men, machines and materials) formulate some type of scheduling scheme for the project. The schedule is then refined using knowledge of working capacities and outputs and the site layout is decided at this stage and tends to be largely dependent on the project working schedule. Site layout drawings that are prepared at this stage are rarely (often never) updated as the work proceeds consequently they are virtually separated from the more dynamic planning and scheduling system (Chau et al, 2003).

A 3-D geometrical model of a construction project (inclusive of all TF) is prepared at the same time as the planning engineers construct the associated construction schedule and a 4-D site management model is implemented which then has the functionality of being able to perform site management functions over the spatial and temporal domains. This system (4-D Site Management Model) then incorporates the whole spectrum of site management activities incorporating, construction planning, resource analysis, site layout generation and management, material allocation and cost control. The key features of such a visualisation system are said to be.

 (1) Conventional site planning - The conventional site management procedure including the construction schedule and a graphical site layout facility, which are already used by site planners, are included in the 4DSMM as far as practicable. In prototype systems, the bar charts representing the project schedule and the graphical site plan drawing can be generated, modified and displayed in a convenient fashion.

(2) Representation of 3D geometrical model - Based on the geometrical data input by the planning engineers together with the graphical user interface (GUI), 4DSMM’s are able to produce 3D models of the construction project and permit the visualization of almost all 3D model components from different viewing angles.

(3) 4D visualization - The 4D simulation for a specific construction project can be generated automatically by integrating the 3D geometrical model with the associated activity schedule. Using this modelling technique, the visualization of ongoing building construction at an individual activity level together with the 3D site space utilization at any specific temporal instant can be displayed moving forward or backward within the temporal window under consideration.

(4) Integration of symbolic and graphical data - One of the key characteristics of a 4DSMM is to evaluate the resource requirements including 1abour, material and plant with the ability to assess the corresponding cost for a specific temporal period through the integration of symbolic and graphical data. The model should be able to compare and rank different construction plans via the, ever expanding, knowledge base of the 4DSMM.

(5) Linkage between geometrical model and schedule – Using a 4DSMM the linkage between the 3D geometrical model and the project schedule is designed to be bidirectional. Consequently the user can modify the construction plan through the 3D graphical environment or through the conventional bar chart scheduling environment. Consider the theoretical situation whereby certain construction activity in the 4D simulation of a construction project is modified graphically on the screen, the bar schedule for that specific activity will be automatically adjusted in a synchronized manner. Due to the bidirectional nature of the software linkage then if the project schedule were to be altered, the corresponding 4D model will be modified simultaneously and automatically. Moreover, if either one of the aforementioned modifications takes place, the estimate of allocation of limited resource requirements will also be updated to reflect the current scenario.

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Commercially developed software that integrates management techniques with the ongoing progress of construction contracts is now becoming widely available. The crucial aspect of the planning process that was often dealt with poorly or in an ad hoc manner i.e. the planning of the layout of the construction village is now recognised as having a significant bearing on the profitability of construction contracts. As margins have become ever tighter (2-3% is not considered unusual) focus has shifted to ensuring that every aspect of the construction contract is planned and executed efficiently. The energy usage aspects of construction villages that are dealt with elsewhere in this report are vital in controlling cost and in reducing carbon emissions (which can, of course, be seen as another form of cost, an environmental cost which may well turn out to be directly taxable by central government) but it is every bit as important to ensure that as large a slice as possible of the 1.6% (on average) of the contract cost that is spent on temporary facilities is spent efficiently and wisely.

The planning systems investigated in the text above would be of great benefit in achieving this and it would seem likely that the capital cost of implementing such a system, in a large organisation, would be recouped very quickly. Computing costs have fallen markedly in recent years and as this trend looks likely to continue the problems identified by researchers in the field (too little computing power available) are already unlikely to have an adverse effect on the implementation of a 4DSMM for example.

Future research should focus on how plant can be controlled efficiently and utilised in the most effective manner by integrating real time tracking of the plant and its associated activities with the work breakdown scheme for each activity so that the 4DSMM becomes all encompassing. The real time tracking of staff and operatives is undoubtedly a much more problematic area! 

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CHAU, K.W., ANSON, M. and ZHANG, J.P., 2003. Implementation of visualisation as planning and scheduling tool in construction. Building and Environment, 38, pp. 713-719.

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