Consideration between Site Layout Facilities, Provision of Work Equipments and Construction Planning for Extremely Large and Complicated Construction Projects

The effectiveness in site layout and construction planning for extremely large-scale and complicated construction projects not only affects productivity and cost, it also controls whether a project can be handled and completed in a practical, safe, orderly, efficient and engineering feasible manner. Projects qualified to be extremely large and complicated can be in a variety of forms. Take for examples in Hong Kong’s situation. Construction cost of projects sometimes exceeds billions of dollars. Site covers more than a few hectares of land with building areas in term of hundred thousands square meters. Or, projects sometimes involve the construction of super high-rise buildings with more that 60 or 70 storeys in height. This kind of building development projects, very often, consists of a number of annexed facilities such as a very deep basement, or a podium with very large interior space and long-span elements. Special structures like buildings constructed in structural steel or in composite manner. Some projects are located within very congested urban environment, or located in close proximity to steep slope, or adjacent to sensitive facilities like underground tunnels. In case of civil engineering projects, sometimes they also involve special provisions, diversion and interfacing arrangement to very busy servicing traffic and other urban facilities. This paper will identify various types of construction cases qualified to be of extremely large and complicated nature under the built environment of Hong Kong. The paper will also illustrate how builders solve such problems using innovative methods. Relevant brief case examples from civil engineering works in particular for transportation facilities will also be referred in order to substantiate the explanation of the subject matter. c) Items or facilities that are required for the overall site logistics, operation and management such as site entrance provision, site office, meeting or conference areas, supply and routing of essential services, site laboratory, or other security provisions. d) Items that are statutory required for the carrying of the construction works such as fencing or hoarding, signage, wheel washing facility; equipment for waste disposal, water treatment, noise and dust control, or arrangement for temporary traffic diversion etc. These facilities usually have specific work targets or operation nature, however, they still have the following characteristics in common: a) Essential or not easy to be substituted for the carrying out of the specific construction works, b) Fairly temporary in nature, c) The positioning of these facilities often affects the efficiency of the construction in particular when they are not properly located, d) The positioning of the facilities often occupy significant work spaces and may affect the regular progress of other major activities, e) Often required to be relocated to meet the advancement of works or progress of construction, f) Some of these facilities may have very important operational, structural or safety concerns, g) The provision, installation and maintenance of these facilities can be quite timely and costly thus the providing, relocating, maintaining or dismantling of these facilities should be planned in a very careful manner in order not to interrupted with the master planning of the construction works. 2 INTRODUCTION PROVISION OF SITE LAYOUT FACILITIES Provision of site layout facilities can be further classified according to stages of construction and types of project. Below are some of the examples of these classifications and provisions. A. Provision of site layout facilities according to stages of construction a) At the commencement of the construction project Site layout facilities to be set-up at this stage usually include provisions that must be provided before the effective carrying out of other major construction works, or other work items that are required by the concerning statutory requirements. These facilities include, for example, the site fencing, supply and routing of water, surface drainage system, forming and arrangement of access routing, setting up of site offices, arrangement for the delivery and positioning of the essential work equipments, and other provisions as required by relevant statutory requirements. b) At the peak period of the construction project when the permanent structural works are to be carried out. Facilities to be set-up at this stage are more specific for the carrying out of particular works, some of them are more temporary in nature. Examples of these facilities include the tower crane, workers lift, material hoist, access provision to working fronts, work scaffold, temporary platform, falsework or additional support to the required structures, and other equipments or mounting up which are required for the external works of the building such as a power wincher system for the installation of curtain wall units which is operated on a temporarily provided track rail. c) At the final stage of the project when the touching up, finishing works or other handing over arrangement are to be carried out. At this stage of construction majority of the site layout facilities are required to dismantle and remove from site. For some particular equipments or facilities, some kind of additional provisions may be required to assist in the dismantling of them. For example, a winching machine and a lifting rod may be erected and set on the roof level to help the dismantling of a tower crane and lowering its components down to the ground level for removal. And of course, provision for the touching up of the disturbed areas after the dismantling and removal of the facilities is also required. B, Provision of major site layout facilities according to types of construction Site layout facilities is relatively a general term for the setting up and operation of a construction site for the nature, scale and type of works diversify greatly from project to project. Situation for building projects is relative much simpler when compare to civil projects. Below are the highlights of some of their feature according to the types of construction. a) Building projects involve the construction of super high-rise tower/s in a relatively confined site. The site layout facilities for this kind of projects, for example, include: (i) Facilities and work spaces for the delivery of construction materials or placing of concrete, (ii) tower crane, mainly to assist work activities on floor-top work front, Photo 1 – Tower crane used in high-rise building construction projects can be mounted in a number of ways. This photo shows a climbing crane used in the construction of a steel frame building. (iii) hoisting equipment (for delivery of materials or components to structurally completed floors), (iv) handling spaces for building materials and semi-completed components including precast items, (Photo 2) Photo 2 – Storage of material can be very difficult for single tower type high-rise building. This photo shows the temporary storing of semi-prefabricated steel components on partially completed steel floor beams Photo 3 – Delivery and storage of precast components for congested site can be very difficult in particular when the sequence of installation is taken into consideration. (v) loading platform on intermediate floors for the removal of materials such as formwork panels or propping components to other floors, (vi) temporary workers hoist or lift, (vii) safety provisions in particular setting up to prevent workers or materials falling from height etc. b) Large-sized building projects in particular with very large site area or involves works on site with complicated shape or layout. This includes, for example, deep and large-scale excavation, work adjacent to slope or sensitive structures either at grade or underground. The involved facilities for this kind of project, for example, include: Photo 4 – Super-sized building site (the International Finance Centre) with major excavation for basement construction and other associated work activities in various locations carried out at the same time. Photo 5 – Another super-sized project example located on sloping site with site formation, cut-off walling and foundation works carried out at the same time. Site access is a primary problem in the project. (i) Similar to site layout facilities as described in the above but with the addition of some other facilities such as access road and equipments for site internal transportation. (ii) Set-up for temporary shoring works for the protection of deep excavation, slope cutting or sensitive structure. Photo 6 – A commercial development located in congested built-up area with the basement work in the peak period. Complicated shoring and ground supporting works can idle a congested site for months unless stringent site layout planning arrangement is introduced (iii) Involve the construction of a large-size and deep basement using sophisticated method such as in top-down or other hybrid approach. Photo 7 – Special layout and equipments provision for the construction of large-size basement is required such as the use of a spoil removal hoist in this 5-level basement constructed in top-down method. (iv) Handling or storage area in particular for intermediate materials handling purposes. (v) Waste water treatment facilities due to the collection of surface or construction waste water from the large area of site. (vi) Other environmental protection related facilities such as dust screen, catch fan or noise barrier. (c) Various types of large-scale and complicated civil projects. Examples of these types of projects include site formation, slope treatment, marine works, water supply or drainage works, highways projects, railway construction, tunnel works, bridge construction, and other infrastructure development projects. Site layout provisions for civil work projects are often in a highly dynamic nature due to the involved works are mainly in a horizontallyspread layout without a lot of tall and independent structures. Equipments or facilities involved are usually different for various kinds of civil works but in general they are very heavy duty in nature for the requirement to handle huge amount of materials or very heavy components, or for the supporting of very large loading. Very large operating space and additional equipments are normally required for the erection, maneuvering, operation and dismantling of these facilities. Below are some of the examples of these facilities that are used in civil engineering works: (i) Temporary accesses for work machines or manual workers. These accesses can be erected over water, over large area of undulated surfaces, down to deep excavation pits, climb to great height or span between very tall structures (e.g. bridge towers), or provide access to very steep slope. Photo 8 – The construction of a 1.2 km-long temporary ramp above sea surface to facilitate the construction of the bridge piers for an elevated expressway.. Photo 9 – Provision of a steel ramp from the portal area down into a tunnel constructed using drill-and-blast method. (ii) Equipments and provisions for the transportation and lifting of bulky or very heavy materials such as excavated spoil materials, structural steel, precast or semi-completed components. These materials sometimes can weigh up to hundreds of tons. The involved equipments, for example, can be various types of work machines for earthwork, conveyor systems, cranes, launching equipment, portal frame, hydraulic trolley or jack systems etc. Sometimes, such provisions may even include the setting up of temporary unloading facilities such as a pier for marine works or for the delivery of large and heavy materials transported to site by sea. And of course, an appropriate access routing should also be provided for the working and handling of these equipments. (iii) Falsework system for various purposes such as support for temporary work platform for machine stationing, for material handling and storage, provision of additional work spaces (elevated or suspended), for the support of long-span reinforced concrete structure which is constructed in insitu manner, support for a working platform over an open-cut basement excavation pit, or as support to freshly concreted structure preparing for the temporary placing of additional loadings etc. Photo 10 – Typical falsework arrangement erected for the support of a pier head for the construction of a section of viaduct. Note that part of the system is erected over a section of water channel. (iv) Site layout and equipments for large scale earthworks, site formation or foundation works. A large number of very large work machines such as excavating machines, graders, rock crushing machines, dumper trucks, conveyor system, drilling equipments, piling rack or foundation equipments for large diameter piles are involved in these kind of projects. These equipments are often required to work in difficult typographic condition where access problem for both delivery of the machine or the removal of excavated spoil away from the work spot always exist. They will be stationed in one location within a short period and required to be removed at the earliest time when the work has been completed for the onward progress of the other works. Photo 11 – The use of large-sized foundation machine such as the Reverse Circulation Drill to form large diameter bored pile occupies a large operation space including areas for the working of the associated equipments. Photo 12 – Large-scale site formation project often involed a number of heavy equipments such as dumper trucks, excavating, drilling or crushing machines. It may take years to complete and a realistic site layout planning is important for this kind of project. (v) Equipments for specialized construction works such as launching gantry for the construction of viaduct or elevated bridges, tunnel boring equipments including the tunnel boring machine (TBM), traveling formwork systems or equipments for tensioning works etc. These equipments have a lot of common features. They are usually very large sized and in very heavy weight. They require very long time and large working space to erect, place to the required location to commence work, or require additional equipments to erect them or when they are to be dismantled. Photo 13 – Erection of a launching gantry in a highway project which took 2 months and a 3000 m2 work area for the completion of the works. Photo 14 – Installation of a medium-sized tunnel boring machine at the portal of a tunnel. The portal at a later stage will serve also as an depot and materials handling area, as well as an important transport route to support the tunnleing works. (vi)Provision for diversion works in particular to traffic or other major services located both above or underground. The involvement of this kind of works usually contains a number of temporary provisions such as the temporary closure of some existing facilities, providing of the temporary replacing facilities, coordinate with the related agents for the diversion works, controlling and monitoring of the facilities throughout the process, or to reinstate the items to meet the future conditions etc. The said diversion works may be carried out on ground surface, underground or even over water. Typical examples such as the diversion of box-culvert (large-size underground water discharge system) in reclamation projects, or to construct a section of railway tunnel under existing busy road surface, can be often found in civil work in the built-up area of a city. Photo 15 – Construction of a section of elevated bridge using precast box-girder within a busy highway network in which complicated traffic diversion arranged in various phases were required. Photo 16 – An extremely complication diversion arrangement for a large storm water discharge in newly reclaimed area. Tunnel tube for a new railway line will be constructed under the new discharge culvert system.. 3 CONCERNS AND RELATIONSHIP OF SITE LAYOUT, CONSTRUCTION FACILITIES AND CONSTRUCTION PLANNING From the contractual point of view, site layout facilities and other construction related logistic support is very difficult to be accurately predicted or priced before the commencement of a project. However, the reasonable catering and costing allowance of such work items will practically dominate the success or profitability of a project. Construction planning in reality can hardly be worked out using any programming software not because of the imperfection of these tools. The unpredictability mainly comes from the highly dynamic situation, existence of numerous work variables as well as the involvement of complicated human factors in such project. Summarized in below are some of the common scenarios that show these concerns and relationship. A. Require additional time in the setting up, maintenance, relocating and dismantling the facilities, as well as the touching up of the related areas after their removal. Some equipments may need a very long time to have it set up, tuned, tested and commissioned before it can be put into actual operation. Routine maintenance is also essential to ensure they can work effectively and safely. Sophisticated access provision is also required for the placing or final removing of the equipments that may introduce large amount of additional cost input. Typical situation can be found in, for examples, tunneling project using TBM, construction of elevated bridges using precast segments erected by launching gantry, or the hoisting of extremely large and heavy prefabricated component like sections of long-span trusses onto the roof Photo 17 – Erection of an 8.5m diameter tunnel boring machine inside a 60m x 200m x 25m deep tunnel portal. The tunnel machine will be dismantled after the completion of the tunnel drilling at an access shaft which is about 1.8 km away from the portal.