Coastal Protection: Design and Construction - Case Study Example

Coastal Protection: Design and Construction Coastal areas have long served as ideal locations for town development because of the scenery and proximity to the sea. Nevertheless, these areas are also subjected to continuous erosion and instability due to the scouring action of seawater and the flow of groundwater to the sea which carries with the soil bearing man-made structures. Engineers are called upon to design solutions and determine appropriate construction techniques to protect coastal areas. In the presentation, four cases studies were presented and are discussed below: a) Military Road The cliff near the military road was unstable and unprotected. Cliff recession was imminent due to the scouring action of waves at the toe of the cliff. To guard against this, concrete bored piles were installed at the cliff-facing side of the road. This is then tied to anchor blocks with pullout being prevented by tension piles. b) Castlehaven Coast Protection Scheme A developed unprotected coastline is subjected to coastal retreat and landslide instability. The combined action of cliff erosion and collapse together with the flow of groundwater from high levels to the sea is triggering landslide reactivation. Coastal protection is limited by environmental sensitivity of the site. There are two requirements for the project: to arrest recession of the cliffs and reactivation of the landslide system and to improve the stability of the coastal through an intensive drainage system. For the first requirement, a rock armor revetment was chosen. For the second problem, a deep pumped well solution using siphon and electro-pneumatic systems. c) Lyme Regis Environmental Improvements – Phase II The project involves a developed coastal town threatened by existing coastal defense, landslide reactivation and coastal recession. Coastal erosion by wave action, earth slippage due to rainfall & groundwater, inappropriate excavation and construction and climate change have ultimately resulted to the reactivation of landslide complexes. Due to the severe consequences if the problem was left unchecked, an extensive program of land stabilization and foreshore works was undertaken. Different strategies were used including reinforced slope buttresses, soil nails, pile grids, slope regarding, drains, seawall improvements and beach replenishment. d) Barton-on-Sea A developed coastal town is experiencing deterioration of coastal defenses with previously installed stabilization measures such as cut-off drain have all but failed. Nevertheless, the cliff top assets are not foreseen to be affected for several years making coastal protection measures not warranted for the time being. Only monitoring and investigations of the ground and rainfall are the actions being undertaken. Aside from illustrating the different methods for coastal protection and slope stabilization, the presentation also provide an understanding of the different matters that needs to be taken into consideration for the design such as geologic and geotechnical data, rainfall and groundwater conditions, effects of climate change, environmental constraints and construction risks. All of these should be taken into consideration for the effectiveness of the perceived solutions. Geotechnical Engineering in Cities Inside the classroom, an aspiring Civil Engineer is taught the concepts of Geotechnical and Structural Engineering. He then proceeds to solve problems by considering the given loads and geotechnical properties to come up with suitable load-bearing structures. Computations are made as if the area being developed had not undergone any previous construction work. In reality, however, many spaces contain previous structures and utility lines. This is especially true in urban settings where the construction of tall buildings becomes a huge challenge because of its geotechnical requirements among a few. Construction can affect nearby buildings and utility lines due to settlements and loss of bearing capacity of the soil. Existing foundations such as piles, footings and retaining walls present challenges to designers as they are limited in locating load-bearing structures for new developments. This becomes more troublesome when the project is a tall building. Taking a more positive outlook, these existing structures can present opportunities for the designer and builder especially in terms of cost savings. With deliberate consideration, some structures can be reused instead of being demolished saving time, money and effort in the process. Existing piles can complement new foundation schemes and retaining walls can also help in providing stability and load-bearing capacity when integrated into the scheme. Reuse of existing foundations requires intensive assessment to ascertain its performance when integrated into a new development. The designer should assess the integrity of the concrete through testing and visual inspections, calculate column loads and bearing capacity for footings and retaining walls. Settlements should also be accurately predicted especially differential settlement between adjacent columns. Monitoring of settlements and movements of adjacent soil and structures becomes a requisite for safe construction. At this point, however, there exists a very important concept that an aspiring designer should appreciate: design should be flexible enough to accommodate the reuse of certain structures. In many construction projects, building can only proceed when all the design plans and drawings have all been made and approved with revisions coming only in minor form and reflected in as-built drawings. The presentation tells us that certain site conditions can also result to major changes in the design if existing structures are to be integrated and reused. Lansdowne Road Stadium Roof Steelwork Construction Aldo Constantini’s presentation discusses the elements of project management and construction of the Lansdowne Road Stadium steel roofing. The presentation is divided into five topics namely project structure, project description, site conditions, the roof structure itself and the construction phases. This presentation provides the audience an understanding of the different aspects of project management using the steel roof construction as an example. The project structure of the project indicates the organizations involved in the project together with their relationships and responsibilities. While this may come simply as an organizational chart, the project structure is a very powerful tool as it provides a clearer understanding not only of responsibility but also of authority and decision making processes. The presentation also provides a description of the project including the scope of works and site working conditions. Accurate information regarding the project and the prevailing conditions at the site itself including permissible working hours facilitates realistic and achievable planning schedules. In the classroom, civil engineers would usually solve truss problems through the use of their imagination. The presentation provides real life examples as it illustrates primary, secondary, tertiary, 3D edge truss elements as well as purlins and gantries and discusses functions, diameter and weights encountered in construction. As such, it helps the aspiring construction engineer in visualizing truss design and recognizing issues in construction. The topic regarding construction, while confined mostly to photographs, illustrates the different elements of work involved namely planning, choice of material, fabrication & preassembly, painting, logistics, access, production plant and the resources. While the discussion is particular to the project, all of these work elements can be found in most construction projects. Thus, it gives the audience a basic awareness of the processes that can be used in their project construction career. What is striking, however, is the small number of people involved in the steel roof construction on site. There were 15 erectors but only one welder, one surveyor and two absailors despite the complexity of the project. This indicates that with the right people on the job, even if they come from different national backgrounds, the construction process can be greatly streamlined. New Tyne Crossing Design Engineers are usually captivated by the design and construction of high rise buildings with roads and tunnel construction pavements seen as quite unchallenging. Kevin Stone’s presentation of the New Tyne Crossing project, however, illustrates the high degrees of complexity involved in Transportation Engineering. The New Tyne Crossing project calls for the construction of submerged access for vehicles to cross the River Tyne as well as support buildings, roads and tunnels. The Tyne presentation highlights one of the foremost design considerations in the construction of roads and tunnels which is the geology and site stratigraphy of the work area. This is especially true for the tunnel and immersed tubes whose design and construction warrants an in-depth geotechnical analysis. This is done thru a Ground Investigation (GI) program. There are several objectives of GI listed in the presentation but it can be summarized into three important points: cross-section variation of soil material, groundwater level and determination of soil bearing capacity. ‘The ultimate goal is to ascertain the nature of the ground material to minimize as much as possible significant variations in the construction phase that could lead to redesign or long delays. With geologic and geotechnical properties data acquired and analyzed, the designer can now proceed to the reinforcement design of earth-retaining structures and method of construction. In this presentation, we are further enlightened on the different types of tunneling methods namely immersed tubes, cut and cover and sprayed concrete lined. The use of immersed tubes necessitated the development of the riverbed to acquire the required formation level. This is done thru dredging. There is also the task of fabrication, transport and immersion of the tunnels. The presentation provided an overview of how these activities are being conducted in the field. Particularly interesting was the use of survey towers for accurate immersion and the ‘pin and catcher’ system to align the tunnels to fit each other for continuity. Cut and cover usually give images of dozers, shovels and earthworks but the presentation provided an understanding of the different elements such as external wall design, fire boarding to roof slabs and the use of props to support structure against caving in. The presentation of the SCL tunneling method as used in the New Tyne Crossing project was less detailed though it also gave an understanding on how the technology is applied as well as the issue of waterproofing lining. The NTC project presentation delve more on the complexity of construction but the illustrations of the phases of construction, especially those photographs showing massive props to guard against cave-in, impressed the safety issues involved in earthworks. Scaffolding Design and Safety Considerations Scaffolding is a critical activity in construction as it allows workers to transport themselves and their materials up and down an unfinished building during construction. MGW Consulting Engineers presents design and safety considerations regarding the erection of scaffolding for different construction purposes. Scaffolding has five major components namely standards, ledgers, transoms, bracing and ties. Standards are the vertical tubes whose spacing depends on the loading while ledgers are the horizontal tubes keeping the standards equidistant and fixed with right angle couplers. Transom are boards which keep the inner and outer row of standards equidistant. Bracing is used for stiffening the structure and should never be removed to allow passage of materials. Ties provide the resistance of the scaffolds to inward and outward movement. The design of scaffolding should consider the configuration of these scaffolding elements based on the load and type of work where it is deployed. In the design of scaffolding, it is very important to consider not only the explicit loads such as human and material loading schedule but also loads arising from wind and snow. Scaffoldings transfer loads from point of application to the base supporting it which is often times the ground or soil. Hence, it is important to determine the bearing capacity of the soil in conjunction with the load being supported. This would not only minimize the possibility of over stressing but also provide opportunities for cost effectiveness as MGW Consulting Engineers (MGWCE) highlighted in their storage gantry project example. The scaffolding designer is faced with different situations that require engineering expertise. He may be called upon to design scaffolding that supports walls and prevent them from falling inwards or provide plans and details for independent scaffolds. In some cases, he may act as a consultant in providing solutions to problems encountered in the site like in the situation where MGWCE was asked to solve the situation where the standards used in the scaffolding for a church repair and maintenance were buckling. In all these cases, the designer should ensure that drawings and accompanying engineering solutions are provided and that it complies to with local standards. The goal is to ensure that the scaffolding is safe and viable before it is even implemented and used in the site. Failure to provide structurally sound scaffolding can lead to collapse and be fatal for workers. One such event occurred in Milton Keynes in 2006 where one worker died and two suffered serious injuries. Aside from the loss of life, scaffolding collapse also presents significant financial damage to building firms as it represents not only delay in construction but also monetary penalties as was the case in the collapse of 30 tons of scaffolding used in the construction of a multi-storey building in Cardiff City Centre. There is one very significant aspect regarding the use of scaffolding that the presentation seems to have provided less attention. This is the implementation of the designed scaffolding system on site. Investigations into the collapse of the scaffolding in the Cardiff City Centre pointed out that the reason for the failure was the use of untrained workers and insufficient monitoring of the quality of work as evidenced by the absence of 70% of the required ties. Hence, even when the best of efforts is applied during the design, failure becomes likely due to negligence at the site. In retrospect, scaffolding design and construction is a very risky endeavour since its failure could lead to death and severe financial losses. Designers are tasked to consider the loading, environmental factors and the bearing capacity of the foundation supporting it. Care should also be taken during the implementation stage as negligence and insufficient attention could defeat the design effort. Read More