Foundation Design and Construction - Assignment Example

Name : xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Tutor :xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Title : Institution : xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Date :xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx @ 2011 Part 1: Introduction The construction site is found opposite Harris building at the meeting point of Hope Street and Corporation Street. ‘It is at the rear of numbers 91a to 87 Friar gate.’ The purpose of this report is to provide information about both the above ground and underground conditions on the site to a developer who is intending to purchase the site. It should provide all the necessary details including the place the site is located, potential hazards site history, surrounding buildings and streets, the shape and the size of the site Tomilson 2001). It is also required to provide information concerning the design’s foundation. This foundation design will be the most appropriate for the site considering the risks and conditions prevailing in Preston city. The report is expected to help in the calculation of the costs necessary for the preparation of the site as well as the costs for constructing a hotel with 5 storeys. The information availed in the report is critical in the appraisal of the impact of site conditions on the building of the structure and the laying of its foundations. The research was carried out in the month of December 2010 by a company that compiled this report (Jennings C. 1968 p. 891-916).The details of the report were gathered from outside the site on the nearby streets since entry into the site was prohibited Part 2 – Initial Site Appraisal The site takes an almost rectangular shape although it is not a perfect rectangle since one side has a shorter width when compared to the other. It has good accessibility since on all of its sides there are streets. The site was formerly a garage for vehicle repair but currently it serves as a car park. However a big number of the buildings have been brought down in demolitions. However there is no indication as to whether or not there are some remains of these buildings underground. There is also no indication as to what size of buildings existed on the site prior to demolition. This might however pose a challenge to the future construction plans (ACI) 1980. On the site there are buildings named ‘depot’ which are to be destroyed before the site is levelled. The buildings were in use as part of the garage and the present owner of the site says there is an underground petrol tank at the car park that is not in use but formerly it was used in the garage. On one side of the site there is Kendal Street while another road called Hope Street lies on the opposite side (Jennings C. 1968 p. 891-916).The two streets are joined together by Corporation Street and the site is found lying between the two streets and closed on one side by Corporation Street. The specific location of the site is at the point Corporation street meets Kendal Street Christian, J.E. (1989.) Since the site was formerly a garage and there remains an underground tank it will be detrimental for the construction to be made on top of this tank. The strength of the foundation of the building will be compromised by something that can make it sink in case the tank crashes under the heavy weight of the building. A five storey building needs a firm base to sit on. It will therefore be necessary for this tank to be removed before the place is levelled (Christian, J.E. 1989pp. 45-89).The presence of the tank under the ground might also be a source of a weak floor if it is not removed. Because there is no proper consolidation of foundation material underground there might result a cracking of the floor (ACI) 1980. Figure1: The location the site plan. (Kuroiwa 1968 pp.90). Since the site has buildings near it especially on the upper side adjacent to Hope Street it will be necessary to consider the effect of such realities before any construction is done. The buildings with numbers 91a to 87 Friar Gate is too close to the site and this might be a challenge to the developer. The close proximity of other buildings poses a threat of damage to those buildings in case construction begins. A 5 storey building needs the foundation to have a deep excavation before building starts. When the excavation is done the material that retains the surrounding earth in place is removed (Kuroiwa 1968 pp.90). This result in lateral movement of the soil portion left in suspension and unsupported. The building components supported by the moving soil undergo a vertical settlement Jennings, P. C. and Kuroiwa, J.H.,(1968). The site is covered by “man made fill material consisting of brick, ash and organic waste up to 1m deep lying on an organic peat layer that has an average depth of 15.00 metres.” This may be a suggestion that the surrounding areas have this type of ground. The information being send across is that the ground is unstable and may be easily destabilized in case the soil is disturbed through excavations (ACI) 1980. ‘The magnitude of vertical settlement depends on how the earth retaining system is flexible, the type of soil, distance from excavation and excavation depth.’ The developer will therefore need to temporarily install earth supports like cantilevered systems, anchored systems and strutted systems. There are a number of risks on adjacent buildings associated with various construction activities. In order for the nearby building to accommodate the 5 storey hotel building they will have to be underpinned using concrete pit. This will be necessary since the storey building will be constructed only 3 metres away from the nearest buildings (Tomilson M.J. 2001pp.89. 101). The excavation of the storey building might require dewatering which might possibly be a threat to the foundations of the buildings near it. Dewatering can result in ground settlement from draw down or when wood pile foundation systems rot. Soil can become stressed and therefore consolidate and result in settlement. Vibrations resulting from the excavations may also be noisy to the occupants of the nearby buildings. They may also be damaging to the buildings especially the exterior façade and interior finishes or general structural damage Labs, K et al (1988). Because the buildings on the site called ‘depot’ will be demolished to pave way for the construction, it will be necessary to observe the possible effects of demolition risks on the adjacent buildings. Demolitions of the depot will need to be done carefully to avoid damage on the other buildings. Demolition can have the potential of adjusting the support systems of the nearby or adjacent buildings. Since the site lies next to four streets on all of its sides excavations will necessarily generate dust which is a nuisance to traffic and pedestrians Christian, J.E. (1989). Part 3 – Foundation Design The design of the foundation will definitely take that of a tall building since it is a five storey hotel. The foundation will need a pit to be dug for it to be sustained. Since there will be no basement floors the digging might not be too deep. It will have to go as far as the bedrock is. It is necessary to reach the bedrock in order to have a strong foundation. This means all the man made fill material comprising of brick, organic waste and ash together with the inorganic peat layer will have to be removed. The pit will then have to be dug to a depth of 16 meters before reaching the bedrock (ACI) 1980. The excavation will however have to go to the point of removal of the underground petrol tank. Since there are houses and streets adjacent to the site it will be necessary to construct a diaphragm wall in order to help prevent surrounding soils from moving since this might cause instability in the nearby buildings and streets. Jennings, P. C. and Kuroiwa, J.H.,(1968). To make a diaphragm wall around the site a deep trench is dug all around the pit then it is filled with watery clay called slurry to prevent the collapse of its walls. When a part of the narrow trench has acquired the right depth reinforcing steel is put into it before concrete is forced into the trench displacing the slurry. The displaced slurry can be extracted and utilised in other parts of the narrow trench. When the bedrock is reached especially if it is found to be lying near the surface, part of it should be removed to ensure that the building foundation is planted into the bedrock. A level and fairly smooth platform should be made on the bedrock for the foundation to be made Labs, K et al (1988).To ensure the firm support of the structure it will be necessary to use footings. These are holes drilled into the bedrock to create room for anchoring the support columns of the storey building. Concrete or steel columns will then be placed inside the footings. This will be important since a five storey hotel will have to support a huge amount of weight which should be given a strong base (Tomilson 2001). From observation done on the outside it was not easy to tell if the site has shallow or deep bedrock. In case the bedrock will be found to be very deep and far from the soil surface, then digging all the way to the bedrock will be uneconomical. In such a case it will be wise to make vertical beams which should be sunk into the soil layers through into the bedrock. Shafts can be drilled into the bedrock through the soil then steel rods for reinforcement then the shafts are filled with concrete Labs, K et al (1988). It will also be necessary for waterproofing to be done in order to ensure that underground moisture does not weaken the foundation and walls of the building. The exact level of the water level may not be known but the developer needs to take no risk. Drainage and water proofing should be done in order to prevent incidences of ground water building up in the soil which can result in a raise water table. A high water table can cause the exerting of hydrostatic pressure under the floors of the basement and on the walls. Water is forced through cracks formed in the walls of the foundation and into the cracks of the floors. Hydrostatic pressure may result in structural damage to the walls of the foundation which may also cause moisture problems like mould and decay Christian, J.E. (1989). The developer will therefore have to consider waterproofing through both ‘interior water drainage’ and sealers. Interior drainage system otherwise called basement ‘waterproofing solution’ is effective from handling basement water. This method drains underground water pilling along the footer foundation and under the floor of the basement. The water is channelled away from the site through a French drain or sump pump system or PVC pipe which pumps it out of the basement. “Interior basement waterproofing systems should be prepared to work in the case of a power outage, the failure of a sump pump, and in the face of overwhelming torrential rain.” Jennings, P. C. and Kuroiwa, J.H.,(1968) A good sup pump will have to be installed inside a sump pit having a tight lid to ensure safety and also to avoid cases of humidity penetrating into the basement where moulds can grow. The tight lid can also be useful in preventing radon gases from seeping into the living areas. Another method of controlling moisture is using exterior water proofing which helps to prevent the entry of water into the walls of the foundation which prevents the molding and wicking on the building materials. Water intrusion can effectively be controlled by this method. The site might have a big problem of water seepage since in winter the water table rises to only 1.5 metres under the surface of the soil. In summer it goes a bit lower to 2.5 metres below ground surface Tomilson M.J. (2001). Another water proofing system which will work well if combined with the interior water drainage method is the use of sealers made from sodium silicate for foundation wall and floor water proofing. If this method will be used on this storey building then sodium silicate will be applied in a mixture with water to fill in the basement floors and walls. Sodium silicate will penetrate to about 4 inches inside the substrate. The sodium silicate will penetrate and react with lime in the concrete. This will form a crystalline structure in solid form which will then seal the tiny pores and cracks inside the substrate. This process will then harden and make the concrete have a high density which makes it hard for moisture and other gases to pass through by capillarity. Gases are also prevented from entering into the basement. When the substrate has been cured it looks as if there was no sealing done on it. It maintains its original surface without any sheen or film (ACI) 1980. ‘Benefits of Sodium Silicate for Building Waterproofing’ When the walls of the basement are sealed with sodium silicate, it will be impossible for water vapour to enter the basement. This will enable it to be dryer than what is was before. This will greatly reduce the chances of having mildew and mould growing inside the hotel kitchens something that can result into poor air quality. It is important to consider this since the kitchens of the hotel will be a very sensitive area that requires high air quality and optimum hygienic conditions Labs, K et al (1988). Because the wall and floor surfaces will have been hardened there will be few possibilities of chalking and dusting. It will also lower the possibility of transmission of gases from underground into the basement. This is another advantage that will help raise the quality of air in the kitchens. It will also help in the preservation of the paint applied on the walls by hindering the penetration of moisture and water vapour under the paint (ACI) 1980. If the walls and floors were not sealed, water vapour can very easily be trapped under that paint. With time the water vapour would break the bond existing between the paint and the wall causing the paint to peel off. “After application of a sodium silicate the walls and floors can be painted without fear of the paint peeling and flaking.  Also, adhesives for tiles or other floor coverings can be used.” Christian, J.E. (1989.) Sodium Silicate Application The application of sodium silicate is done on bare concrete, masonry or concrete block. Any material on the surface which can hinder the absorption of the sodium silicate will have to be cleaned off. “No grease, dirt, soil, adhesives, oil, sealer or paint can be on the surface to be sealed prior to application.” A garden sprayer, brush or a roller will be applicable for the application. A brush or mop is used to dampen the surface using water. Many light coats are then applied on 10 inch by 10 inch areas. Each of the coats is applied after duration of 10 or 20 minutes. Masonry and concrete blocks will take about 3 to 4 coats while concrete may take 2 to 3 coats. Any excess sodium silicate will have to be wiped off Labs, K et al (1988). Conclusion This report was meant to collect information about a site which is supposed to be purchased by a developer in the city of Preston. It was formerly a garage and currently it serves as a car park. The developer seeks information on site conditions below and above the ground because he wants to construct a 5 storey hotel on the site (Christian 1989).Among the things he has to consider are the hazards that can be cause to the occupants of the adjacent buildings such as noise from vibrations and damage of their buildings through demolitions and excavations. Since the storey building will carry a lot of weight he will have to choose a proper foundation design as the one outlined in this report as well as a good method of water proofing. This will prevent moisture from entering the basement floor or seeping through its walls. References Tomilson M.(2001) Foundation design and construction.Harlow: Pearson Prentice Hall. Jennings, P. C. and Kuroiwa, J(1968) Vibration and Soil Structure Interaction Tests of a Nine- Story Reinforced Concrete Building. Bull. Seisnl . Soc. Am., -58, 3, p. 891-916. Christian, J.E. (1989) Worksheet for Selection of Optimal Foundation Insulation, Conference on Thermal Performance of the Exterior Envelopes of Buildings IV, Orlando, Florida, December 4-7 Labs, K., Carmody, J., Sterling, R., Shen, L.,Huang, Y.J., Parker, D. (1988) Building Foundation Design Handbook, ORNL/Sub/86-72143/1, American Concrete Institute (ACI) 1980.Guide to Concrete Floor and Slab Construction, 302.1R-80, 46 pp., Detroit, Michigan Read More