8/7/2022
B.U. BUILDERS & CONSULTANTS PVT. LTD.
CONSTRUCTION PROJECT ANALYSIS
6-Storey In-Situ Concrete Framed Building | Antara Nandy
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Introduction The project involves the construction of a 6 storey in-situ concrete framed building that lies in an industrial site, Greater London area. The site gets overlain by a shallow perennial steam that feeds into the River Thames on the outskirts of the Canning Town. The proposed structure consists of a single storey deep basement housing a loading bay and storage rooms for the building. The remaining 6 stories comprise of flush slabs supported by circular, mushroomheaded 6 columns.
Figure 1: Proposed Grid Plan (NOT TO SCALE)
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Figure 2: Section-Longitudinal Cross-Section taken at 'GG'
Challenges presented by the proposed all in-situ concrete framed building project Upon conducting subsoil investigation it has been found out through the stratigraphy tests that the site contains controlled amounts of fill in the form of cobbles and boulders in a very sandy matrix within the designated footprint for the foundations. Shallow foundation may prove to be incapable for bearing the load of the structure that is as high as 6 stories. It is recommended to opt for deep foundation, preferably mat or pile foundation in this case.
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Construction method most suited for the project Mat foundation can be easily built along the grid lines and it will be robust enough to support the structure.
Figure 3: Mat Foundation Details
Figure 4: Ribbed Mat Foundation
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Raft foundation, also known as mat foundation comprises of a continuous slab resting on the soil that spreads across the entire footprint of the building and in the process transfers the load of the building on to the ground. Usually practiced on weak soil, mat foundation distributes the weight of the building over the entire area thus lowering the stresses on the soil underneath. Mat foundation is ideal for basements. This kind of foundation is dug by excavating soil to an optimum level in order to reach out to strong, compact and undisturbed natural soil which is much stronger than the surface level. Ribbed mat is formed when concrete walls are built around the periphery of the foundation. Membrane waterproofing enables water clogging inside the foundation. To take additional loads the raft below the columns can be thickened. When the soil outside a basement gets saturated or clogged with water during heavy rains, then the basement begins to float like a ship in a sea of water. This process is known as uplift. Absence of balancing forces, when the upward and downward forces are not in equilibrium, causes great damage to the foundation (Anon., n.d.). Also, in such conditions where the soil has low bearing capacity, the heavy structural loads owing to the multiple floors in a building can be managed by proving mat or raft foundation. Vulnerability of the structure due to subsidence for being located in mining area or because of the uncertain behavior of its sub-soil water condition can be resolved by providing mat or raft foundation. Mat foundation comprises of thick reinforced concrete slab spanning the entire area beneath the structure. This slab contains reinforcement bars that run at right angles to each other near the top
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and bottom face of the slab. An arrangement of inverted main beams and secondary beams cast monolithically with the raft slab can carry the excessive column load (Anon., n.d.). Mat footings help to reduce differential settlement of foundation due to construction on nonhomogenous soils or uneven distribution of load on footing.
Figure 5: Raft Foundation
Raft foundation construction is fast paced and is relatively inexpensive since they do not need deep excavations. Also, they require led material since they make use of the foundation with the ground slab (Designing Building Wiki, 31 Jan 2019). Ease of project’s execution and within the constraints of Time & Budget The existing fill needs to be removed and the site must be cleaned. This initial activity will ease off the further processes.
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Figure 6: Loading bay details for basement:
Bibliography 1. Anon., 2013. Mat Foundation | Types of Mat Foundation. [Online] Available at: https://bestengineeringprojects.com/mat-foundation-types-of-matfoundation/ [Accessed 9 March 2019]. 2. Anon., n.d. Raft or Mat Foundations. [Online] Available at: https://www.theconstructioncivil.org/raft-or-mat-foundations/ [Accessed 9 March 2019]. 3. Anon., n.d. RAFT OR MAT FOUNDATIONS. [Online] Available at: http://www.understandconstruction.com/raft-foundations.html [Accessed 9 March 2019].
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4. Designing Building Wiki, 31 Jan 2019. Raft Foundation. [Online] Available at: https://www.designingbuildings.co.uk/wiki/Raft_foundation [Accessed 9 March 2019]. 5. Fine civil engineering, n.d. Mat footing. [Online] Available at: https://www.finesoftware.eu/geotechnical-software/solutions/shallowfoundations/mat-footing-foundations/ [Accessed 9 March 2019]. 6. Science Direct, n.d. Raft foundations. [Online] Available at: https://www.sciencedirect.com/topics/engineering/raft-foundation [Accessed 9 March 2019]. 7. The Constructor Civil Engineering Home, n.d. Raft Foundations-Types and Advantages. [Online] Available at: https://theconstructor.org/geotechnical/raft-foundations-typesadvantages/7184/ [Accessed 9 March 2019]. 8. Whirlwind Steel Buildings and Components, 2017. MAT VS. PILE FOUNDATIONS. [Online] Available at: https://www.whirlwindsteel.com/blog/bid/307994/mat-vs-pile-foundations [Accessed 9 March 2019].