Site Description and Soil Condition

The site to be developed is located in Charlestown NSW Australia on the North eastern side of pacific highway, sandwiched by Kahibah road and George Street. It is generally scrub vegetation with a few trees along the site edges. The topography is gently sloping with predominant mix of clay and sandy soils. The ground slopes towards the Karibah road in the South East region. The development entails construction of Child care centre project; a low rise commercial building. The architectural design was done by Daryl Jackson Robindyke Pty Ltd and therefore, a bulk of this report was derived from the designs. 

1. FOUNDATION SYSTEM

• Characteristics of the buildings and site conditions

It is generally scrub vegetation with a few trees along the site edges. The topography is gently sloping with predominant mix of clay and sandy soils. It slopes towards the Karibah in the South East region.  However, it is surrounded by other buildings from all sides hence making it difficult to maneuver with construction materials. From the geotechnical information, rocks and cohesive soils are predominant in Charlestown square. The average soil bearing capacity is between 75 and 150 kN/m^2.  Due to the nearby growing trees especially in the western side of the building site, cracking of the walling element due to moisture absorption is inevitable. There are also possible vibrations due to nearby traffic hence this must also be considered during foundation design and selection. Settlement due to ground water change is also likely to occur. In soft clay, if the building loads are unmatched, sinking is inevitable and this may cause catastrophic failures such as overturning.

• Comparison of the alternative solution methods

Foundation is the lower portion of a building which rests on the earth and is normally designed to carry both live and dead loads of the walling element while adequately resisting some movements due to soil condition in which it is established. The substructure therefore is that portion of a building sunk in the ground while the substructure is erected outside such that load path is from the roof via the walling element into the foundation. The live loads could be due to wind actions or soil actions among others like rain water, snow and occupants while the dead loads are imposed by the weight of the roof and walling elements. Commonly, for residential low rise buildings (like the child care centre development), the best alternative foundations to consider are either pad or strip foundation. Hence these two are reviewed and the best match will be selected.  From the architectural drawings provided, it can be deduced that the buildings is low rise hence most loading is transmitted horizontally. However, a strong foundation must still be built.  

• Pad foundation

 This is the most appropriate foundation system for both medium and low rise building structure as each foundation is independent of each other and they can have different designs catering for the various imposed loads. This makes them ideal for both symmetrical and unsymmetrical floor plans and building shapes. The load in this case is transferred directly from the columns into the footing and in some case; more than one column can reside on a single pad footing. This type of footing is applicable in a wide variety of structural systems ranging from ordinary moment resisting frames and portal frames to shear wall building frames. This therefore means that they can be used on almost every building material from concrete to stone. Notably, however, the area in which the building is to be seated is in one of the streets of Charlestown and from various soil tests carried out, it reveals that clay soils could be dominating implying that the soils are verily reactive (this is categorized as class H according to AS 2870 and AS 1726) hence need to integrate another foundation type to accommodate the changing soil properties like moisture content. AS 2870 provides further technical requirements for this kind of foundation. Nevertheless, pad footings are only applicable in providing support to the columns hence it is normally restrictive to localized vertical support. In the drawing plan, position of piers to be sunk provides a rough indication of the exact location of these pad foundations as they are linked directly. Besides, safeguards on shear and bending moments will only be sufficient if the concrete mix strength and the reinforcement are appropriately done (Murty et al, 2002). Area of the foundation often depend on load to be transmitted, bearing and shear strength of the soils, thickness, exaction method adopted and the concrete formwork.

Table 1: Comparing Pad and Strip foundations

• Strip footing

Wide strip foundation often comes in handy in conditions of extreme swelling and shrinkage. They have more advantages over other systems as they allow for either one or more basement levels while being relatively unaffected by changing soil conditions. The strips provide a firm foundation structure against such movements as they are sunk deeper than the normal foundation. It is suitable for this type of dwelling as its applicability ranges from low to medium rise constructions. Since soils in Charlestown square are predominantly clay, we will need a thick and wide strip all round 

• Graphical information for the proposed solutions  

1. FLOORING SYSTEM

• Comparison of the alternative solution methods

The options available for consideration in this section include: concrete and composites flooring systems.

• Concrete flooring systems

From the architectural drawings, it can be observed that most of the design elements are in tandem with a concrete screed floor system. In the building in our case, the screed is applied on top of the existing concrete slab and from there any other floor finishes can be applied as per the specifications of the occupants. In most cases there is usually a series of ground beams on which the concrete slab rests and the architectural drawings gives an indication of the same. The concrete slab is reinforced before concreting to make it stronger and it is then possible to carry loads imposed on the floor as per the design (Nawy, 2000). 

• Composites flooring system

Instead of the conventional concrete reinforcements where meshes are used; this case     utilizes fiber composites providing same strength characteristics as the conventional flooring system. It has the best quality of finish and it is less expensive in construction as meshes are eliminated. During construction, incidences of safety are reduced as handling is minimized. Besides, it greatly saves on concrete. Tripping hazards are also reduced.

Table2: Comparison of the flooring systems options

Graphical information for the proposed solutions  

Conclusion and Recommendations

From the above technical description of the available option, it can safely be said that the best foundation that matches the site conditions and the planned development is pad foundation. Flooring system to be used in this case should be the composite system as it greatly matches with the site conditions and the building design.  The superstructure which is composed of walling and roofing elements are to be built such that walling materials will mainly be masonry and concrete for the columns; the truss of the roof will be made of timber for all of the rooms in the building. This can be deduced from the drawings provided. The major criteria for selection were the site condition, the purpose of the building, the building classification and the cost constraints.

References

Idrus, A. (2008). Evaluating Construction Time Performance of Building Floor System Design at the (Early) Conceptual Design Stage.  Selangor University of Industry (UNISEL), Jalan Zirkon. 

Kingspan. (2018). Composite Slab Flooring System. Sherburn, Malton, North Yorkshire Available at:www.kingspanstructural.com

Murty, C. V. R., et al. (2002). “Reinforced concrete structures.” Earthquake spectra 18.S1: 149-185.

Nawy, E.(2000). Reinforced concrete: A fundamental approach. Available at: https://www.structuraldrafter.com/pad-footing-detail.html.