Foundations - Necessity, Challenges & Solutions in Execution.

Foundation systems are crucial in the building construction process and depend mainly on the requirement and design of the structure.

Foundation is one of the most significant elements that transmit the load of structure to the ground. Foundation anchors the structure by increasing its lateral stability. It distributes the load of the structure over a large area by bringing the intensity of loading within the safe bearing capacity of the underneath soil. Foundations also prevent the ingress of ground moisture. The relative importance of these functions changes with the type of land underneath the building and its design. Broadly the foundations are classified as shallow foundations and deep foundations. Shallow foundations are applicable for lightweight structures and have lower lateral stability whereas deep foundations offer a good degree of lateral support and help in resisting uplift. However, it is advisable to know the suitability of each type of foundation before their selection. The types of foundations are classified in the tree diagram as follows:

Challenges Encountered in Concreting of Foundations

Concreting operations for foundations encounters multiple challenges. For concrete structures, size effect has gained increasing importance in recent past. Size effect plays a significant influence in structural strength and brittleness.  Building foundations rest on soils which have a variable range of bearing capacity and shear strength. Precipitation, runoff and erosion may cause damage to the foundations. Soils can be of aggressive chemical natures that may lead to the ingress of various undesirable environmental agencies in concrete, which ultimately compromise the service life of a structure. Throughout the year, the soil expands and contracts due to natural variations in moisture and temperature levels. Sections of the soil can have different moisture levels causing the soil to swell and shrink at various locations. Some sections of the soil can become much drier or wetter than other parts causing stress on the foundation. Concreting is also required for construction of foundation bases. These pouring points often constitute of narrow trenches and channels which may have difficult accessibility for pumping. Moreover the concreting for foundation bases should be economically viable. Piles, which are an element of deep foundations, require concreting at greater depths. Concrete has to be poured at greater depths in piles, without causing segregation at minimal compaction. Concrete must be uniformly homogeneous and consistent throughout.  Among shallow foundations, rafts are being executed widely for various infrastructural projects. When the allowable soil pressure is low, or where the walls and columns are placed so close that the individual footings would overlap or nearly touch each other, a raft foundation is generally preferred. Hence raft foundations are gaining importance as several columns and walls can be supported under a large part of the structure. 

Raft foundations are usually constructed with specific structural design. The substructure requires execution within a stipulated span of time. Mass concreting needs to be executed for raft foundations. Large volumes of concrete have to be poured at a continuous pace without stoppages, to avoid the possibility of construction joints. Proper precautionary measures need to be undertaken to cope with the generation of heat and cracking. Thermal cracks may appear due to increase in temperature of the inner core of concrete. This temperature difference leads to differential thermal expansion. The design of raft consists of congested steel reinforcement that leads to difficulty in compaction. All these challenges can be combated to a greater extent if concreting ensures that foundations become exceptionally firm and provide increased sustenance and control. Nuvoco has worked out in identifying those challenges and has developed a few products that can combat these challenges.

Nuvoco's solution

On the concrete segment, Nuvoco Vistas Corp Ltd has value added products (VAP) which is used for constructing foundations. One of them is Agile a self-compacting, self-levelling and free-flowing concrete which was used in the construction of 'Lodha's World One Tower'. Its free-flowing property eliminates the need for vibration and allows easy placement; thereby reducing the number of pour points on a work site leading to early project completion. Based on granular dense packing model, Agile is cohesive, extremely durable, as it has very low permeability owing to excellent consolidation. This product is specially used for deep foundation techniques. In the construction of 'World One Tower' the substructure was massive with a raft measuring five meters in depth and 13,600m3 of concrete consumed, which was done in two layers of M40 and one layer of M60 with concreting spread over three days to achieve the desired results. The specially designed high-performance self-compacting concrete ensured filling of every corner of the congested reinforced raft.

The main concern with a big raft is thermal cracks as concrete is a poor conductor of heat. The setting of concrete is a heat-generating exothermic process, which results in extreme heat in the middle section of the raft. To tackle this problem Regletherme concrete is designed to reduce the elevation of concrete temperature due to high heat of hydration, thus reducing the thermal stress and Fluide a high flow workable concrete ideal for piling in a wide range of compressive strength are some other concrete products of Nuvoco which have been used in foundation for projects like Mumbai metro and Siddhi Vinayak Station Slab. Regletherme enables to control temperature difference between core and surface < 20 degrees Celsius. It lowers the heat of hydration by limiting the maximum temperature. This helps in elimination of thermal differential cracks, thereby blocking the ingress of ions from external environmental agencies, and resulting in a dense and durable structure.

Nuvoco's cement and concrete products have a lion's share in major projects across the country for building strong and firm foundation. Concreto, Duraguard, and PSC are few cement offerings by Nuvoco which provide a cutting edge for designing firm and durable foundations. Concreto is versatile and premium slag cement which offers unmatched strength for foundations and heavy casting work. It provides superior workability which gives the best finish for intricate designs. The inclusion of Concreto cement reduces the heat of hydration thereby reducing the probability of thermal cracking. It also offers low chloride ion diffusion. Duraguard, Nuvoco's Portland cements can be used for smaller structures foundation creation. Duraguard's Void Reduction Technology (VRT) factor reduces inter-granular space, preventing ingress of chlorides and sulphates, providing resistance to corrosion of reinforcing bars and durability of the structure.

Foundation systems are crucial in the building construction process and depend mainly on the requirement and design of the structure. A good foundation helps in various ways and essentially keeps the moisture out, resists movement, and provides stability to structure. There are many layers, combinations, and techniques to be followed for safe and good results in the foundation in the building and construction industry.

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