The Construction Challenges
The construction of concrete buildings in areas with structural challenges is difficult. Thus, the ongoing report incorporates theoretical applications of building and construction technology to help address the inadequacies presented by the area selected for construction. Inadequate analysis and investment into a construction site might compromise the structural integrity of buildings; hence it may impact the safety of the users negatively in the long term. Therefore, it is imperative that a cost-effective approach is adopted to maximize safety at the least construction costs. The geotechnical investigations show that the area is rife with limitations to constructing a building with good structural integrity. More succinct investigations on the stratigraphic sequences of and the physiographic setting of the soil layers ought to be conducted to establish the variables to consider when designing a foundation.
Soil-Related Factors
Soil-related factors are usually the primary variables in the selection of a foundation. Naturally, soils with high moisture content and clay type of soils have limited bearing capabilities due to the inferior shear resistance as compared to dry and dense soils. Therefore, the 6-story building in consideration in the ongoing analysis should have its wind, dead and live load transmitted to the ground to preserve the structural integrity of the building over time. The geotechnical report showed that there was a high percentage of clay soils; these are known for having high water contents. Practically, clay soil can be overcome by digging deeper and cautiously to avoid compromising the safety of the building. However, factors, for instance, plasticity should be considered before making recommendations on the approaches to be taken to maximize safety while minimizing costs.
Importance of Designing a Foundation
According to studies, soils with low density and increased looseness (especially alluvial soils deposited by rivers) are usually susceptible to bearing capacity weaknesses, differential settlements, and residual slants (Cubrinovski & McCahon, 2011, p. 5). From the latter finding the importance of design a foundation that can overcome soil structure weaknesses, environmental factors (for instance, wind) and seismic activities. The areas selected for construction of the six-story building in the ongoing report is affected by fill from illegal dumping. Thus, the soil structure might have been reinforced by the introduction of different elements in the soil; for instance, the liquidation characteristic of the soil structure had diminished considerably. The suggested foundation is efficient; however, there are concerns about its robustness. Further, the project involves the construction of a basement (figure 2); thus, unique considerations must be made due to the water depth and structural composition of the soil. Figure 1 and Figure 2 below show the initially suggested plans.
Uncontrolled Fill and Impurities
The stratigraphy tests indicate that the soil contains significant amounts of unregulated fill. Therefore, the structural integrity of the building built on the site may be worrying as uncontrolled fill creates pouches of unoccupied space that may damage foundations. According to a study by Guyer (2013, p. 3), uncontrolled fill leads to an inconsistent bearing capacity of the soil and may also contain impurities that may be chemically active; thus, compromising the integrity of the foundation. Additionally, since the uncontrolled fill is primarily comprised of boulders and cobbles voids might be formed due to uneven spread; thus, it may affect the foundation of the six-story building. The construction site of the six-story building is to be done on an unguarded area that had been subject to illegal dumping; thus, there may be impurities like sulphates that may react with lime and some of the building components leading to cracking, erosion, and imminent failure of the foundation over time. The geotechnical report also confirmed the presence of sulphates in the soil. Studies proved that sulphates react with chemical compounds in concrete form a crystallized salt; they also act with compounds in groundwater (Bonic et al., 2015, p. 414). Furthermore, the diverted stream is contaminated thus, posing a risk of chemical reaction leading to erosion or karstification in case the impurities find their way to the foundation of the building. The geotechnical report shows that the water depth is 4.7m from the uncontrolled fill of alluvial deposits which are 9m in depth. This poses a challenge to the construction of the one-story basement as suggested in figure 2. In addition to alluvial deposits and a sand matrix, the site also contains soft clays; these are usually subject to water retention issues that may lead to shrinking and expansion. Researchers have found a connection between the soft clays and structural failures in buildings (Mohamad et al., 2016, p. 2; Daly, 2010, p. 1). Thus, they also pose an additional challenge to the design of a cost-effective in-situ foundation.
Solutions
The challenges presented by the geotechnical report and stratigraphy tests are not new in construction. Methods to overcome each of the individual weaknesses are available; however, they are costly. The primary aim of the ongoing report is to advise on a cost-effective approach to building a foundation; thus, the methods discussed herein are aligned with contemporary research on construction. The six-story building requires a strong foundation that will overcome the challenges posed by the proximity of the site to the diverted stream, the water depth level, the deep alluvial deposits, and the uncontrolled amounts of fill. The main factors to consider when designing a proper foundation are the bearing capacity and the ability of the foundation to overcome the environmental elements of the site.
Dynamic Compaction and Deep Foundations
Researchers have advocated for the use of dynamic compaction to reinstate the integrity of the soil in sites with uncontrolled fill in the form of cobbles, boulders, and a sand matrix (Tarawneh & Matraji, 2014, p. 1008). The method involves using large weights impacting the site repeatedly. The latter suggestion could be implemented on the site before constructing a foundation; however, dynamic compaction requires a significant amount of energy that may increase the cost of construction (Pankrath et al., 2015, p. 391). Furthermore, since the building is constructed in-situ, there is a need to select cost-effective, energy-efficient methods of overcoming the environmental challenges on-site. Additionally, tall buildings constructed in soils with a high risk of liquefaction due to the unsuitable soil in the top layers require deep foundations.
An In-Situ Pile Foundation
The suggested foundation in figure 2 can be easily implemented. However, the integrity of the building with regard to the bearing capacity of the soil; erosion; soil liquefaction; expansion and shrinkage cannot be assured. Thus, an in-situ pile foundation could be implemented in the basement. Despite this being a possible solution, there is a challenge of the water depth as it is 4.7m from the layer of uncontrolled fill. Using piles and a deep foundation under the loading bay showed in figure 2 would help to transfer the weight of the story building and help to overcome the challenges posed by soft clays found in the site. Since the construction is meant to happen on-site, the bored pile method can be used. The loose areas with sand and uncontrolled fill can be tackled with dynamic compaction to restore the structure of the soil and optimize it for building the six-story building as shown in figure 2. Although some studies have suggested the use of "ground replacement, lime stabilization, and bridging" (Daly, 2010), the current report chose the most cost-effective and most used approaches.
References
Bonic, Z., Curcic, G. T., Davidovic, N. " Savic, J., 2015. Damage of Concrete and Reinforcement of Reinforced-Concrete Foundations Caused by Environmental Effects. Procedia Engineering, Volume 117, pp. 411-418.
Cubrinovski, M. " McCahon , I., 2011. Foundations on Deep Alluvial Soils, Christchurch : Canterbury Earthquakes Royal Commission.
Daly, J., 2010. Design, Construction and Performance of Buildings Foundations on Soft Clays in the Brisbane Region, Southern Queens Land: University of Southern Queensland.
Guyer, J. P., 2013. An Introduction to Fill and Backfilling, New York: Contibuing Education and Development.Inc.
Mohamad, N. O. et al., 2016. Challenges in Construction Over Soft Soil - Case Studies in Malaysia. s.l., IOP Publishing Limited, pp. 1-8.
Pankrath, H. et al., 2015. Dynamic Soil Compaction–Recent Methods and Research Tools for Innovative Heavy Equipment Approaches. Procedia Engineering, Volume 1225, pp. 390-396.
Tarawneh, B. " Matraji, M., 2014. Ground Improvement Using Rapid Impact Compaction: Case Study in Dubai. Gradevinar, 66(11), pp. 1007-1014.
