“A tree with strong roots laughs at storms”. Like the quote indicates the strength of a tree lies in its root. If the foundation of a structure is strong then no storm or natural hazards can easily destroy it. So to make a good foundation do the things in right way or follow the norms, so that in future the strength of home will not be deteriorated. We all know something about the construction process of a building but we don’t know the details of a foundation process. So we are giving here some idea about this process where your builder can’t cheat you if you absorb these things in your mind.
So the first step for the strong root of your dream home would be marking the boundaries before preparing for excavation. For marking the boundary you must follow the plot map, so that there will be no error & which will not put you into any legal complications in future. Always use a right angle and line-string to mark perpendicular lines at various distances for foundations & columns, as shown in your design drawings. Always maintain the depth and level of the excavation with a water level & plinth level.
Then next important process is to make sure that there is no underground water present after excavation and before laying foundation. Because the underground water seeps into the foundation pits, ultimately causing damage. Whenever the excavation takes place bellow the water table it must affect the project .It affects the function & design of the facility & the cost of its construction. Ground water is a frequent cause of dispute between owner & contractor. Dewatering by unsuitable method may harm to the environment. In some areas dewatering process is closely monitored. Sometime to get the permission from the authority is tedious & sometime authorities require special procedure which can cost a lot to the project.
Design of structures bellow water table:-
Waterproofing like More elaborate methods are necessary, particularly with very deep structures, to insure watertight integrity. Flexible membranes are recommended so that minor structural cracking does not cause leaks.
Hydrostatic Pressure Slabs and walls must be designed to carry both soil loads and water pressure. Where column spacing is wide, slab strengthening can be a major cost.
The weight of the structure must be sufficient to resist buoyancy. If the calculations credit the weight of the upper floors of a building for example, or the equipment in a lift station, then temporary dewatering must be continued until the necessary weight is in place. Open pumping is not effective in nonplastic sands and silts, since boiling can loosen the soil at subgrade, harming its bearing capacity. When excavating into an aquifer of high transmissibility, a large initial rate of pumping will occur during storage depletion. Open pumping will be cumbersome, unless the excavation is carried out very slowly. Where there are existing structures nearby, loss of soils due to open pumping may cause damage. If artesian pressure exists in a confined aquifer below subgrade, the condition cannot be relieved by open pumping. During project planning, open pumping should not be budgeted for unless there is reasonable probability that conditions favorable to the method exist.
METHODS OF GROUNDWATER CONTROL:-
- Open Pumping:-
Open Pumping is the process in which as the excavation is advanced the water is allowed to flow in and is collected in ditches and sumps, then pumped away. The open pumping method is lowest in direct dewatering cost, and is viable under certain conditions. Under other conditions it can seriously hamper other operations, and can result in catastrophic failure. Conditions favorable for open pumping include shallow subgrades, no more than a few feet below water table, and stable soils of low to moderate permeability such as dense, well-graded tills, clayey sands, firm clays, or fissured rock.
Deep Wells with individual pumps are most suitable for free-draining soils, and where the bottom of the aquifer is well below the subgrade of the excavation. In this situation the yield per well in the dewatered condition is high, and relatively few wells are required. Since-the cost per well is high, if the wells must be spaced very closely to accomplish the desired result the method may not be cost-effective.
- wellpoint system:-
WellpointSystems utilize groups of closely spaced wellpoints connected to a common suction header and pump. The cost per wellpoint is low, and in stratified soils where the spacing must be close the installation cost is lower. However, wellpoints depend on atmospheric pressure to lift the water to the pump, and the amount the water can be lowered with the method is limited to about 15 to 18 ft (5 to 6 m) at sea level, less at higher elevations. For greater drawdowns, multistages of wellpoints are required.
So draining out of water is important to protect the foundations from damage. So the excavation must be done until we reach the hard strata. It is advisable to lay 2-3 inch thick plain cement concrete bellow the RCC foundation.
Then next thing is foundation:-
“foundation” means that part of a structure, which is in direct contact with and meant for transmitting loads to the ground.
Following are different types of foundations used in construction:
- Individual footing or isolated footing
- Combined footing
- Strip foundation
- Raft or mat foundation
- Pile foundation
- Drilled Shafts or caissons
In case of black cotton soil or soil types with low load bearing capacity, use pile foundations or continuous foundations.
Then next process is Soil filling.
Fill in the trench up to floor level,when the foundation is cast or plinth is constructed, by soil filling. Murram filling is a good choice. Filling should be done in layers for maximum 6”thickness, sprinkling each soil layer with water before compaction, using a ram or plate compactor .If murram or good quality clay is not available, use sand for filling with adequate water.
Hope it will help you to understand the essence of good foundation system for home construction.So comment bellow what are your opinion regarding this.