Posts by Kanwarjot Singh

Most of design codes assume that pile fails during strong earthquake by lateral spreading. Lateral spreading is based on bending mechanism where the inertia and slope movement causes bending in piles. In essence, piles are considered as beams which are subjected to lateral loads such as slope movement leading to pile failure.
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The use of prestressed tiebacks gets rid of the need of interior bracing. Prestressed tiebacks are anchored into rock or granular soils and excavation can be conducted by using powerful shovel instead of using hand excavation or other small excavators. It provides less restraint and allows free movement for excavation.
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The quality of slurry plays an important role in the quality of diaphragm walls. Firstly, if a thick slurry cake is formed in the interface between slurry and in-situ soil, it has a tendency to fall off during concreting works and it mixes with freshly placed concrete. Moreover, large thickness of slurry cake would reduce the concrete cover and affect the future durability performance of diaphragm walls.
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The most ideal situation is to supply each tremie pipe with a single concrete truck. However, if only one concrete truck is available, all the fresh concrete in the truck should not be placed in one single tremie pipe.

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Grouting can be implemented in two common modes, namely compaction grouting and fracture grouting. For compaction grouting, high viscosity grout is commonly used for injection into soils. Upon reaching the soils, the grout would not penetrate into soil spaces. Instead it forms a spherical bulb and remains as a homogeneous mass. The formation of bulb displaces the nearby soils.
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By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

In India 0.93 kg of CO₂ is emitted in the production of one kg of cement. In the financial year 2009-10 India produces 200 million tonnes of cement. In the production of this cement 186 million tonnes of CO₂ was emitted in the atmosphere during financial year of 2009-10.

The availability of water in India per person per year in 1950 was 5177 cu.m. In the year 2009 it is reduces to 1700 cu.m.

If 50 million tonnes cement in making concrete uses water reducers 7500000 tonnes of cement can be saved. 3750000 kl of potable water will be saved and the saving of Rs. 3300 crores per year to construction industry. This amount is worked out after adjusting the cost of water reducers. Less cement used means less cement required to be produce by the cement factories resulting 6975000 tonnes of CO₂ will be prevented to be emitted to the atmosphere. These are worked out with an average saving of 15% cement and 15% water.

CO₂ emission is word problem, but for India in addition to CO2 it has problems of Air, Water, Soil, Food and Noise pollutions. Less densily populated countries may cope with these problems but for India it is of the top concern. The population figures of 2009 is, India 350 person per sq.km, China 132 person per sq.km and USA only 34 person per sq.km. The figures of 2006 CO¬2 emissions are USA 658.60 tonnes per sq.km, China 611.76 tonnes per sq.km and India 459.35 tonnes per sq.km. Every one should contribute his or her efforts to save the environment from pollution. Those involve in the construction activities can contribute their share by proper design of concrete Mixes. This is best illustrated by the following examples.
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The critical depth of piles are normally assumed as 10-20 pile diameter deep and is the depth beyond which the resistance is constant and is equal to respective value at critical depth.
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The type of connection between piles and pile caps affects the load carrying capacity of pile groups. The fixity of pile head into pile cap, instead of pinning into pile cap, enhances higher lateral stiffness of the pile groups. For instance, for the same deflections, a cap with fixed connected piles can sustain far more loads than that of pinned connected piles. To satisfy the criterion of fixed connection, the minimum embedded length of piles into pile caps should be at least two times the diameter of piles.
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(i) Use slender pile sections (e.g. H-pile or precast pile) because smaller pile area when subject to the same working load would produce higher deformation, thus increasing the relative downward movement of piles.

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The advantages of top-down approach are listed below:

(i) The structures above ground can be carried out simultaneously with the structures below ground. This greatly reduces the time for construction.
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