Dear Sir ,
how much Geo tech-investigation Is necessary before Home Construction (In Earth Quack Point of View) ? What is the benefit of this ?
Dear WAQAR, Fraternal greetings!
sorry for the delay in my answer as I am very busy with my project work.
My answer is as follows.
Although earthquakes can produce more than one kind of shock wave (some travel vertically, some horizontally, and others in circular patterns), it is horizontal acceleration(the side-to-side movement of the earth) that causes the greatest amount of severe damage. The concrete foundation of a building tends to move with these vibrations during a tremor, and if the above-ground portion of the structure is not firmly secured to the base, the framework can break away . . . resulting, of course, in partial or total collapse.
As a standard for all new construction, wood-frame structures with concrete or reinforced masonry foundations must be affixed to their bases by a specific method: First, anchor bolts of at least 1/2" in diameter (most builders use hardware that's 5/8" in diameter by 10" long) are embedded vertically 7" or more into the foundation all along the perimeter, at intervals of no more than 6' with a portion of each bolt projecting above the mortar or concrete. Then the building's sill plates (the bottommost, horizontal wooden members of a frame structure) are drilled so they'll slip down over the protruding anchor bolts, and once the plates are set in place flush against the foundation nuts are tightened down onto the wood.
This method of anchoring sill plates does keep the boards attached to the foundation during an earthquake, but it fails to help the structure as a whole absorb and withstand the forces of seismic shock. However, my technique a simple variation of the standard procedure allows a building to move with its foundation during the course of a quake, and also provides a bit of flexibility and cushioning between the base and the sill . . . thus offsetting at least some of an upheaval's shearing effect.
In fact, there's probably no real protection from the forces of a truly substantial quake (the energy released by the 1964 Alaska earthquake, for instance, was estimated to equal the power of 12,000 Hiroshima-type nuclear bombs!). But at least there's something you can do for relatively little money to give your home and outbuildings a better chance of surviving tremors or a quake of minor, or perhaps even moderate, magnitude. And that extra measure of protection, I think, is well worth the little additional expense and effort!
There are of course, engineering techniques that can be used to create a very sound structure that will endure a modest or even strong quake. However, during a very strong earthquake, even the best engineered building may suffer severe damage. Engineers design buildings to withstand as much sideways motion as possible in order to minimize damage to the structure and give the occupants time to get out safely. Buildings are basically designed to support a vertical load in order to support the walls, roof and all the stuff inside to keep them standing. Earthquakes present a lateral, or sideways, load to the building structure that is a bit more complicated to account for. One way to to make a simple structure more resistant to these lateral forces is to tie the walls, floor, roof, and foundations into a rigid box that holds together when shaken by a quake.
The most dangerous building construction, from an earthquake point of view, is unreinforced brick or concrete block. Generally, this type of construction has walls that are made of bricks stacked on top of each other and held together with mortar. The roof is laid across the top. The weight of the roof is carried straight down through the wall to the foundation. When this type of construction is subject to a lateral force from an earthquake the walls tip over or crumble and the roof falls in like a house of cards.
Construction techniques can have a huge impact on the death toll from earthquakes. An 8.8-magnitude earthquake in Chile in 2010 killed more than 700 people. On January 12, 2010, a less powerful earthquake, measuring 7.0, killed more than 200,000 in Haiti.
The difference in those death tolls comes from building construction and technology. In Haiti, the buildings were constructed quickly and cheaply. Chile, a richer and more industrialized nation, adheres to more stringent building codes.
As the buildings get bigger and taller other techniques are employed such as base isolation. During the past 30 years, engineers have constructed skyscrapers that float on systems of ball bearings, springs and padded cylinders.