DISASTER RESISTANT ARCHITECTURE

SITE SELECTION, SITE PLANING & SITE DEVELOPMENT FOR EARTHQUAKE RESISTANT

DESIGN

SITE SELECTION• The selection of suitable site is a crucial step in the design of a

building or planning a settlement in an earthquake prone area.• There are a number of earthquake related hazards which should

always be considered when choosing a site, together with the influence of the ground conditions at the site on the ground motion which the building may experience in a future earthquake.

• An assessment of extent of earthquake hazard should always form a part of overall site assessment and of specification for the design of any structures to be built there.

• No site can be expected to be ideal in all respects, so the choice of site will often involve a judgment about relative risks and the costs of designing to protect from them.

• But there can be some sites which could be so hazardous that they should be avoided if at all possible, since the cost of building is likely to be prohibitive.

• A few important considerations for selecting the an appropriate site are given below

Site selection – macro level• Before taking considerations for site at micro level

we have to look at the parameters which influence at macro level.

• Statistical analysis for considerations at macro level can be done in following steps:

1. By knowing the position of site on the tectonic plate,

2. By classifying the site in respective seismic zones which the country is divided into,

3. And even evaluating other risk factors which the site is subjected to..for example the presence of hills and rocky areas near the site increases the risk of landslides during earthquake.

Motion of seismic plates

Seismic zones in India

Earthquake risk zones in India

SITE SELECTION – MICRO LEVEL• The site conditions play a vital role in seismic safety of a building.

Hazardous sites should be avoided for building construction to minimize risks against natural disasters. Site Investigations will assist in identifying potential danger of sliding, erosion, land subsidence or liquefaction during an earthquake.

• Site Investigations will assist in identifying potential danger of sliding, erosion, land subsidence or liquefaction during an earthquake.

• The local practice of managing any such hazard should be given due considerations.

A safer site is the one having:• No danger of landslides• Sufficient plantation on slope• Trees not too close to the house• Mild slope• Far from river banks

POTENTIAL HAZARDOUS SITES

Steep and unstable slopes

Building should not be constructed near steep and unstable slopes. Cliffs made of soft orcrumbly, clay loam; deposits materials, etc. should be avoided.

Areas susceptible to landslides and rock fall• Landslides or rock fall areas should be avoided while

selecting a site for building construction.• Apparently some slopes may look stable, but failure

could be triggered by an earthquake.• Landslides and rock fall can damage buildings

partially or completely. However, building in these areas can be constructed after providing proper retaining walls and green barriers.

• Simple indication of sustained stability of a slope is the presence of upright standing trees on it.

• Abnormally inclined trees on a slope indicate instability of the hill slope.

Rock falls

Instable hill slope

River banks

• Buildings should be far enough from the river to avoid flash flood and earthquake damage.

Geological fault and Ruptured areas• Geological fault and ruptured areas that are usually

visible, permanent, deep and active should be avoided for construction.

• Buildings should be constructed at least 250 m away from these lines.

Site planning• Considerations to be taken while designing the

site are:1. Steep slopes2. Filled up soil3. Raft and pile foundations

Steep slopes• Buildings should be sufficiently away

from steep slopes. Sites located on or very close to steep slopes are always prone to landslides, especially in the earthquake prone regions.

• Even if the building has good earthquake resistant construction, they are prone to damages or total destructions on such sites.

• The periodic landslides are triggered by other aspects like excess rains, seepage etc.

• The Himalayan regions are particularly prone to landslides. Such landslides often prove to be more disastrous than the actual earthquake event.

Buildings located nearsteep slopes

Filled up soil• Foundation should rest

only on firm soil and not on filled up soil.

• Such constructions on filled up soils have witnessed extensive damages in the January 2001 Gujarat earthquake.

Buildingslocated on filled – up soil

should be avoided

Raft and pile foundations

• Many times it is unavoidable to construct the structure on filled up soil, as in most cases choice of site is not the option we have.

• In such situations raft on pile foundations have to be provided as shown in figure.

Buildings located onfilled – up soil should be provided

with raft on pile foundations

Forest and trees• The forests are really useful to stop landslides but buildings

should not be constructed close to any big tree, as there might be a possibility of falling of the trees during earthquake.

• The distance between tree and house should preferably be at least equal to the height of tree or house, whichever is greater.

Too Close building• Building should not be constructed close to another

building: there might be a possibility of falling of building during earthquake.

• The distance between two houses should be at least equal to the height of house.

CONCLUSITION• Finally it must be recognized that the

architectural requirements will often make asymmetrical design difficult or sometimes impossible.

• In these circumstances it is necessary, depending upon the size of the building and the type of asymmetry, to subdivide the major masses of the building to improve the seismic performance.