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The number and disposition of bore holes are varied, depending upon _______
Surroundings
Strata
Subsoil condition
Ground water
Subsoil condition
The number and disposition of boreholes during a geotechnical site investigation are primarily determined by the variability and complexity of the subsoil conditions. Since the subsurface profile is unknown beforehand, the spacing and depth of borings are adjusted to define geological stratigraphy, soil/rock properties, and groundwater levels accurately.
The number and disposition of boreholes during a geotechnical site investigation are primarily determined by the variability and complexity of the subsoil conditions. Since the subsurface profile is unknown beforehand, the spacing and depth of borings are adjusted to define geological stratigraphy, soil/rock properties, and groundwater levels accurately.
N=f(V,A,S) тАФ where N is number of borings, V is soil variability, A is area, and S is structural load intensity
Site investigation aims to obtain a representative soil profile. In areas with highly variable subsoil or complex stratification, a denser grid of boreholes is required to capture lateral and vertical heterogeneities. Conversely, in uniform soil deposits, fewer boreholes are sufficient. This ensures that the determined geotechnical parameters, such as bearing capacity or shear strength, are reliable for structural design.
IS:1892 provides guidelines for site investigation and depth of boreholes.
Borehole spacing typically ranges from 10m to 30m for detailed investigations.
The disposition (layout) should be staggered if the site area is large to ensure total coverage.
Depth of exploration is determined by the zone of influence of the foundation load.
Reduces risk of foundation settlement or failure.
Optimizes project cost by avoiding excessive or inadequate investigation.
Increased investigation cost and time for complex sites.
Potential for missing localized soil anomalies even with grid layouts.
Foundation design for high-rise buildings.
Slope stability analysis in civil infrastructure projects.
In highly variable soil, the number of borings must be increased to delineate lenses of soft or compressible material.
Option B (Strata) is a component of subsoil conditions, but 'subsoil condition' is the broader and more accurate engineering term.
Groundwater (Option D) affects the sampling method, but not primarily the grid layout frequency.
C is correct тАФ the number and distribution of boreholes depend on the variability of the subsoil conditions to ensure an accurate site representation.
Always remember that geotechnical design is iterative; if initial boreholes reveal unexpected variability, you must increase the number of subsequent borings before finalizing the foundation design.