This code of practice provides detailed procedures for determining the settlement of deep foundations subjected to symmetrical static vertical loads. It covers methods to evaluate immediate and consolidation settlements by considering soil characteristics, pile types, and load transfer processes. The standard is indispensable for geotechnical and foundation engineers focused on ensuring the stability and functionality of deep foundation systems.
Overview
This code of practice provides detailed procedures for determining the settlement of deep foundations subjected to symmetrical static vertical loads. It covers methods to evaluate immediate and consolidation settlements by considering soil characteristics, pile types, and load transfer processes. The standard is indispensable for geotechnical and foundation engineers focused on ensuring the stability and functionality of deep foundation systems.
Audience
Contents
Structure
Overview of the standard’s purpose and the symbols used in settlement computations for pile foundations in compressible soils. Applicable to pile groups, equivalent raft foundations, and calculation of consolidation settlements.
Clarification of critical symbols essential for settlement calculations including pile dimensions, soil parameters, load values, and settlement components.
Fundamental concepts regarding settlement estimation, including assumptions about soil consolidation, use of equivalent raft models, and factors influencing settlement behavior.
Guidance on modeling soil as single or multiple layers depending on uniformity, and the necessary structural data required for accurate settlement analysis.
Key assumptions about soil stress behavior, static vertical loading, and consolidation theory employed in settlement computations.
Description of load transmission via base resistance and shaft friction, and how these contribute separately to overall settlement.
Procedures and formulas to estimate the elastic settlement occurring immediately upon loading, including determination of modulus of elasticity and influence factors.
Calculation methods for primary consolidation settlement over time using consolidation parameters and degree of consolidation concepts.
Approaches for estimating settlement in end-bearing and friction piles, accounting for soil interaction and group effects.
Formulas and methods to predict settlement progression using consolidation degree and time factors related to soil properties.
Use of depth correction factors to refine estimated settlements accounting for increased soil confinement and stiffness with depth.
Recommended in-situ and laboratory tests for different soil types to obtain parameters necessary for settlement calculations.
Methods to estimate group settlement using equivalent footing concepts and empirical formulas derived from pile load testing.
Guidance on settlement evaluation in non-uniform, erratic, or cohesive soils, including sampling and testing frequency recommendations.
Discussion of assumptions, standard limitations, and recommended practices such as use of equivalent raft concepts and updated test standards.
Frequently Asked
IS 8009 Part 2 outlines procedures including elastic deformation of the foundation structure, calculation of immediate settlement using soil elastic response, and estimation of primary consolidation settlement based on consolidation theory. Additionally, it provides guidance on assessing the rate of settlement over time using consolidation parameters like the coefficient of consolidation (Cv). These methods focus on symmetrical static vertical loads and treat settlement components as additive to give total settlement.
The standard treats immediate settlement as the instantaneous elastic deformation occurring right after load application, predominantly in cohesionless soils and as an elastic response in clays, estimated via undrained triaxial testing. Consolidation settlement, on the other hand, develops gradually due to pore water pressure dissipation, mainly in clayey soils, and is evaluated using consolidation test data. The total settlement is considered as the sum of these components, ensuring a comprehensive assessment of foundation performance.
The code assumes that total soil stresses induced by the structure remain constant during settlement, and that induced stresses can be approximated through elasticity theory or simplified methods. It presumes the load applied to the foundation is static and vertical. Accurate assessment requires accounting for initial effective stresses, pore water pressures, and the soil's stress history. Additionally, overconsolidation effects are considered to enhance prediction accuracy.
For end bearing piles, settlement is primarily the sum of compressible soil layer settlement above the bearing stratum plus compression of the bearing sand layer itself, reflecting load transfer mainly through the pile tip. Friction piles rely largely on skin friction along the shaft, and their settlement is generally less than that of a single test pile due to soil compaction effects. Group settlement for friction piles is approximated as the settlement of an equivalent well foundation. Negative skin friction, if present, is added to the pile load for design considerations.
Settlement estimates are adjusted using a depth correction factor obtained from graphical charts like Fig. 12 in Part 1 of IS 8009. This factor accounts for increased soil stiffness and confinement effects with greater embedment depth, typically reducing settlement values. Both immediate and consolidation settlements can be corrected by multiplying the initially calculated settlement by this depth factor to obtain more accurate predictions for deep foundations.
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