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Ground Improvement is carried out to improves the subsoil properties like shear strength, stiffness and permeability etc. to reduce settlement of structure foundation before the start of actual construction work.

1.0

Introduction to Ground Improvement:

  • In poor and weak subsoils, design of conventional shallow foundation for structures and equipment may present problems concerning both sizing of foundation as well as control of foundation settlements
  • Traditionally, pile foundations have been employed often at enormous costs 
  • A more viable alternative in certain situations is to improve the subsoil itself to an extent such that the subsoil would develop an adequate bearing capacity and foundations constructed after subsoil improvement would have resultant settlements within acceptable limits 
  • The techniques for ground improvement has found large scale application in projects 

2.0

Objective:

Enhancement of the in-place properties of the ground/foundation strata by controlled use of technique suited to the subsoil.

3.0

Guidelines for Ground Improvement:

  • Specification for road and bridge works, 5th revision, 2013 of MORTH by IRC: clause no. 314
  • IRC:SP:13-2004: Guidelines for the design of small bridges and culverts, article no. 22 and 23
  • IS 13094: 1992 (Reaffirmed 1997): Selection Of Ground Improvement Techniques For Foundation In Weak Soils – Guidelines 
  • IS 15284 (Part 1): 2003: Design And Construction For Ground Improvement – Guidelines, Part 1 Stone Columns 
  • IS 15284 (Part 2): 2004: Design And Construction For Ground Improvement – Guidelines, Part 2 Preconsolidation Using Vertical Drains 

4.0

Necessary data for Ground Improvement Work:

  • Subsoil profile and soil properties up to a depth near two times of the width of the loaded zone or up to hard soil strata if found earlier. The information shall be collected by carrying soil investigations as per Guidelines
  • Engineering subsoil properties shall include index properties, shear parameters, compressibility properties etc.
  • Boreholes shall be completed by carrying a suitable number of static/dynamic cone penetration tests up to the required depth, which will be to be improved. In connection with selected boreholes, these tests work as an economical and fast method of learning the state of subsoil before and after the ground improvement work
  • Information shall be obtained with respect to the nature of structure and area covered by it, intensity and nature of applied loading, permissible distortions, the structure can withstand

5.0

Considerations for Ground Improvement:

  • Ground Improvement is indicated if the net applied loading intensity of the foundation beats the allowable bearing pressure estimated using in-situ foundation strata following Guidelines
  • Ground improvement work is also shown if even for relatively low loading intensities, the resultant settlement exceeds the acceptance criteria for the structure both from the viewpoint of distortions produced in the structure and from operation angle
  • Loose cohesionless sediments in seismic zones may be prone to liquefaction throughout earthquakes, especially under high water table positions. In such cases, the analysis should be continued for establishing the liquefaction potential of the subsoil. Ground improvement is offered if such analysis establishes that the subsoil is likely to liquefaction

6.0

Ground Improvement Methods:

  • Removal and replacement of poor in-situ sub-soil with competent backfill 
  • In-situ soil densification:

vibroflotation, Vibrocompaction, compaction piles, blasting and dynamic compaction (cohesionless) and dynamic consolidation (Cohesive) 

  • Pre-compression / pre-consolidation of in-situ soil:

Preloading with or without Vertical Drain like Sand Drain, PVBD etc., Surcharge Fills and Electro-osmosis 

  • Injections and grouting into in-situ soil:

Particulate Grouting, Chemical Grouting, Pressure injected Lime, Displacement Grout, Electro-kinetic Injections, Jet Grouting

  • In-situ soil reinforcement:

Vibroreplacement Stone Columns, Sand Columns, Root Piles, Soil Nailing, Strips and Membranes 

  • Use of admixtures:

Structural Fills, Mix-in-place Piles and Walls 

  • Thermals 

Heating and Freezing 

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7.0

Control and monitoring:

  • Before the commencement of ground improvement works, pilot boreholes with appropriate field and laboratory tests shall be done in locations particular to the area to be improved
  • After completion of ground improvement related work in a particular zone, the field and laboratory tests shall be repeated to assess the degree and plenty of improvement of subsoil
  • For medium to major activity, it is desirable, to initially allocate a trial zone for learning the pattern a deficiency of the ground treatment technique employed and optimization of the same
  • It will also be useful to include a program of instrumentation to observe the behaviour of subsoil throughout loading by measurement of pore pressure, soil movements, earth pressures, foundation settlement etc.

8.0

Quality Control: 

8.1

Field observations / instrumentation:

  • Heave Stake / Pegs 
  • Settlement Platform / Settlement Gauges 
  • Piezometers
  • Inclinometers

8.2

Recording of data:

  • A competent inspector shall be present to record the necessary information during the execution of the ground improvement work
  • Data to be recorded shall include
  • The sequence of operation of the work
  • Sequence and spacing of treatment points
  • Depth of treatment
  • Details of equipment employed and installation procedure followed
  • Records of instrumentation, if any;
  • Results of soil tests before and after treatment; and
  • Settlements during preloading

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Summary
The role of ground improvement in the foundation of Structure
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The role of ground improvement in the foundation of Structure
Description
Ground Improvement is carried out to improves the subsoil properties like shear strength, stiffness and permeability etc. to reduce settlement of structure foundation before the start of actual construction work.
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Construction Civil
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