0

Geotechnical investigations are carried out to obtain necessary data related to engineering properties of soil for proposed structures foundation and the repair of distress earthworks for another type of structures caused by subsurface conditions. The geotechnical investigation includes surface and subsurface exploration of a site. Subsurface exploration usually requires soil sampling and laboratory tests. In contrast, surface exploration can include geologic mapping, geophysical methods, and photogrammetry.

  • Foundation soil and rock condition is primary information required for economic design and construction of any structure
  • Required for Soundness, Safety and longevity of Structures
Geotechnical Investigation
Geotechnical Investigation

2.0

Geotechnical Investigation Objectives:

  • To find out the nature of the soil and rock deposit.
  • Depth and thickness of various soil and rock strata for structure foundation requirement.
  • Location of Ground Water Table (GWT)
  • In-situ properties by different Subsurface exploration field tests (SPT, DCPT, SCPT, Vane Shear Tests, PMT etc.)
  • Collection of soil and rock samples for determination of engineering properties in laboratory
  • Selection of foundation type and depth
  • Geotechnical engineering assessment of Foundation regarding its load bearing capacity and settlement aspects.

3.0

Geotechnical Investigation Stages:

3.1

Reconnaissance Stage:

  • Soil and groundwater conditions
  • Topography, drainage pattern, vegetation
  • Condition of existing structures
  • Suitability of site for the proposed project
  • Types of soil and rock formations from geology
  • Presence of natural resources
  • Stream pattern, if any
  • Seismic activity in the area

3.2

Planning of Geotechnical Investigation:

Planning of geotechnical investigations includes the following stages.

  • Location of geotechnical investigations.
  • Numbers of geotechnical investigations (i.e.) Boreholes
  • Depth of investigation.

3.2.1.1

Guidelines for Location, Nos and Depth of Borehole:

  • IS: 1892-1979 – Code of practice for site investigation for foundations
  • IRC: 78-2014 – Standard specifications and code of practice for road bridges, section-Vii: Foundations and substructures (revised edition) – Appendix-2 under clause no-704.3
  • Specification for road and bridge works, fifth revision, 2013 of MORTH by IRC -section 2400 (surface and subsurface investigation), section 2100 (open foundation), section 1100 (pile foundation) and section 1200 (well foundation)

3.2.1.2

General Locations of Investigation for Structure:

(i) Substructure: Pier and abutment locations for the following Structures (if any):

  • Major bridges
  • Minor bridges
  • Grade separators/flyovers
  • Vehicular underpasses (VUP)
  • Overpass
  • ROB (i.e. bridge over railway track)
  • RUB (i.e. bridge under railway track)
  • Pedestrian and cattle underpasses (PUP/CUP)
  • Culverts (pipe or slab or box)
  • Foot over bridges (FOB)

(ii) Approach embankment locations for all the following structures (if any):

  • Major and minor bridges
  • Grade separators/flyovers/vehicular underpasses (VUP)
  • ROB (i.e. bridge over railway track)
  • RUB (i.e. bridge under railway track) / overpass
  • Pedestrian and Cattle underpasses (PUP & CUP)

(iii) Any running embankment locations having height 6.00 m and above

(iv) Any building like administrative building and toll booths (if any)

(v) Pond and waterlogged area/ swampy locations (if any)

(vi) Hill and valley slope including landslide locations (if any)

3.2.2.1

Minimum number of geotechnical investigations for Foundation:

3.2.2.2

The structure having Shallow/Pile/Well Foundation in Soil or Rock:

  • As per IS: 1892 (Reaffirmed 1997): At an interval of 50m c/c (Ref: Clause No. 2.3.2.1)
  • As per IRC: 78 – 2014 (Structure foundations in soil): Investigations shall cover the entire length of the bridge and also extend on either side for a distance about twice the depth below the bed of the last main foundation (Ref: Clause No. 3.2 of Appendix 2 of IRC:78-2014)
  • As per IRC: 78 – 2014 (Structure foundations in rock): One drill hole per pier and abutment (Ref: Clause No. 3.2 of Appendix 2 of IRC:78-2014)
  • As per MORTH technical specification, fifth revision, 2013:
  1. At each pier and abutment of the bridge (Ref: Clause No. 2402.1 of Section 2400)
  2. In case of viaducts in the approaches on either side of the bridge, bores shall be taken at the location of each foundation of the viaduct spans (Ref: Clause No. 2402.1 of Section 2400) 
  3. If foundation strata variation appreciably affect the construction (especially in case of bridge foundations resting on rock), it will be necessary to take additional bores in the transverse direction also, to establish the complete profile of the underlying strata (Ref: Clause No. 2402.2 of Section 2400)

3.2.3.1

Minimum depth of Geotechnical Investigation(Beyond Depth of Foundation):

3.2.3.2

Structure having Shallow Foundation in Soil and rock:

  • As per IS: 1892 (Reaffirmed 1997) Structure foundations in soil: One and half times the width of foundation (Ref: Table 1 under clause no. 2.3.2.1)
  • As per IS: 1892 (Reaffirmed 1997) structure foundations in rock: 
  1. For massive and sound rock, half of the effective width of the foundation
  2. For moderately jointed and foliated rock, the effective width of the foundation 
  3. For heavily jointed and weathered rock, two times of the effective width of the foundation 
  4. Minimum 3.00m depth inside rock mass (Ref: For buildings, clause no. 4.9.3.2 of IS:13063)
  • As per IRC: 78 – 2014 (Structure foundations): 
  1. One and half times the proposed width of the foundation 
  2. If any unsuitable/questionable foundation material is found beyond the depth of investigation stated above, then exploration shall be extended to a sufficient depth into a firm or stable soil or well into the sound rock (Ref: Clause No. 3.2, 6.2.2, 6.3.2 and 7.2.2 of Appendix-2 of IRC:78-2014)
  • As per MORTH technical Specification, Fifth Revision, 2013:
  1.  One and half times the proposed width of the foundation
  2. If any suitable foundation material of doubtful bearing capacity is found beyond the depth of investigation stated above, then exploration the depth of investigation shall be extended to 4 times the width of foundation or till firm and stable soil or rock is met with (Ref: Clause No. 2403.1 of Section 2400)
  3. If the rock is met with, the depth of drilling into rock having ROD more than 75%, may be limited to 3 meters. (Ref: Clause No. 2403.1 of Section 2400)

3.2.3.3

Structure having Pile / Well Foundation in Soil and rock:

  • As per IS: 1892 (Reaffirmed 1997): One and half times the width of foundation from the bearing level, i.e. toe of pile or bottom of well (Ref: Table 1 under clause no. 2.3.2.1)
  • As per MORTH technical specification, fifth revision, 2013(for soil): 1.5 times estimated length of the pile in soil or 15m below the proposed founding Level (Ref: clause no. 1102.1 of section 1100 for “Pile Foundation” and clause no. 1202.3 of section 1200 for “Well Foundation”)
  • As per MORTH technical specification, fifth revision, 2013(for rock) : 
  1. 15 times diameter of the pile in weak/jointed rock but minimum 15 m in such rock
  2. Four times diameter of the pile in hard rock but minimum 3 m in such rock (Ref: Clause No. 1102.1 of Section 1100 for “Pile Foundation” and Clause No. 1202.3 of section 1200 for “Well Foundation”)

3.3

Field Investigation:

3.4

Laboratory Investigation:

3.5

Geotechnical Investigation Report:

  • Geological history and geographical background of the area
  • Total scope of work and a plot plan showing locations of all tests
  • Brief description of procedure adopted for field and laboratory tests.
  • Detailed bore-log/drill-log in the approved format
  • Laboratory test results in approved tabular and graphical form with the summary
  • True cross-sections/profile of all boreholes and or trial pits
  • All geotechnical engineering parameters
  • Recommendations on geological and lithological information of the area
  • The details of the landslide, if any
  • Recommendation for the foundation system of structures
  • Recommendations for ground treatment/improvement, foundation and embankment/subgrade treatment in case of weak sub-soil, expansive clay, liquefaction and artesian condition etc.

Your Opinion Matters: How easy is it to understand the information on our website?

View Results

Loading ... Loading ...
0
Summary
Geotechnical Investigation Objectives and Guidelines
Article Name
Geotechnical Investigation Objectives and Guidelines
Description
Geotechnical investigations are carried out to obtain necessary data related to engineering properties of soil for proposed structures foundation and the repair of distress earthworks for another type of structures caused by subsurface conditions. The geotechnical investigation includes surface and subsurface exploration of a site.
Author
Publisher Name
Construction Civil
Publisher Logo

WhiteHelmet

ConstructionCivil is a learning platform for all the Civil Engineers and Civil Engineering Students throughout the world. I have started this Website to educate and keep people notified by forming a trusted source of knowledge, everything related to Civil/Construction Engineering.
Subscribe
Notify of
guest
0 Comments
Inline Feedbacks
View all comments