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April 2004

     Previous Geotechnical Investigation

     Benefits of ADSS Contract 160 Series

     Geotechnical Information Management System (GIMS)

 Previous Geotechnical Investigation
How Geotechnical Investigation used to be carried out prior to
establishment of ADSS Contract 160 Series?

             Geotechnical Investigation used to be carried out under different Consultants

             Funding of soil investigation was through savings from SPC Contracts

             Roads Directorate undertakes soil investigations in their own way, through their

             This random approach resulted in the following disadvantages:
              - No control on the investigation techniques used.

              - Inconsistent site supervision.

              - No unified national specifications, standards.
              - No control on rates and quantities of work.

              - No quality control on reporting.
              - No proper archiving, resulting in work replication in areas already investigated.

Geotechnical Investigation
Field Observation       Cavities in Khalifa City (B) area caused serious problems for construction works

650mm micro2mwide
2m height x tunneling
Large cavity,2m height x
5m wide, with high
10m wide,encountered
cave was with heavy
machine collapsed water
flow formed under KB39
water flow encountered
between manholes weak in
during construction work
sandstone layer Contract
gypsum layer (ADSS
and KB40 (ADSS6m
of ADSS Contract 212.
212B), existing ground
Contract 218B).
below 10m below ground
surface was serious
The cave
Without for the
219B). geophysical
surveys, this of sewer
construction subsurface
The photo shows traces
hazards could remain
of inaccurate grouting,
undetected, to threaten
due to non- precise
future constructions.
identification of the cavity
location and size led to
collapse of tunnellling

Field Observation

Very deep cavity
exposed in a weak
layer of sandstone.

It runs into under
ground channels in
different directions.

The extent of this
cavity is not

Al Falah Area – massive cavity in sandstone, encountered during site levelling
           Khalifa City (B) – surface collapse occurred under a tractor while excavating
                      Ground Ground collapse under machine while
         Al Falah Area – D8 excavator slippedat Al Bahiainto huge cavity
                      for development of farm hanging – North
               drilling to confirm cavityadetected by Resistivity of Shahama Town.

Conventional Geotechnical Investigation

             Limitations of conventional soil investigation techniques (e.g. boreholes drilling):

                    -The random distribution of cavities associated with inconsistent subsurface strata in Khalifa
                    City (B), requires extensive survey coverage which can not be achieved by boreholes alone.

                   - Borehole data represent materials and features encountered within the diameter of the
                     borehole only (100mm), therefore chances of encountering cavities by boreholes are low.

                   - Time and cost involved in drilling boreholes are considerably high compared to that of
                     geophysical methods.

Integrated Solution

                          Integrated Solution for
                      soil investigation was needed

Geophysical Investigation
What is Geophysics?

          - Geophysics: Study of the physical properties of the ground.

          - Measured physical properties (parameters) are converted into geotechnical
            information, using specialised software.

          -In the last 20 years, Geophysical Survey methods have been widely used in
           ground investigation for civil engineering purposes.

Geotechnical Investigation
Geophysical Methods

          Geophysical Survey methods, tested in Abu Dhabi, for ground investigations are:

             1- Resistivity Imaging Method:
                 Measures the resistance of subsurface materials to induction of electrical current.

             2- Seismic Method:
                 Measures the time taken by seismic wave to travel from the source through the medium and
                 back, that reflects type of medium.

             3- Microgravity Method:
                 Measures changes in the earth’s gravitational field caused by local changes of materials.

             4- Geo-Radar Method:
                 Electromagnetic waves reflected from the subsurface materials, provide information about the
                 properties of the materials.

             5- Electro-Magnetic Method (conductivity):
                 Measures the electrical      conductivity   of   subsurface   materials   when   subjected   to
                 electromagnetic current.

Geotechnical Investigation
Significance of Integrated Solution using Geophysical Methods

          Compared to the conventional borehole drilling, the Geophysical Surveys have
          the following advantages:

               1- COMPLETE ground information can be acquired.

               2- Non-destructive.

               3- Time Saving.

               4- Cost Effective.

          Geophysical Survey methods used in combination with borehole drilling for
          verification; provide the most integrated solution for the identification of
          subsurface problems.

Resistivity survey – Khalifa B Extension

Resistivity survey – Contract 705

   Resistivity section showing cavity
      along proposed sewer line

    Cavity confirmed on site during
      excavation for sewer line

Benefits of ADSS Contract 160 Series
ADSS Contract 160 Series Geotechnical Cycle
           Contract 160 Series adopted a systematic approach of investigation                                             Advantages of the cycle:
                                                                                                                            The most practical and reliable method
                DESK STUDY
                                                                                                                            in solving the geotechnical problems.
                   Geological Maps
Data are                                                                                                                    Utilizes existing data and saves results
                   Previous Studies
re-used                                                                                                                     for future use
                   Aerial Photographs
                                                                                                                            Global integrated view of the case
                   Satellite Imagery                                                                                        under study.
                                                        Geological Maps                        Satellite Imagery
                   Site Walkovers                                                                                           Ensures Quality Control.

                                                                                          Topographical Surveys    Hydrological Studies
                                                                                          Geophysical Surveys      Observations
                                                                                          Exploratory Holes        In Situ Testing
                             Observations                  Geophysical
                                                                                          Trial Pits               Laboratory Testing

                                            Borehole Location Maps
                                            Geological Cross Sections
     DataBase                               Contour Maps
 Management System                          3D Meshes
                                            3D Ground Models                                                                              3D Ground Models
                                                                                              Cross Sections
   Spatial Data Server
                                            Foundation Design / Construction Mitigation                            Contour Maps
    over the internet

  Benefits of ADSS Contract 160 Series
  Benefits to the Sewerage Directorate

• Assessment during preliminary

• Assessment prior to construction.

• Assessment following construction.

• Mitigation
    - Change of location.

    - Change of alignment.

    - Change of methods.

    - Stabilisation of weak strata.

                                           along Trunk Sewerage (ADSS Contract No. 713A) – Shawamekh
                     Section 7.2 Km lengthSection 4.5 Km length along Storm Water Line (Contract 219B)

Benefits of ADSS Contract 160 Series
Benefits to the Buildings Directorate

         Khalifa City (B) – Sector 4, Plot 25                    Khalifa City (B) – Sector 15, Plot 6
                                                              - In case of cavities overlain by thick rock strata, shallow
     - Several cases proposed for piling, were converted to     foundation is advisable.
       shallow foundations, saving cost and time.
                                                              - Detailed study for each plot has been completed.

Benefits of ADSS Contract 160 Series
Benefits to the Town Planning
                                       Sectors Risk Map
                                                            Colour indicates
                                                            anomalous ground
                                                            and the cavities size

                                                             Depth indicates the
                                                             cavities level below
                                                             ground surface

                                                             Boreholes provides
                                                             strata details

                                                          These risk maps are
                                                          used by Town
                                                          Planning, for
                                                          finalisation of land

Benefits of ADSS Contract 160 Series
Areas Investigated under ADSS Contract 160 Series

                                                    Completed Geotechnical
                                                    Completed Geophysical

                                                    Ongoing Geophysical

Random Distribution of Cavities


Geotechnical Information Management System (GIMS)
Mission Statement

       Mission Statement:
            To establish a comprehensive central system for the management and
            electronic transfer of data related to ground investigation work covering the
            Emirate of Abu Dhabi that will fulfill the requirements of the Municipality and
            Town Planning and all other related departments, authorities and

       Departments, authorities and establishments to benefit from the system:
            1. Abu Dhabi Municipality and Town Planning

            2. Works Department

            3. Water and Electricity Authority

            4. Department of Social Services & Commercial Buildings

            5. Etisalat

            6. Military Survey Section

Geotechnical Information management System (GIMS)
End-Users Profiles

          Two categories of anticipated users are as follows:

                Engineers, Designers and Planners
                     The essential need for these users is to locate easily, fast and accurate the
                     geotechnical engineering parameters, required to accomplish their daily duties

                Geologists and Geophysists
                     These users will carry out analysis and interpretation of the data, depending on
                     the type of the project and the purpose of the study

         More than 95% of GIMS users will be of the first category, and the system is
         mainly aimed to provide easy, fast and accurate access of data by these users

Geotechnical Information management System (GIMS)
Modules included in the system

                        Geotechnical Information Centre Modules
                                                    Geotechnical Services
Geotechnical Information Management System
         Boreholes                                     Specifications / Guidelines

        Groundwater                                    Geotechnical National Register

         Laboratory Tests                              Geotechnical Contracts Register

                                                       Satellite Imageries

         Cavity Maps

         Observation Photographs

         Cut and Fill

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