Consulting April 2004 Consulting Contents Previous Geotechnical Investigation Benefits of ADSS Contract 160 Series Geotechnical Information Management System (GIMS) Consulting 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 contracts 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. Consulting 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 surface.(ADSSaContract The cave Without for the 219B). geophysical obstacle surveys, this of sewer construction subsurface The photo shows traces hazards could remain of inaccurate grouting, pipeline. undetected, to threaten due to non- precise future constructions. identification of the cavity location and size led to collapse of tunnellling machine. Consulting 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 known. 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. Consulting 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. Consulting Integrated Solution Integrated Solution for soil investigation was needed Consulting 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. Consulting 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. Consulting 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. Consulting Resistivity survey – Khalifa B Extension Consulting Resistivity survey – Contract 705 Resistivity section showing cavity along proposed sewer line Cavity confirmed on site during excavation for sewer line Consulting 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. INVESTIGATION Topographical Surveys Hydrological Studies Geophysical Surveys Observations Exploratory Holes In Situ Testing Observations Geophysical Trial Pits Laboratory Testing Surveys Exploratory Holes OUTPUT Borehole Location Maps Geological Cross Sections Relational DataBase Contour Maps Management System 3D Meshes Geological 3D Ground Models 3D Ground Models Cross Sections Spatial Data Server Foundation Design / Construction Mitigation Contour Maps over the internet Consulting Benefits of ADSS Contract 160 Series Benefits to the Sewerage Directorate • Assessment during preliminary design. • 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) Consulting 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. Consulting 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 use. Consulting Benefits of ADSS Contract 160 Series Areas Investigated under ADSS Contract 160 Series Completed Geotechnical Works Completed Geophysical Surveys Ongoing Geophysical Surveys Consulting Random Distribution of Cavities Cavities Consulting 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 establishments. 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 Consulting 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 Consulting Geotechnical Information management System (GIMS) Modules included in the system Geotechnical Information Centre Modules GIMS Geotechnical Services Geotechnical Information Management System Boreholes Specifications / Guidelines Groundwater Geotechnical National Register Laboratory Tests Geotechnical Contracts Register Satellite Imageries Geophysics Cavity Maps Observation Photographs Cut and Fill
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