1610537947SITE_INVESTIGATION for foundation of a structure.pptx

SITE_INVESTIGATION for foundation of a structure.pptx

1. BASIC CIVIL ENGINEERING CVE 301 ENGR. VICTOR ADEBAYO CIVIL ENGINEERING DEPARTMENT COLLEGE OF ENGINEERING

2. AIMS AND OBJECTIVES Describe processes or stages of work to be followed for a site investigation. Describe information required to design foundations . Indicate standards of skill, workmanship and reporting, which are to be applied.

3. TABLE OF CONTENTS INTRODUCTION BACKGROUND OF STUDY APPROACHES TO SITE INVESTIGATION FACTORS INFLUENCING THE SELECTION OF METHODS OF INVESTIGATION PROCESS OF SITE INVESTIGATION PRELIMINARY INFORMATION & PLANNING THE WORK OBJECTIVES OF SITE INVESTIGATION DESK TOP STUDY DOCUMENT REVIEW SITE RECONNAISSANCE GROUND INVESTIGATION SUBSURFACE EXPLORATION BORINGS GEOTECHNICAL REPORTS CONCLUSIONS AND RECOMMENDATIONS CONCLUSION

4. INTRODUCTION Site and subsurface characteristics directly affect the choice of foundation type, capacity of the foundation, foundation construction method, and bridge cost. Subsurface and foundation conditions also frequently directly and indirectly affect the route alignment, bridge type selection, and/or foundation span length.

5. INTRODUCTION CONTD. The elements of a site investigation depend heavily on the project but generally should provide the following: 1. Information to determine the type of foundation required (shallow or deep). 2. Information to allow the geotechnical consultant to make a recommendation on the allowable load capacity of the foundation. 3 . Sufficient data/laboratory tests to make settlement predictions.

6. INTRODUCTION CONTD. 4. Location of the groundwater table (or determination of whether it is in the construction zone). 5. Information so that the identification and solution of construction problems (sheeting and dewatering or rock excavation) can be made. 6. Identification of potential problems (settlements, existing damage, etc.) concerning adjacent property. 7. Identification of environmental problems and their solution .

7. BACKGROUND OF STUDY Geotechnical investigations are performed to evaluate those geologic, seismologic, and soils conditions that affect the safety, cost effectiveness, design, and execution of a proposed engineering project. Insufficient geotechnical investigations, faulty interpretation of results, or failure to portray results in a clearly understandable manner may contribute to inappropriate designs, delays in construction schedules, costly construction modifications, use of substandard borrow material, environmental damage to the site, post construction remedial work, and even failure of a structure and subsequent litigation.

8. BACKGROUND OF STUDY CONTD. Investigation of the distribution, type, and physical properties of subsurface materials are, in some form or other, required for the final design of most civil engineering structures. These investigations are performed to obtain solutions to the following groups of problems: Foundation problems or determination of the stability and deformations of undisturbed subsurface materials under superimposed loads, in slope and cuts, or around foundation pits and tunnels; and determination of the pressure of subsurface materials against supporting structures when such are needed .

9. BACKGROUND OF STUDY CONTD. Construction problems or determination of the extent and character of materials to be excavated or location and investigation of soil and rock deposits for use as construction materials in earth dams and fills, for road and airfield bases and surfacing, and for concrete aggregates. Groundwater problems or determination of the depth, hydrostatic pressure, flow, and composition of the ground water, and thereby the danger of seepage, underground erosion, and frost action; the influence of the water on the stability and settlement of structures; its action on various construction materials; and its suitability as a water supply.

10. APPROACHES TO SITE INVESTIGATION Approach 1: Desk-study and geotechnical advice. Approach 2: ‘Standard’ ground investigation Approach 3: Limited investigation, coupled with monitoring Approach 4: The observational method

11. Factors Influencing the Selection of Methods of Investigation Nature of subsurface materials and groundwater conditions. Size of structure to be built or investigated. Scope of the investigation, e.g., feasibility study, formulation of plans and specifications. Purpose of the investigation, e.g., evaluate stability of existing structure, design a new structure. Complexity of site and structure .

12. Factors Influencing the Selection of Methods of Investigation Topographic constraints. Difficulty of application. Degree to which method disturbs the samples or surrounding grounds. Budget constraints. Time constraints. Environment requirements/consequences. Political constraints .

13. PROCESS OF SITE INVESTIGATION Objectives of Site Investigation Desk Study Site Reconnaissance Planning Ground Investigation: Trial Pits Boreholes Sampling Reporting

14. PRELIMINARY INFORMATION & PLANNING THE WORK Project Location. Type of Project. Scope of Work. Budget and scheduling considerations Selection of the interdisciplinary team (such as geotechnical engineer, engineering geologist, structural engineer, hydrogeologist and the like) that will work on the project. Preliminary subsurface exploration plan, such as the number, location, and depth of borings. Document collection. Laboratory testing requirements. Types of engineering analyses that will be required for the design of the foundation.

15. OBJECTIVES OF SITE INVESTIGATION Suitability Design Construction Materials Effect of Changes Identify Alternatives

16. DESK TOP STUDY Every site investigation should commence with a desk study directed towards collecting, collating and reviewing the following: Design drawings from any previous structure at the site. Previous site investigation reports, borehole logs, penetrometer results and construction experience e.g. piling records. Geological and Topographical maps, survey data and records. Hydrological data. Aerial photographs. Regional seismicity data. Survey records, local knowledge and resources.

17. DOCUMENT REVIEW Prior Development. Aerial Photographs and Geologic Maps Topographic Maps Building Code and Other Specifications Documents at the Local Building Department . Forensic Engineering.

18. SITE RECONNAISSANCE Legal and physical aspects of access to site and bridge alignment – both riverbed and adjoining properties. Availability of any services or supplies of water, electricity, earthworks plant. Buried or overhead services. Photographs of surface conditions. Traffic control requirements.

19. SITE RECONNAISSANCE CONTD The possible effects of alternative investigation techniques on the environment (for example, ground disturbance, vegetation removal, water discharge, noise etc.). On-ground survey details. Tide , river level or other natural constraints. Notes on any exposed geology, for example the presence of boulders, bedrock exposure, swamps etc. The physical relationship of the proposed construction to the immediate natural surroundings and any existing developments.

20. GROUND INVESTIGATION This stage of the Geotechnical Investigation is involved with the exploration of subsurface conditions and retrieval of test data for generating geotechnical parameters and geotechnical profiles . Defining the scope of the investigation (e.g. number of test locations, type of test, frequency and depth ) is not covered explicitly by these guidelines. The number, location and depth of tests is to consider: Expected sub-surface conditions Previous geotechnical information available Likely extent of zones in ground influenced by loading

21. GROUND INVESTIGATION CONTD Need to achieve a reliable geotechnical model for analysis Size and importance of the structure Requirement to minimise contractor and MRWA risk of changes during the construction Programme due to variations in the subsurface conditions from that reported during the Investigation stage.

22. GROUND INVESTIGATION CONTD Groundwater must be investigated to determine: the level of the permanent water table at the time of the investigation occurrence of a perched water table condition and its level estimated rates of inflow to excavations effects of de-watering on water table levels and on adjacent structures the presence of sub-artesian conditions the potential aggressiveness of the soil and groundwater, for example SO4, Cl, pH and Total Dissolved Solids (TDS) to buried concrete and steel.

23. SUBSURFACE EXPLORATION Document review Purpose of subsurface exploration Borings layout , and depth of subsurface exploration Test pits and trenches Preparation of logs Geophysical techniques Subsurface exploration for geotechnical earthquake engineering Subsoil profile

24. BORINGS The most widely used method of subsurface investigation for compact sites as well as for most extended sites is boring holes into the ground, from which samples may be collected for either visual inspection or laboratory testing. Several procedures are commonly used to drill the holes and to obtain the soil samples. Exploratory holes into the soil may be made by hand tools , but more commonly truck- or trailer-mounted power tools are used.

25. GEOTECHNICAL REPORTS Part 1 – (“Site Investigations Report”) details of all field and laboratory test data to be represented Part 2 – (“Interpretative Report”) the geotechnical evaluation, interpretation, conclusions and recommendations Part 1 – Presentation of Site Investigation Purpose and scope of the geotechnical investigation Brief description of the project Dates between which field and laboratory work were performed. Detailed description of methods used for the field and the laboratory work with reference to accepted standards followed Presentation of field observations Data on fluctuations of groundwater table Compilation of individual boring logs, penetrometer results etc. Colour photographs of rock core. Grouping and presentation of field and laboratory test results in appendices and as summary tables. Names of the persons responsible for geotechnical site investigations and report writing.

26. GEOTECHNICAL REPORTS Part 2 – Presentation of Evaluations, Conclusions and Recommendations Review of the field and laboratory work by the Geotechnical Engineer. Tabulation and graphical presentation of the results of the field and laboratory work in relation to the requirements of the projects. Determination of the depth to the groundwater table and its seasonal fluctuations. Sub-surface profile(s) in graphic form (geotechnical profile or model), showing the disposition of the various sub-surface formations. Comments on irregularities such as pockets, cavities etc. Collating and presentation of the geotechnical data for each sub-surface formation. This presentation should be in a form which would enable selection of characteristic values for design.

27. CONCLUSIONS AND RECOMMENDATIONS Classification of the project according to geotechnical complexity. Selection of suitable characteristic values for the requirements of the project (geotechnical design parameters). Settlement and stability computations. Recommendations concerning problems that may be encountered during excavations, pumping operations , construction of retaining structures and ground anchors, placement of earth materials etc. Comment on likely interaction of work on nearby structures. Recommendations on any other issues e.g. for surface drainage if required. Comments on liquefaction potential, scour depth, unsuitable soil etc. if applicable

28. REFERENCES M. J. Tomlinson; ‘‘Foundation Design And Construction,’’ 5th Edition, John Wiley & Sons, Inc., New York. 2001. C. R. I. Clayton, M. C. Matthews And N. E. Simons; “Site Investigation”. 2nd Edition. Department Of Civil Engineering, University Of Surrey. F. Chowdhury And S. Rehman ; “Guidelines For Geotechnical Investigation Of Bridge Structures” . Main Roads Western Australia, March 2009. Australian Standard As1726 “Geotechnical Site Investigations” Australian Standard As1170 “Structural Design Actions” Australian Standard As2159 “Piling – Design And Installation” Australian Standard As5100 “Bridge Design-foundations And Soil Supporting Structures” Standards Australia Geotechnical Site Investigation, As1726. Standards Australia Structural Design Actions, As1170 Standards Australia Bridge Design – Part 3: Foundation And Soil Supporting Structures, As5100.3.