Ground Investigations - Lecture 1: Introduction & Planning Stage

Flashcards covering the key concepts from the lecture, focusing on vocabulary related to geotechnical and ground investigations.

Ground Investigation

Generally is the starting point for medium to large projects in geotechnical design.

Geotechnical Investigation

Finding out what lies below the ground surface, including stratigraphy/profile, ground conditions, bedrock profile and water conditions.

Objectives of Ground Investigation

Determine the stratigraphy of the subsoil/rock including underground water conditions.

Objectives of Ground Investigation

Obtain samples for lab testing to determine soil/rock properties to enable an economical and technically sound design to be prepared.

Objectives of Ground Investigation

Foresee and provide against difficulties that may arise during construction owing to ground conditions.

Objectives of Ground Investigation

Assess the general suitability of the site for the proposed engineering works.

Objectives of Ground Investigation

Determine the cause of defects on an existing structure.

Risks of Inadequate Ground Investigations

Under design leading to failure plus cost of remediation.

Risks of Inadequate Ground Investigations

Overdesign with associated high costs.

Risks of Inadequate Ground Investigations

Cost overruns due to unforeseeable ground conditions.

Risks of Inadequate Ground Investigations

Project delays and associated costs.

Subsurface Investigation

Measurement of the engineering properties of subsoil through boreholes & trial pitting, laboratory testing, field testing and geophysics approach.

Ground Investigation Stages

Planning -> Desk study -> Site reconnaissance -> Ground investigation report.

Geotechnical design requirement

Evaluation of soil/rock properties of all building and civil works.

Imperatives of planning

To ensure smooth data collection process and avoid data gaps.

Investigation Scope

Design and constructability requirements, identify engineering analyses to be performed, identify engineering properties and parameters required for these analyses.

Desk Study

Process of gathering existing information about the site under consideration while in the office.

Principal objective of Desk Study

Obtain as much information about probable ground conditions, previous use of site and access to the site.

Sources of Information for Desk Study

Geological survey maps, Arial survey photographs, Local authorities, Local contractors, Local people and Public utility organizations.

Arial photographs

Identify manmade features on site and potential borrow source areas. Provides geologic and hydrological information which can be used as a basis for site reconnaissance.

Site Reconnaissance

Site walkabout to develop a feel for the site and confirm desk study information.

Important information gathered during Site Reconnaissance

Soil/rock type in any adjoining cutting, State of adjacent properties, Problem of confined access and Overhead cables.

Preliminary geotechnical/site model

Representation of the geology (solid and drift) that underlies the site and includes soil and rock stratigraphy and anticipated groundwater levels.

Subsurface exploration programme

Involves decisions on selection of appropriate investigation techniques, sampling methods, trial pits/borehole locations, Number of samples, Number and types of laboratory tests, Number and types of in-situ tests.

Categories of urban geotechnical investigation

Planning investigations, Urban development investigations and Specialised investigations.