Geotechnical Investigations Overview

Site investigations are conducted to analyze the soil and rock conditions beneath a construction site. This information is crucial for designing appropriate foundations and earthworks to support the proposed structures, ensuring their stability and preventing issues arising from unfavorable subsurface conditions.

Surface exploration typically involves geological mapping, geophysical methods, and photogrammetry. It might also include a simple visual inspection of the site by a geotechnical professional to assess its physical characteristics.

Subsurface exploration is crucial to obtain information about the soil conditions beneath the surface. This data is necessary to understand the composition, density, and other properties of the soil, which directly impact the design and construction of foundations.

<p>Geophysical methods utilize physical properties of the earth, such as magnetic fields or seismic waves, to gather information about subsurface conditions without the need for direct excavation. This technique allows for non-invasive exploration, which can be particularly beneficial in sensitive areas or where excavation is impractical.</p> Signup and view all the answers

<p>The primary objective in this context is to gather information for a thorough risk assessment. This involves identifying the presence and significance of any contaminants present on the site to ensure safety and minimize potential environmental hazards.</p> Signup and view all the answers

<p>Typical samples include soil, water, and gases. Soil samples provide information about the physical and chemical properties of the ground. Water samples help assess groundwater contamination, while gas samples indicate the potential presence of volatile compounds.</p> Signup and view all the answers

<p>Identifying pathways and receptors is crucial because it helps understand how contaminants might migrate from the source and reach potentially vulnerable populations or ecosystems. This information guides the development of mitigation strategies to prevent or minimize the spread of contamination.</p> Signup and view all the answers

<p>Clearly defined objectives ensure that the investigation collects the right type and amount of data to answer specific questions about the site. This avoids unnecessary data collection, maximizes efficiency, and ensures a robust risk assessment.</p> Signup and view all the answers

<p>A piston sampler is preferred when soils are sensitive to disturbance or consist of silts and silty sands, which have some cohesion.</p> Signup and view all the answers

<p>A scraper bucket is used when soil deposits contain sand mixed with pebbles, which may be difficult to obtain with a split spoon sampler.</p> Signup and view all the answers

<p>The primary purpose is to gather information for dam designers to safely design the structure and accurately estimate its cost.</p> Signup and view all the answers

<p>Investigations should include regional geological mapping, dam axis survey, landslide possibility survey, and environmental impact assessment.</p> Signup and view all the answers

<p>Diamond core drilling recovers an undisturbed, cylindrical sample (core sample) from various depths, providing detailed geological insights.</p> Signup and view all the answers

<p>Geological mapping involves examining surface rock outcrops, conducting geophysical surveys using methods like seismic refraction, and excavating trenches and pits.</p> Signup and view all the answers

<p>Site investigations for bridges aim to plan, cost, conduct, and report on the investigation process, providing essential information for bridge foundation design.</p> Signup and view all the answers

<p>The objectives include describing the stages of work involved, gathering information for bridge foundation design, and assessing the site's suitability for bridge construction.</p> Signup and view all the answers

<p>The two main types of borings are large-diameter and small-diameter. Large-diameter borings are rarely used due to safety concerns and expense but are sometimes used to allow a geologist or engineer to visually and manually examine the soil and rock stratigraphy in-situ. Small-diameter borings are frequently used to allow a geologist or engineer to examine soil or rock cuttings or to retrieve samples at depth using Soil Samplers and to perform in place soil tests.</p> Signup and view all the answers

<p>The three types of samples are Disturbed Sample, Block Sample and Push in tube sample. Disturbed samples do not retain the soil's in-situ properties. Block samples retain some in-situ properties while Push in tube samples consist of soil in a tube.</p> Signup and view all the answers

<p>A borehole's primary purpose is to determine the nature of the ground, usually below 6m depth, in a qualitative manner and to recover undisturbed samples for quantitative examination. It is essential to compare borehole results with desk study data because the information gained from a borehole provides a limited picture of the subsurface structure and needs to be corroborated with expected findings from the desk study.</p> Signup and view all the answers

<p>Sealing core samples with paraffin and end sealing them helps maintain the water conditions and prevent physical interference. Paraffin sealing preserves the water content within the sample, while end sealing prevents physical tampering, ensuring the sample's integrity for accurate analysis.</p> Signup and view all the answers

<p>Including the detailed location of all boreholes, trial pits, and other excavations is crucial for providing a comprehensive overview of the site and its geological features. This information allows for accurate interpretation of the collected data and facilitates future site planning and development.</p> Signup and view all the answers

<p>The SPT test measures the resistance of the soil to penetration by a standard weight dropped from a specific height. The number of blows required to drive the sampler a certain distance is directly proportional to the density of the soil, making the SPT test a reliable indicator of soil density.</p> Signup and view all the answers

<p>Including an assessment of the proposed route's viability ensures that the chosen route is feasible and minimizes potential risks. Identifying alternative routes provides flexibility and facilitates informed decision-making regarding the optimal highway route selection.</p> Signup and view all the answers

<p>Bulk samples are necessary in soils with little or no cohesion because these soils are easily disturbed and do not maintain their in-situ structure. Collecting a bulk sample allows for comprehensive and reliable analysis of the soil's properties despite its lack of cohesion.</p> Signup and view all the answers

<p>The desk study aims to gather geological and historical information about the site to aid in planning the Ground Investigation.</p> Signup and view all the answers

<p>Information collected during site reconnaissance includes overall site layout, topography, basic geology, and local conditions.</p> Signup and view all the answers

<p>Signs of slope instability include bent trees, hummocks on the ground, and displaced fences or drains.</p> Signup and view all the answers

<p>Previous site investigation reports provide valuable historical data and context for assessing current site conditions.</p> Signup and view all the answers

<p>Access is essential for conducting investigations and can reveal potential obstructions like low overhead cables or watercourses.</p> Signup and view all the answers

<p>A trial pit is a shallow excavation used to investigate subsurface conditions, with a maximum depth of 6 meters.</p> Signup and view all the answers

<p>Two crucial sources of information for a desk study are geological maps and historical records of previous site investigations.</p> Signup and view all the answers

<p>During site reconnaissance, aspects such as the presence of wet marshy ground, springs, ponds, and stream flows should be examined.</p> Signup and view all the answers

<p>An undisturbed soil sample retains conditions close to those in situ, allowing for accurate tests of structural properties.</p> Signup and view all the answers

<p>Disturbed samples have had their soil structure altered significantly, making them non-representative of in-situ conditions.</p> Signup and view all the answers

<p>Offshore soil samples are collected using Kullenberg-type samplers or seabed samplers.</p> Signup and view all the answers

<p>Both standard shovels and trial pits produce disturbed samples by digging out soil from the site.</p> Signup and view all the answers

<p>A continuous flight auger retrieves soil by being screwed into the ground and retaining soil on its blades as it is pulled out.</p> Signup and view all the answers

<p>Shelby tubes are used to take undisturbed samples for routine site investigation works.</p> Signup and view all the answers

<p>The piston in deepwater soil samplers helps improve the collection of undisturbed samples by applying pressure to the soil.</p> Signup and view all the answers

<p>Disturbed soil samples can accurately determine properties like grain size distribution, Atterberg Limits, and water content.</p> Signup and view all the answers