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Encyclopedia > Geotechnical investigation
A drill rig operator advances a direct push soil sampler.

Geotechnical investigations are performed by geotechnical engineers or engineering geologists to obtain information on the physical properties of soil and rock around a site to design earthworks and foundations for proposed structures and for repair of distress to earthworks and structures caused by subsurface conditions. A geotechnical investigation will include surface exploration and subsurface exploration of a site. Sometimes, geophysical methods are used to obtain data about sites. Subsurface exploration usually involves soil sampling and laboratory tests of the soil samples retrieved. Image File history File links Size of this preview: 800 × 586 pixelsFull resolution (969 × 710 pixels, file size: 276 KB, MIME type: image/jpeg) (All user names refer to en. ... Image File history File links Size of this preview: 800 × 586 pixelsFull resolution (969 × 710 pixels, file size: 276 KB, MIME type: image/jpeg) (All user names refer to en. ... Earthworks can refer to: Civil engineering earthworks based on moving massive quantites of soil; The Earthworks audio equipment company; The novel Earthworks by Brian Aldiss; The earthworks style of art. ... A foundation is a structure that transmits loads from a building or road to the underlying ground. ... Exploration geophysics is the applied branch of geophysics which uses deep and primarily near surface methods to probe or image the earth. ...


Surface exploration can include geologic mapping, geophysical methods, and photogrammetry, or it can be as simple as a geotechnical professional walking around on the site to observe the physical conditions at the site. A geologic map is a special-purpose map made for the purpose of showing subsurface geological features. ... Photogrammetry is a remote sensing technology in which geometric properties about objects are determined from photographic images. ...


To obtain information about the soil conditions below the surface, some form of subsurface exploration is required. Methods of observing the soils below the surface, obtaining samples, and determining physical properties of the soils and rocks include test pits, trenching (particularly for locating faults and slide planes), boring, and in situ tests. Geologic faults, fault lines or simply faults are planar rock fractures, which show evidence of relative movement. ... This article is about geological phenomenon. ... In situ is a Latin phrase meaning in the place. ...

Contents

Soil sampling

Borings come in two main varieties, 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 examine soil or rock cuttings from the drilling operation, to retrieve soil samples at depth, and to perform in-place soil tests.


Soil samples are obtained in either "disturbed" or "undisturbed" condition; however, "undisturbed" samples are not truly undisturbed. A disturbed sample is one in which the structure of the soil has been changed sufficiently that tests of structural properties of the soil will not be representative of in-situ conditions, and only properties of the soil grains can be accurately determined. An undisturbed sample is one where the condition of the soil in the sample is close enough to the conditions of the soil in-situ to allow tests of structural properties of the soil to be used to approximate the properties of the soil in-situ.


Soil samplers

Soil samples are taken using a variety of samplers; some provide only disturbed samples, while others can provide relatively undisturbed samples.

  • Shovel. Samples can be obtained by digging out soil from the site. Samples taken this way are disturbed samples.
  • Modified California Sampler. Similar in concept to the SPT sampler, the sampler barrel has a larger diameter and is usually lined with metal tubes to contain samples. Samples from the Modified California Sampler can be considered undisturbed if the soil is not excessively soft, does not contain gravel, or is not a very dense sand.
  • Piston samplers. These samplers are thin-walled metal tubes which contain a piston at the tip. The samplers are pushed into the bottom of a borehole, with the piston remaining at the surface of the soil while the tube slides past it. These samplers will return undisturbed samples in soft soils, but are difficult to advance in sands and stiff clays, and can be damaged (compromising the sample) if gravel is encountered. The Livingstone corer is a commonly used piston sampler. A modification of the Livingstone corer with a serrated coring head allows it to be rotated to cut through subsurface vegetable matter such as small roots or buried twigs.
  • Pitcher Barrel sampler. This sampler is similar to piston samplers, except that there is no piston. There are pressure-relief holes near the top of the sampler to prevent pressure buildup of water or air above the soil sample.

Shovel with wide blade - especially appropriate for lifting snow or coal A shovel is a tool for lifting and moving loose material such as coal, gravel, snow, soil, or sand. ... Water borehole in northern Uganda A borehole is a deep and narrow shaft in the ground used for abstraction of fluid or gas reserves below the earths surface. ...

In-situ tests

A standard penetration test (SPT) is an in-situ dynamic penetration test designed to provide information on the properties of soil, while also collecting a disturbed soil sample for grain-size analysis and soil classification. The Standard Penetration Test (SPT) is an in-situ dynamic penetration test designed to provide information on the geotechnical properties of soils. ...


A cone penetration test (CPT) is performed using an instrumented probe with a conical tip, pushed into the soil hydraulically at a constant rate. A basic CPT instrument reports tip resistance and shear resistance along the cylindrical barrel. CPT data has been correlated to soil properties. Sometimes instruments other than the basic CPT probe are used, including: The (Dutch) Cone Penetration Test (CPT) is a test to measure the strength or bearing capacity of (soft) soils. ...

  • CPTu - Piezocone Penetrometer. This probe is advanced using the same equipment as a regular CPT probe, but the probe has an additional instrument which measures the groundwater pressure as the probe is advanced.
  • SCPTu - Seismic Piezocone Penetrometer. This probe is advanced using the same equipment as a CPT or CPTu probe, but the probe is also equipped with either geophones or accelerometers to detect shear waves and/or pressure waves produced by a source at the surface.
  • Full Flow Penetrometers - T-bar, Ball, and Plate: These probes are used in extremely soft clay soils (such as sea-floor deposits) and are advanced in the same manner as the CPT. As their names imply, the T-bar is a cylindrical bar attached at right angles to the drill string forming what look likes a T, the ball is a large sphere, and the plate is flat circular plate. In soft clays, soil flows around the probe similar to a viscous fluid. The pressure due to overburden stress and pore water pressue is equal on all sides of the probes (unlike with CPT's), so no correction is necessary, reducing a source of error and increasing accuracy. Especially desired in soft soils due to the very low loads on the measuring sensors. Full flow probes can also be cycled up and down to measure remolded soil resistance. Ultimately engineers can use the measured penetration resistance to estimate undrained and remolded shear strengths.

Flat Plate Dilatometer Test (DMT) is a flate plate probe often advanced using CPT rigs, but can also be advanced from conventional drill rigs. A diaphragm on the plate applies a lateral force to the soil materials and measures the strain induced for various levels of applied stress at the desired depth interval.


Laboratory tests

A wide variety of laboratory tests can be performed on soils to measure a wide variety of soil properties. Some soil properties are intrinsic to the composition of the soil matrix and are not affected by sample disturbance, while other properties depend on the structure of the soil as well as its composition, and can only be effectively tested on relatively undisturbed samples. Some soil tests measure direct properties of the soil, while others measure "index properties" which provide useful information about the soil without directly measuring the property desired.

Atterberg limits 
The Atterberg limits define the boundaries of several states of consistency for plastic soils. The boundaries are defined by the amount of water a soil needs to be at one of those boundaries. The boundaries are called the plastic limit and the liquid limit, and the difference between them is called the plasticity index. The shrinkage limit is also a part of the Atterberg limits. The results of this test can be used to help predict other engineering properties.[1]
California bearing ratio 
ASTM D 1883. A test to determine the aptitude of a soil or aggregate sample as a road subgrade. A plunger is pushed into a compacted sample, and its resistance is measured. This test was developed by CalTrans, but it is no longer used in the CalTrans pavement design method. It is still used as a cheap method to estimate the resilient modulus.[2][3]
Direct shear test 
ASTM D3080. The direct shear test determines the consolidated, drained strength properties of a sample. A constant strain rate is applied to a single shear plane under a normal load, and the load response is measured. If this test is performed with different normal loads, the common shear strength parameters can be determined.[4]
Expansion Index test 
This test uses a remolded soil sample to determine the Expansion Index (EI), an empirical value required by building design codes, at a water content of 50% for expansive soils, like expansive clays.[5]
Hydraulic conductivity tests 
There are several tests available to determine a soil's hydraulic conductivity. They include the constant head, falling head, and constant flow methods. The soil samples tested can be any type include remolded, undisturbed, and compacted samples.[6]
Oedometer test 
This can be used to determine consolidation (ASTM D2435) and swelling (ASTM D4546) parameters.
Particle-size analysis 
This is done to determine the soil gradation. Coarser particles are separated in the sieve analysis portion, and the finer particles are analyzed with a hydrometer. The distinction between coarse and fine particles is usually made at 75 μm. The sieve analysis shakes the sample through progressively smaller meshes to determine its gradation. The hydrometer analysis uses the rate of sedimentation to determine particle gradation.[7]
R-Value test 
California Test 301 This test measures the lateral response of a compacted sample of soil or aggregate to a vertically applied pressure under specific conditions. This test is used by CalTrans for pavement design, replacing the California bearing ratio test.
Soil compaction tests 
Standard Proctor (ASTM D698), Modified Proctor (ASTM D1557), and California Test 216. These tests are used to determine the maximum unit weight and optimal water content a soil can achieve for a given compaction effort.
Soil suction tests 
ASTM D5298.
Triaxial shear tests 
This is a type of test that is used to determine the shear strength properties of a soil. It can simulate the confining pressure a soil would see deep into the ground. It can also simulate drained and undrained conditions.
Unconfined compression test 
ASTM D2166. This test compresses a soil sample to measure its strength. The modifier "unconfined" contrasts this test to the triaxial shear test.
Water content 
This test provides the water content of the soil, normally expressed as a percentage of the weight of water to the dry weight of the soil.

The Liquid Limit, also known as the upper plastic limit, and the Atterberg limit, is the water content at which a soil changes from the liquid state to a plastic state. ... Wikipedia does not yet have an article with this exact name. ... Caltrans logo The soaring ramps in the stack interchanges favored by Caltrans often provide stunning views. ... A direct shear test is a laboratory test used by Professional Engineer Mohamed Fazlin to find the shear strength parameters of soil. ... Expansive clay is a clay that is prone to large volume changes that are directly related to changes in water content. ... written by AmerHydraulic conductivity, mathematically represented as , is a property of soil or rock, in the vadose zone or groundwater, that describes the ease with which water can move through pore spaces or fractures. ... Soil gradation describes the sizes of individual particles in soil. ... A sieve analysis is a practice or procedure used to assess the particle size distribution of a granular material. ... A hydrometer is an instrument used for determining the specific gravity of liquids. ... The R-Value test, California Test 301, measures the response of a compacted sample of soil or aggregate to a vertically applied pressure under specific conditions. ... Soil compaction occurs when weight of livestock or heavy machinery compresses the soil, causing it to lose pore space. ... The Proctor compaction test, and the related Modified Proctor compaction test, are tests to determine the maximum practically-achievable density of soils and aggregates, and are frequently used in geotechnical engineering. ... A triaxial shear test is a common method to measure the mechanical properties of many deformable solids, especially soil, sand, clay, and other granular materials or powders. ... Soil composition Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, or wood on a volumetric or gravimetric basis. ...

Geophysical exploration

Geophysical methods are used in geotechnical investigations to evaluate a site's behavior in a seismic event. By measuring a soil's shear wave velocity, the dynamic response of that soil can be estimated.[8] There are a number of methods used to determine a site's shear wave velocity: Exploration geophysics is the applied branch of geophysics which uses deep and primarily near surface methods to probe or image the earth. ... Geophysics, the study of the earth by quantitative physical methods, especially by seismic reflection and refraction, gravity, magnetic, electrical, electromagnetic, and radioactivity methods. ... Seismology (from the Greek seismos = earthquake and logos = word) is the scientific study of earthquakes and the movement of waves through the Earth. ... A type of seismic wave, the S-wave, secondary wave, or shear wave, sometimes called an elastic S-wave, is one of the two main types of elastic body waves, so named because they move through the body of an object, unlike surface waves. ...

  • Crosshole method
  • Downhole method (with a seismic CPT or a substitute device)
  • Surface wave reflection or refraction
  • Suspension logging (also known as P-S logging or Oyo logging)
  • Spectral analysis of surface waves (SASW)
  • Reflection microtremor (ReMi)

See also

Bostons Big Dig presented geotechnical challenges in an urban environment. ... Engineering Geology is the application of the science of geology to the understanding of geologic phenomena and the engineering solution of geologic hazards and other geologic problems for society. ...

Notes and references

  1. ^ D4318-05 Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils. ASTM International. Retrieved on 2007-02-07.
  2. ^ D1883-05 Standard Test Method for CBR (California Bearing Ratio) of Laboratory-Compacted Soils. ASTM International. Retrieved on 2007-02-07.
  3. ^ CALIFORNIA BEARING RATIO (CBR) AND ROAD PAVEMENT DESIGN. The Idiots' Guide to Highways Maintenance. Retrieved on 2007-02-07.
  4. ^ D3080-04 Standard Test Method for Direct Shear Test of Soils Under Consolidated Drained Conditions. ASTM International. Retrieved on 2007-02-07.
  5. ^ D4829-03 Standard Test Method for Expansion Index of Soils. ASTM International. Retrieved on 2007-02-07.
  6. ^ D5084-03 Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter. ASTM International. Retrieved on 2007-02-07.
  7. ^ D422-63(2002)e1 Standard Test Method for Particle-Size Analysis of Soils. ASTM International. Retrieved on 2007-02-07.
  8. ^ Kavand, A (2006-06-06). "Determination of Shear Wave Velocity Profile of Sedimentary Deposits in Bam City (Southeast of Iran) using Microtremor Measurements". Site and Geomaterial Characterization, Shanghai, China: ASCE. Retrieved on 2007-02-06. 

ASTM International (ASTM) is an international standards developing organization that develops and publishes voluntary technical standards for a wide range of materials, products, systems, and services. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 38th day of the year in the Gregorian calendar. ... ASTM International (ASTM) is an international standards developing organization that develops and publishes voluntary technical standards for a wide range of materials, products, systems, and services. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 38th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 38th day of the year in the Gregorian calendar. ... ASTM International (ASTM) is an international standards developing organization that develops and publishes voluntary technical standards for a wide range of materials, products, systems, and services. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 38th day of the year in the Gregorian calendar. ... ASTM International (ASTM) is an international standards developing organization that develops and publishes voluntary technical standards for a wide range of materials, products, systems, and services. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 38th day of the year in the Gregorian calendar. ... ASTM International (ASTM) is an international standards developing organization that develops and publishes voluntary technical standards for a wide range of materials, products, systems, and services. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 38th day of the year in the Gregorian calendar. ... ASTM International (ASTM) is an international standards developing organization that develops and publishes voluntary technical standards for a wide range of materials, products, systems, and services. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 38th day of the year in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 157th day of the year (158th in leap years) in the Gregorian calendar. ... The American Society of Civil Engineers (ASCE) was founded in 1852 to represent members of the civil engineering profession worldwide. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 37th day of the year in the Gregorian calendar. ...

External links

  • UC Davis Video on typical drilling and sampling methods in geotechnical engineering.

 
 

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