The Canadian Foundation Engineering Manual is a publication ofthe Canadian Geotechnical Society. It is originally based on a manual prepared under the. he CFEM () provides background information and accepted design guidelines on geotechnical aspects of foundation engineering, as practiced in Canada. Canadian Foundation Engineering Manual. Cohesionless Soils. For cohesionless soil. 9, = 0,'KM tand' = Bor'. 96 - No where B!! a combined shaft.
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The Canadian Foundation Engineering Manual covers fundamental matters common to all aspects of foundation engineering, such as notation, definitions of . Canadian foundation engineering manual /. prepared by the Foundations Committee. imprint. Montreal: The Society, description. 4 v. in 1: ill. format( s). Canadian foundation engineering manual by Canadian Geotechnical Society. Foundations Committee., , Canadian Geotechnical Society.
In addition, it is generally recognized that in granular soils of the same density, blow counts increase -- with increasing grain size above a grain size of about 2 mm. F or the foregoing reasons, it is readily apparent that the repeatability ofthe Standard Penetration Test is questiopable. In addition, relationships developed for SPT N value versus an exact density should be used with caution. The Standard Penetration Test is, however, useful in site exploration and foundation design and provides a qualitative Site Investigations 39 guide to the in-situ properties of the soil and a sample for classification purposes.
The evaluation of the test results should be undertaken by an experienced geotechnical A detailed discussion of the possible errors in SPT results has been presented by Schmertmann and Skempton Overdrive sampling spoon.
Higher N-values usually result from overdriven sampler. Sampling spoon plugged by gravel. Plugged casing " Higher N-values result when gravel plugs sampler, and resistance of an underlying stratum of loose sand could be highly overestimated. High N-values may be recorded for loose sand when sampling below the groundwater table if hydrostatic pressure causes sand to rise and plug casing.
Overwashing ahead of casing. Low N-values may result for dense sand since sand is loosened by overwashing. Drilling method. Not using the standard hammer drop Free fall of the drive hammer is not attained Energy delivered per blow is not uniform European countries have adopted an automatic trip hammer, which currently is not in common use in North America Using more than 1 Yi tums of rope around the drum andior using wire cable will restrict the fall of the drive hammer.
The use of wash boring with a side discharge bit or rotary with a tricone drill bit and mud flush is recommended. Using drill holes that are too large Holes greater than mm in diameter are not recommended; use of large diameter-holes may decrease the blow count, especially in sands.
Inadequate supervision Frequently a sampler will be impeded by gravel or cobbles, causing a sudden increase in blow count; this is often not recognized by an inexperienced observer accurate recording of drilling, sampling, and depth is always required Improper logging of soils Not describing the sample correctly Using too large a pump Too high a pump capacity will loosen the soil at the base of the hole causing a decrease in blow count Numerous studies have shown considerable variations in the procedures and equipment used throughout the world for this supposedly standardized test.
However, the SPT, with all its problems, is still the most commonly used in- situ test today. As a result considerable research on individual aspects of the standard penetration test equipment and procedures have been carried out in North America and Japan in an effort to better understand the factors affecting the test Schmertmann, ; Kovacs and Salomone, ; Y oshimi and Tokimatsu, Considerable improvements in the understanding of the dynamics of the SPT have occurred in recent years Schmertmann and Palacios; , Kovacs et aI.
Skempton and Decourt present thorough reviews of SPT corrections and correlations with soil properties. On the basis ofthe studies referred to above and other investigations, several corrections for adjusting or standardizing the field standard penetration test value, N, are considered in the following paragraphs.
While the corrected N values may be required for design purposes, the original field N values should always be given on the borehole logs.
These corrections or adjustments to N values can include: Correction for the actual energy delivered to the drill rod. Energy levels vary significantly, depending on the equipment and procedures used. Although the maximum value of of2. Approximate correction factors are given in Table 4. Wave equation studies Schmertmann and Palacios, show that the theoretical energy ratio decreases with rod length less than about 10m.
The approximate correction factor, Cr, is given in Table 4. Note, however, that when applying Seed's simplified liquef3ftion procedure, the N 1 60 value should be COlTected by multiplying with a rod length COlTection factor of 0. The corresponding correction factor in Table 4.
The effect of testing within relatively large diameter boreholes can be significant in sands and probably negligible in clays. Approximate correction factors for the borehole diameter, Cd' are given in Table 4.
In addition to the foregoing, there are some other factors which may require consideration and possible correction for specialized applications. These factors include grain size, overconsolidation, aging and cementation Skempton, Also, special consideration may be required ifheavy or long rods greater than about 20 m are used. Energy losses and damping may result in N-values that are too high, While using normalized N 1 60 values together with other corrections as appropriate has merit, many ofthe standard penetration N-value empirical relationships given in this Manual were developed before it was common practice to correct field N-values.
The question then arises as to whether, and in what manner the N-values should be cOlTected and the following comments are provided for guidance. A review of the procedures recommended for correcting N-values by authors offoundation engineering text books indicates that there is some difference of opinion. Das and Fang both recommend the use of the overburden pressure cOlTection for the Standard Penetration Test.
Bowles perhaps provides one ofthe more comprehensive evaluations ofN-value corrections. He states that since there are several opinions on N corrections, then the following three basic approaches are possible: Do nothing which, with current equipment and conditions, may be nearly correct for some situations. It must, however, be kept in mind at all times that the CPT provides an indication of soil type behaviour, which is different from explicit soil type in some instances, but is what the geotechnical engineer ultimately requires for design purposes.
Robertson presents stress nonnalized soil classification charts. A significant development in the electric cone-penetration testing has been the addition of a pore-pressure gauge at the base of the cone. Pore-pressure measurement during static cone-penetration testing provides more information on the stratification and adds new dimensions to the interpretation of geotechnical parameters, especially in loose or soft, fine-grained deposits Konrad and Law, a.
The continuous measurement of pore pressures along with the point resistance and side shear makes the electric cone penetrometer the premier tool for stratification logging of soil deposits Campanella and Robertson, ; Tavenas, The excess pore pressure measured during penetration is a useful indication ofthe soil type and provides an excellent means for detecting stratigraphic detail, and appears to be a good indicator of stress history Konrad and Law, b.
In addition, when the steady penetration is stopped momentarily, the dissipation of the excess pore pressure with time can be used as an indicator of the coefficient of consolidation. Finally, the equilibrium pore-pressure value, i.
Cone resistances and pore pressures are governed by a large number of variables, such as soil type, density, stress level, soil fabric, and mineralogy. Many theories exist to promote a better understanding ofthe process of a penetrating cone, but correlations with soil characteristics remain largely empirical. Empirical correlations have also been proposed for relating the results of the cone penetration test to the Standard Penetration Test SPT , as well as to soil parameters, such as shear strength, density index, compressibility, and modulus Campanella and Robertson, ; Robertson and Campanella, a, b.
Z E M 0 The dashed lines show the upper and lower limits ofobservations. The relationship between the CPT, represented by the tip resistance, qc' and the SPT, represented by the blow count N, has been determined in a number of studies over the past 30 years eMeigh and Nixon, ; Thornbum, ; Schmertmann, ; Burbidge, ; Robertson et aI. The drill is now widely used in North America in mining explorations and in geotechnical investigations for drilling, sampling and penetration testing in sand, gravel and boulder formations.
The drill consists of driving a specially designed double-walled casing into the ground with a double-acting diesel pile hammer and using an air injection, reverse-circulation technique to remove the cuttings from the hole.
The Becker drill system is more or less 'standardized', being manufactured by only one company, Drill Systems, in Calgary, Alberta. The hammer used in the Becker system is an international Construction Equipment, Inc. ICE Model double-acting atomized fuel injection diesel pile hammer; with a manufacturer's rated energy of The casings come in 2. The main advantage of the Becker hammer drill is the ability to sample or penetrate relatively coarse-grained soil deposits at a fast rate.
More details of the hammer drill can be found in Anderson The Becker casing can be driven open-ended with a hardened drive bit for drilling and sampling, in which case compressed air is forced down the annulus of the casing to flush the cuttings up the centre of the inner pipe to the surface.
The drilling can be stopped at any depth and the open-ended casing allows access to the bottom of the hole for tube sampling, standard penetration test or other in-situ tests, or for rock coring.
Undisturbed sampling or penetration testing conducted through the casing in saturated sand and silt may not be reliable, since stoppage of drilling and air shutoff result in unequal hydrostatic conditions inside and outside the casing, causing disturbance or "quicking" of the soil formation below the casing level.
This is manifested in the field by soil filling up the bottom section of the casing when drilling is stopped. On completion ofdrilling, the casing is withdrawn by a puller system comprising two hydraulic jacks operating in parallel on tapered slips that grip the casing and react against the ground. The Becker casing can also be driven close-ended, without using compressed air, as a large-scale penetration test to evaluate soil density and pile driveability. In this mode, commonly referred to as the Becker Penetration Test BPT , the driving resistances or blowcounts are recorded for each OJ m of penetration.
Because of the larger pipe or sampler diameter to particle size ratio, the BPT blowcounts have been considered more reliable than SPT N-values in gravelly soils. As a result, numerous attempts have been carried out in the past to correlate the BPT blowcounts to standard penetration test SPT N-values for foundation design and liquefaction assessment. Like all diesel hammers, the Becker hammer gives variable energy output depending on combustion conditions and soil resistances.
Harder and Seed have proposed a practical method using hammer bounce chamber pressure measurements to correct the measured BPT blow counts to a reference "full combustion rating curve" before correlating with corrected SPT N-values.
A more fundamental method of correcting BPT blowcounts based on transferred energy is proposed by Sy and Campanella 1 a. The vane is best suited for soft-to-firm clays; it should not be used in cohesion less soils.
The vane equipment consists of a vane blade, a set of rods, and a torque measuring apparatus. The vane blade should have a height-to-diameter ratio of 2; typical dimensions are by 50 mm.
The effect of soil friction on the measured torque should be eliminated or be measurable. The torque-measuring apparatus should permit accurate, reproducible readings, preferably in the form of a torque-angular deformation curve.
The vane may be rectangular or tapered. The vane-test performance and interpretation are subject to some limitations or errors, which should be taken into account when using the test results. The insertion of the vane blade produces a displacement and remolding of the soil. Experience shows that thicker blades tend to produce reduced strengths.
The failure mode around a vane is complex. The test interpretation is based on the simplified assumption of a cylindrical failure surface corresponding to the periphery of the vane blade Aas, The undrained shear strength can be calculated from the measured torque, provided that the shear strengths on the horizontal and vertical planes are assumed equal, by the following relation: CD L--Ll l. Two major types of pressuremeters have been developed which are cunentiy in use in Canada; the pre-bored pressuremeter and the self-boring pressuremeter.
The Menard-type pressuremeter is a well-known type of pre-bored pressuremeter. Each type of pressuremeter has advantages and limitations largely governed by the type of material to be tested and the method of geotechnical analysis to be canied out.
All types ofpressuremeter tests are sensitive to the method ofprobe installation and testing, and highly trained staff who possess a thorough understanding of the equipment and test procedures are required to obtain reliable results. The pressuremeter test was first developed by Louis Menard in The Menard-type pressuremeter test procedure basically consists of horizontal expansion of a membrane mounted on a relatively long probe placed in a slightly oversized, pre-bored hole.
Lateral displacement of the membrane and borehole wall is achieved by injecting either liquid or gas into the probe at selected pressure increments. Displacements are measured either in tenus of the volume ofliquid injected into the probe or more directly by callipers or displacement transducers for the gas inflated systems.
Pressures are measured either with a surface gauge or pressure transducer in the probe. The pressuremeter test allows the detenuination of the load-defonnation characteristics of the tested soil. The Menard-type tests are sensitive to the degree of soil disturbance caused by drilling the borehole.
In order to minimize the soil disturbance, the self-boring pressuremeter was developed independently in France Baguelin et aI. The principles of the test are similar to the Menard-type test, however, a small rotating cutting head is located in the tip ofthe probe. The probe is advanced by pushing the probe into the soil.
Displaced soil enters the cutting head where it is removed using water or a bentonite slurry pumped through a double rod assembly. Self-boring pressuremeters can be equipped with a pore-pressure transducer mounted on the exterior of the probe. The membrane is inflated using either liquid or gas in a manner similar to the Menard-type pressuremeter. Similarly, lateral displacements of the borehole wall during the test can be measured either by the volume of injected liquid, or more commonly, with displacement transducers, and the test pressures are measured with a surface gauge or pressure transducers located in the probe.
Relatively small, full displacement pressuremeters have also been combined with static cone penetrometers Hughes and Robertson, ; and Withers et aI. This discussion may not be entirely applicable to other pressuremeter designs. Equipment The standard Menard pressuremeter consists ofa probe connected to a pressure-volume control unit with stiff tubing. Probes are generally available in three diameters consistent with commonly utilized drill hole sizes A, Band N.
The probe consists of a metal cylinder covered with an inflatable membrane and protective sheath comprised of a series of metal strips. The probe is separated into three independent cells; the two end cells are guard cells used to reduce end effects on the middle cell to produce predominantly radial strains in the soil interval tested.
Lateral displacements are measured only in the middle cell. All cells are nonnally filled with water or antifreeze although some systems use gas to inflate the guard cells. Pressure is applied to the fluid in a series of increments by a gas Site Investigations 51 control system acting on a reservoir in the control unit. Volume changes in the reservoir are measured by graduated transparent tubes on the control unit.
A more complete description of the Menard system is presented in Baguelin et al. Other pressuremeter probes without the two end cells have been introduced. The test results from such probes may need to be corrected before use in common pressuremeter design methods. Appropriate drilling procedures are described by Baguelin et aI. Normal drilling and sampling techniques are generally intended to minimize disturbance of the collected samples and may not be suitable for pressuremeter testing.
Drilling methods should be selected to prevent collapse of the borehole wall, minimize erosion of the soil, and prevent softening of the soil Finn et aI. When pressuremeter tests are conducted in a soil type where limited local experience in pressuremeter testing is available, several methods of drilling should be evaluated to determine the optimum method.
General guidance regarding the initial selection of drilling methods for various soil types is presented in Table 4. The maximum pressure expected during the test should be divided into a minimum often equal pressure increments. Each pressure increment is maintained for a one minute period with volume or radial strain measurements recorded at intervals of 15, 30, and 60 seconds. All pressure increments should be maintained for the same time period. Tests are generally considered to be complete when the volume of the liquid injected during the test is equal to the initial volume of the borehole.
In hard. If the sides of the borehole are enlarged excessively either by improper sizing of the drilling equipment or erosion of the borehole wall, the maximum inflation volume of the probe may be reached prior to injection of the required volume.
Pushed or driven tube with internal camfer Stiff to Hard Clay. Core drilling with mud or possibly foam flush Continuous flight auger Silt! Computer controlled load application greatly simplifies the test procedure; however, the availability of the equipment is limited.
Strain rate selection is important for clays, particularly in the plastic stress range Anderson, ; Windle and Wroth, Test Interpretation The results ofa standard Menard-type pressuremeter test corrected for volume and membrane resistance are shown in Figure 4. The pressure must be corrected for the hydrostatic pressure in the measuring circuit above the water table.
In the first stage ofthe test, the volume increases rapidly with small changes in pressure as the probe is inflated against the soil. The volume at the point where the curve becomes approximately linear is termed v o ' which is equal to the difference between the volume of the hole and the initial volume of the probe.
The corresponding pressure at this point is called Po; however, this pressure does not represent the true in-situ pressure in the ground because of stress relief during the formation of the hole. At higher pressures the volume increases slowly with pressure. The creep volume change in this pressure range is small and approximately constant, which indicates pseudo-elastic behaviour of the soil.
The slope of the volume - pressure curve in this range is related to the shear modulus of the soil as discussed below. The pressure corresponding to the end of the constant creep volume measurements is called the creep pressure Pr At higher pressures the volume and the creep volume increase rapidly indicating the development of soil failure around the probe.
The pressure - volume curve tends to an asymptotic limit corresponding to the limit pressure PI' The theoretical basis for the pressuremeter test is the radial expansion of a cavity in an infinite elastic medium which was developed first by Lame Details of the cavity expansion theory are presented in Baguelin et al. The equation for the radial expansion of a cylindrical cavity in an infinite elastic medium is: The modulus value calculated from the pressuremeter test is, therefore, a shear modulus G M.
While the slope of the pressuremeter curve, b. V is constant from Vo to vf' the volume V is not. Therefore, the shear modulus G is dependent on the volume of the cavity selected, which for the pressuremeter test is, by convention, selected at the midpoint ofthe pseudo - elastic portion of the pressure - volume curves Figure 4.
Vf If these design methodologies are used, the tests must be carried out in accordance with standardized test procedures. Foundation designs must be limited to soil conditions similar to those used to , develop the empirical correlations.. The pressuremeter test is a useful tool for investigation of firm to hard clay, silt, sand, glacial till, weathered rock, and low to moderate strength intact rock.
The test can also be used for frozen soil and soil containing gas in the pores. The Menard-type pressuremeter is not recommended for general use in clean gravelly sailor soft clay. The sell-boring pressuremeter is similar to a Menard-type pressuremeter as it consists essentially of a thick-wall tube with a flexible membrane attached to the outside.
The instrument is pushed into the ground and the soil displaced by a sharp cutting shoe is removed up the centre of the instrument by the action of a rotating cutter or jetting device just inside the shoe of the instrument.
The cuttings are flushed to the surface by drill mud, which is pumped down to the cutting head. Once the instrument is at the desired depth, and following the dissipation of excess pore-water pressure, the membrane surrounding the instrument is expanded against the soil. The expansion at the centre of the instrument is measured by displacement transducers. Pore pressure cells can be incorporated into the membrane to monitor changes in pore-water pressures.
The self-boring pressuremeter can be installed into relatively soft soils and the test results can be interpreted using analytical methods. A summary of the methods of interpretation is presented in Mair and Wood Site Investigations 55 The Menard-type pressuremeter test and the self-boring pressuremeter test should considered as two distinct and separate tests.
The Menard-type pressuremeter test is usually interpreted using empirical correlations related to specific design rules. The tool can be classified as a logging tool that is easy to use and provides a range of empirically predicted soil parameters.
Detailed requirements for equipment, test procedure, accuracy of measurements and presentation of test results were recommended by ASTM Subcommittee D. A good review ofthe dilatometer test is provided by lamiolkowski et al.
An overview of the dilatometer test and interpretation of in-situ test results is given by Lunne et al. Details of equipment developments are presented by Mitchell The flat plate dilatometer is 14 mm thick by 95 mm wide, with a flexible steel membrane 60 mm in diameter on the face of the blade.
The pressure for lift-off of the diaphragm, the pressure required to deflect the centre of the diaphragm 1 mm into the soil, and the pressure at which the diaphragm returns to its initial position closing pressure are recorded at each depth. Correlations have been developed between dilatometer readings and soil type, earth pressure at rest, overconsolidation ratio, undrained shear strength, and constrained modulus.
However, correlations should be used with. Plate-load tests involve measuring the applied load and penetration of a plate being pushed into a soil or rock mass. The test is most commonly carried out in shallow pits or trenches but is also undertaken at depth in the bottom of a borehole, pit or adit.
In soils, the test is carried out to determine the shear strength and deformation characteristics of the material beneath the loaded plate. The ultimate load is not often attainable in rock where the test is primarily used to determine the deformation characteristics. In the former, the ground is allowed to consolidate under each load before a further increment is applied; this will yield the drained deformation characteristics and also strength characteristics if the test is continued to failure.
In the latter, the rate of penetration is generally such that little or no drainage occurs, and the test gives the corresponding undrained deformation and strength characteristics. The degree of drainage is governed by the size of the plate, the rate of testing, and the soil type. The results of a single plate-load test apply only to the ground which is significantly stressed by the plate and this is typically a depth of about one and a half times the diameter or width of the plate.
The depth of ground stressed by a structural foundation will, in general, be much greater than that stressed by the plate-load test and, for this reason, the results of loading tests carried out at a single elevation do not normally give a direct indication of the allowable bearing capacity and settlement characteristics of the full-scale structural foundation. To determine the variation of ground properties with depth, it will generally be necessary to carry out a series of plate tests at different depths.
These should be carried out such that each test subjects the ground to the same effective stress level it would receive at working load. Because of the difficulty in undertaking a series of tests at different depths, screw-plate tests which are described later, may be considered. Excavation causes an unavoidable change in the ground stresses, which may result in ilTeversible changes to the properties which the test is intended to study.
For example, in stiff fissured over- consolidated clay, some swelling and expansion of the clay due to opening of fissures and other discontinuities will inevitably occur during the setting-up process, and can considerably reduce the values of the deformation moduli. In a project that involves a large deep excavation, the excavation may cause disturbance to the ground beneath, with a consequent effect on the deformation characteristics.
In such a case, it will be necessary to allow for this unavoidable disturbance when interpreting the results of loading tests.
It is recommended that dial gauges, reading to an accuracy of 0. An alternative method developed in Europe is the screw-plate test, which uses a flat-pitch auger device that can be screwed to the desired depth in the soil and loaded in a similar manner to a plate-load test.
The horizontally projected area over the single 0 auger flight is taken as the loading-plate area. A variety of loading procedures for the screw-plate test can be applied depending on the soil type and data required. Constant rate ofload or deformation can be applied and load versus deformation plotted to obtain the modulus and strength of the soil.
Some success has been reported Janbu and Senneset, in obtaining consolidation data from the screw-plate test. It may also be possible to estimate the pre consolidation pressure in a sand deposit from the test Dahlberg, Plate-load tests and screw-plate load tests are only a part of the necessary procedure for soil investigation for foundation design, and should be undertaken in conjunction with other methods.
These tests should be calTied out under the direction of experts thoroughly conversant with foundation investigations and design. The quality of the samples depends mainly on the boring method, the sampling equipment, and the procedures used to retrieve them. The more common boring methods are summarized in Table 4.
The method of advancing a casing and washing the inside with water washboring is one of the most commonly used in Canada. It results in a good quality borehole, provided the washing is done properly, i.
In loose sands and silts, material may rise up in the casing during washing; bentonite mud should be used instead of water in such cases. Auger boring, including hollow stem auguring, and rotary drilling are also commonly used methods of drilling boreholes in Canada.
Care should be exercised in excavating such pits, especially in loose sands, soft clays, or close to the water table. General comments on test pits and test trenches are summarized in Table 4. Site Investigations 57 4. Mechanical properties, which serve as bases for the design of foundations, can be measured only on samples of Class 1. Such samples should usually be retrieved for the design of foundations on clays.
Problem soils, as referred to in Chapter 5, may require special sampling procedures as indicated therein. Common samplers for disturbed and undisturbed soil samples and disturbed rock cores are summarized in Tables 4.
In some cases continuous auger may be used requiring only one withdrawal. Changes indicated by examination of material removed. Casing generally not used. Power operated. Hollow stem serves as a casing. Chopping, twisting, and jetting action of a light bit as circulating drilling fluid removes cuttings. Changes indicated by rate of progress, action of rods, and examination of cuttings in drill fluid. Casing may be needed to prevent caving. Power rotation of drilling bit as circulating fluid removes cuttings from hole.
Changes indicated by rate of progress, action of drilling tools, and examination of cuttings in drilling fluid. Casing usually not required except near surface.
Power chopping with limited amount of water at bottom of hole. Water becomes a slurry that is periodically removed with bailer or sand pump.
Changes indicated by rate of progress, action of drilling tools, and composition of slurry removed. Casing required except in stable rock.
Power rotation of a core barrel as circulating water removes ground-up material from hole. Water also acts as coolant for core barrel bit. Generally hole is cased to rock. Appli cability Ordinarily used for shallow explorations above water table in partly saturated sands and silts, and soft to stiff cohesive soils.
Can clean out hole between drive samples. Fast when power-driven. Large diameter bucket auger permits hole examination. Hole collapses in soft and sandy soils below. Access for sampling disturbed or undisturbed or coring through hollow stem. Should not be used with plug in granular soil. Not suitable for undisturbed sampling in sand and silt below groundwater table. Used in sands, sand and gravel without boulders, and soft to hard cohesive soils.
Usually can be adapted for inaccessible locations, such as on water, in swamps, on slopes, or within buildings. Difficult to obtain undisturbed samples. Applicable to all soils except those containing large gravel, cobbles, and boulders where it may be combined with coring. Difficult to determine changes accurately in some soils. Not practical in inaccessible locations for heavy truck-mounted equipment track-mounted equipment is available.
Soil and rock samples usually limited to mm diameter. Not preferred for ordinary exploration or where undisturbed samples are required because of difficulty in determining strata changes, disturbance.
Sometimes used in combination with auger or wash borings for penetration of coarse gravel, boulders, and rock formations. Could be useful to probe cavities and weakness in rock by changes in drill rate.
Used alone and in combination with other types of boring to drill weathered rocks, bedrock, and boulder formations. Core Wire-Line Efficientfordeepholecoringover30monlandand Drilling samplesobtainedbyremovinginnerbarrel offshorecoringandsampling.
Theinnerbarrelis releasedby aretrieverloweredbyawire-linethrough drillingrod. Bulksampling, in- situtesting,visual BackhoeExcavated generallylessthan5m limitedto depthsabove inspection,excavation TestPitsandTrenches. UndIsturbedsamples thanhandexcavatIOn. Bedrockcharacteristics, depthofbedrockand groundwaterlevel, Relativelylowcost, rippability,increase Explorationlimitedtodepth DozerCuts exposuresforgeologic depthcapabilityof abovegroundwaterlevel.
TrenchesforFault Investigations Evaluationofpresence andactivityoffaulting and sometimeslandslide features. Definitivelocationof faulting, subsurface observationupto 10m. Costly,time-consuming,requires shoring,onlyusefulwhere dateablematerialsarepresent, depthlimitedtozoneabove groundwaterlevel. Blocksamplesare bestwhen dealingwith sensitive, varved, orfissured clays. Whereverpossible,block samplesshouldbetakenin suchsoils. SamplesofClass I arebeststoredinaverticalpositioninaroomwithconstanthumidityandataconstant temperature.
Thedisturbancedependsonthe consistencyofthesampledsoilandincreaseswithdepthofsampling. Smalldiameter spiralaugersaresuitable for obtainingwater-contentsamplesofcohesive soils,ifcareistakento remove freewaterfromthesample,aswellas allsoilscrapedfromupperlayersinthewallof theborehole.
Water- contentsamplesshouldbeplacedimmediatelyinairtightcontainerstopreventevaporation. Gravels invalidatedrivedata. Methods of penetration Hammer driven. Causes of disturbance or low recovery Vibration. Remarks SPTis madeusing standardpenetrometer with Undisturbed samplesoftentaken withliners. Some sampledisturbanceis likely. Retractable Maximum of F or silts, clays, fine Plug six tubes can be and loose sands. Hammer filled in single penetration.
Will not Helical Can penetrate to penetrate hard soils Flight depths in excess or those containing driven. Improper soil types for sampler. Hard soils, cobbles, boulders. Light weight, highly portable units can be hand carried to job. Sample disturbance is likely. Rapid method of determining soil profile. Bag samples can be obtained. Log and sample depths must account for lag I sample at surface.
Soil too hard to penetrate. A special type of flight auger with hollow centre through which undisturbed of 15 m. I Up to mm diameter Bucket Up to i mm diameter common. Larger available. With extensions, depths i greater than 25 m are possible. Standard sizes samples or SPT cal. Rapid method of Hard soils, determining soil Same as flight auger.
For most soils above water table. Can Several types of dig harder soil than buckets available, above types, and including those with Soil too hard to can penetrate soils Rotation. Barrels Barrel lengths 1. Hard rock. All barrels can be fitted with Rotation. Fractured rock.
Rock too soft. Dlill fluid must circulate around core rock must not be subject to erosion.
Single tube not often used for exploration. Double Tube Non-uniform, fractured friable and soft rock.
Improper rotation or feed rate in fractured or soft rock. Has inner barrel or swivel which does not rotate with outer tube. For soft, erodible rock. Cast-in-placeboredpilesareoftenreferredtoas caissonsinCanada. Pile head - theupperendofapile. Symbols and Units 5 Pile toe the bottom end of a pile. Pore pressure ratio the ratio between the pore pressure and the total overburden stress. Rock a natural aggregate of minerals that cannot readily be broken by hand.
Rock shoe a special type of pile shoe.
Rock quality designation RQD - a measure of the degree of fractures in rock cores, defined as the ratio of the accumulated lengths minimum mm of sound rock over the total core length.
Safety factor - a factor modifYing reducing overall capacity or strength as used in working stress design. The safety factor is defined as a ratio of maximum available resistance to mobilized resistance or to applied load. Safety margin - the margin dimensional between mobilized resistance, applied load, or actual value and maximum available resistance or acceptable value, e.
Shaft resistance - the resistance mobilized on the shaft side of a deep foundation. Edited by F. William and J. Geotechnical Special Publication No. Google Scholar Kulhawy, F. Interpretation of load tests on drilled shafts — Part 2: Axial uplift. Elasto-plastic stress strain theory for cohesionless soil. Axial testing and numerical modeling of square shaft helical piles under compressive and tensile loading.
Three-dimensional lower bound solutions for the stability of plate anchors in sand. The Ultimate uplift capacity of foundations. Abstract Mitsch, M. The uplift capacity of helix anchors in sand. Edited by S. The behaviour of model screw piles in cohesive soils. Drilled shafts: Construction procedures and design methods.
Publication No. Google Scholar Prakash, S. Pile foundations in engineering practice. John Wiley and Sons, New York.
Google Scholar Puri, V. Helical anchor piles under lateral loading. In Laterally loaded deep foundations: Analysis and performance. Edited by J. Langer, E. Mosley, and C. Google Scholar Reese, L.