Discretizaci´ on del Principio de Equidistribuci´ on

TESTING PROCEDURES AND SOUNDING CLOSURE

grease-filled slot to record porewater pressures (Elmgren grease-filled slot to record porewater pressures (Elmgren 1995; Larsson 1995). This avoids problems associated with 1995; Larsson 1995). This avoids problems associated with vacuum presaturation of elements, assembly difficulties in vacuum presaturation of elements, assembly difficulties in the field, and desaturation of elements in the unsaturated the field, and desaturation of elements in the unsaturated vadose zone, however, at the expense of a more sluggish vadose zone, however, at the expense of a more sluggish transducer response and less detailing in the

transducer response and less detailing in the uummprofiling.profiling.

BASELINE READINGS BASELINE READINGS

Before each sounding, electronic baselines or “zero readings”

Before each sounding, electronic baselines or “zero readings”

of the various channels of the penetrometer are recorded. It is of the various channels of the penetrometer are recorded. It is also recommended that a set of baseline readings be secured also recommended that a set of baseline readings be secured after the sounding has been completed and the penetrometer after the sounding has been completed and the penetrometer withdrawn to the surface. These baselines should be recorded withdrawn to the surface. These baselines should be recorded in a field log booklet and checked periodically to forewarn of  in a field log booklet and checked periodically to forewarn of  any mechanical or electronic shifts in their values, as possible any mechanical or electronic shifts in their values, as possible damage or calibration errors may occur.

damage or calibration errors may occur.

ADVANCING THE PENETROMETER ADVANCING THE PENETROMETER

The standard rate of push for CPT soundings is 20 mm/s, The standard rate of push for CPT soundings is 20 mm/s, usu-ally applied in one-meter increments (standard cone rod ally applied in one-meter increments (standard cone rod length). With dedicated CPT rigs, the hydraulic system is length). With dedicated CPT rigs, the hydraulic system is automatically established to adjust the pressures accordingly automatically established to adjust the pressures accordingly to maintain this constant rate. Using a rotary drill rig, to maintain this constant rate. Using a rotary drill rig, however, the driller must be attentive in manually adjusting however, the driller must be attentive in manually adjusting pressures to seek a rate of approximately 20 mm/s (0.8 in./s).

pressures to seek a rate of approximately 20 mm/s (0.8 in./s).

Therefore, in those cases, it would be desirable to measure Therefore, in those cases, it would be desirable to measure time as well as depth so that the actual rate can be ascertained time as well as depth so that the actual rate can be ascertained..

TESTS AT INTERMITTENT DEPTHS TESTS AT INTERMITTENT DEPTHS At each one-meter rod break, there

At each one-meter rod break, there is an opportunity to con-is an opportunity to con-duct intermittent testing before the next succession of duct intermittent testing before the next succession of push-ing as the next rod is added. Two common procedures ing as the next rod is added. Two common procedures include: (1) dissipation testing, and (2) downhole

include: (1) dissipation testing, and (2) downhole shear waveshear wave velocity measurements.

velocity measurements.

Porewater Dissipation Tests Porewater Dissipation Tests

Dissipation testing involves the monitoring of porewater Dissipation testing involves the monitoring of porewater pressures as they decay with time. The

pressures as they decay with time. The installation of a full-installation of a full-displacement device such as a cone penetrometer results in displacement device such as a cone penetrometer results in the generation of excess porewater pressures (

the generation of excess porewater pressures (ΔΔuu) locally) locally around the axis of perturbation. In clean sands, the

around the axis of perturbation. In clean sands, the ΔΔuu willwill dissipate almost immediately because of the high

dissipate almost immediately because of the high permeabil- permeabil-ity of sands, whereas in clays and silts of low permeabilpermeabil-ity ity of sands, whereas in clays and silts of low permeability the measured

the measured ΔΔuu will require a considerable time to equili-will require a considerable time to equili-brate. Given sufficient time in all soils, the penetrometer brate. Given sufficient time in all soils, the penetrometer porewater channel will eventually record the

porewater channel will eventually record the ambient hydro-ambient hydro-static condition corresponding to

static condition corresponding to uu00. Thus, the measured. Thus, the measured porewater pressures (

porewater pressures (uumm) are a combination of transient and) are a combination of transient and hydrostatic pressures, such that:

During the temporary stop for a rod

During the temporary stop for a rod addition at one-meteraddition at one-meter breaks, the rate at which

breaks, the rate at which ΔΔuu decays with time can be moni-decays with time can be moni-tored and used to interpret the coefficient of consolidation tored and used to interpret the coefficient of consolidation and hydraulic conductivity of the soil media. Dissipation and hydraulic conductivity of the soil media. Dissipation readings are normally plotted on log scales; therefore, in readings are normally plotted on log scales; therefore, in clays with low permeability it becomes impractical to wait clays with low permeability it becomes impractical to wait for full equilibrium that corresponds to

for full equilibrium that corresponds to ΔΔuu0 and0 anduummuu00.. A standard of practice is to record the time to achieve 50%

A standard of practice is to record the time to achieve 50%

dissipation, designated dissipation, designated t t 5050..

Shear Wave Testing Shear Wave Testing

A convenient means to measure the profile of shear wave A convenient means to measure the profile of shear wave velocity (

velocity (V V _ss) with depth is ) with depth is through the seismic cone penetra-through the seismic cone penetra-tion test (SCPT). At the one-meter rod breaks, a surface shear tion test (SCPT). At the one-meter rod breaks, a surface shear wave is generated using a horizontal plank or autoseis unit.

wave is generated using a horizontal plank or autoseis unit.

The shear wave arrival time can be recorded at the test The shear wave arrival time can be recorded at the test ele-vation by incorporating one or more geophones within the vation by incorporating one or more geophones within the penetrometer. The simplest and most common is the use of penetrometer. The simplest and most common is the use of aa single geophone that provides a

single geophone that provides a pseudo-interval downholepseudo-interval downholeV V ss

(Camp

(Campanellanella et al. 1986), as depica et al. 1986), as depictedted in Figure 20. Thiin Figure 20. Thiss approach is sufficient in accuracy as long as the geophone approach is sufficient in accuracy as long as the geophone axis is kept parallel to the source alignment (no rotation of  axis is kept parallel to the source alignment (no rotation of  rods or cone) and a repeatable shear wave source is generated rods or cone) and a repeatable shear wave source is generated at each successive one-meter interval.

at each successive one-meter interval.

A more reliable

A more reliableV V _ssis achieved by true-interval downholeis achieved by true-interval downhole testing; however, this requires two or more geophones at two testing; however, this requires two or more geophones at two elevations in the penetrometer [usual

elevations in the penetrometer [usually 0.5 or ly 0.5 or 1.0 m vertically1.0 m vertically apart (1.5 to 3.0 ft)]. Provision of a biaxial arrangement of  apart (1.5 to 3.0 ft)]. Provision of a biaxial arrangement of  two geophones at each elevation allows

two geophones at each elevation allows correction for possi-correction for possi-ble cone rod rotation, because the resultant wave can be used ble cone rod rotation, because the resultant wave can be used (

( R R_vv²² x x²² y y²²). For downhole testing, incorporation of a tri-). For downhole testing, incorporation of a tri-axial geophone with vertical component offers no benefit, axial geophone with vertical component offers no benefit, because shear waves only have movement in their direction because shear waves only have movement in their direction of motion and direction of polarization (only two of three of motion and direction of polarization (only two of three Cartesian coordinate directions). The vertical component Cartesian coordinate directions). The vertical component could be used in a crosshole test arrangement (e.g., Baldi could be used in a crosshole test arrangement (e.g., Baldi et al. 1988).

et al. 1988).

HOLE CLOSURE HOLE CLOSURE

After the sounding is completed, a number of possible paths After the sounding is completed, a number of possible paths may be followed during or

may be followed during or after extraction:after extraction:

•

“loss tip” or retractable portal.

“loss tip” or retractable portal.

•

• After After withdrwithdrawal, hawal, hole iole is rees reenterentered usind using a seg a separateparate grouting system.

grouting system.

The need for grouting or sealing of holes is usually The need for grouting or sealing of holes is usually estab-lished by the state or province, or by local and specific lished by the state or province, or by local and specific con-ditions related to the particular project. For instance, fo

ditions related to the particular project. For instance, for CPTsr CPTs

FIGURE 20

FIGURE 20 Setup and procSetup and procedure for pseuedure for pseudo-indo-interval seisterval seismic conemic cone penetration testing (SCPT).

penetration testing (SCPT).

FIGURE

FIGURE 2121 Hole Hole closurclosure methe methods: (ods: (left left ) reentry techniques; () reentry techniques; (right right ) retraction with expendable tip (Lutenegger and) retraction with expendable tip (Lutenegger and DeGroot 1995).

DeGroot 1995).

advanced through asphalt pavements, sealing of the hole advanced through asphalt pavements, sealing of the hole would be warranted to prevent water infiltration and/or would be warranted to prevent water infiltration and/or long-term damage. Most often, the state or province will deem the term damage. Most often, the state or province will deem the need or requirement for hole closure by grouting or sealing in need or requirement for hole closure by grouting or sealing in specific geologic settings where the groundwater aquifer(s) specific geologic settings where the groundwater aquifer(s) needs to be protected against vertical cross talk, needs to be protected against vertical cross talk, contamina-tion, or water transmission. The requirement of borehole tion, or water transmission. The requirement of borehole closure can significantly reduce CPT production rates.

closure can significantly reduce CPT production rates.

Hole sealing can be

Hole sealing can be accomplished using either a bentoniteaccomplished using either a bentonite slurry or a lean grout made from portland cement, gypsum, slurry or a lean grout made from portland cement, gypsum, or a bentonite–cement mix. Pozzolan-based grouts can also or a bentonite–cement mix. Pozzolan-based grouts can also be adequate, but they tend to setup more slowly (Lee et al.

be adequate, but they tend to setup more slowly (Lee et al.

1998). The grout or slurry sealants can be placed using 1998). The grout or slurry sealants can be placed using sur-face pour methods, flexible or rigid tremie pipes, or special face pour methods, flexible or rigid tremie pipes, or special CPT systems that provide grouting during advancement or CPT systems that provide grouting during advancement or during withdrawal,

during withdrawal, as depicted ias depicted inn Figures 21 and Figures 21 and 22. A full22. A full discussion of these systems and their advantages and discussion of these systems and their advantages and disad-vantages is given by Lutenegger and DeGroot (1995) and vantages is given by Lutenegger and DeGroot (1995) and Lutenegger et al. (1995).

Lutenegger et al. (1995).

Results of the questionnaire on the subject of CPT hole Results of the questionnaire on the subject of CPT hole closure indicated that 43% allow the hole to remain open, closure indicated that 43% allow the hole to remain open, 20% backfill with soil, 18% grout during retraction, and 20% backfill with soil, 18% grout during retraction, and 18% grout using a secondary deployment system (e.g., a 18% grout using a secondary deployment system (e.g., a GeoProbe).

GeoProbe).

24 24

FIGURE

FIGURE 2222 Hole Hole closurclosure methe methods: ods: ((left left ) temporary casing; () temporary casing; (right right ) grouting through ports in fric) grouting through ports in friction reducer (Lutenegger andtion reducer (Lutenegger and DeGroot 1995).

DeGroot 1995).

In this chapter, the presentation of CPT data

In this chapter, the presentation of CPT data for use in detail-for use in detail-ing subsurface stratigraphic features, soil layerdetail-ing,

ing subsurface stratigraphic features, soil layering, determi- determi-nation of soil behavioral type, and identification of  nation of soil behavioral type, and identification of  geomaterials will be presented.

geomaterials will be presented.

GEOSTRATIGRAPHIC PROFILING GEOSTRATIGRAPHIC PROFILING

By recording three

By recording three continuous measurements vertically withcontinuous measurements vertically with depth, the CPT is an excellent tool for profiling strata depth, the CPT is an excellent tool for profiling strata changes; delineating the interfaces between soil layers; and changes; delineating the interfaces between soil layers; and detecting small lenses, inclusions, and stringers within the detecting small lenses, inclusions, and stringers within the ground. The data presentation from a CPT sounding should ground. The data presentation from a CPT sounding should include the tip, sleeve, and porewater readings plotted with include the tip, sleeve, and porewater readings plotted with depth in side-by-side graphs, as illustrated by Figure 23.

depth in side-by-side graphs, as illustrated by Figure 23. ForFor DOT projects wishing to share CPT information with DOT projects wishing to share CPT information with con-tractors in bidding documents, perhaps these are the only tractors in bidding documents, perhaps these are the only graphical plots that should be presented, because they graphical plots that should be presented, because they repre-sent the raw uninterpreted results.

sent the raw uninterpreted results.

The total cone tip resistance (

The total cone tip resistance (qqt t ) is always preferred over) is always preferred over the raw measured value (

the raw measured value (qqcc). For SI units, the depth (). For SI units, the depth ( z z) is pre-) is pre-sented in meters (m), cone tip stress (

sented in meters (m), cone tip stress (qqt t ) in either kilopascals) in either kilopascals (1 kPa

(1 kPa1 kN/m1 kN/m²²) or megapascals (1 MPa) or megapascals (1 MPa 1000 kN/m1000 kN/m²²),), and sleeve resistance (

and sleeve resistance ( f  f _ss) and porewater pressures () and porewater pressures (uu_mm) in kPa.) in kPa.

For conversion to English units, a simple conversion is: 1 tsf  For conversion to English units, a simple conversion is: 1 tsf 



1 bar1 bar100 kPa100 kPa0.1 MPa.0.1 MPa.

If the depth to the water table is known (

If the depth to the water table is known ( z zww), it is convenient), it is convenient to show the hydrostatic porewater pressure (

to show the hydrostatic porewater pressure (uu00) if the ground-) if the ground-water regime is understood to be an unconfined aquifer (no water regime is understood to be an unconfined aquifer (no drawdown and no artesian conditions). In that

drawdown and no artesian conditions). In that case, the hydro-case, the hydro-static pressure can be calculated from:

static pressure can be calculated from:uu00(( z z z zww))ww, where, where



ww9.8 kN/m9.8 kN/m³³62.4 pcf for freshwater;62.4 pcf for freshwater;ww**10.0 kN/m10.0 kN/m³³



64.0 pcf for saltwater. In some CPT 64.0 pcf for saltwater. In some CPT presentations, it is com-presentations, it is com-mon to report the

mon to report theuummreading in terms of equivalent height of reading in terms of equivalent height of  water, calculated as the ratio of the measured porewater water, calculated as the ratio of the measured porewater pres-sure divided by the unit weight of water, or

sure divided by the unit weight of water, or hhwwuumm /  / ww..

SOIL TYPE BY VISUAL INTERPRETATION SOIL TYPE BY VISUAL INTERPRETATION OF

OFCONE PENETRATICONE PENETRATION TESTION TESTING DATANG DATA

Because soil samples are not normally taken during CPT, soil Because soil samples are not normally taken during CPT, soil types must be deduced or inferred from the measured types must be deduced or inferred from the measured read-ings. In critical cases or uncertain instances, the

ings. In critical cases or uncertain instances, the drilling of andrilling of an adjacent soil boring with sampling can be warranted to adjacent soil boring with sampling can be warranted to con-firm or verify any

firm or verify any particular soil classification.particular soil classification.

As a general rule of thumb, the magnitudes of CPT As a general rule of thumb, the magnitudes of CPT mea-surements fall into the following

surements fall into the following order:order:qqt t  f  f ssandandqqt t uu11 u

u22 uu33. The measured cone tip stresses in sands are rather. The measured cone tip stresses in sands are rather high (

high (qqt t 5 MPa or 50 tsf), reflecting the prevailing drained5 MPa or 50 tsf), reflecting the prevailing drained strength conditions, whereas measured values in clays are strength conditions, whereas measured values in clays are low (

low (qqt t 5 MPa or 50 tsf) and indicative of undrained soil5 MPa or 50 tsf) and indicative of undrained soil response owing to low

response owing to low permeability. Correspondingly, mea-permeability. Correspondingly, mea-sured porewater pressures depend on the position of the sured porewater pressures depend on the position of the fil-ter element and groundwafil-ter level. At test depths above the ter element and groundwater level. At test depths above the groundwater table, porewater pressure readings vary with groundwater table, porewater pressure readings vary with capillarity, moisture, degree of saturation, and other factors capillarity, moisture, degree of saturation, and other factors and should therefore be considered tentative. Below the and should therefore be considered tentative. Below the water table, for the standard shoulder element, clean water table, for the standard shoulder element, clean satu-rated sands show penetration porewater pressures often near rated sands show penetration porewater pressures often near hydrostatic (

hydrostatic (uu22 ^ uu00), whereas intact clays exhibit values), whereas intact clays exhibit values considerably higher than hydrostatic (

considerably higher than hydrostatic (uu22 uu00). Indeed, the). Indeed, the ratio

ratiouu22 /  / uu00increases with clay hardness. For soft increases with clay hardness. For soft intact clays,intact clays, the ratio may be around

the ratio may be around uu22 /  / uu00 ^ 33 , which increases to, which increases to about

aboutuu22 /  / uu00^1010for stiff clays, yet as high as for stiff clays, yet as high as 30 or more30 or more for very hard clays. However, if the clays are fissured, then for very hard clays. However, if the clays are fissured, then zero to negative porewater pressures are observed (e.g., zero to negative porewater pressures are observed (e.g., Mayne et al. 1990).

Mayne et al. 1990).

The friction ratio (FR) is defined as the ratio of the sleeve The friction ratio (FR) is defined as the ratio of the sleeve friction to cone tip resistance, designated FR

friction to cone tip resistance, designated FR  R R f  f  f  f ss /  / qqt t , and, and reported as a percentage. The friction ratio has been

reported as a percentage. The friction ratio has been used asused as a simple index to identify soil type. In clean quartz sands to a simple index to identify soil type. In clean quartz sands to siliceous sands (comparable parts of quartz and feldspar), it siliceous sands (comparable parts of quartz and feldspar), it is observed that friction ratios are low:

is observed that friction ratios are low: R R f  f 1%, whereas in1%, whereas in clays and clayey silts of low

clays and clayey silts of low sensitivity,sensitivity, R R f  f 4%. However,4%. However, in soft sensitive to quick clays,

in soft sensitive to quick clays, the friction ratio can be quitethe friction ratio can be quite low, approaching zero in many

low, approaching zero in many instances.instances.

Returning to Figure 23, a visual examination of the CPTu Returning to Figure 23, a visual examination of the CPTu

Returning to Figure 23, a visual examination of the CPTu Returning to Figure 23, a visual examination of the CPTu

In document Generación Numérica de Mallas Armónicas-Adaptivas y su Aplicación a la Solución de Algunas EDP s. Adriana de La Cruz Uribe (página 46-0)