Method of processing a sleeve friction value obtained via a cone penetration test

Abstract

A method of processing a sleeve friction value obtained via a Cone Penetration Test, CPT using a cone penetrometer is disclosed. The method is performed by a processor and comprises a step of processing the sleeve friction value considering variation of geometry of the cone penetrometer, ground stress, and water pressure. Unlocking insights from Geo-Data, the present invention further relates to improvements in sustainability and environmental developments: together we create a safe and liveable world.

Description

METHOD OF PROCESSING A SLEEVE FRICTION VALUE OBTAINED VIA A CONE PENETRATION TEST FIELD OF THE INVENTION

[0001] The present disclosure generally relates to geotechnical data processing, and morespecifically to a method of and a device for processing a sleeve friction value obtained via aCone Penetration Test, CPT, using a cone penetrometer. Unlocking insights from Geo-Data,the present invention further relates to improvements in sustainability and environmental developments: together we create a safe and liveable world. BACKGROUND OF THE INVENTION

[0002] The Cone Penetration Test, CPT, is an in-situ testing method used in geotechnicalengineering to determine the properties of soil or geological materials beneath the ground surface. It is the most prominent in-situ test for geotechnical characterisation of onshore and offshore sites dominated by sands, clays and very weak rock. The CPT involves pushing a cone-shaped penetrometer into the ground at a constant rate and measuring the resistance encountered as the penetrometer advances. The primary parameters measured during a CPTinclude cone resistance ^^ , sleeve friction ^^ , and pore pressure ^ and depth below groundsurface.

[0003] Over time, components of the cone penetrometer, such as the cone and the frictionsleeve, can experience wear, deformation, or damage due to repeated use and contact with abrasive soil particles. This wear and damage can alter the geometry and surface properties ofthe penetrometer, causing measured parameters such as cone resistance and sleeve friction todeviate from desired reference values.

[0004] Sleeve friction ^^ is the frictional resistance between an outer surface of the frictionsleeve of the cone penetrometer and surrounding soil as the penetrometer advances. Geometry factors such as manufacturing tolerances, wear and deformation of the friction sleeve can affectthe accuracy of measured sleeve friction values.

[0005] The issue of tolerances, wear and deformation of cone penetrometers is widelycovered by prior art documents. Correction methods for measured sleeve friction values havebeen suggested by e.g. Peuchen, J. & Terwindt, J. in Introduction to CPT accuracy, 3rdInternational symposium on cone penetration testing CPT14: May 12-14 (2014) - Las Vegas,Nevada, the content of which is incorporated herein by reference.

[0006] Available information however indicates no evidence of actual implementation ofcorrection methods for the measured values of the CPT parameters, in particular for correctingmeasured sleeve friction values, such that the difference between the measured values andreference values is reduced. The available prior art is incomplete on how to implement acorrection method for correcting sleeve friction data in practice, such that it adequately accounts for development of cone penetrometer wear and provides consistent results for commonly observed CPT ground profiles.

[0007] Therefore, there is a need for a method for processing measured sleeve friction data,which can help to improve the reliability and accuracy of geotechnical analyses andinterpretations based on CPT data. BRIEF SUMMARY OF THE INVENTION

[0008] In one aspect of the invention there is provided a method of processing a sleevefriction value obtained via a Cone Penetration Test, CPT, using a cone penetrometer, themethod is performed by a processor and comprises a step of processing the sleeve friction valueconsidering variation of geometry of the cone penetrometer, ground stress, and water pressure.

[0009] Though it is recognized that measured values of CPT parameters, especiallymeasured sleeve friction values, can be negatively influenced in terms of its accuracy byvariation of geometry of cone penetrometers, in practice there is no available methodconsidering such influence when correcting the sleeve friction values. The inventor of the present disclosure insightfully proposes a method of implementing a correction method for sleeve friction values that considers variation of geometry of the cone penetrometer.Particularly, the correction method considers influence of ground stress on the accuracy of thesleeve friction values. Water pressure as conventionally used in correction is also considered.

[0010] The correction method of the present disclosure explicitly recognizes the influenceof ground stress on sleeve friction values by calculating stress-related influence from measurement of the geometry of the cone penetrometer and by using a combination of each of the primary CPT parameters, i.e. cone resistance, sleeve friction, pore pressure and depth below ground surface.

[0011] The method of the present disclosure therefore accounts for commonly observedCPT ground profiles and allows a more consistent and more accurate presentation of CPTresults.

[0012] In an example of the present disclosure, considering variation of geometry of thecone penetrometer comprises considering a geometry factor for a diameter of a friction sleeveof the cone penetrometer.

[0013] A geometry factor can be used to account for the effects of variation of geometryon the penetrometer components, particularly the cone and friction sleeve. The geometry factor can be used to correct the measured CPT parameters including the sleeve friction values and toimprove the accuracy of CPT interpretations by quantifying relationships between variation ofgeometry and the corresponding changes in the measured values of the CPT parameters.

[0014] In an example of the present disclosure, considering a geometry factor for adiameter of the friction sleeve comprises considering a first geometry factor for a first diameterof a lower end of the friction sleeve and considering a second geometry factor for a seconddiameter of an upper end of the friction sleeve, wherein the lower end of the friction is an end of the friction sleeve proximal to a cone of the cone penetrometer, the upper end of the friction sleeve is an end of the friction sleeve distal to the cone of the cone penetrometer.

[0015] The diameter of the friction sleeve of the cone penetrometer is not necessarilyuniform over a whole length of the friction sleeve. By considering two geometry factorsrespectively for the lower and upper ends of the friction sleeve, the variation of geometry of the friction sleeve can be accounted for in a better way, which helps to allow improved correction of the sleeve friction values.

[0016] In an example of the present disclosure, the first and second geometry factors areestimated based on at least one of available measurements and soil mechanical models.

[0017] As can be contemplated by those skilled in the art, the geometry factor in CPT canbe determined by empirical data collection and calibration tests. It can involve analysingmeasurements of surface roughness of the friction sleeve to help identifying correlations andtrends. The thus obtained geometry factors can be conveniently used in the present disclosure to correct the sleeve friction values.

[0018] The geometry factors may also be estimated, separately or in combination withmeasurement, based on soil mechanical models such as continuum models using effectivestress principles. These models include factors such as ground behaviour type, ground densityand mechanical properties to simulate the behaviour of the interface between the cone penetrometer and the surrounding ground. These models can therefore provide insights intomechanisms of geometry change with wear and the effects of ground conditions on measuredsleeve friction values.

[0019] In an example of the present disclosure, considering the variation of geometry ofthe cone penetrometer comprises considering a deployment index representing cumulative resistance experienced by the cone penetrometer as the cone penetrometer advances throughground tested using the CPT. It allows the variation of geometry of the cone penetrometer isconsidered as a function of wear.

[0020] This wear of the cone penetrometer can be reflected in the deployment index, whichprovides a measure of the total resistance encountered by the penetrometer throughout theentire penetration depth, between measurements of cone penetrometer geometry. In the casethat limited measurements of the cone penetrometer geometry are available for determining thewear of the cone penetrometer, the deployment index may be used as an alternative way of accounting for variation in geometry of the cone penetrometer.

[0021] The deployment index is derived based on the penetration length, the measured coneresistance and pore pressure, which are used as input parameters for calculating the deploymentindex for any data point of a CPT.

[0022] In an example of the present disclosure, the deployment index is derived based oncurrent and preceding CPT results.

[0023] Preceding test results serve as a baseline for comparison when analysingdeployment index profiles from subsequent CPT tests. Therefore, the preceding test results may be conveniently used to derive the deployment index.

[0024] In an example of the present disclosure, the considered ground stress is representedby corrected cone resistance derived from measured cone resistance by considering waterpressure at the cone of the cone penetrometer.

[0025] The cone resistance measured during a CPT is closely related to the stress state ofthe soil surrounding the penetrometer. When the cone penetrometer is advanced into the soil,it experiences resistance from the surrounding soil particles and water pressure around the conepenetrometer. Therefore, the corrected cone resistance can be conveniently used for processing the sleeve friction value so that the processed sleeve friction is of improved accuracy.

[0026] In an example of the present disclosure, the considered water pressure compriseswater pressure at a cylindrical extension of a cone of the cone penetrometer and water pressure above a friction sleeve of the cone penetrometer.

[0027] In other words, the considered water pressure comprises water pressures near thelower and upper ends of the friction sleeve.

[0028] The water pressure at the cylindrical extension of the cone, or near the lower end ofthe friction can influence the effective stress state around the cone, affecting the soil's shearstrength and the resistance encountered by the penetrometer as it advances, which may in turnaffect the measured sleeve friction. Moreover, the water pressure above the friction sleeve canalso affect the effective stress state and soil shear strength around the friction sleeve, influencing the measured sleeve friction. Considering both water pressures allows the corrected sleeve friction to be less biased from the reference sleeve friction value.

[0029] Those skilled in the art will understand that the used water pressure can bedetermined based on measurement or estimation or both.

[0030] In an example of the present disclosure, the step of processing further considersvariation in measured sleeve friction values due to variation in radial ground stresses acting onthe friction sleeve resulting from the variation of geometry of the cone penetrometer.

[0031] As can be contemplated by those skilled in the art, variation in the geometry of thepenetrometer may result in increased or decreased contact between the penetrometer and the soil, which will lead to higher or lower radial ground stresses exerted on the friction sleeve.Higher radial ground stresses can lead to enhanced shear resistance along the surface of thefriction sleeve. The soil particles in contact with the friction sleeve experience higher stresses, which can result in greater interlocking and frictional resistance between the soil and the friction sleeve. It therefore makes sense to consider such influence when correcting the sleevefriction. The reverse can apply for lower radial ground stresses.

[0032] Specifically, the variation in measured sleeve friction values due to the variation,that is, increase or decrease, in radial ground stresses resulting from the variation of geometryof the cone penetrometer is represented by a first friction coefficient for a surface area of the friction sleeve which is dependent on an initial stress state and a difference between the diameter of the cone and the diameter of the friction sleeve.

[0033] Such a first friction coefficient can be used to account for the increase or decreasein radial ground stresses and can be conveniently used for deriving values of corrected sleevefriction.

[0034] In an example of the present disclosure, the step of processing further considers avariation in drag acting on the friction sleeve due to variation in cone penetrometer geometry.

[0035] This happens when the diameter of the friction sleeve differs from the diameter ofthe cone and where the diameter of the friction sleeve differs from the diameter of the cylindrical part of the cone penetrometer above the upper end of the friction sleeve.

[0036] Those skilled in the art will understand that the diameter of the cone refers to thediameter of the cylindrical extension of the cone.

[0037] Specifically, the variation in drag due to variation in cone penetrometer geometryis represented by friction coefficients for a cross-sectional area at the lower end of the frictionsleeve and for a cross-sectional area at the upper end of the friction sleeve.

[0038] Considering such variation helps to improve the accuracy of the processed sleevefriction values.

[0039] A second aspect of the present disclosure provides a device for processing a sleevefriction value obtained via a Cone Penetration Test, CPT using a cone penetrometer, the devicecomprising a processor for performing the method according to the first aspect of the presentdisclosure.

[0040] A third aspect of the present disclosure provides a computer program product,comprising a computer readable storage medium storing instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to the first aspect of the present disclosure.

[0041] The above mentioned and other features and advantages of the disclosure will bebest understood from the following description referring to the attached drawing. In the drawings, like reference numerals denote identical parts or parts performing an identical or comparable function or operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to describe the manner in which the above-recited and other advantagesand features of the disclosure can be obtained, a more particular description of the principles briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only exemplary embodiments of the disclosure and are therefore not to be considered to be limiting of its scope, the principles herein are described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0043] FIG. 1 schematically illustrates geometry of a cone penetrometer considered whenpost processing CPT data or parameters according to the method of the present disclosure.DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0044] Embodiments contemplated by the present disclosure will now be described in moredetail with reference to the accompanying drawing. The disclosed subject matter should not be construed as limited to only the embodiments set forth herein. Rather, the illustrated embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0045] In the present disclosure, the terms “processing” and “post processing” are usedinterchangeably.

[0046] In the present disclosure, the “corrected cone resistance” is calculated in a differentway than following the conventional method.

[0047] In the present disclosure, the wording “considering variation of geometry of thecone penetrometer, ground stress, and water pressure” means that factors influencing measured sleeve friction values measured by the CTP, such as the geometry of the cone penetrometer, ground stress, and water pressure, are directly or indirectly accounted for during the correctionprocess of measured sleeve friction values. In other words, the measured sleeve friction valuesare corrected according to the method of the present disclosure based on or using the factorsinfluencing measured sleeve friction values, including for example the geometry of the cone penetrometer, ground stress, and water pressure.

[0048] It will be understood by those skilled in the art that improved accuracy ofcorrected / processed sleeve friction data as used in the present disclosure means the deviationbetween the corrected / processed sleeve friction data and reference sleeve friction values isreduced. Reference sleeve friction values refer to benchmark or baseline values that areconsidered to be accurate or reliable for comparison purposes. Such reference sleeve frictionvalues can be derived based on cone penetrometers with manufactured geometry or desiredgeometry.

[0049] Cone resistance ^^, sleeve friction ^^ and pore pressure ^ measured during a ConePenetration Test, CPT, are relative to the reference level of the test, which can be ground surface for onshore tests, and the seafloor for nearshore and offshore tests.

[0050] Corrected cone resistance ^^ , also known as total cone resistance, includescorrections for hydrostatic and transient pore pressures, and cone construction, and correctedsleeve friction ^^ includes corrections for pore pressures acting on end areas of the frictionsleeve.

[0051] Some corrected CPT data obtained following conventional methods showsanomalously high values of corrected sleeve friction values, that is, the corrected sleeve frictionvalues differ significantly from reference values. The present disclosure provides a method of post-processing of CPT data to account for differences between geometries of cone penetrometers. The differences between geometries of cone penetrometers result from forexample wear of the friction sleeve of a cone penetrometer during penetration and duringretraction when a CPT is performed. This method of the present disclosure can be regarded as ‘penetrometer geometry tolerance variance’ within a context of CPT data.

[0052] A conventional method for post-processing of CPT results is described in Petroleumand natural gas industries – specific requirements for offshore structures – Part 8: marine soilinvestigations (ISO 19901-8:2023) by International Organization for Standardization.

[0053] The method of the present disclosure makes use of additional input parametervalues for geometry of cone penetrometers compared to the conventional method. Theadditional values are derived by considering geometry change of the cone penetrometers andoptionally makes use of a deployment index which accounts for deployment conditions actually encountered.

[0054] Specifically, according to the present disclosure, when the geometry of a conepenetrometer is considered in the post processing of measured cone resistance and measuredsleeve friction data, instead of using a nominal, fixed values which are based on design,calibration and verification, variable values based on design, calibration, verification and assessment are used. In addition, values of ground stresses are considered during the post processing of measured sleeve friction data.

[0055] Referring to Figure 1, geometry of a cone penetrometer 10 considered when postprocessing the measured CPT data or parameters according to the method of the presentdisclosure is illustrated. In Figure 1 a cone penetrometer 10 is illustrated as comprising a cone11 and a friction sleeve 12. The cone 11 includes a conical part, represented by a triangle 111, and a cylindrical extension 13. A gap 14 is present between the cylindrical extension 13 of thecone 11 and the friction sleeve 12. It is noted that different parts of the cone penetrometer inFigure 1 are for illustrative purposes and therefore not drawn to scale.

[0056] Diameter 15 of an upper end, that is, the end of the friction sleeve 12 which is distalto the cone 11 is ^^^. Diameter 16 of a lower end of the friction sleeve 12 is ^^^. Diameter 17of the cylindrical part 13 of the cone 11 is ^^.

[0057] As discussed above, the cone 11 including the conical part 111 and the cylindricalpart 13 as well as the friction sleeve 12 will experience wear during the CPT and the geometryof the cone penetrometer will change compared to nominal values of a new cone penetrometer.

[0058] As an example, the shape and dimensions of the cone directly influence theresistance encountered as the penetrometer advances into the soil. Changes in the geometry of the cone, such as wear or deformation, can affect the measured cone resistance.

[0059] As another example, the outer surface of the friction sleeve provides resistance tomovement as the penetrometer advances through the soil. Changes in the geometry of thefriction sleeve, such as wear or deformation can affect the measured sleeve friction.

[0060] Cone resistance is measured concurrently with sleeve friction during CPT. Coneresistance provides valuable information about the soil properties encountered by the cone penetrometer.

[0061] Moreover, cone resistance and sleeve resistance are interrelated parameters thatdepend on soil properties, cone penetrometer geometry and testing conditions. Changes in soilconditions or cone penetrometer geometry that affect measured cone resistance can also influence measured sleeve friction, leading to correlated uncertainties between the two parameters.

[0062] Based on the above, in the present disclosure, when the sleeve friction data isprocessed, corrected cone resistance values are also considered. The corrected cone resistancevalue is therefore an additional input parameter used for post processing the sleeve frictiondata.

[0063] In illustrating the present disclosure, wear of a cone penetrometer is considered forgeometry change, such that the reference parameter values for cone resistance and sleevefriction apply to first use of a cone penetrometer, i.e. a new cone penetrometer. The suffices^^, ^^ and ^^ are used for post-processed, first-use and in-use, respectively. Therefore, qc;fu,qc;iu, qc;pp, fs;fu, fs;iu, and fs;pp are respectively used to represent cone resistance at first use, coneresistance measured in-use, and post-processed cone resistance, sleeve friction at first-use,sleeve friction measured in-use, and post-processed sleeve friction.

[0064] The method illustrated in the following can further consider a deployment index fordevelopment of wear of a cone penetrometer. The deployment index requires observational and empirical input data that are specific to a particular design of cone penetrometer. Alternatively,test-specific geometry measurements may also be used to account for development of wear ofthe cone penetrometer.

[0065] For a cone penetrometer that is used in the CPT, the corrected cone resistance ^^ iscalculated according to present disclosure based on the following equation (1):^ ^^^^^^ ^− ^;^^ ^ ^ ∙, derived based on^ ^^;^^=^^;^^^^;^^, where ^^^;^^is the in-use axial force on the cone of the cone penetrometer, and ^^;^^is in-use cross sectional area of the cone of the cone penetrometer.

[0068] In equation (1), ^^^ is diameter of the shaft of the cone penetrometer in the gap 14between the cone 11 and the friction sleeve 12 and independent of geometry change. Therefore,^^^ has a nominal value.

[0069] Due to the wear experienced by the cone during the CPT, diameter of the cylindricalpart of the cone in-use ^^;^^ deviates from the diameter of the cylindrical part of the cone forfirst use ^^;^^ , which is a nominal value. In the present disclosure, the diameter of thecylindrical part of the cone in-use ^^;^^ is calculated according to equation (2):

[0071] where ^^^ is a geometry factor for ^^, which is estimated based on measurementdata or based on mechanical models, ^^^^is a deployment index.

[0072] The deployment index ^^^^ represents cumulative soil resistance experienced by thecone and is defined as ^ =for a piezocone penetrometer and as ^^^^ =∫^^ ∙ ^^ ∙ ^^ for a friction cone penetrometer, where l is length of penetration of thecone penetrometer in soil, where ^^;^^is in-use corrected cone resistance, ^^;^^is in-use pore pressure at the cylindrical extension of the cone of the cone penetrometer, ^^;^^is measured in- use cone resistance, ^^^is in-use net area ratio of the cone of the cone penetrometer and ^^ishydrostatic pore pressure relative to the reference level of the test.

[0073] The measured data for calculating the deployment index are not limited to dataobtained only from the current test, instead, measurement data from preceding tests may also be considered.

[0074] The in-use axial force on the cone of the cone penetrometer ^^^;^^ is measuredduring the CPT, for which multiple tests may be performed to obtain a sequence of values, and^ ^^;^^is calculated from ^^;^^following ^^;^^= ^∙ ^^^;^^.

[0075] Based on the above description, the post processed corrected cone resistance ^^;^^correcting for geometry change of the cone penetrometer is obtained. The post processedcorrected cone resistance ^^;^^will be considered in the post processing of the sleeve frictiondata.

[0076] Conventionally, corrected sleeve friction ^^ is calculated according to the followingequation (3):

[0077] ^^ = ^^ −(^^∙^^^^ ^^∙^^^) ^^(3)

[0078] The present disclosure proposes a different way of post processing the measuredsleeve friction data. In the present disclosure, the post processed sleeve friction is derived based on equation (4): ^on use, and ^surface area of the friction sleeve in-use and calculated from ^^;^^ following ^^;^^ = ^ ∙^^;^^ ∙ ^^. ^^ is length of the friction sleeve and has a nominal value. ^^;^^ is average diameterof the friction sleeve in-use, calculation of which will be discussed in the following.

[0081] ^^^;^^ is calculated according to equation (5):^

[0083] Parameters in equation (5) are described as follows:

[0084] ^^^;^^ is friction coefficient for surface area of friction sleeve ^^;

[0085] ^^^;^^ is friction coefficient for cross-sectional area ∆^^^;^^ , at the lower end offriction sleeve;

[0086] ^^^;^^ is friction coefficient for cross-sectional area ∆^^^;^^ , at the upper end offriction

[0087] which is change insleeve upper

[0088] ^which is change inlower cross-sectional area, relative to first use.

[0089] Moreover, ^2^;^^ and ^2u;^^ are respectively diameter of the lower end and diameterof the upper end of the friction sleeve for first use and are nominal values. ^3;^^ is diameter ofthe part of the cone penetrometer above the upper end of the friction sleeve (not shown inFigure 1), which also has a nominal value.

[0090] ^2^;^^ and ^2u;^^ are respectively diameter of the lower end and diameter of theupper end of the friction sleeve in-use, which are subject to wear and calculated as ^2^;^^ =^2^;^^ − ^^2^ ∙ ^^^^ ; ^2u;^^ = ^2^;^^ − ^^2^ ∙ ^^^^ , herein ^^^^ and ^^^^ are respectivelygeometry factors for ^^^ and ^2u . The geometry factors, mdc, ^^^^ and ^^^^ are estimatedbased on available measurement and / or laboratory data. Example values for the geometryfactors used in the present disclosure are listed in below Table 1.

[0091] Table 1: Cone penetrometer geometry factorsParameter Cone Penetrometer Type 1715 Unit^^^^ , ^^^^ 1.00·10-8m / (MPa·m) ^^^ 2.40·10-8m / (MPa·m)

[0092] The deployment index ^^^^ is the same as described above in relation to ^^;^^.

[0093] The average diameter of the friction sleeve in-use ^^;^^ is calculated from ^2^;^^and ^2u;^^ according to ^^;^^ =^+ ^^^;^^^, which is then used to calculate ^^;^^.

[0094] The proposed post processing method considers three friction coefficients forsleeve friction as follows.

[0095] 1. Friction coefficient for surface area of the friction sleeve ^^, denoted as ^^^;^^.This coefficient considers variation, for example increase, in measured sleeve friction valuesdue to variation, for example increase, in radial ground stresses, attributed to geometricalchange. It will be understood by those skilled in the art that the decrease in measured sleevefriction values may result from decrease in radial ground stresses. This coefficient is assessedto be dependent on the initial stress state and the difference between the cone and friction sleeve diameters.

[0096] 2. Friction coefficient for lower cross-sectional area of the friction sleeve, denotedas ^^^;^^. Coefficient ^^^;^^ considers a variation in ‘drag’ acting on the lower end of the frictionsleeve due to, for example, additional exposure because of wear of the cone relative to wear ofthe friction sleeve.

[0097] 3. Friction coefficient for upper cross-sectional area of the friction sleeve, denotedas ^^^;^^. Coefficient ^^^;^^considers a variation in ‘drag’ acting on the upper end of the frictionsleeve. Values of ^^^;^^ can be of limited importance, as the upper end of the friction sleevegenerally wears in tandem with the part of the cone penetrometer above the upper end of the friction sleeve.

[0098] The friction coefficients are described by the following functions:

[0099] ^ =^ (6)

[0102] ∆^^^;^^ is change in sleeve lower cross-sectional area, relative to first use asdescribed above. Coefficients ^ to ^ are - 3^ ^ 0.075, -75·10 , 0.25 and 0.4, which are estimatedbased on measurement and / or soil mechanical models.

[0103] Corrected cone resistance ^^;^^ and pore pressure ^^;^^ refer to post-processedvalues. In the present disclosure, ^^;^^ = ^^;^^ = ^^;^^.

[0104] The above describes an example implementation of the method of post processingthe measured sleeve friction in accordance with the present disclosure. In the conventional method of correcting the sleeve friction as illustrated by equation (3), the input parameters used are values for water pressured as well as nominal fixed values for the geometry of the conepenetrometer. In contrast, following the post processing method of the present disclosure asillustrated in equations (4) and (5), the geometry of the cone penetrometer has variable valuesderived not only based on design, calibration but also on assessment conducted as part of thetest. Moreover, by considering the post processed cone resistance ^^;^^, influence from ground stresses is also considered in the correction.

[0105] In the following, an example calculation is presented to give a broad understandingof the significance of each contributing factor in the post-processing method. A comparison with data presented by Powell et al. (2021) in “The friction sleeve measurement in CPTU -does size matter? - A new study”. In ISC'6 conference, Budapest, 26-29 September 2021: 6thInternational Conference on Geotechnical and Geophysical Site Characterisation. HungarianGeotechnical Society is also provided.follows:^^^^^^^^^ ^

[0108] The example considers ^^,^^ = 2.5 MPa, friction ratio ^^ = 4 % and ^^^^ = 18500MPa∙m. These values are selected based on CPT results obtained from a project. For thisexample, the influence of pore pressure effects is taken as negligible, so that ^^;^^is selectedas 0 MPa. The geometrical values and coefficients as listed in Table apply.

[0109] Table 2: Geometric values for a deployment index of 18500 MPa∙mParameter First-use, ^^ In-use, ^^ UnitCone diameter, ^^ 0.04385 0.04341 [m]Sleeve diameter, ^^ 0.04410 0.04392 [m]Length of friction sleeve, ^^ 0.16500 0.16500 [m]

[0110] From the above geometry values, the parameters used in equation (5) are derived asin Table 3.

[0111] Table 3 parameters used for post processingParameter First-use, ^^ In-use, ^^ UnitArea of friction sleeve, ^^ 0.02286 0.02276 [m2] Change in sleeve upper cross-sectional area, relative0 0 [m2]to first use, ∆^^^Change in sleeve lower cross-sectional area, relative0 0.000018 [m2]to first use, ∆^^^Friction coefficient for surface area of the friction1 1.18 for 2.5 MPa [-]sleeve, ^^^Friction coefficient for lower cross-sectional area of1 1.29 [-]the friction sleeve, ^^^Friction coefficient for upper cross-sectional area of1 1 [-]the friction sleeve, ^^^

[0112] Example

[0113] For ^^,^^ = 2.5 MPa and ^^;^^ = 0.1 MPa, using following equation, the frictionalforce is

[0114] ^0.02286[m^] ∙ 0.1[MPa] =0.002286 [MN]

[0115]

[0116] ^∙ 0.002286[MN]^ ^^;^^^^^;^^^.^^^^^[^^]∙^.^^ =0.001947 [MN]

[0117] ^^^;^^,^^^^^^^^^,^ = ∆^^^;^^ ∙ ^^^;^^∙^^^;^^ − ^^;^^^ = 0[m^] ∙ 1(2.5[MPa] −0

[0124] For comparison, the method of Powell et al. (2021) would have yielded ^^ =2.5 %, as follows:

[0126] Taking ^^^ = 0.0084, factor ^ can be calculated according to:

[0128] Powell et al. (2021) are not fully clear on whether to use in-use or first-use valuesfor the calculation of ^, as a fixed value is proposed. In this example first-use values are used. The influence on the corrected sleeve friction however is limited.

[0129] The correction according to Powell et al. (2021) is then:^^25[MPa] 43.92[mm]^ − 43.41[mm]^^ ^;^^^^^^ = ^100[kPa] − ^^^ ^64^^ ^1− 0.0084^43.92[mm] ^ ^^ − 43.41[mm]^ ^^ = 62[kPa]

[0130] The friction ratio estimated based on the method of Powell et al. (2021) is thereforeabout 2.5%, which is comparable to the result obtained using the method of the present disclosure.

[0131] The method of the present disclosure addresses inevitable wear of steel of CPT conepenetrometers upon use in various soil conditions. The present disclosure provides a practicalimplementation of a correction method for measured sleeve friction values. The methodadequately accounts for development of cone penetrometer wear and provides consistent results for commonly observed CPT ground profiles.

[0132] The invention has been described by reference to certain embodiments discussedabove. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.

[0133] Further modifications in addition to those described above may be made to thestructures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.

Claims

CLAIMS1. A method of processing a sleeve friction value obtained via a Cone Penetration Test,CPT, using a cone penetrometer, the method performed by a processor and comprising a stepof processing the sleeve friction value considering variation of geometry of the conepenetrometer, ground stress, and water pressure.

2. The method according to claim 1, wherein considering variation of geometry of thecone penetrometer comprises considering a geometry factor for a diameter of a friction sleeve of the cone penetrometer.

3. The method according to claim 2, wherein considering a geometry factor for a diameterof the friction sleeve comprises considering a first geometry factor for a first diameter of alower end of the friction sleeve and considering a second geometry factor for a second diameterof an upper end of the friction sleeve, wherein the lower end of the friction sleeve is an end ofthe friction sleeve proximal to a cone of the cone penetrometer, the upper end of the friction sleeve is an end of the friction sleeve distal to the cone of the cone penetrometer.

4. The method according to claim 3, wherein the first and second geometry factors areestimated based on available measurement and / or soil mechanical models.

5. The method according to any of the previous claims, wherein considering variation ofgeometry of the cone penetrometer comprises considering a deployment index representing cumulative resistance experienced by the cone penetrometer as the cone penetrometer advancesthrough ground tested using the CPT.

6. The method according to claim 5, wherein the deployment index is derived based oncurrent and preceding CPT results.

7. The method according to any of the previous claims, wherein the considered groundstress is represented by corrected cone resistance derived from measured cone resistance byconsidering water pressure at the cone of the cone penetrometer.

8. The method according to any of the previous claims, wherein the considered waterpressure comprises water pressure at a cylindrical extension of a cone of the cone penetrometer and water pressure above a friction sleeve of the cone penetrometer.

9. The method according to claim 8, wherein the considered water pressure is determinedbased on at least one of measurement and estimation.

10. The method according to any of the previous claims, wherein in the step of processingfurther considers variation in measured sleeve friction values due to variation in radial ground stresses acting on the friction sleeve resulting from the variation of geometry of the cone penetrometer.

11. The method according to claim 10, wherein the variation in measured sleeve frictionvalues due to the variation in radial ground stresses acting on the friction sleeve resulting from the variation of geometry of the cone penetrometer is represented by a first friction coefficient for a surface area of the friction sleeve which is dependent on an initial stress state and a difference between the diameter of the cone and the diameter of the friction sleeve.

12. The method according to any of the previous claims, wherein the step of processingfurther considers a variation in drag acting on the friction sleeve due to variation in conepenetrometer geometry.

13. The method according to claim 12, wherein the variation in drag due to variation incone penetrometer geometry is represented by friction coefficients for a cross-sectional area at the lower end of the friction sleeve and for a cross-sectional area at the upper end of the friction sleeve.

14. A device for processing a sleeve friction value derived based on measurementperformed by a Cone Penetration Test, CPT using a cone penetrometer, the device comprising a processor for performing the method according to any of the previous claims 1 to 13.

15. A computer program product, comprising a computer readable storage medium storinginstructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to any of the claims 1 to 13.

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