Cone Tip Resistance Research Articles

Geotechnical characterization of a river dyke by surface waves

ABSTRACTThe need for effective and reliable methods to survey and monitor the structure of earth‐fill dams recently became pressing in light of the increasing number of flood events in central Europe. Among geophysical techniques, dam imaging using electrical resistivity methods is applied in most cases. Occasionally, ground‐penetrating radar is applied in the framework of the search for subsurface facilities. Seismic methods are rarely used.This paper focuses on the multichannel analysis of the surface waves (MASW) method to determine dynamic soil properties and aims to extend its application field to dyke and dam structures. The standard processing procedure of the MASW assumes a flat free surface of infinite extension. The flat surfaces of a dyke, in contrast, are in the order of 1–10 times smaller than the wavelengths in the soil; disturbing side reflections will occur. Even though MASW has already been applied on a few dyke sites, the effect of such an obvious breach of preconditions needs to be studied before the method can be recommended.In this paper the influences of the dyke’s topography on the test results are studied by means of a numerical analysis. Typical cross‐sections are modelled using 2.5D finite and boundary elements. The results of models taking the topography into account are compared with models neglecting the topography. The differences are evaluated on the level of the dispersion curves and for one cross‐section on the level of the S‐wave velocity. They were found to be insignificant for dykes with a width‐to‐height ratio larger than four.A testing campaign was conducted providing the chance to collect experience in the practical use of the MASW method on dykes. Test results obtained at two test sites are selected and compared to the results of borehole logs and cone penetration tests. A remarkable relation between the S‐wave velocity and the consistency of the clay sealing was found at one site; a distinct positive correlation to the measured cone tip resistances was achieved on the other test site. Valuable information on the composition of the dyke body and base could be obtained but the resolution of the method to identify small areas of inhomogeneity should not be overestimated.

Experimental Research on Determining the Geotechnical Parameters with CPTU Methods

Cone penetration test is a fast and efficient in-situ test technique. With the development of sensor technology and the use of new probes, such test is employed in more fields and reveals more soil parameters. Based on the advanced CPTU equipment, porewater pressure dissipation processes were measured at different depths, dissipation characteristics of the sandy soil and cohesive soil were analyzed respectively; Then, consolidation and permeability coefficients of the cohesive soil were calculated, the results are close to the laboratory test results. Undrained shear strength of soft clay were determined use theoretical and empirical methods, calculation accuracy of these methods were analyzed and the results show that the total cone tip resistance method is in good consistence with the measured values. CPTU is able to provide plenty of geotechnical parameters; therefore, more experience of regional tests should be drawn so as to produce more economic and technical benefit in the future.

Characterisation of subsurface spatial variability using a cone resistivity penetrometer

The subsurface spatial variation in clay soils, such as thin-layered sand seams, affects the mechanical strength and electrical resistivity. The objective of this study is the development and application of cone resistivity penetrometer (CRP), which measures the cone tip resistance, sleeve friction, and electrical resistivity to evaluate the subsurface spatial variability. The electrical resistivity is measured at the cone tip to increase its resolution. Two outer diameters of the cone resistivity penetrometers (CRPs) are developed: D=10 mm CRP with a projected area of 0.78 cm 2 and D=15 mm CRP with a projected area of 1.76 cm 2. The cone tip resistance is effectively separated using a friction sleeve. Strain gauges are used to measure the mechanical strength, and coaxial type electrodes monitor the electrical resistivity. The application tests in the laboratory are conducted using layered soils and saturated sands. In addition, the penetration tests in the field are carried out and compared with the standard piezocone test. The penetration tests show that the soil layers and the density changes are clearly detected by the electrical resistivity and mechanical strength. Field tests show that CRP clearly evaluates the subsurface profile. This study suggests that CRP may be a useful technique for the evaluation of subsurface spatial variability during penetration testing.

Influence of particle size on the correlation between shear wave velocity and cone tip resistance

The construction of the Péribonka dam involved deep compaction of its foundation using vibroflotation and dynamic compaction. Surface wave testing was used, in addition to classical tests (cone penetration tests (CPTs) and standard penetration tests (SPTs)) for the assessment of vibrocompaction. More than 900 shear wave velocity (Vs) and 1000 CPT profiles were obtained. This set of tests performed prior to and following vibrocompaction constitutes an important data bank, used in this study to establish a relationship between normalized shear wave velocity, Vs1, normalized tip resistance, qc1, and mean grain size, D50. Using the Péribonka project data obtained on fairly coarse sands in conjunction with the Canadian Liquefaction Experiment (CANLEX) project data obtained on fine sands has confirmed the significant effect of particle-size distribution on the relationship between Vsand qc. The paper proposes a correlation between Vs1, qc1, and D50for uncemented and Holocene-age granular soils in continuity with the relation developed by Wride et al. from the CANLEX project.

전단파, 전자기파 및 콘 관입저항력을 이용한 직접전단실험시 전단영역 특성 평가

조립토로 구성된 지반구조물의 안정성은 전단변형에 따른 전단영역의 특성변화에 의해 영향을받는다. 본 연구의 목적은 전단파와 전기비저항 및 콘 선단저항력을 이용하여 직접전단실험시 발생하는 전단영역의 특성을 파악하는 것이다. 전단영역의 특성을 파악하기 위하여, 아크릴 재질로 직접전단상자를 제작하였으며, 직접전단상자의 벽면에는 전단파와 전기비저항의 측정을 위하여 벤더엘리먼트와 전기비저항 프로브를 설치하였다. 벤더엘리먼트와 전기비저항 프로브는 전단영역과 비전단영역에 각각 설치되어, 전단변형에 따른 조립토의 거동을 비교할 수 있도록 하였다. 또한, 콘 선단저항력을 측정할 수 있도록 개발한 마이크로 콘을 첨두강도상태와 잔류강도상태에서 관입하여 깊이에 따른 시료의 강도분포를 관찰하였다. 실험결과, 바닥부근과 하부전단영역에서는 전단변형에 따른 전단파 속도는 일정하였지만, 상부전단영역에서의 전단파 속도는 증가하였다. 또한, 바닥부근의 전기비저항은 변화가 없는 반면, 하부전단영역에서 전기비저항은 상대밀도에 따라 수직변형률과 반비례관계로 나타났다. 콘 선단저항력의 변화도 전단파 속도의 변화와 유사하게 상부전단영역에서 큰 변화가 관찰되었다. 본 논문에서 제시한 직접전단실험시 전단파와 전기비저항을 관찰하는 것과 실험완료 후 콘 관입실험은 조립토의 전단영역 특성을 파악하기 위한 매우 효과적인 방법이 될 수 있음을 보여준다. The characteristics of shear zone in granular soils largely affect the stability of geo-structures. The goal of this study is to evaluate shear zone in a direct shear test using shear wave, electrical resistivity, and cone tip resistance. Bender elements and electrical resistivity probe are embedded into the wall of a direct shear box made of transparent acrylic material to estimate the shear wave velocities and the electrical resistivity at shear and non-shear zones. At the point of peak and residual strength, micro cone penetration test which can be available to measure tip resistance has been performed. Experimental results show that the shear wave velocities at upper shear zone increase during shearing while the values remain constant at bottom and lower shear zone. Also, resistivities at lower shear zone depend on relative density while resistivities at bottom remain constant. The results of cone penetration test demonstrate the correlation of the cone tip resistance and small strain shear modulus at shear zone. This study suggests that the application of the modified direct shear box including shear wave, electrical resistivity and the micro cone tip resistance may become effective tools for analyzing the characteristics of a shear zone.

Estimating Embankment Settlement from Piezocone Penetration Test Data

The in situ piezocone penetration test (PCPT) has been widely used by the geotechnical engineering community for subsurface soil identification and classification and for the evaluation of many engineering soil properties, such as consolidation parameters. PCPT-derived consolidation properties can be used to estimate the magnitude and time rate of the consolidation settlement of loaded soils. This paper presents a case study on implementing PCPT technology to evaluate the embankment settlement at the Juban Road-I-12 Interchange Bridge in Louisiana. The soil underneath each embankment site of the bridge was instrumented with a horizontal inclinometer and vertical magnet extensometers. In each embankment site, PCPT tests were performed, and the soundings of cone tip resistance were used to estimate the constrained modulus (M) profiles. Dissipation tests were conducted at specified penetration depths and used to estimate the vertical coefficient of consolidation (cv). Shelby tube soil samples were collected and tested in the laboratory to evaluate the consolidation properties. The embankments’ consolidation settlements were monitored with time, and the field-measured values were compared with the magnitude and rate of settlements estimated with parameters derived from PCPT data and laboratory consolidation tests. The piezocone penetration and dissipation data reasonably estimated the magnitude and rate of consolidation settlement of both embankment sites. The backcalculated M and cv parameters from field measurements were in good agreement with PCPT-derived values.

Discussion of “Axial Compression of Footings in Cohesionless Soils. I: Load-Settlement Behavior” by Sami O. Akbas and Fred H. Kulhawy

The discussers would like to commend the authors for their investigation of the characterization and parameterization of the load-settlement behavior of axially loaded footings on cohesionless soils because of its importance in geotechnical practice. In this discussion, the discussers would like to: 1 provide the results of a comparative assessment of the performance of loaddisplacement models in approximating the results of a set of fullscale load tests on large footings; 2 stress the importance of investigating load-displacement uncertainty by addressing quantitatively not only second-moment statistics of model parameters but also the correlation between the parameters themselves; and 3 examine the adequateness of load-displacement models for the generation of multivariate distributions for simulation purposes. A database of 30 footings on 12 different sands that were subjected to vertical loading in the field was used for these purposes. The origins of these sands included natural marine deposits, alluvial sediments, aeolian dune sands, and compacted sand fills. The footings included 18 square, 7 rectangular, and 5 circular shallow foundations, with the equivalent footing width B varying from 0.5 to 6 m. Only full-scale foundations were considered to avert difficulties associated with 1-g model tests and scaling problems e.g., Cerato and Lutenegger 2007 . A summary of the sand sites, test locations, sand origin, index number in the database, footing sizes, embedment depth, groundwater depth, median grain size, and CPTU net cone tip resistance qnet representative of capacity is given in Uzielli and Mayne 2010 . The applied stress was normalized by qnet; settlement s was normalized by foundation width B. Three load-displacement model types were considered:

Void Ratio Estimation of Soft Soils Using Electrical Resistivity Cone Probe

Electrical properties of soils have commonly been used to estimate geotechnical properties. This paper introduces a new device, an electrical resistivity cone probe (ERCP), to determine the electrical resistivity of seashore soft soils and estimate void ratio in the field. The probe consists of inner and outer electrodes with a coaxial structure. The probe tip is conical to minimize disturbance during penetration. A four-terminal pair configuration is used to prevent electrical interference. The electrical resistance is measured during a consolidation test, penetration tests in a large-scale calibration chamber, and at two field sites. With the resistivity of soils and electrical resistivity of pore water extracted from undisturbed soils, the void ratio is estimated using Archie’s law. The void ratio estimated by the ERCP in an oedometer cell is almost the same as the volumetric void ratio of sand determined from consolidation tests. In addition, the void ratio profile obtained by the ERCP agrees well with the volume-based void ratio in a sand-clay mixture prepared in the calibration chamber. The void ratio profile estimated in the field is inversely proportional to the standard penetration testing N-value and the cone-tip resistance of the cone penetration test. This paper demonstrates that the ERCP may be an effective device for the estimation of the void ratio of seashore soft soils.

Prediction of embankment settlements over marine clay using piezocone penetration tests

The paper discusses the use of piezocone penetration testing (CPTU) and evaluates four methods of interpretation for predicting the deformation constrained modulus (M) used to calculate the consolidation settlement of cohesive soil. CPTU tests were performed at eight embankment sites in the Lianyungang marine clay and high-quality samples for laboratory testing were collected close to the CPTU test locations. The constrained modulus (M) values predicted using the different interpretation methods were compared with the reference values determined from the laboratory consolidation tests. A new correlation was also developed to predict M from the net cone tip resistance (q t − σ vo ). The paper discusses a simple approach to the use of the CPTU method to estimate the settlements of expressway embankments

Design of a piezovibrocone and calibration chamber

This paper presents the details of indigenous development of the piezovibrocone and calibration chamber. The developed cone has a cylindrical friction sleeve of surface area, capped with a apex angle conical tip of cross sectional area. It has a hydraulic shaker, coupled to the cone penetrometer with a linear displacement unit. The hydraulic shaker can produce cyclic load in different types of wave forms (sine, Hover sine, triangular, rectangular and external wave) at a range of frequency 1-10 Hz with maximum amplitude of 10 cm. The piezovibrocone can be driven at the standard rate of 2 cm/sec using a loading unit of 10 ton capacity. The calibration chamber is of size . The sides of the chamber and the top as well as the bottom portions are rigid. It has a provision to apply confining pressure (to a maximum value of ) through the flexible rubber membrane inlined with the side walls of the calibration chamber. The preliminary static as well as dynamic cone penetration tests have been done sand in the calibration chamber. From the experimental results, an attempt has been made to classify the soil based on friction ratio () and the cone tip resistance ().

Field evaluation of deformation characteristics of a lacustrine clay deposit using seismic piezocone tests

The use of the seismic piezocone test (SCPTU) in geotechnical site investigation offers direct field measurement on stratigraphy and soil behaviour. Compared with some traditional investigation methods such as drilling, sampling and field inspecting method or laboratory test procedures, SCPTU can greatly accelerate the field work and hereby reduce corresponding operation cost. This paper presents the methods review to predict the constrained modulus ( M) and to measure small strain shear modulus ( G max) from SCPTU data. The capacity of current interpretation methods to predict the constrained modulus ( M) was evaluated for Lixia River lagoonal soils. Several sites in Lixia River area were selected for this study. In each site, SCPTU tests were performed and the soundings of cone tip resistance ( q c), sleeve friction ( f s), pore pressure ( u 2), and shear wave velocity ( V s ) were recorded. The predicted M values obtained from the SCPTU interpretation methods were compared with the reference values determined from the laboratory consolidation tests. Results of this study showed that the Sanglerat method was able to predict M better than the other methods. Two new correlations were also developed to predict M from the corrected cone tip resistance ( q t) and the net cone tip resistance ( q n). Small strain shear stiffness can be tentatively estimated in the absence of direct measurement of shear wave velocity. The reliable result was obtained using an association between G max, q t and pore pressure parameter B q . Compared to field downhole wave velocity measurements, SCPTU can lead to a more reliable measurement of maximum stiffness profile with depth. The stress–strain–strength response of the clays was evaluated by the maximum shear stiffness and undrained shear strength.

Effect of artificial cementation on cone tip resistance and small strain shear modulus of sand

A series of cone penetration and bender element tests were performed on sands artificially cemented with gypsum in a calibration chamber to investigate the effect of cementation on the cone tip resistance (q c) and small strain shear modulus (G max) of sand. It was found that both the q c and G max of cemented sand are significantly affected by the degree of cementation while the effects of stress and density are reduced due to the cementation bonds. As the degree of cementation increases, the relationship between the $$ q_{{\text{c}}} {-}D_{{\text{R}}} {-}\sigma _{{\text{v}}}^{\prime } $$ of cemented sand is observed to be similar to that of quartz sand with low compressibility. As the density and stress level affect q c more significantly than G max, the G max/q c of cemented sand decreases with increasing q c. However, as the cementation causes a larger increase in G max than q c, the G max/q c ratio of cemented sand increases as the gypsum content increases. It was also observed from the $$ G_{{\max }} /q_{{\text{c}}} - (q_{{\text{c}}} /p_{{\text{a}}} )(p_{{\text{a}}} /\sigma _{{\text{v}}}^{\prime } )^{{0.5}} $$ relation that the G max/q c ratio of cemented sand locates above the upper bound suggested by previous studies.

Characterization of Norwegian marine clays with combined shear wave velocity and piezocone cone penetration test (CPTU) data

A database of research-quality piezocone cone penetration test (CPTU) and shear wave velocity, Vs, information for Norwegian marine clays has been assembled to study the small-strain stiffness relationships for these materials and to examine the potential use of CPTU and Vs data in combination for the purposes of characterizing these soils. Data for sites where high-quality block sampling was carried out have mostly been used. Improvements have been suggested to existing correlations between the small-strain shear modulus, Gmax, or Vs and index properties for these soils. Recent research has shown that CPTU corrected cone tip resistance, qt, and especially the pore pressure measured during CPTUs, u2, and Vs can be measured reliably and repeatably and are not operator or equipment dependant. Therefore, a new soil classification chart involving the normalized cone resistance, Qt, and normalized shear wave velocity, Vs1, or Vs1 and Δu/[Formula: see text] (where u is the pore-water pressure and [Formula: see text] is the in situ vertical effective stress) is presented. Using this chart it is possible to clearly distinguish between clays of different overconsolidation ratios (OCRs).

Effect of spatial correlation structure and transformation model on the design of shallow strip footing

Directional variability of spatial correlation is observed in natural soils due to their depositional characteristics and it influences the response of structures founded on these deposits. Nonetheless, the results presented in most of the available literature are based on the assumption of either isotropic spatial correlation or perfect spatial correlation of soil properties in horizontal and vertical directions. It is also observed from past studies that the effect of transformation model on the total uncertainty is quite significant. Hence, an effort has been made in this paper to study the effect of anisotropy of autocorrelation characteristics of cone tip resistance (qc) and the transformation model on the bearing capacity of a shallow strip footing, founding on the surface of a spatially varying soil mass. The statistics in the vertical direction of the soil mass are taken from 8 Cone Penetration Test (CPT) records and statistics in the horizontal direction are assumed. For the case considered, it is observed that the transformation model significantly influences the degree of variability of design parameter. The results also show that isotropic correlation structure based on the vertical autocorrelation distance underestimates the variability of design parameter. On the other hand, perfect correlation in horizontal or vertical, or both directions, overestimates the variability of design parameters, and produces conservative estimates of allowable bearing capacity.

Estimating spatial correlation structures based on CPT data

Spatial correlation structures are usually used while modelling inherent uncertainty associated with soil properties. To retrieve this information a sufficient number of measurements and equal intervals between measurements or samples are always required. However, in practice, it is not usual to conduct site investigation in that way subject to a limited budget. Therefore, it is of interest to understand the possible bias created by using samples with unequal intervals. This research focuses on estimating the vertical spatial correlation structures of cone penetration tests (CPT) data conducted at a liquefaction site in Taiwan. The appropriate fitting range used in calibrating the correlation model is also discussed. The results show that cone tip resistance has larger correlation distances than that of sleeve friction. The estimated correlation distances of the CPT profiles are similar while using an equal sampling interval within a certain fitting range (denoted as the critical interval of measurements in this research). The results indicate that the effect of using different curve-fitting ranges is relatively insignificant for correlation distances of sleeve friction, whereas the correlation distances of cone tip resistance are more sensitive to different curve-fitting ranges. Moreover, the mean values of correlation distances are more constant for the equal sampling interval cases than for the unequal interval cases.

Temperature-Compensated Cone Penetration Test Mini-Cone Using Fiber Optic Sensors

Abstract The mechanical properties obtained by using a strain gauge are influenced by the temperature change that occurs due to the electrical resistance change of the strain gauge and cable. The temperature change, which occurs during cone penetration testing, can produce an unreliable cone tip resistance. Several types of cone penetrometers with diameters ranging from 1 to 7 mm are developed by using fiber Bragg grating (FBG) sensors for the temperature compensation. The design concerns include the configuration, active and temperature sensor installation, and calibration. FBG active sensors monitor both the tip resistance and the temperature change, while the FBG temperature transducer only measures the temperature change. The experimental studies show that the tip resistance estimated by strain gauges is affected by the temperature change in both full and half Wheatstone bridges, but the tip resistance determined by the FBG sensors is independent of the temperature change. The tip resistances determined by the strain gauges and the FBG sensors are reliable after the temperature is compensated for. This study demonstrates that by using FBG sensors, cone penetrometers produce a more reliable cone tip resistance.

Spatial correlation structures of CPT data in a liquefaction site

In this paper the spatial structures of cone penetration test parameters in a liquefaction site in Taiwan are estimated based on multiple CPTs conducted in-situ. The study area was divided into three sub-regions based on the geological condition of the study area. The results show that in the vertical profile, cone tip resistance ( q c ) has a larger scale of fluctuation (SOF) than that of sleeve friction ( f s ). The soil profile which is composed of various sources and complex process of deposition has a smaller SOF in q c parameter. However, the spatial structure in f s parameter is not sensitive to the geological formation. The analysis results of the CPT data in horizontal direction indicate that the correlation distances of q c and f s in horizontal direction are similar. The horizontal spatial structure is dominated by the anisotropy of the geological and river systems. In conclusion, this study demonstrates that a proper geological zonation is necessary for estimating the spatial structure in both the vertical and horizontal directions.

Field Evaluation of the Cyclic Strength versus Cone Tip Resistance Correlation in Silty Sands

ABSTRACT The liquefaction potential assessment under the framework of simplified procedure that involves the use of cone penetration tests (CPT) typically relies on empirical correlations between the soil cyclic resistance ratio, CRR and cone tip resistance qt. For sands that contain fines (particles passing #200 sieve), an adjustment based on fines content in the CRR-qt correlation is called for in currently available procedures. Earlier laboratory calibration tests in reconstituted silty sand specimens performed by the authors have indicated that partial drainage in CPT played an important role in the CRR-qt correlations. A series of laboratory tests on undisturbed samples and field piezocone penetration tests (CPTU) were carried out in an alluvial soil deposit at two test sites in Central and Southern Taiwan. The results indicated that unlike the uniformly mixed specimens reconstituted in laboratory, the tested natural alluvial silt/sand soils can be heterogeneous with closely spaced clean sand layers embedded in a matrix of silty material. This stratification can render the CPTU a drained test even at fines contents well in excess of 50%. The ignorance of free draining effects on CPTU due to stratification in alluvial soils may lead to overestimation of CRR. Because of these factors, calibration of the CRR-qt correlations by performing tests in local soil and field procedures to ascertain the drainage conditions in CPTU are important to the proper application of the CRR-qt correlations in the liquefaction potential assessment.

Effect of soil variability on the bearing capacity of clay and in slope stability problems

Site-specific geotechnical data are always random and variable in space. In the present study, a procedure for quantifying the variability in geotechnical characterization and design parameters is discussed using the site-specific cone tip resistance data ( q c) obtained from static cone penetration test (SCPT). The parameters for the spatial variability modeling of geotechnical parameters i.e. ( i) existing trend function in the in situ q c data; ( ii) second moment statistics i.e. analysis of mean, variance, and auto-correlation structure of the soil strength and stiffness parameters; and ( iii) inputs from the spatial correlation analysis, are utilized in the numerical modeling procedures using the finite difference numerical code FLAC 5.0. The influence of consideration of spatially variable soil parameters on the reliability-based geotechnical deign is studied for the two cases i.e. ( a) bearing capacity analysis of a shallow foundation resting on a clayey soil, and ( b) analysis of stability and deformation pattern of a cohesive-frictional soil slope. The study highlights the procedure for conducting a site-specific study using field test data such as SCPT in geotechnical analysis and demonstrates that a few additional computations involving soil variability provide a better insight into the role of variability in designs.

Micro-Cone Penetrometer for More Concise Subsurface Layer Detection

Abstract As the disturbance zone and measurement of soil properties are affected by the size of the penetrometer, a more local value may be measured by a smaller penetrometer. An ultra small Micro-Cone penetrometer with a 5 mm outer diameter is designed and manufactured to characterize soil properties with minimum disturbance during penetration tests. The tip resistance is measured by using strain gages attached near the Micro-Cone (MC) tip. A friction sleeve is adopted to effectively remove the skin friction from the tip resistance. Design concerns include the installation of strain gages, circuits, operating temperature, input voltage, penetration systems, penetration rate, sampling rate, and calibration. Application tests show that the air-clay interface, and the soil layers that consist of clay and sand are closely detected by the MC penetrometer. The cone tip resistances measured by the MC and the miniature cone with a 16 mm outer diameter are similar in clay. The strength change in sand after multiple liquefactions is clearly identified. This study shows that, with a relatively high resolution, the MC penetrometer may effectively detect the soil interface and yield the reasonable cone tip resistance.