Cone Resistance Research Articles

낮은 구속응력에서 모래-실트 혼합토의 동결강도 평가를 위한 동적 콘 저항력 및 전단강도 상관성 연구

극한지에서는 환경적 요인과 접근성의 한계에 따라, 동결토의 강도를 현장 상태에서 파악하기 어렵다. 본 연구에서는 극한지 현장의 동결강도를 평가하기 위하여 계장화된 동적 콘 관입기로부터 산정된 동적 콘 저항력과 직접전단실험으로부터 획득된 전단강도 간의 상관성을 조사하였다. 실트가 혼합된 주문진사를 함수비 2.3%로 동일하게 조성하였으며, 시료를 냉동 챔버 내에서 동결시킨 후 직접전단실험과 동적 콘 관입실험을 진행하였다. 실험은 동결과정 및 전단과정, 그리고 동적 콘 관입과정에서 수직응력을 5kPa 및 10kPa로 조합한 4가지 경우로 구성하였으며 이에 따른 동적 콘 관입지수와 전단강도를 산정하였다. 또한 해머타격으로부터 전달되는 에너지의 손실에 대한 영향을 최소화하기 위하여 선단에서 산정된 에너지 및 변위를 이용함으로써 동적 콘 저항력을 산출하였다. 직접전단실험 및 동적 콘 관입실험을 수행한 결과 구속조건에 의한 전단강도의 증가에 따라 동적 콘 관입지수는 비선형적으로 감소하였으며, 동적 콘 저항력은 전단강도와 선형적으로 비례하는 관계로 나타났다. 본 연구는 동결토에 대한 동적 콘 관입실험과 직접전단실험을 통한 강도정수를 비교 및 평가한 연구이며 본 연구에서 도입된 동적 콘 저항력은 극한지 현장에서 동결토의 강도를 추정하기 위한 유용한 지표가 될 수 있을 것으로 기대된다. Investigation of in-situ ground in cold region is difficult due to low accessibility and environmental factors. In this study, correlation between dynamic cone resistance and shear strength is suggested to estimate the strength of frozen soils by using instrumented dynamic cone penetrometer. Tests were conducted in freezing chamber after preparing sand-silt mixture with 2.3% water content. Vertical stresses of 5 kPa and 10 kPa were applied during freezing, shearing, and penetration phase to compare the dynamic cone resistance and shear strength. The dynamic cone resistance, additionally, is calculated to minimize the effect of energy loss during hammer impact. Experimental results show that as the shear strength increases, the dynamic cone penetration index (DCPI) decreases nonlinearly, while the dynamic cone resistance increases linearly. This study provides the useful correlation to evaluate strength properties of the frozen soils from the dynamic cone penetration and direct shear tests.

Assessment of natural slopes susceptible to failure in heavy rainfall based on in-situ cone resistance data

Assessment of natural slopes susceptible to failure in heavy rainfall based on in-situ cone resistance data

An Alternative Method for Determination of Liquefaction Susceptibility of Soil

This article focuses on the application of extreme learning machine (ELM) for prediction of liquefaction susceptibility of soil based on cone penetration test data. The determination of liquefaction susceptibility of soil has been taken as a classification problem. ELM predicts liquefaction susceptibility of soil based on earthquake magnitude (M), cone resistance (qc), mean grain size (D50), total vertical stress (σ0), effective vertical stress (σ′0), normalized peak horizontal acceleration at ground surface (α/g), cyclic stress ratio \(\left( {\frac{\tau }{{\sigma^{\prime}_{0} }}} \right)\). Six models have been developed. The results of ELM have been compared with the artificial neural network models. This study shows that the developed ELM is a potential robust method for solving different problems in geotechnical engineering.

Microstructural study of deformation zones during cone penetration in silt at variable penetration rates

During conventional cone penetration testing in silt, the soil will normally be partially drained. If the penetration rate varies, time for drainage is altered and therefore the measured cone resistance and pore pressure will change. This paper studies the change in soil microstructure around the probe during cone penetration carried out at different penetration rates to investigate the failure mechanism and the processes controlling drainage in silt. Backscattered electron images of polished thin sections prepared from frozen samples at the end of penetration were used. Making use of advanced image-processing techniques, the statistical distribution of particle orientations and the local porosity were investigated for zones around the cone tip and shaft. The spatial distribution of the measured microscale parameters in the region near the probe indicates that the soil deformation during a piezometric cone penetration test (CPTU) in silt leads to the formation of both contractive and dilative zones. The macro response of the material, presented by the pore pressure and cone penetration resistance measured during the test, results from the competition between these zones during penetration, which is shown to be dependent on the penetration rate.

CPT-based method for toe resistance of driven piles in sand

This study proposes a cone penetration test (CPT)-based toe resistance method for predicting toe resistance of pre-tensioned spun high-strength concrete (PHC) piles driven into sand. In total, 82 CPTs and 190 pile-driving analyser test piles were conducted at a construction site Myoungji site in the Nakdong River deltaic area west of Busan City in South Korea. Based on the toe resistance results obtained from the pile-driving analyser test analysis, the reliability of which was verified by comparison with on-site O-cell tests, a new CPT-based method for predicting the toe resistance of the PHC driven pile is proposed based on a statistical rank index. The new method consists of the geometric average of the CPT cone resistance and the loose soil ratio within the influence zone of 8D above and 4D below the pile toe (where D is pile diameter). The new method is found to provide better toe resistance prediction than previously suggested CPT-based methods.

Unidirectional cyclic resistance of Ticino and Toyoura sands from centrifuge cone penetration tests

The evaluation of the undrained cyclic resistance of sandy deposits is required to forecast the soil behaviour during an earthquake (liquefaction, cyclic mobility); due to the difficulties in obtaining undisturbed samples of most liquefiable soils, it is usually deduced from field test results such as cone penetration tests. This paper proposes a methodology to evaluate the undrained cyclic resistance from normalised cone resistance of two well-studied silica sands (Ticino and Toyoura), with different mineralogy, one mainly composed of feldspar, the other of quartz. The determination of the cyclic resistance of Ticino and Toyoura sands was achieved through undrained cyclic triaxial tests on reconstituted specimens. The tip resistance was deduced from CPTs performed in centrifuge with a miniaturised piezocone on homogeneous reconstituted models. Both the undrained cyclic and tip resistances were correlated with the state parameter ψ. Results of centrifuge and triaxial tests were combined through ψ to deduce the cyclic resistance ratio CRR directly from the normalised cone resistance. The shape of the curve relating CRR to the normalised cone resistance resulted unusual respect to all the recognised curves widespread in the geotechnical literature. The aim of the proposed correlations is to provide a useful instrument to improve the actual knowledge on liquefaction and to give a contribution based on the critical state soil mechanics framework to the development of refined correlations between the cyclic resistance of a sand and the results of cone penetration tests.

CPT-based p-y analysis for piles embedded in clays under cyclic loading conditions

The design of offshore mono-piles is subjected to various uncertainties more than inland cases, due to experimental difficulties in characterizing required soil parameters under offshore environment. In this study, a CPT-based p-y method is proposed for monopiles embedded in clay under cyclic loading conditions. As offshore mono-piles are particularly targeted in this study, the cyclic loading condition was introduced as an important design consideration. Based on the effective cone factor, the ultimate lateral soil resistance and p-y function were formulated as a function of CPT cone resistance and cyclic loading effect factor with consideration of the number of loading cycle. As the CPT-based p-y function utilizes the continuous CPT profile directly, detailed depth profile of soil characteristics can also be directly taken into account for the analysis without additional sampling and testing procedure. The load transfer analysis using the proposed CPT-based p-y analysis for cyclic loading condition was programmed using the discretized implementation algorithm for the beam-on-elastic foundation model. To validate the CPT-based p-y analysis method, the calculated lateral load responses were compared with the results obtained from the finite element analysis and case examples for static and cyclic loading conditions.

Interaction effects on load-carrying behavior of piled rafts embedded in clay from centrifuge tests

In the present study, various interaction effects and load-carrying behavior of piled rafts embedded in clay were investigated. For this purpose, a series of centrifuge load tests were conducted using different types of model foundations, including single pile, group piles, piled raft, and unpiled raft. Different clay conditions were considered to prepare for centrifuge specimens. It was found that the pile group effect in clays is significant within initial loading range, showing lower load-carrying capacity. As settlement increases, the pile group effect becomes less pronounced. For both soft and stiff conditions, the values of the raft-to-pile (R-P) interaction factor varied initially, which became converged to some values around unity with increasing settlement. Similar tendency was observed for the pile-to-raft (P-R) interaction factor. The load responses of different pile components within the piled raft were not significantly different for the soft condition. For the stiff condition, the corner and inner piles showed the highest and lowest load-carrying capacities, respectively, due to piled-raft interaction effects. Correlations to cone resistance were analyzed and presented for the base and shaft resistances of piles for piled rafts.

CPT-based p-y analysis for mono-piles in sands under static and cyclic loading conditions

In the present study, a CPT-based p-y analysis method was proposed for offshore mono-piles embedded in sands. Static and cyclic loading conditions were both taken into account for the proposed method. The continuous soil profiling capability of CPT was an important consideration for the proposed method, where detailed soil profile condition with depth can be readily incorporated into the analysis. The hyperbolic function was adopted to describe the non-linear p-y curves. For the proposed hyperbolic p-y relationship, the ultimate lateral soil resistance pu was given as a function of the cone resistance, which is directly introduced into the analysis as an input data. For cyclic loading condition, two different cyclic modification factors were considered and compared. Case examples were selected to check the validity of the proposed CPT-based method. Calculated lateral displacements and bending moments from the proposed method were in good agreement with measured results for lateral displacement and bending moment profiles. It was observed the accuracy of calculated results for the conventional approach was largely dependent on the selection of friction angle that is to be adopted into the analysis.

Cone penetration data classification with Bayesian Mixture Analysis

ABSTRACTThis paper presents an application of the Bayesian Mixture Analysis (BMA) to deal with the classification of spatially variable soil data from the cone penetration test. The cone penetration data classification postulates a problem where a set of cone penetration measurements is used to identify “hidden or unobserved” soil classes. The problem is formulated as an incomplete-data Gaussian mixture where the observed data are defined by the natural logarithm-transformed values of the normalized friction and the normalized cone resistance, while the soil classes to be identified are considered as hidden data. The solution for the incomplete-data problem which consists of class-dependent mixture probabilities and Gaussian distribution parameters is defined in a Bayesian framework. The implementation of conjugate priors for the Gaussian mixtures enables an efficient sampling of the posterior parameters by the Gibbs algorithm of the Markov Chain Monte Carlo method. When compared to the well-established Robertson classification charts, the BMA formulation has an advantage due to the Bayesian framework which enables the definition of soil classes through mixture priors, class-dependent posterior parameter estimates, and a probabilistic soil classification. The presented approach is applied to the cone penetration data from the Sheringham Shoal Offshore Wind Farm site.

Evaluation of geotechnical parameters of a lagoonal clay deposit in Jiangsu Lixia River area of China by seismic piezocone tests

The use of the Seismic Piezocone Test (SCPTU) in geotechnical site investigation offers field assessment on stratigraphy and soil behavior. 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. The results of a site investigation on the soft, normally to slightly overconsolidated, Lixia River lagoonal clay deposit underlying several expressway lines, including a seismic piezocone penetration test, undisturbed sampling from an adjacent borehole, and laboratory testing, are reported. The determination of soil profile and the main geotechnical properties is facilitated by the use of seismic piezocone penetration test that can provide up to four independent reading with depth from a single sounding. The coupled use of normalized cone resistance and pore pressure parameter provides a simple and quick soil classification for highly interbedding of Lixia River lagoon ground. Comparison of the results reveals the validity of SCPTU tests to interpret the engineering properties of Lixia River lagoonal clay. These data will also be particularly useful for future local construction work.

Interpretation of Cone Penetration Testing in Silty Soils Conducted under Partially Drained Conditions

The standard penetration rate used in cone penetration tests (CPTs) is 20 mm/s, regardless of soil type, which yields fully drained penetration in sand and fully undrained penetration in clay. However, for silty soils that represent an intermediate grain size composition and unique characteristics compared with sand and clay, the standard rate of penetration results in partially drained penetration, often leading to misinterpretation of this soil type. In this study, 15 CPTs, with penetration rates varying from 0.5 to 60 mm/s, were performed at a test site in northern Denmark, where the subsoil consisted primarily of sandy silt with clay bands. The results illustrated that when the penetration rate is reduced, the cone resistance increases, but the pore pressure decreases. The transition between undrained and fully drained penetration was determined by converting the results into a normalized penetration rate. Also evaluated and presented in this paper is how cone resistance obtained under partially drained conditions underestimates the interpreted relative density Dr and friction angle ϕ. Triaxial test results on undisturbed silt samples were applied for this analysis.

Validation of impact penetrometer data by cone penetration testing and shallow seismic data within the regional geology of the Southern North Sea

This study presents the assessment of total cone resistance from in situ deceleration measurements using the Lance Insertion Retardation meter (LIRmeter) in the Southern North Sea. The penetrometer is equipped with a measurement lance that is up to 6 m in length. The aim was to validate LIRmeter data interpretation within the regional geological context by comparison with static velocity cone penetration testing (CPT) and sub-bottom profiles. In total, 13 datasets were taken, in addition to preexisting hydroacoustical and static velocity CPT datasets. The dynamically acquired data were processed and compared to the reference static velocity data. The validation encourages the use of acceleration-based dynamic penetration tests, since a high degree of agreement was demonstrated between independently acquired dynamic and static cone resistance data. Moreover, the results reveal evidence of two successive formations with different geotechnical properties, consistent with existing knowledge on the regional setting. Additionally, there is novel indication of an incised glacial valley with muddy low-permeability sediments extending much further than reported to date, which would necessitate updating of older maps. The main advantage of penetrometer-based deceleration measurements lies in the robustness of the method, and the reliability of the sensors. However, penetration depth is, for dimensioning reasons, limited to the order of a few meters. Additionally, data processing includes the dependency of knowledge about the soil type to correct the dynamic data. These limitations can be satisfactorily outweighed by combination with reference data from static velocity tests, as demonstrated by integrating these data into a soil classification scheme.

Interpretation of cone resistance and pore-water pressure in clay with a modified spherical cavity expansion solution

A theoretical approach to interpreting the cone penetration resistance and the pore-water pressure measured on the face of the cone during piezocone tests of clays is proposed. The mechanism for the penetration of the piezocone is assumed to be spherical cavity expansion in modified Cam clay critical-state soil. Using large strain theory, the spherical cavity expansion problem is reduced to solving a system of first-order ordinary differential equations for effective stresses in the plastic zone. By taking the normal and shear stresses acting on the cone face to be the ultimate cavity expansion pressure and the effective friction at the cone–soil interface, respectively, the cone resistance was evaluated at force equilibrium. The pore-water pressures induced by cone penetration include components caused by changes in normal and shear stresses, for which the normal term can be predicted by integrating the radial equilibrium equation in terms of total stress. As it is based on an exact constitutive relationship, the present method takes more factors (such as the effects of interface shear and the traditional overconsolidation ratio) into account than other methods of tackling this problem. Comparisons between the predicted and measured values of cone resistance and pore-water pressure at different well-documented sites are in good agreement for most relatively homogeneous low- and medium-sensitivity clay sites.

Measurements of driving energy in SPT and various dynamic cone penetration tests

Driving energy was measured in a standard penetration test (SPT) and 12 types of dynamic cone penetration tests (DCPTs) having different configurations for the hammer, driving rod, anvil and cone tip. The driving energy transferred from the free falling hammer to the driving rod was estimated from the measurements of strain and acceleration below the anvil. Basically, the driving energy was estimated for 21 successive blows in order to obtain the mean value, the standard deviation (σ) and the coefficient of variance (COV) in the SPT and DCPTs. The dynamic cone resistance, qdyn, was estimated from the driving energy, the corresponding set per blow, and masses of the hammer and the total rods. Thus, the estimated dynamic cone resistance was compared with the static cone resistance, qt, from a cone penetration test (CPT). The main objective of this report is to provide information on the driving efficiency in the SPT and each DCPT. The mean values for ef in the tests ranged from 52% to 76%. The values of COV for ef ranged from 0.024 to 0.265. Even though the test results are limited, the dynamic cone resistance, qt, estimated from the dynamic measurements were relatively good measures of the cone resistance from the CPT, showing the importance of the dynamic measurement in the SPT and DCPTs.In addition, possible factors influencing the driving efficiency, such as the hammer mass, the configuration of the driving rod (solid or hollow), the ratio of the diameter of the anvil and the diameter of the hammer, and the existence of a cushion or cushions between the anvil and the hammer, are discussed on the basis of the limited test results.

Estimating slope of critical state line from cone penetration test — an update

Estimation of density from cone penetration test (CPT) results is challenging, as cone resistance is a function of a number of soil properties, particularly compressibility. While many of the relevant soil properties can be determined from laboratory testing of recovered samples, this process is not feasible when investigating a deposit of soil with significant variations in gradation and (or) properties across depth and lateral extent. To provide a first-order estimate of density from CPT results alone, a number of correlations have been developed to ascertain other soil properties, particularly compressibility, from CPT data. In particular, friction ratio and soil behaviour type index have been suggested as providing indications of soil compressibility, referenced as the slope of the critical state line. Two of these correlations are critically assessed through the identification and analysis of data from 31 sites where both CPT and relevant laboratory testing were conducted. This process indicates that while the additional data analyzed in this study are generally consistent with previous correlations in terms of trend, significant scatter is evident. In addition, the difficulty in directly relating recovered samples to specific CPT data is outlined.

Evaluation of liquefaction potential based on CPT results using C4.5 decision tree

The prediction of liquefaction potential of soil due to an earthquake is an essential task in Civil Engineering. The decision tree is a tree structure consisting of internal and terminal nodes which process the data to ultimately yield a classification. C4.5 is a known algorithm widely used to design decision trees. In this algorithm, a pruning process is carried out to solve the problem of the over-fitting. This article examines the capability of C4.5 decision tree for the prediction of seismic liquefaction potential of soil based on the Cone Penetration Test (CPT) data. The database contains the information about cone resistance (q_c), total vertical stress (σ_0), effective vertical stress (σ_0^'), mean grain size (D_50), normalized peak horizontal acceleration at ground surface (a_max), cyclic stress ratio (τ/σ_0^') and earthquake magnitude (M_w). The overall classification success rate for the entire data set is 98%. The results of C4.5 decision tree have been compared with the available artificial neural network (ANN) and relevance vector machine (RVM) models. The developed C4.5 decision tree provides a viable tool for civil engineers to determine the liquefaction potential of soil.

Correlation of SPT-CPT Data from the Subsidence Area in Gölcük, Turkey

Previous correlative studies The relationship between SPT N values and cone tip resistance q c , n = (q c /N) was analyzed by many authors. De Alencar Velloso [3] indicated ratios of SPT N values and cone tip resistance for different soil types and introduced 0.35 MPa for clay and silty clay, 0.2 MPa for sandy clay and silty clay, 0.35 MPa for sandy silt, 0.6 MPa for fine grained sand, and 1.0 MPa for sand. Meigh and Nixon [6] indicated that this relation did not consider the effect of grain size and recommended n-values as 0.2 MPa for coarse grained sand and 0.3-0.4 MPa for gravelly sand. Schmertman [9] called attention to the conversion of SPT data to cone penetrometer values if only SPT data are available. He recommended 0.2 MPa for silt, sandy silt, and slightly cohesive silt-sand mixture, 0.3-0.4 MPa for clean, fine to medium sand and slightly silty sand, 0.5-0.6 MPa for sandy gravel and gravel. He also suggested that the correlation of sleeve friction (f s ) with N values is better than that of q c and N value, especially for cohesive A correlation of standard penetration test (SPT) and cone penetration test (CPT) data was carried out by this study. The SPT provides information on the resistance and properties of soils and weathered rocks. In addition to the SPT, the CPT is widely used for site investigation and geotechnical design especially in alluvial areas, based on soil types. In order to determine the CPT values of the investigation areas, where only reliable SPT values are available, the SPT blow counts (N values) can be converted into CPT cone resistances (q c values) by an SPT-CPT correlation. The correlation of SPT-CPT test results from the subsidence area was performed using statistical methods. The soils in this area are recent alluvial deposits, consisting mainly of silty clay, clayey silt, clay and sandy clay. The qc values are not increased when SPT values are increased as it is expected.

CPT-based lateral displacement analysis using p-y method for offshore mono-piles in clays

In this study, a CPT-based p-y analysis method was proposed for the displacement analysis of laterally loaded piles. Key consideration was the continuous soil profiling capability of CPT and cone resistance profiles that do not require artificial assumption or simplification for input parameter selection. The focus is on the application into offshore mono-piles embedded in clays. The correlations of p-y function components to the effective cone resistance were proposed, which can fully utilize CPT measurements. A case example was selected from the literature and used to validate the proposed method. Various parametric studies were performed to examine the effectiveness of the proposed method and investigate the effect of property profile and its depth resolution on the p-y analysis. It was found that the calculation could be largely misleading if wrongly interpreted sub-layer condition or inappropriate resolution of input soil profile was involved in the analyses. It was also found that there is a significant influence depth that dominates overall load response of pile. The soil profile and properties within this depth range affect most significantly calculated load responses, confirming that the soil profile within this depth range should be identified in more detail.

준설토의 간극비 변화 관찰을 위한 물리탐사기법의 적용

해성점토를 활용한 준설매립공사에서는 준설토의 거동분석이 선행되어야 한다. 본 연구에서는 침강압밀하는 준설토의 밀도와 간극비 변화를 관찰하기 위해 물리탐사기법을 적용하였다. 서해안에서 채취한 흙에 대한 기본물성시험을 실시하였고, 침강압밀시험기에 시료를 단계적으로 투기하여 시간에 따른 계면고와 탄성파의 변화를 관찰하였다. 흙의 침강압밀이 완료된 후 하방향의 투수시험을 실시하여 조간대의 영향이 준설토의 물리적 특성에 미치는 영향을 관찰하였다. 또한 초소형 전기저항탐침을 관입하여 깊이에 따른 시료의 전기비저항을 측정하였다. 모든 실험이 완료된 후, 시료를 채취하여 간극비를 계산하였다. 실험결과, ML 시료의 특성상 급격한 침강을 보여 침강압밀특성을 육안으로 관찰하기 어려웠으나, 단계투기가 계속될수록 탄성파의 속도는 증가하는 경향을 보였다. 하방향 투수에 따른 조간대 영향은 매우 적어 관찰할 수 없었다. 한편 탄성파 속도로 추정한 시료의 간극비는 단계투기에 따라 선형적으로 증가하는 경향을 나타내었다. 전기비저항으로부터 계산된 간극비는 깊이에 따라 반복적으로 증가, 감소하는 형태를 나타내었으며 이는 단계투기에 따라 층을 이루고 있는 시료의 영향으로 파악된다. 시료채취, 탄성파 속도, 그리고 전기비저항으로부터 구한 간극비를 비교한 결과, 서로 유사한 관계를 나타내었다. 본 연구는 물리탐사기법이 준설토의 간극비 관찰에 효과적으로 활용될 수 있음을 보여준다. It is necessary to understand the behavior of the soils for the dredging constructions. The objective of this study is to estimate void ratio and density changes of the dredged soils by using the geophysical testing methods. A series of laboratory tests is performed to obtain geotechnical index properties of the specimen, retrieved from the west coastal of Korea. The sedimentation and self-weight consolidation tests are carried out with observing changes of the interfacial height and the elastic wave velocities. The same amounts of the soils are poured into the testing column at intervals of 12 hours until the interheight reaches to a certain level. After the completion of the sedimentatation and self-weight consolidation tests, downward permeability test is performed to assess a tidal influence in the nearshore. The mini resistance cone is penetrated into the specimen to measure the electrical resistivity with depth. All tests are completely finished, the weight of specimens are measured to calculate the void ratio with the depth. Experimental results show that the aspects of the self-weight consolidation are invisible during dredging process because of rapid sedimentation characteristics of ML. However, the elastic wave velocities increase with increasing in the effective stresses. During permeability test, measured permeability and the elastic wave velocities maintain almost identical values. Void ratio based on the elastic wave velocities changes linearly with time during the step dumpings. Void ratio estimated by the electrical resistivity represents the repeatedly layered depositions according to the step-by-step dumpings. Void ratio determined by soil sampling is similar to those of elastic waves and electrical resistivity profiles. This experimental study demonstrates that the geophysical testing methods may be an effective method for evaluating the behavior of dredged soils.