Piezocone Penetration Test Research Articles

Comparison of CPT charts for soil classification using PCPT data: Example from clay deposits in Jiangsu Province, China

Geotechnical engineers worldwide practice a variety of in-situ techniques to classify soils in order to obtain their physical and engineering properties. An electric piezocone, which is an advanced version of the cone penetrometer, is capable of measuring cone resistance, sleeve friction and pore pressure. The piezocone testing data not only provide valuable information on soil types but are also useful in deriving correlations with the engineering properties of soil for the purposes of analysis and design of foundations. In a view to establish a region-specific correlation between piezocone penetration resistance and soil properties, piezocone penetration tests (PCPT or CPTu), borings, and other in situ tests were carried out at seven locations in Jiangsu Province, China. PCPT data were first used for classifying soil; thus the data were fully analyzed and validated for providing a reasonable soil classification. Several available CPT based classification charts are used to determine soil types; these results are further validated with the soil classification determined from the field samples and basic soil test results. This paper summarizes these analysis results, including description of the available charts and their performance in soil classification.

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.

Selection among CPTU-Based Liquefaction Models

In this paper, a process is taken to select probabilistic models for liquefaction/cyclic softening potential evaluation based on case histories with piezocone penetration test (CPTu) data. Emphasis of the paper is placed on establishing a relationship between the probability of liquefaction/cyclic softening and the safety factor determined with a recently developed deterministic CPTu-based model. The significance of the developed probabilistic model lies in the fact that the model is applicable to both sand-like and clay-like soils, which is ideal as a stand-alone tool for evaluating liquefaction and cyclic softening potential. Furthermore, the developed model is shown to hold advantages over existing CPT-based methods. Examples for applying the proposed CPTu-based models to characterize the liquefaction/cyclic softening potential at a given site are provided.

Stabilization Effectiveness of Treatment with T-Shaped Deep-Mixing Column for Low-Volume Roads

Deep-soil mixing using column elements is a widely used technology for improving soft soil properties for low-volume roads in China. The deep-mixing method has some limitations, because a high-treatment area over the entire column length makes this method expensive and impractical. On the basis of a stabilization mechanism and factors that affect column construction quality, a T-shaped bidirectional soil–cement deep-mixing column has been successfully developed and proved to be effective and economical. As part of quality control of field improvement of these columns, seismic piezocone penetration tests (SCPTUs) were used. The tests can provide near-continuous measurements of tip resistance, sleeve friction, and pore pressure induced during the penetration. This paper discusses field SCPTUs that were performed in the untreated soils and the interpile soils between the T-shaped bidirectional soil–cement deep-mixing columns at the Huzhou lacustrine clay site in China. Soil properties estimated from the SCPTU data both before and after improvement methods were compared to assess the effectiveness of soil improvement. These results indicate that the use of SCPTUs will improve understanding of the changes in soil behavior achieved by this novel deep-soil mixing method for low-volume roads.

Variation for Soil Stress on CPTU Model Test

Through a series of Piezocone Penetration Test (CPTU) model tests with saturated clay soil, by CPTU probe penetrating soil stress measured by soil pressure mini-cells embedded into soil has been acquired, the variation rules of soil stress by penetrating has been analyzed, the results show that with probe close to the second cell layer, the stress measured by the cells has been increased rapidly; when probe has arrived at the position of the second cell layer, the maximum stress value has been attained; and with probe away from the second cell layer, the stress value has been decreased rapidly. Based on the achieved soil stress value, the axial and radial subsidiary stress field causing by penetrating has been acquired, the conclusions can be obtained that the main stress style of the axial subsidiary stress is compression stress, around the probe the highest stress field has been occurred; the stress style of the radial subsidiary stress is compression stress, this phenomenon shows that by penetrating the compaction effect of the soil around the probe has been created; during the course of penetrating, the radial subsidiary stress is less than the axial subsidiary stress obviously. The achieved result can provide a foundation for further study for CPTU mechanism.

Interpretation of the lime column penetration test

Dry soil mix (DSM) columns can be used to reduce the settlement of embankments constructed on soft clays and to improve the stability. During construction the shear strength of the columns needs to be confirmed for compliance with technical assumptions. However, the measurement of the column shear strength can be a contentious issue. All methods of assessing the ultimate shear strength of DSM columns have limitations. These are caused by uncertainties in empirical probe factors required to convert pullout or push in force measured during the lime column penetration test to shear strength and/or testing a small proportion of the DSM column volume and determining whether it is representative of the strength of the entire column. The penetration resistance measured using the lime column test is considered to be more representative of average column shear strength than some other test types. This test can be carried out as a pullout resistance test (PORT) or a push in resistance test (PIRT). Both PORT and PIRT require empirical correlations of measured resistance to an absolute measure of shear strength, in a similar manner to the Piezocone test. In this paper, finite element techniques developed for assessment of T-bar, Ball and Piezocone penetration tests [7,8,10] are used to assess bounds for the empirical probe factor, N. To simulate the cemented DSM columns, analyses have incorporated a model for a strain softening material. Measured settlements from an embankment constructed on DSM ground improvement are then compared with finite element calculations to infer the shear strength of the columns. These inferred shear strengths are then compared with the results of PORT tests performed beneath the embankment.

Reliability of CPT Ic as an index for mechanical behaviour classification of soils

This paper presents results of an analysis of a set of high-quality, side-by-side piezocone penetration test (CPTu) and standard penetration test (SPT) data for examining mechanical behaviour-based classification of soils. The results show that the soil behaviour type index (Ic), either defined by Jefferies and Been (denoted herein as Ic,BJ) or by Robertson and Wride (denoted herein as Ic,RW), is an effective parameter for mechanical behaviour classification. Additionally, an effort is made to find the most suitable Ic cut-off (or boundary) value that can delineate cohesionless (sand-like) soils from cohesive (clay-like) soils. The Robertson and Wride's formulation, Ic,RW = 2·67 is found capable of delineating these two classes of soils. Similarly for the Been and Jefferies' formulation, Ic,BJ = 2·58 is found to be the most suitable Ic cut-off value for such classification purpose. These cut-off Ic values for distinguishing sand-like soils from clay-like soils are found to be reliable in a case study of liquefaction susceptibility.

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

Field Evaluation of Undrained Shear Strength from Piezocone Penetration Tests in Soft Marine Clay

The use of the piezocone penetration test (CPTU) in a geotechnical site investigation offers direct field measurement on stratigraphy and soil behavior. Compared with some traditional investigation methods, such as drilling, sampling and field inspecting method or laboratory test procedures, CPTU can greatly accelerate the field work and hereby reduce corresponding operation cost. The undrained shear strength is a key parameter in estimation of the stability of natural slopes and deformation of embankments in soft clays. This paper provides the measurements of in situ CPTU, field vane testing and laboratory undrained triaxial testing of Lianyungang marine clay in Jiangsu province of China. Based on the literature review of previous interpretation methods, this paper presents a comparison of field vane testing measurements to CPTU interpretation results. The undrained shear strength values from both the field vane tests and cone penetration resistances are lowest at the mid-depths of the marine clay layers, and the excess pore water pressures are highest at the mid-depths of the marine clay layers, indicating that the marine clay layer is underconsolidated.

Hydraulic Property Estimation Using Piezocone Results

Governing underground water flow, hydraulic properties such as hydraulic conductivity or coefficient of consolidation are major geotechnical parameters. Determination of hydraulic properties, however, is traditionally time consuming and expensive. This research proposes an easy and economical way of determining the hydraulic properties of soils through piezocone penetration tests. Pore pressure responses of soils from piezocone penetration tests are numerically analyzed herein by the coupled theory of mixtures, which is based on the large strain elastoplasticity. Using the numerical results, the effects of input parameters are evaluated. Simple equations are also derived for a faster estimation of the hydraulic conductivity or the coefficient of consolidation of soils. The hydraulic properties predicted by these derived equations agree reasonably with the measured results.

액상화 가능 지수를 이용한 국내 서해안 지역의 액상화 평가

느슨한 포화 사질토 층에 위치한 구조물은 지진 시 액상화로 인해 막대한 인적 경제적 피해가 발생하기 때문에 액상화 발생 가능 지반으로 분류된 지역은 구조물의 설계 및 운영 시 액상화 발생 가능성에 주의를 기울어야 한다. 한반도의 경우 중진 지역에 해당되고 역사 문헌의 발생 기록을 제외한 어떤 액상화 피해도 보고되지 않음에 따라 오랫동안 액상화에 대해서는 안전지대로 여겨져 왔다. 하지만, 최근 해외 지진 사례에 의하면 국내 서해안 지역 지반과 유사한 비소성 실트질 흙에서의 액상화 발생과 이로 인한 피해 사례가 종종 보고되고 있다. 본 연구에서는 국내에서의 액상화 가능성 평가 기법 합리화의 일환으로 서해안 두 부지를 대상으로 피에조콘 관입시험(CPTu)과 표준관입시험(SPT) 결과를 이용하여 액상화가능지수(LPI)를 산정하였다. LPI는 심도 20m까지의 액상화 가능성을 통합 적분하여 액상화로 인한 지표면 피해 발생 정도를 지수로 제시한다. 먼저 대상 현장에 대해 시나리오별 액상화 발생 가능성을 평가한 후, CPTu와 SPT로부터 산정된 LPI 값을 비교하였다. 액상화 저항 강도를 의미하는 진동저항응력비(CRR) 값에 의하면, CPTu로부터 구한 보정 콘 선단저항력 (qc1N)CS가 40에서 120 사이인 경우 또는 CRR이 0.23 이하인 경우에 SPT로부터의 산정된 값보다 작게 평가되었다. 또한 CRR 차이는 세립질 함유량이 큰 흙에서 두 방법 간의 차이가 더 크게 나타났다. Liquefaction is a significant threat to structures on loose saturated sandy soil deposits in the event of an earthquake, and can often cause catastrophic damage, economic loss, and loss of life. Nevertheless, the Korean peninsula has for a long time been recognized as a safe region with respect to the hazard of liquefaction, as the peninsula is located in a moderate seismicity region, and there have been no reports of liquefaction, with the exception of references in some historical documents. However, some earthquakes that have recently occurred in different parts of the world have led to liquefaction in non-plastic silty soils, a soil type that can be found in many of the western coastal areas of Korea. In this study, we first present procedures for evaluating the liquefaction potential, and calculate the liquefaction potential index (LPI) distribution at two western coastal sites using both piezocone penetration test (CPTu) data and standard penetration test (SPT) data. The LPI is computed by integrating liquefaction potential over a depth of 20m, and provides an estimate of liquefaction-related surface damage. In addition, we compared the LPI values obtained from CPTu and SPT, respectively. Our research found that the CRR values from CPTu were lower than those from the SPT, particularly in the range between 40 and 120 for the corrected tip resistance, (qc1N)CS, from the CPTu, or in the range of CRR less than 0.23, resulting in relatively high LPI values. Moreover, it was observed that the differences in the CRR between the two methods were relatively higher for soils with high fine contents.

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.

Estimating clay undrained shear strength using CPTu results

Estimation of the undrained shear strength su of clays using piezocone penetration test (CPTu) results has been based mainly on the cone factor Nk. In this study a new CPTu-based method for estimating su is proposed and evaluated. It is aimed at reducing uncertainties in the estimation of su and enhancing the application of CPTu results. To develop the method, a selected site on a marine clay deposit was subjected to an extensive experimental testing programme. The proposed method defines a direct correlation between su and the cone resistance qt, involving the initial in situ pore pressure but excluding the need for overburden pressure calculation and therefore the need for undisturbed soil sampling. To verify the proposed method, additional test sites and example sites from the literature that encompass a variety of soil conditions are selected and examined. Values of su obtained from the proposed method are in good agreement with measured values of su for all the selected verification cases.

CPTu Simplified Stress-Based Model for Evaluating Soil Liquefaction Potential

This paper presents a piezocone penetration test (CPTu) method for evaluating soil liquefaction potential covering a wider range of soil types than previous approaches and using simplified stress-based procedures. In the approach, the adjusted cyclic stress ratio is calculated with a recent formula created by Idriss and Boulanger, and the cyclic resistance ratio is determined as a function of both adjusted cone tip resistance ( q t1N ) and soil behavior type index ( I c ). The new method is established through artificial neural network learning of documented cases. One unique feature of this method is the inclusion of excess porewater pressure ratio ( B q ) in the formulation of I c as per Jefferies and Davies. The proposed method is shown to be more applicable to a wider range of soils, including geomaterials that were previously considered “too clay-rich to liquefy.” The ability of this method to delineate liquefied cases from non-liquefied cases is clearly depicted with 3-D and 2-D graphs. Case studies of selected ground failure sites in Adapazari using the proposed method yield results that agree well with field observations in the 1999 Kocaeli earthquake.

Assessing probability of surface manifestation of liquefaction at a given site in a given exposure time using CPTU

This paper is a follow-up to a previous paper on the subject of liquefaction potential index (LPI), a parameter that is often used to characterize the potential for surface manifestation of liquefaction at a given site subjected to a given shaking level (represented by a pair of peak ground surface acceleration a max and moment magnitude M w). In the previous paper by Juang and his coworkers, the LPI was re-calibrated for a piezocone penetration test (CPTU) model, and a simplified model based on LPI was created for computing the conditional probability of surface manifestation of liquefaction ( P G). In this paper, the model for this conditional probability P G is extended into a complete framework for assessing the probability of surface manifestation of liquefaction in a given exposure time at a given site subjected to all possible ground motions at all seismic hazard levels. This new framework is formulated and demonstrated with an example site in 10 different seismic regions in the United States.

Assessment of direct CPT and CPTU methods for predicting the ultimate bearing capacity of single piles

Twelve methods to determine axial pile capacity directly based on cone penetration test (CPT) and piezocone penetration test (CPTU) data are presented, compared and evaluated. Analyses and evaluation were conducted on three types of piles of different size and length. All the tested piles have failed at the end of static load test. Both the CPT methods and the CPTU methods were used to estimate the load bearing capacities of the investigated piles ( Q p). The static load test was performed to determine the measured load bearing capacities ( Q m). The pile capacities determined through different methods were compared with the measured values obtained from the static load tests. Two criteria were selected as bases of evaluation: the best fit line for Q p versus Q m and the arithmetic mean and standard deviation for the ratio Q p/ Q m. Results of the analyses showed that the best methods for determining pile capacity are the two CPTU methods. Furthermore, the CPTU method is simple, easy to apply, and not influenced by the subjective judgements of operating staff. Therefore, it is quite suitable for the application in pile engineering practice.

Approach on the Engineering Properties of Lianyungang Marine Clay from Piezocone Penetration Tests

The use of the piezocone test (CPTU) in geotechnical site investigation offers direct field measurement on stratigraphy and soil behavior. Compared with some traditional investigation methods such as drilling, sampling, field inspecting method, or laboratory test procedures, CPTU can greatly accelerate the field work and thereby reduce corresponding operation cost. This article reviews previous interpretation methods of obtaining undrained shear strength, overconsolidation ratio, and coefficient of consolidation of soft soils from CPTU data, and introduces a new method, which the measured pore pressure into account. Piezocone tests with Vertek-Hogentogler CPTU truck have been complemented in a widely explored area in the soft marine deposit of Lianyungang City. Geotechnical design parameters (q t , f s , and u) obtained from CPTU and dissipation tests are evaluated for the marine clay in this area through methods based on cavity expansion (CE) and critical state (CS) theory proposed by Mayne, and compared with the result of vane shear tests and laboratory tests of undisturbed soil samples. Comparison of the results reveals the validity of CPTU tests to interpret the engineering properties of Lianyungang marine clay.

전단파속도와 지반공학적 현장 관입시험 자료의 상관관계 도출

다양한 탄성파 시험으로부터 획득할 수 있는 전단파속도(<TEX>$V_S$</TEX>)는 주로 지진공학 분야에서의 내진 설계 및 내진 성능 평가를 위한 대표적 지반 동적 특성으로 강조되어 왔다. 일반적인 지반공학적 부지 조사 기법의 지반지진공학적 활용을 목적으로, 표준관입 시험(SPT)과 피에조콘관입시험(CPTu)을 국내 여러 부지들을 대상으로 다양한 시추공 탄성파시험과 함께 수행하였다. 본 연구에서는 현장시험 자료들의 통계학적 모델링을 통해 전단파속도와 표준관입시험의 타격수(N 값)및 선단저항력(<TEX>$q_t$</TEX>), 주면마찰력(<TEX>$f_s$</TEX>)과 간극수압계수(<TEX>$B_q$</TEX>)로 구성되는 피에조콘관입 자료 간의 상관관계를 도출하고 전단파속도 결정을 위한 경험적 방법으로 제안하였다. 비록 일반적인 지반공학적 관입시험과 시추공 탄성파시험의 대상 변형률 수준이 상이하다 할지라도, 본 연구에서 제안된 상관관계들은 국내 토사 지층의 예비적 전단파속도 산정에 활용될 수 있을 것으로 보인다. Shear wave velocity(<TEX>$V_S$</TEX>), which can be obtained using various seismic tests, has been emphasized as representative geotechnical dynamic characteristic mainly for seismic design and seismic performance evaluation in the engineering field. For the application of conventional geotechnical site investigation techniques to geotechnical earthquake engineering, standard penetration tests(SPT) and piezocone penetration tests(CPTu) together with a variety of borehole seismic tests were performed at many sites in Korea. Through statistical modeling of the in-situ testing data, in this study, the correlations between <TEX>$V_S$</TEX> and geotechnical in-situ penetrating data such as blow counts(N value) from SPT and piezocone penetrating data such as tip resistance (<TEX>$q_t$</TEX>), sleevefriction(<TEX>$f_s$</TEX>), and pore pressure ratio(<TEX>$B_q$</TEX>) were deduced and were suggested as an empirical method to determine <TEX>$V_S$</TEX>. Despite the incompatible strain levels of the conventional geotechnical penetration tests and the borehole seismic tests, it is shown that the suggested correlations in this study are applicable to the preliminary estimation of <TEX>$V_S$</TEX> for Korean soil layers.

OCR Prediction Using Support Vector Machine Based on Piezocone Data

The determination of the overconsolidation ratio (OCR) of clay deposits is an important task in geotechnical engineering practice. This paper examines the potential of a support vector machine (SVM) for predicting the OCR of clays from piezocone penetration test data. SVM is a statistical learning theory based on a structural risk minimization principle that minimizes both error and weight terms. The five input variables used for the SVM model for prediction of OCR are the corrected cone resistance ( qt ) , vertical total stress ( σv ) , hydrostatic pore pressure ( u0 ) , pore pressure at the cone tip ( u1 ) , and the pore pressure just above the cone base ( u2 ) . Sensitivity analysis has been performed to investigate the relative importance of each of the input parameters. From the sensitivity analysis, it is clear that qt =primary in situ data influenced by OCR followed by σv , u0 , u2 , and u1 . Comparison between SVM and some of the traditional interpretation methods is also presented. The results of...

변형률속도-의존 구성모델의 현장 시험 적용

본 연구에서는 실제 현장에서 수행한 피에조콘관입 및 소산시험결과와 변형률 속도를 고려한 구성모델의 이론적 해석을 비교하였다. 이를 위하여 변형률 속도 의존적 구성모델의 수학적 유도과정을 전개하였다. 해석 결과 변형률속도를 무시한 구성모델보다 변형률속도-의존 구성모델을 활용한 지반의 거동 해석이 비의존적 구성모델인 경우의 해석 보다 현장의 시험결과와 잘 일치하므로 변형률속도-의존 구성모델의 적용이 바람직하다. The rate-dependent constitutive model and the rate-independent model were analyzed for comparing with the piezocone penetration test and dissipation test. The mathematical expressions of the rate-dependent constitutive model were introduced, and the predictions using the both models were compared with the experimental results of in-situ field test. The rate-dependent model analysis gave better results than the rate-independent model analysis, that is appreciated since the process of the piezocone penetration and dissipation depends on the strain rate. Therefore, it is recommended the concept of the rate-dependent model for the prediction of soil behaviors using the field penetration test.