Normalized Cone Tip Resistance Research Articles

Deformation analysis of underwater shield tunnelling based on HSS model parameter obtained by the Bayesian approach

Deformation analysis and control of underwater large-diameter shield tunnels is a prerequisite for safe tunnel construction. Reasonable selection of constitutive model and its parameters is the key to accurately predicting the deformation induced by underwater shield tunnelling. In this paper, the finite element analysis of cavity expansion during the piezocone penetration test (CPTU) based on the hardening soil model with small strain stiffness (HSS) model was carried out, and the correlation model of the normalized cone tip resistance Q with the reference secant modulus E50ref and the effective internal friction angle φ’ was established and verified using mini CPTU chamber test. Then, a Bayesian probability characterization approach for E50ref of silty clay based on CPTU was proposed. Furthermore, the deformation analysis of Jinan Yellow River tunnel crossing the south embankment was carried out to verify the reliability of the proposed approach. The good agreement between the field measurement and numerical simulation confirms that the parameters obtained by the Bayesian approach are reliable. Finally, a sensitivity analysis was performed to study the law of riverbed settlement induced by underwater large-diameter shield tunnelling. The results show that the increasing support pressure could effectively reduce the riverbed settlement, but there is an upper limit. The optimal support pressure of established model is between 0.45 MPa and 0.5 MPa. The uphill section causes greater riverbed settlement than the downhill section. Under the same condition, increasing buried depth and water level will lead to a more significant settlement.

A novel PSO-KELM based soil liquefaction potential evaluation system using CPT and Vs measurements

Evaluation of soil liquefaction potential is an essential step in geotechnical engineering design. This study presents a novel soil liquefaction potential evaluation system using cone penetration test (CPT) and shear wave velocity test (Vs) measurements. To this end, a new hybrid machine learning model called PSO-KELM model that combines the kernel extreme learning machine (KELM) with particle swarm optimization (PSO) is developed to assess soil liquefaction potential. Then, the PSO-KELM based searching technique is adopted to search the nonlinear relationship between CRR and CPT along with Vs measurements. Finally, a new probabilistic model is developed by considering the model uncertainty and sampling bias based on weighted maximum likelihood estimation. Results demonstrate that the performance of PSO-KELM model is significantly better than that of many other machine learning methods. The cyclic stress ratio, equivalent clean sand normalized cone tip resistance, normalized friction ratio, fines content, and soil behavior type are the recommended input variables for PSO-KELM model. The combined use of CPT and Vs measurements can significantly improve the prediction accuracy since it can more fully reflect soil liquefaction phenomenon. The proposed evaluation system can improve the performance of seismic CPT (SCPT) in soil liquefaction potential evaluation.

Friction angle and overconsolidation ratio of soft clays from cone penetration test

The cone penetration test (CPT) is a method widely used for site characterization as measurements are continuous, fast and economical compared to laboratory testing. However unlike laboratory testing that quantifies soil properties directly, readings obtained from CPT are indirect and needs to be interpreted. Hence many correlations have been proposed to infer a wide range of soil properties from CPT readings. Existing correlations have discovered separate relationships between normalized cone tip resistance (Qt) and effective friction angles (ϕ’), as well as Qt and overconsolidation ratio (OCR). This study employs the press-replace method (PRM), a novel simplified numerical technique, to perform systematic and extensive undrained investigations of CPT in a modified Cam-clay (MCC) soil model. It is the first comprehensive numerical study with an advanced soil model that considers rough cone-soil interactions. The PRM numerical approach overcomes the need to assume the CPT process as analogous to spherical or cylindrical cavity expansions, therefore produces results that are more authentic to real CPT. From the large database of numerical results, an equation is formulated that provides a framework on how Qt is related to both ϕ’ and OCR, rather than separately to ϕ’ or OCR as described in previous correlations. The proposed equation is then simplified so that ϕ’ and OCR can be easily estimated from Qt. Numerical results and predictions from the new equations are then compared to soil behaviour charts, other correlations and field data from different sites.

The Spatial Distribution of Liquefaction Susceptibility by Logistic Regression Model Adapted for Adapazari, Turkey

A logistic regression model has been developed for evaluation of soil liquefaction by the use of cone penetration test (CPTu, PCPT) on data collected from Adapazarı, Turkey. The model inputs are the clean sand equivalent normalized cone tip resistance (qc1N,cs) and cyclic stress ratio corrected for moment magnitude of 7.5 earthquake (CSRM=7.5) that was experienced in 1999. Liquefaction probabilities (PL) are obtained for each district of the city for which CPTu data is available with the proposed logistic regression model. Average liquefaction probabilities of the depth interval 0-6 m and coordinates (Longitude, Latitude) of CPT soundings were plotted to construct a liquefaction probability map by longitude and latitude. In order to show the effect of depth in liquefaction potential, the obtained liquefaction probability contours were reconstructed by dividing 0-6m depth into three narrow sublayers of 0-2m, 2-4m and 4-6m wherein liquefaction was observed during the earthquake. For each depth interval, liquefaction probabilities of the districts are compared with the observed liquefied and non-liquefied sites in the city after 1999 Adapazarı Earthquake.

A cavity expansion–based solution for interpretation of CPTu data in soils under partially drained conditions

SummaryA cavity expansion–based solution is proposed in this paper for the interpretation of CPTu data under a partially drained condition. Variations of the normalized cone tip resistance, cone factor, and undrained‐drained resistance ratio are examined with different initial specific volume and overconsolidation ratio, based on the exact solutions of both undrained and drained cavity expansion in CASM, which is a unified state parameter model for clay and sand. A drainage index is proposed to represent the partially drained condition, and the critical state after expansion and stress paths of cavity expansion are therefore predicted by estimating a virtual plastic region and assuming a drainage‐index–based mapping technique. The stress paths and distributions of stresses and specific volume are investigated for different values of drainage index, which are also related to the penetration velocity with comparisons of experimental data and numerical results. The subsequent consolidation after penetration is thus predicted with the assumption of constant deviatoric stress during dissipation of the excess pore pressure. Both spherical and cylindrical consolidations are compared for dissipation around the cone tip and the probe shaft, respectively. The effects of overconsolidation ratio on the stress paths and the distributions of excess pore pressure and specific volume are then thoroughly investigated. The proposed solution and the findings would contribute to the interpretation of CPTu tests under a random drained condition, as well as the analysis of pile installation and the subsequent consolidation.

Investigation of gravity effect on penetration resistance in Tongji-1 lunar regolith simulant by centrifuge tests

Cone Penetration Tests (CPTs) are usually performed on the lunar regolith simulant on the Earth to study the geotechnical characteristics of lunar soil, which will be then used for the possible human activities on the Moon in the future. However, the gravity effect should be fully investigated before applying these experimental results to the Moon exploration, because the gravity level on the Moon is much lower than that on the Earth. For this aim, a series of CPTs was carried out in a centrifuge with a carefully designed testbed made of Tongji-1 lunar regolith simulant (TJ-1 simulant). The measured results were employed to examine the applicability of two traditional solutions and linear equation in describing the gravity effect along with some other existing experimental data. In addition, the linear equation fitted by the experimental data was used to predict the values of normalized tip resistances of lunar soil on the Moon. The results show that the two traditional solutions cannot describe the gravity effect well while the linear relationship between the peak (stable) normalized cone tip resistance and the reciprocal of gravity level can quantitatively describe the gravity effect on the penetration resistance. The predicted normalized peak (stable) tip resistances are larger than those of lunar soil on the Moon, which may be probably due to the unique in-situ conditions on the Moon.

Multivariate correlation analysis of seismic piezocone penetration (SCPTU) parameters and design properties of Jiangsu quaternary cohesive soils

A recent trend of geotechnical correlation analysis is to construct a multivariate distribution model to describe the multiple dependency characteristics of different soil parameters. In this study, the feasibility of this multivariate method to model the multivariate dependency of seven soil parameters including the undrained shear strength ratio, overconsolidation ratio, sensitivity, normalized cone tip resistance, normalized sleeve frictional resistance, pore pressure parameter, and normalized shear wave velocity.is studied. A database containing 372 sets of observations of these seven parameters is collected from 25 sites in the Jiangsu province, China. Two data transformations including the Johnson system of distribution and Box-Cox method were used in the construction of the multivariate model for the Jiangsu cohesive soils. The correlations derived from these two local models were compared with the compiled Jiangsu database, data points at other testing sites in China, and database and correlations published in the literature for validation. It was shown that the local models developed in this study were capable of the multivariate dependency of the soil parameters for the Jiangsu cohesive soils, whereas the global model developed in the literature tends to overestimate the uncertainties associated with the design parameters for the Jiangsu soils. A potential explanation is that the soil parameters in a local region were less variable with stronger correlations than those over the global sites, due to the site-specific effect. However, caution shall be taken if the local models for the Jiangsu soils are used at other sites. Besides, the Johnson system of distribution is superior to the Box-Cox transformation in the construction of the multivariate distribution model in the sense that the former is more effective to achieve the standard normal distribution, especially for the soil parameters with a bounded distribution.

At-Rest Lateral Stress Coefficient in Sands from Common Field Methods

AbstractA new relationship for estimating the in situ at-rest lateral stress coefficient (K0) in sands consisting predominantly of silica particles is derived in this technical note using the calibration chamber test results reported in the literature. Variables in the relationship, in order of significance, are overconsolidation ratio, dilatometer horizontal stress index, and normalized cone tip resistance. Values of in situ K0 estimated with the new relationship generally compare well with K0 determined from self-boring pressuremeter tests. Estimates of K0 in Pleistocene sands are, on average, about 10% higher than in Holocene sands.

Investigation of the effect of different gravity conditions on penetration mechanisms by the Distinct Element Method

Purpose– The purpose of this paper is to present an investigation of the effect of different gravity conditions on the penetration mechanism using the two-dimensional Distinct Element Method (DEM), which ranges from high gravity used in centrifuge model tests to low gravity incurred by serial parabolic flight, with the aim of efficiently analyzing cone penetration tests on the lunar surface.Design/methodology/approach– Seven penetration tests were numerically simulated on loose granular ground under different gravity conditions, i.e. one-sixth, one-half, one, five, ten, 15 and 20 terrestrial gravities. The effect of gravity on the mechanisms is examined with aspect to the tip resistance, deformation pattern, displacement paths, stress fields, stress paths, strain and rotation paths, and velocity fields during the penetration process.Findings– First, under both low and high gravities, the penetration leads to high gradients of the value and direction of stresses in addition to high gradients in the velocity field near the penetrometer. In addition, the soil near the penetrometer undergoes large rotations of the principal stresses. Second, high gravity leads to a larger rotation of principal stresses and more downward particle motions than low gravity. Third, the tip resistance increases with penetration depth and gravity. Both the maximum (steady) normalized cone tip resistance and the maximum normalized mean (deviatoric) stress can be uniquely expressed by a linear equation in terms of the reciprocal of gravity.Originality/value– This study investigates the effect of different gravity conditions on penetration mechanisms by using DEM.

Evaluation of subsurface spatial variability in site characterization based on RCPTU data

The resistivity piezocone penetration test (RCPTU) does not only include a conventional piezocone penetration test, but also provides a continuous profile of electrical resistivity. Therefore, RCPTUs have the potential for wide application in environmental geotechnics. Electrical resistivity is a fundamental parameter characterizing soil conductivity, one of the inherent physical properties of soil. The objective of this study was to evaluate subsurface spatial variability using RCPTU data and laboratory tests. Normalized electrical resistivity was proposed for developing the relationships between electrical resistivity and soil behavior type index, relative density and cyclic resistance ratio. These relationships are used for evaluation of subsurface spatial variability. The soil behavior type index can be represented by the function of normalized electrical resistivity R and normalized cone tip resistance. Additionally, there is a positive correlation between relative density and normalized electrical resistivity. The evaluation of cyclic resistance ratio adopting the normalized electrical resistivity and normalized cone tip resistance was effective.

Postsurcharge Secondary Compression Characteristics of Marine Clay from Piezocone Penetration Tests on a Low-Volume Road

Secondary compression is a major concern for road construction situated on marine clayey soil conditions in the eastern and southeastern provinces in China. Marine clay characterization in the field is hence an important step in the design of low-volume roads. Piezocone penetration tests (CPTu) were conducted for site investigation of a low-volume road situated in Lianyungang, Jiangsu Province, China. The compressibility of relatively homogeneous marine clay at the site was analyzed, with a focus on the postsurcharge secondary compressibility. The primary compression index (CCL) was obtained from odometer tests on undisturbed samples. The postsurcharge secondary compression index (Cαε) was backcalculated from the settlement curves and defined with the time-dependent strain response. The ratio of Cαε/CCL fell in the range of 0.05 ± 0.01, indicating that high secondary compressibility is associated with the clay deposits. Finally, regression analysis was performed to correlate the Cαε to the CPTu normalized cone tip resistance (Qtn). A modified empirical correlation between Cαε and Qtn was further developed on the basis of comprehensive evaluation of data from Lianyungang marine clay and the literature.

Analysis of Factors Influencing Soil Classification Using Normalized Piezocone Tip Resistance and Pore Pressure Parameters

This paper discusses the development of a framework for classifying soil using normalized piezocone test (CPTU) data from the corrected tip resistance ( qt ) and penetration pore-water pressure at the shoulder ( u2 ) . Parametric studies for normalized cone tip resistance (Q= qcnet ∕ σ v0 ′ ) and normalized excess pressures (Δ u2 ∕ σ v0 ′ ) as a function of overconsolidation ratio (OCR= σ vy ′ ∕ σ v0 ′ ) during undrained penetration are combined with piezocone data from clay sites, as well as results from relatively uniform thick deposits of sands, silts, and varietal clays from around the globe. The study focuses on separating the influence of yield stress ratio from that of partial consolidation on normalized CPTU parameters, which both tend to increase Q and decrease the pore pressure parameter ( Bq =Δ u2 ∕ qcnet ) . The resulting recommended classification chart is significantly different from existing charts, and implies that assessment of data in Q–Δ u2 ∕ σ v0 ′ space is superior to Q– Bq space when...

Coupled Use of Cone Tip Resistance and Small Strain Shear Modulus to Assess Liquefaction Potential

Resistance against earthquake-related liquefaction is usually assessed using relationships between an index of soil strength such as normalized cone tip resistance and the cyclic resistance ratio (CRR) developed from observed field performance. The alternative approach based on laboratory testing is rarely used, mainly because of the apprehension that laboratory results may not reflect field behavior since the quality of laboratory data is often compromised by sampling disturbance. In this study, a database of laboratory data obtained mainly from cyclic testing of frozen (undisturbed) samples and in situ index measurements from near sampling locations comprised of cone tip resistance, qc, and shear wave velocity, Vs, have been assembled. These data indicate that neither normalized cone tip resistance nor normalized shear wave velocity individually correlate well with laboratory-measured CRR. However, the ratio of qc to the small strain shear modulus, G0, relates reasonably with CRR via separate correlations depending on geologic age. The derived qc∕G0-CRR relationships were also found to be consistent with earthquake field-performance case histories.

The Second James K. Mitchell Lecture Undisturbed sand strength from seismic cone tests

During routine site investigations, high-quality sampling and laboratory testing of sands are not feasible because of inevitable sample disturbance effects and budgetary constraints. Herein, a select database is compiled for calibration of cone penetration test (CPT) interpretative methods, primarily from undisturbed frozen sand samples at 15 sites in Japan, Canada, Italy, Norway, and China. The database is used to evaluate the peak secant friction angle in terms of the normalized cone tip resistance using two analytical approaches: (i) spherical cavity expansion theory with an operational rigidity index , and (ii) a limit plasticity formulation with appropriate angle of plastification . Backfigured values of and are found correlated to the normalized small-strain stiffness . Thus, with measurements taken of both the initial shear modulus and shear strength, seismic cone tests offer the opportunity to derive the entire stress–strain–strength response of sands at all depths.