Interpretation Of Cone Penetration Tests Research Articles

A Case Study on Advanced CPT Data Interpretation: From Stratification to Soil Parameters

AbstractThe cone penetration test (CPT) is considered as one of the most reliable in-situ tests and has found numerous applications in the geotechnical engineering field. Traditional CPT interpretation includes, but are not limited to the identification of the soil stratification and the determination of soil parameters. This paper presents a case study concerning a test site located in Salzburg, Austria, in which we focus on the interpretation of CPTs from different perspectives. The manuscript is divided into three main sections dealing with three different aspects of CPT interpretation, namely stratification, ground variability and soil parameters. The first strategy introduces a machine learning based stratification identification strategy to detect soil layer boundaries from CPT measurements. A comparison with reference solutions demonstrates relative merits of this approach to classical filter algorithms based on empirical CPT classifications. The second strategy introduces an intuitive approach to evaluate the ground variability. This is achieved by calculating the level of fluctuation on the basis of CPT measurements and could be used as a data-driven decision-making tool for the improved design of CPT investigation layouts. The third strategy is embedded in an ongoing research project that aims to determine constitutive model parameters from in-situ tests using a graph-based methodology. In the present work, the developed automated parameter determination framework is applied to evaluate the soil parameters of one selected soil layer identified from the CPT interpretations. Potential lines of research in the context of CPT interpretation are explored throughout this work and may serve as valuable reference in future research.

Quantifying CPT cone factors in clays derived from weathered mudstone

The empirical interpretation of cone penetration test (CPT) cone factors ( N k ) can be subject to considerable variability for clays derived from weathered mudstones, leading to significant deviations in the estimation of undrained shear strength ( S u ). This paper presents a comparison of triaxial and CPT data from a site investigation in clays derived from weathered mudstones in central England. Corrected cone factors ( N kt,UU ) were derived from a one-to-one comparison of 94 pairs of unconsolidated, undrained triaxial and CPT data from equivalent depths. The performance of the cone factors was evaluated using a training set (75 pairs) and a test set (19 pairs). A parametric study was used to explore the variability of N kt,UU , quantified using the coefficient of variation (COV Nkt,UU ), for varied separation distance thresholds ( D s ) between individual triaxial and CPT data. The absolute deviation between the laboratory shear strength ( S u(Lab) ) and that predicted from CPT profiles (S u(CPT) ) was not sensitive to N kt,UU values in the range 25 < N kt,UU < 31. The parametric study showed that D s could be increased from 50 to 250 m, to include more data pairs for estimates of N kt,UU , without substantially increasing COV Nkt,UU .

Cavity expansions in partially drained soils and a comparison to CPT results

Cylindrical and spherical cavity expansions in soils are of interest, especially when interpreting cone penetration tests (CPTs) and pressuremeter tests (PMTs). Here the cavity expansion problem is solved semi-analytically, considering partial drainage of the soil, when the cavity wall velocity is constant. The solutions may assist with the interpretation of CPTs and PMTs when partially drained conditions prevail in the surrounding soils. The solution procedure involves writing the governing partial differential equations in dimensionless form. The modified Cam-clay constitutive model is adopted for the soil to demonstrate the solution procedure, due to its wide familiarity, although other models could be used by making simple modifications. The variables in the partial differential equations are functions of a dimensionless time, T, and a dimensionless radial coordinate, H. T depends on cavity radius, the time after expansion began and a coefficient of consolidation. The equations are solved for when T is fixed, simultaneously as an initial value problem, as the partial differential equations become ordinary differential equations. Important features captured by the analyses include pore water pressure variations with soil volume changes, as well as the differential of the pore water pressure satisfying the no-flow cavity wall boundary condition. Results for a cavity expansion reveal that initially, when T and the cavity are small, drained conditions prevail. As T and the cavity become larger the soil becomes partially drained and eventually undrained. T is analogous to the dimensionless cone penetration velocity used in CPT studies. Normalised cavity wall pressures vary with T similar to that of normalised cone penetration resistances, demonstrated using experimental data. Plots of the normalised cavity wall pressures against the state parameter show that the two key fitting constants are heavily influenced by partial drainage. A similar dependence must exist when plotting a normalised cone penetration resistance against the state parameter when partially drained conditions prevail. The practical ramifications of not dealing with this partial drainage may be huge, especially when assessing liquefaction susceptibility through estimations of the state parameter using correlations developed for when drained conditions prevail. Significant underestimations of state parameter, liquefaction susceptibility and post-liquefaction strengths may result.

Evaluation of Soil Strength from Variable Rate CPTU Tests in Silt

Abstract The interpretation of cone penetration test (CPTU), at the standard rate of 20 mm/s, results in clays assuming undrained penetration tests, whereas the interpretation in sands is carried out using a drained approach. However, for silts, the drainage conditions during a standard rate test are less well understood, and often partial drainage occurs. The main objectives of this work are to show the limitations of applying existing correlations for sand and clay to a silt material and to give guidance to practicing engineers on how to establish strength parameters for silts that allow a safe design. This paper presents the results of a comprehensive laboratory and field test study that was carried out on a silt site in Halsen-Stjørdal, Norway. Varied rate CPTU tests were conducted, and various soil samples were taken. Using a conventional Nkt approach to determine undrained shear strength, standard rate CPTU tests provided 20 % higher values compared with high-rate tests. Thus, the undrained strength may be overestimated from standard rate tests. Care needs to be taken when using undrained shear strength in silts. Nevertheless, this value represents a limiting strength value, which is often of interest when investigating the response as if it were undrained. The friction angle could be successfully determined from CPTU results by applying the modified Norwegian Institute of Technology (NTH) method to the measured data set. The results reveal a rate dependency of the friction angle, resulting in an underestimation of 20 % if a standard rate test is used compared with using low-rate CPTU tests, giving drained results that match the reference values from the laboratory. To overcome uncertainties in picking design strength values, it is highly recommended to carry out at least one fast and one slow CPTU test to evaluate the drainage situation and to adjust the design values accordingly.

Interpretation of Cone Penetration Test Data of an Embankment for Coupled Numerical Modeling

The Nerang Broadbeach Roadway (NBR) embankment in Australia is founded on soft clay deposits. The embankment sections were preloaded and surcharged-preloaded to limit the post-construction deformation and to avoid stability failure. In this paper, we discuss the NBR embankment’s geology, geotechnical properties of the subsurface, and long-term field monitoring data from settlement plates and piezometers. We demonstrate a comparison of cone penetration test (CPT) and piezo cone dissipation test (CPT-u) interpreted geotechnical properties and the NBR embankment’s foundation stratification with laboratory and field measured data. We also developed two elasto-viscoplastic (EVP) models for long-term performance prediction of the NBR embankment. In this regard, we considered both the associated and the non-associated flow rule in the EVP model formulation to assess the flow rule effect of soft clay. We also compared EVP model predictions with the Modified Cam Clay (MCC) model to evaluate the effect of viscous behavior of natural Estuarine clay. Both EVP models require six parameters, and five of them are similar to the MCC model. We used the secondary compression index of clay in the EVP model formulations to include the viscous response of clay. We obtained numerical models’ parameters from laboratory tests and interpretation of CPT and CPTu data. We observed that the EVP models predicted well compared with the MCC model because of the inclusion of soft clay’s viscosity in the EVP models. Moreover, the flow rule effect in the embankment’s performance predictions was noticeable. The non-associated flow rule EVP model predicted the field monitoring settlement and pore pressure better compared to the MCC model and the associated flow EVP model.

Interpretation of CPT in unsaturated sands under drained conditions: A numerical study

AbstractA finite difference‐based numerical model simulating the cone penetration process in unsaturated sands is presented. Mohr–Coulomb model (MCM) with simple modifications and Sun model (SM) were implemented to capture the unsaturated sand behaviour. It was shown that the cone tip resistance values resulting from the two models were fairly comparable. Predicted cone tip resistance values in dry, saturated and unsaturated sands using MCM were validated by the results of field and calibration chamber tests. Sensitivity analyses were performed, and the influence of parameters including relative density, mean effective stress and apparent cohesion due to suction on the tip resistance was investigated. Based on a large number of numerical analyses, a simple relationship was suggested to predict the cone tip resistance in dry, saturated and unsaturated sands. The accuracy of the proposed relationship was evaluated by a large database of Cone penetration test (CPT) results performed in various calibration chambers containing different sands. Finally, the applicability of the suggested equation in the estimation of the soil relative density and friction angle from CPT results was shown through useful and practical charts and illustrative examples.

Interpretation of cone penetration test in clay with smoothed particle finite element method

Interpretation of cone penetration test in clay with smoothed particle finite element method

Unsupervised and Simultaneous Stratigraphic Interpretation of CPT Soundings at Site Scale

Abstract This paper presents a novel Bayesian machine-learning approach for unsupervised and simultaneous soil stratigraphic interpretation of cone penetration test (CPT) soundings at the site scal...

An elastoplastic solution for spherical cavity undrained expansion in overconsolidated soils

In this paper, a novel elastoplastic solution is developed for the undrained expansion of a spherical cavity in overconsolidated soils, with the aim of providing a mechanical model for the interpretation of cone penetration tests in overconsolidated soils. The well-established unified hardening (UH) model is adopted in the present solution to represent the unique mechanical behaviors of the overconsolidated soil during cavity expansion. The problem considered is formulated as a system of first order partial differential equations in terms of a Lagrangian description; these equations are solved as an initial value problem with the code developed based on the Runge-Kutta algorithm. The results, including the expansion-pressure curves, the distributions of the stress components, and the evolution of the potential strength during cavity expansion are presented to show the expansion responses in overconsolidated soils. The results reveal that the unique expansion responses in overconsolidated soil during cavity expansion, such as the development of a negative excess pore water pressure, the strain-hardening and softening behavior, the peak strength and the decay of the potential strength during cavity expansion could be well represented by the present solution.

Cementált talajok jelenlétének előrejelzése helyszíni vizsgálatokkal

A cementált talajok viselkedése jelentősen eltér a megszokottól, így fontos azok jelenlétének minél pontosabb előrejelzése a leggyakrabban alkalmazott helyszíni vizsgálatok segítségével. Ez azonban nem egyszerű feladat, mivel a helyszíni vizsgálatok elvégzése során a talaj szerkezete, a cementációs kötések károsodnak. A szakirodalomban számos ajánlás található a statikus nyomószondázás (CPT) és lapdilatométeres (DMT) mérési eredmények felhasználására, a két vizsgálat fő paraméterei közti korrelációkra, illetve hogy e paraméterek miként alkalmazhatóak a cementáltság előrejelzésére. Célom összefoglalni a szakirodalmi ajánlásokat, majd elvégzem néhány, a várttól eltérő eredményt adó cölöp-próbaterheléshez köthető CPT-eredmény feldolgozását, amelyeknél a cölöp környezetében meszes közepes/kövér agyagok jellemzőek.

Exact solution for drained spherical cavity expansion in saturated soils of finite radial extent

SummaryThis study presents an exact solution for drained spherical cavity expansion subjected to constant stress and zero displacement boundary conditions in finite medium. The solution is exact as no simplification is involved in the solution procedure in the plastic region and can be solved as an initial value problem. The effect of finite radial extent on the results of cavity expanding to a certain radius is accounted for through the initial values at the elastic‐plastic boundary. A critical state constitutive model with a nonassociated flow rule is adopted. The model parameters from literature are then used in generating the results for cavity expansion in infinite and finite radial extent to highlight the difference. Also, the results are presented in a way that can be used to account for the boundary effect for the interpretation of cone penetration tests conducted in calibration chambers.

Preliminary Validation of a Novel Method for the Assessment of Effective Stress State in Partially Saturated Soils by Cone Penetration Tests

A proper assessment of the soil effective stress state is crucial in many cases to identify a potential geological/geotechnical hazard as shallow landslides or failure of levees that may have a significant impact on human activities and development. This paper is aimed at validating a methodology for the expeditious and economic determination of effective stress state in the vadose zone recently proposed by Lo Presti et al. in 2016. The method is based on the interpretation of cone penetration tests (CPTu). Its validation was carried out by comparing the CPTu predicted values of suction against the measured ones in a well-documented and monitored site. The comparison also includes the prediction of suction that was obtained by using the so-called Modified Kovacs model (MK). Moreover, additional data of water content and saturation degree from another site were used to predict the suction by using the MK model. These values of suction were compared with those inferred by the CPTu.

Layered effects on soil displacement around a penetrometer

The interpretation of cone penetration test (CPT) data is important for the in-situ characterisation of soils. Interpretation of CPT data remains a predominately empirical process due to the lack of a rigorous model that can relate soil properties to penetrometer readings. Interpretation is especially difficult in layered soils, where penetrometer response can be affected by several horizons of soil with different properties. This paper aims to provide some insight into the mechanisms of soil displacement that occur as a penetrometer is pushed into layered soils. Data is presented from centrifuge modelling of probe penetration in layered soils in an axisymmetric container where soil deformation patterns around the probe can be measured. Results obtained from uniform soil tests are also presented to illustrate the effects of soil density and stress level (i.e. centrifuge acceleration). A large influence zone is found to relate to the higher penetration resistance obtained in a denser soil. Differing soil displacement patterns at low and high stresses are related to the tendency of the soil to dilate, with the well-known consequence of a non-linear increase of penetration resistance with stress level. Layered soil tests show a clear difference of soil deformation patterns compared to uniform tests, especially for vertical displacements. The peak value of vertical displacement of the soil occurs at dense-over-loose interfaces, while a local minimum occurs at loose-over-dense interfaces. Parameters are proposed to quantitatively evaluate the layered effects on soil deformations and a deformation mechanism is described for penetration in layered soils based on the transition of displacement profiles.

Interpretation of cone penetration tests — a unified approach

The electric cone penetration test (CPT) has been in use for over 40 years and is growing in popularity in North America. This paper provides some recent updates on the interpretation of some key geotechnical parameters in an effort to develop a more unified approach. Extensive use is made of the normalized soil behaviour type (SBTn) chart based on normalized cone resistance (Qt) and normalized friction ratio (Fr). Updates are provided regarding the normalization process and its application to the identification of soil type. The seismic CPT has provided extensive data linking CPT net cone resistance to shear-wave velocity and soil modulus. New correlations are presented in the form of contours of key parameters on the SBTn chart. These new relationships enable a more unified interpretation of CPT results over a wide range of soils. Updates are also provided in terms of in situ state parameter, peak friction angle, and soil sensitivity. The correlations are evaluated using available laboratory and full-scale field test results. Many of the recommendations contained in this paper are focused on low to moderate risk projects where empirical interpretation tends to dominate. For projects where more advanced methods are more appropriate, the recommendations provided in this paper can be used as a screening to evaluate critical regions–zones where selective additional in situ testing and sampling maybe appropriate.

Geotechnical Properties of a Pumice Sand

ABSTRACT The pumice sand found in the North Island of New Zealand has properties which lie beyond those usually associated with cohesionless soils. The grains are very soft and the sand has a high void ratio, thus forming a compressible material. This paper presents the results of a series of drained triaxial and K0 tests on dry pumice sand. The tests were conducted to evaluate the geotechnical properties, particularly the critical state parameters, of the sand and also to provide background information for interpretation of cone penetration tests in the material. The K0 tests were used to evaluate the compression envelope under conditions of no lateral strain and to determine values of constrained modulus. Significant grain crushing was found to occur during testing even at low confining stress, in fact the stress-strain-strength behaviour of the material is dominated by particle crushing. Routine soil testing techniques were found to be inadequate for the evaluation of the specific gravity of pumice sand particles and a different technique was used for this purpose. The angle of friction of pumice sand was found to be larger than that of quartz sands, however pumice sand required very large shear strains to mobilise the peak and critical state shear strength and, for several tests, critical state conditions were not reached.

SW—Soil and Water: State Parameter Interpretation of Cone Penetration Tests in Agricultural Soils

Cone penetrometer resistance in saturated sands has been shown by earlier workers to be an exponential function of a state parameter in critical state space. The present investigation demonstrates that this concept of a state parameter-penetrometer function (SPP-function) also holds good in a partly saturated agricultural soil. The two coefficients which characterize the SPP-function have been evaluated from extensive tests carried out in a miniature penetrometer calibration chamber. These coefficients were found to vary in a systematic manner with the moisture content of the sandy loam soil used in the experiments, as do the three basic parameters necessary to characterize the critical state boundaries of this soil. The paper presents a method of using this experimentally obtained information to interpret the pore space of the soil from measured penetrometer resistance in that soil. The performance of the proposed method was checked against penetrometer readings made under carefully controlled laboratory conditions in an indoor soil tank. The prediction accuracy was poor, but it is felt that this could be improved by using an iterative solution in place of the single step method used in the validation. The tedious and time consuming experimental work described in the paper is confined to a single sandy loam soil, typical of a light agricultural soil. In order to generalize the solution, it is necessary to test the procedure over a wide range of soils, including clay. If the SPP-functions can be established for these conditions then the state parameter concept could prove to be a powerful tool in the interpretation of cone penetrometer readings.

The interpretation of cone penetration tests in clays, with particular reference to rate effects : Powell, J J M; Quarterman, R S T Proc 1st International Symposium on Penetration Testing, ISOPT-1, Orlando,20–24 March 1988V2, P903–909. Publ Rotterdam: A A Balkema, 1988

The interpretation of cone penetration tests in clays, with particular reference to rate effects : Powell, J J M; Quarterman, R S T Proc 1st International Symposium on Penetration Testing, ISOPT-1, Orlando,20–24 March 1988V2, P903–909. Publ Rotterdam: A A Balkema, 1988

Interpretation of cone penetration tests. Part 1: Sand : Robertson, P K; Campanella, R G Can Geotech JV20, N4, Nov 1983, P718–733

Interpretation of cone penetration tests. Part 1: Sand : Robertson, P K; Campanella, R G Can Geotech JV20, N4, Nov 1983, P718–733

Interpretation of cone penetration tests. Part 2: Clay : Robertson, P K; Campanella, R G Can Geotech JV20, N4, Nov 1983, P734–745

Interpretation of cone penetration tests. Part 2: Clay : Robertson, P K; Campanella, R G Can Geotech JV20, N4, Nov 1983, P734–745

Interpretation of cone penetration tests. Part I: Sand

Significant advances have been made in recent years in research, development, interpretation, and application of cone penetration testing. The addition of pore pressure measurements during cone penetration testing has added a new dimension to the interpretation of geotechnical parameters.The cone penetration test induces complex changes in stresses and strains around the cone tip. No one has yet developed a comprehensive theoretical solution to this problem. Hence, the cone penetration test provides indices which can be correlated to soil behaviour. Therefore, the interpretation of cone penetration data is made with empirical correlations to obtain required geotechnical parameters.This paper discusses the significant recent developments in cone penetration testing and presents a summarized work guide for practicing engineers for interpretation for soil classification, and parameters for drained conditions during the test such as relative density, drained shear strength, and deformation characteristics of sand. Factors that influence the interpretation are discussed and guidelines provided. The companion paper, Part II: Clay, considers undrained conditions during the test and summarizes recent developments to interpret parameters for clay soils, such as undrained shear strength, deformation characteristics of clay, stress history, consolidation characteristics, permeability, and pore pressure. The advantages and use of the piezometer cone are discussed as a separate topic in Part II: Clay. The authors' personal experiences and current recommendations are included. Keywords: static cone penetration testing, in situ, interpretation, shear strength, modulus, density, stress history, pore pressures.