Piezocone Penetration Test Research Articles

Development and Application of an in Situ Penetrator for Rapid Strength Testing of Submarine Sediment

In marine engineering, the strength of a submarine sediment is an indispensable parameter for assessment of construction. In this study, a free-fall cone penetrator named IPen was developed to realize a rapid and efficient measurement of sediment strength. The equipment is characterized by modular design and self-contained data acquisition. It is equipped with an acceleration sensor, a water pressure sensor, and a piezocone penetration test (CPTu) probe. It is designed to be released from near seabed surface with a releaser and then fall freely to provide a higher penetration velocity. Its maximum working depth is approximately 2500 m and maximum penetration depth is approximately 3 m. To derive the correlation between penetration resistance and sediment strength, a calibrator was devised to determine the penetration-rate factor. In addition, the factor applicable to in situ test points was determined in laboratory experiments. In June 2016, the IPen was tested in situ in the South Yellow Sea, China, during a shared voyage funded by the National Science Foundation. Meanwhile, undisturbed column samples were collected for laboratory tests. Based on the in situ test results, it was demonstrated that the IPen could accurately record the working states of various sensors during the freely falling course. IPen test results reliably reflected the sediment strength at all the testing points when compared with laboratory calibration tests, in situ vane tests and penetration tests, laboratory penetration tests, and unconsolidated and undrained triaxial compression tests.

Undrained shear strength evaluation for hydrate-bearing sediment overlying strata in the Shenhu area, northern South China Sea

The undrained shear strength of shallow strata is a critical parameter for safety design in deep-water operations. In situ piezocone penetration tests (CPTU) and laboratory experiments are performed at Site W18-19 in the Shenhu area, northern South China Sea, where China’s first marine hydrate exploitation operation is due to be located. The validation of the undrained shear strength prediction model based on CPTU parameters. Different laboratory tests, including pocket penetrometer, torvane, miniature vane and unconsolidated undrained triaxial tests, are employed to solve empirical cone coefficients by statistical and mathematical methods. Finally, an optimized model is proposed to describe the longitudinal distribution of undrained shear strength in calcareous clay strata in the Shenhu area. Research results reveal that average empirical cone coefficients based on total cone resistance, effective resistance, and excess-pore pressure are 13.8, 4.2 and 14.4, respectively. The undrained shear strength prediction model shows a good fit with the laboratory results only within specific intervals based on their compaction degree and gas-bearing conditions. The optimized prediction model in piecewise function format can be used to describe the longitudinal distribution of the undrained shear strength for calcareous clay within all depth intervals from the mud-line to the upper boundary of hydrate-bearing sediments (HBS). The optimized prediction result indicates that the effective cone resistance model is suitable for very soft to firm calcareous clays, the excess-pore pressure model can depict the undrained shear strength for firm to very stiff but gas-free clays, while the total cone resistance model is advantageous for evaluating the undrained shear strength for very stiff and gassy clays. The optimized model in piecewise function format can considerably improve the adaptability of empirical models for calcareous clay in the Shenhu area. These results are significant for safety evaluations of proposed hydrate exploitation projects.

Peat layer accumulation and post‐burial deformation during the mid‐late Holocene in the Po coastal plain (Northern Italy)

AbstractPeat horizons are characteristic features of delta plains worldwide. In this study, we tested the use of peat‐based correlations to assess the deformation of Holocene strata in the Po coastal plain (Northern Italy). The Holocene stratigraphy, about 30 km inland from the modern coastline consists of a peat‐bearing, estuarine and deltaic succession, up to 23 m thick. Through the analysis of 31 core data and 100 piezocone penetration tests, we identified and mapped three 10–40 cm‐thick peat layers (T1–T3) dated to 6.6–5.8, 5.5–5.0 and 3.3–2.7 cal kyr BP respectively. These peat horizons were found to be suitable stratigraphic markers within the Holocene succession over an area of about 200 km2. The mid‐late Holocene palaeogeography, reconstructed through high‐resolution peat correlation, supported by 72 radiocarbon dates, highlights a typical upper delta plain environment, with ribbon‐shaped distributary channels and swamp interdistributary areas. Peat layers are inclined towards E‐NE with gradients that increase downsection from ~0.016% (T3) to 0.021% (T1). The gradient of the oldest peat horizon is one order of magnitude larger than the slope of the modern delta plain (~0.0025%). We infer that peat horizons accumulated during periods of low sediment supply mainly controlled by autogenic processes and were deformed after deposition. Differential compaction of underlying sedimentary strata and recent tectonic activity of the buried Apenninic thrust systems are the most likely drivers of strata deformation. Based on isochore maps, we document that higher sedimentation rates in topographically depressed areas compensated, in part at least, the ongoing deformation, keeping unaltered the topographic gradient and the depositional environment. This study demonstrates that peat‐based correlation and mapping can shed lights on the mechanisms of strata accumulation and deformation in deltaic settings, constituting a robust basis for reconstructing delta evolution.

Pore Pressure Responses of Overconsolidated Soils in a Partially Drained Piezocone Penetration Test

AbstractThis study investigated the pore pressure responses of overconsolidated (OC) soils during a piezocone penetration test (PCPT). The influences of overconsolidation ratio (OCR) and hydraulic ...

Prediction Method for Overconsolidation Ratio of Marine SoftSoil Based on the Piezocone Penetration Tests

Because of the strong structural and sensitive behavior, the properties of marine soft soil change greatly when subjected to external disturbances, which leads to great difficulty in reflecting its real mechanical properties in the laboratory soil tests. The piezocone penetration test (CPTU) is one of the main technologies for in situ testing of geotechnical engineering. CPTU has the advantages of being fast and convenient, no sampling, low disturbance to soil, large amount of data, and reliable testing. The determination of the overconsolidation ratio (OCR) based on the CPTU results can solve the problems of soil disturbance and stress release, which occur during the consolidation test in the laboratory. However, there are still some problems such as lack of strict theoretical analysis of penetration mechanism and incomplete interpretation theory of in situ test parameters of CPTU. In this paper, the CPTU cone head is assumed to be hemispherical considering the penetration mechanism of CPTU. Moreover, the compaction modes of the CPTU probe penetrating into soil are adopted as spherical and cylindrical cavity expansion modes, respectively. The ultimate expansion pressures of the probe penetrating into soil under the spherical and cylindrical cavity expansion modes are first obtained by virtue of the theory of cavity expansion. Then, two prediction methods for OCR considering the roughness and penetration rate of the cone are proposed by combining the ultimate expansion pressures of the probe penetrating the approximate closed solution of cavity expansion in the modified Cambridge model, which is suitable for predicting the OCR of marine soft clay. Finally, to verify the reliability of the two proposed prediction methods, comparisons with the in situ CPTU tests of marine soft clay in two coastal areas and two existing prediction methods are made. The comparison results show that predictions of OCR of marine soft clay in this paper are close to Wayne’s method and more accurate than Chanmee’s method since the factors such as cone roughness and penetration rate are considered in the new proposed prediction methods. In order to improve the applicability in different cases of the OCR predictions, the average values of the two proposed methods are recommended as the reference value for the OCR of marine soft soil.

Evaluation Method for the Liquefaction Potential Using the Standard Penetration Test Value Based on the CPTU Soil Behavior Type Index

Taking the project of the Su‐xin highway treated by using the resonant compaction method as the reference, a new method for the evaluation of liquefaction potential is proposed based on the piezocone penetration test (CPTU) and the standard penetration test (SPT). The soil behavior type index (Ic) obtained from CPTUs and the standard penetration test index (N63.5), obtained from SPTs, are analyzed for saturated silty sand and silt. The analysis result reveals a linear relationship between N63.5 and Ic, given by N63.5 = −18.8Ic + 52.0. The larger the value of Ic is, the greater the viscosity of soil is, and the smaller the value of N63.5 is. According to the method, liquefaction assessment of saturated silty sand and silt foundation can be conducted by using N63.5 based on the Code of Seismic Design of Building. N63.5 is expressed by a single Ic, which is calculated from the CPTU data. Compared with existing evaluation methods, this method can provide continuous standard penetration test values, moreover, this method involves a simple calculation, and the results obtained using the method are reliable.

Characterisation of a subaqueously deposited silt iron ore tailings

A geotechnical investigation was carried out to characterise a subaqueously deposited, primarily silt, iron ore tailings. Piezocone penetration tests (CPTu) were carried out followed by piston tube sampling at a selected target depth. Piston samples provided measures of in situ density (by means of gravimetric water content), and supplied material for reconstituted and intact laboratory testing. Reconstituted samples prepared using moist tamping (MT) for determination of the critical state locus (CSL), along with intact specimens, were both tested. The potential existence of layering within the recovered specimens was also assessed, indicating near-homogenous samples. The laboratory testing of intact specimens suggested that they appeared to tend towards the same CSL as that obtained from reconstituted loose MT specimens. This tentative result differs from some previous comparisons – with the agreement seen in this case being suggested to primarily result from a lack of layering. In situ state as inferred from both CPTu data and comparison of tube densities to the CSL suggested a loose state.

Interpretation of piezocone penetration and dissipation tests in sensitive Leda clay at Gloucester test site

A modified piezocone penetration test (CPTu) analytical solution based on spherical cavity expansion and critical state soil mechanics (SCE–CSSM) is employed for assessing yield stress, undrained shear strength, and flow parameters in sensitive Leda clay at the Gloucester test site. For sensitive and structured clays, the formulation relies on the mobilized effective stress friction angle ([Formula: see text]) defined at two parts of the stress–strain curve: (i) peak stress ([Formula: see text]) and (ii) maximum obliquity ([Formula: see text]). Input parameters for assessing the overconsolidation ratio ([Formula: see text], where [Formula: see text] is preconsolidation stress and [Formula: see text] is current effective vertical stress) from CPTu results include: undrained rigidity index (IR= G/su, where G is shear modulus and suis undrained shear strength), plastic volumetric strain potential (Λ = 1 – (Cs/Cc), where Csis swelling index and Ccis virgin compression index), and effective friction angles ([Formula: see text] and [Formula: see text]). A direct CPTu means of assessing the undrained rigidity index in a reliable manner is also developed that gives the Nktcone factor and matches profiles of undrained shear strength from triaxial compression tests (suTC). The modified solution is also implemented on two additional sites: a sensitive-quick clay in Norway and structured varved clay from New England. Interpretations of the coefficient of consolidation and permeability from pore-water pressure dissipation tests at Gloucester are evaluated using the SCE–CSSM formulation and shown to be comparable with independent laboratory and field tests.

An artificial neural network based model to predict spatial soil type distribution using piezocone penetration test data (CPTu)

Soil types mapping and the spatial variation of soil classes are essential concerns in both geotechnical and geoenvironmental engineering. Because conventional soil mapping systems are time-consuming and costly, alternative quick and cheap but accurate methods need to be developed. In this paper, a new optimized multi-output generalized feed forward neural network (GFNN) structure using 58 piezocone penetration test points (CPTu) for producing a digital soil types map in the southwest of Sweden is developed. The introduced GFNN architecture is supported by a generalized shunting neuron (GSN) model computing unit to increase the capability of nonlinear boundaries of classified patterns. The comparison conducted between known soil type classification charts, CPTu interpreting procedures, and the outcomes of the GFNN model indicates acceptable accuracy in estimating complex soil types. The results show that the predictability of the GFNN system offers a valuable tool for the purpose of soil type pattern classifications and providing soil profiles.

Correlations between Shear Wave Velocity and Geotechnical Parameters for Jiangsu Clays of China

The shear wave velocity ( $$V_{\text{s}}$$ ) is an important factor reflecting the dynamic characteristics of soil. Measured $$V_{\text{s}}$$ values are always used in combination with laboratory parameters (e.g., effective confining pressure, $$\sigma_{\text{m}}^{{\prime }}$$ , and void ratio, e) and in situ penetration parameters from the standard penetration test (SPT) and piezocone penetration testing (CPTU). This study aims not only to estimate Vs based on correlations with other parameters in the absence of site-specific data, but also to outline relationships for estimation of soil properties. A database of seismic CPTU (SCPTU) and soil properties information for Jiangsu clays in East China was used to develop correlations between $$V_{\text{s}}$$ and geotechnical parameters (vertical effective stress, unit weight, preconsolidation stress, site-specific parameters, undrained shear strength, and CPTU net cone resistance). Laboratory tests were carried out on thin-walled tube samples and high-quality block samples to measure soil properties. The results showed that the predicted values of $$V_{\text{s}}$$ were in good accordance with measured values from field tests, especially the Vs values predicted from the CPTU net cone resistance. The relationship between $$V_{\text{s}}$$ and the undrained shear strength showed better performance than the others. The good relationships between $$V_{\text{s}}$$ and geotechnical parameters could be used to interpret engineering properties of Jiangsu clays for site investigation.

Use of functional cluster analysis of CPTU data for assessment of a subsoil rigidity

Abstract This paper shows an example of the grouping of piezocone penetration test (CPTU) characteristics using functional data analysis, together with the results of clustering, in the form of a subsoil rigidity model. The subsoil rigidity model was constructed based on layer separation using the proposed method, as well as the k-means method. In the construction of the subsoil rigidity model, the constrained modulus M was applied. These moduli were determined from empirical relationships for overconsolidated and normally consolidated soils from Poland based on cone tip resistance.

Probabilistic identification of contaminated soils using resistivity piezocone penetration tests

The identification of contaminated soils has gained increasing interest over the decades in the geoenvironmental issues. In this study, a probabilistic method based on the geostatistics and the reliability-based analysis is performed on the resistivity piezocone penetration testing data to evaluate the spatial distribution of the contaminants including the heavy metal ions and chlorobenzene over a site located in Shanghai, China. A sensitivity study revealed that the soil resistivity is a useful indicator of the presence of contaminants. Using the probabilistic method, a regional three-dimensional (3D) map of the probability that the soil is contaminated by the heavy metal ions or chlorobenzene is obtained based on the interpretation of resistivity data. Three selected sections of the resistivity-based 3D map are compared with those derived from the contaminant concentration data measured in the laboratory to demonstrate the effectiveness of the former. It is shown that the resistivity-based map is in accordance with concentration-based maps in a qualitative sense and provides useful information for the distribution of contaminants over the site. However, the resistivity-based probability shall always be judged with the results from the laboratory tests to draw a quantitative conclusion on the contamination status. Besides, it is also observed that the heavy metals may transfer over a narrower area than the chlorobenzene in the clay. The horizontal migration of contaminants is much more significant than that in the vertical direction, and it may be facilitated due to the presence of local geologic conditions.

Effective friction angle of clays and silts from piezocone penetration tests

An existing effective stress limit plasticity solution for piezocone penetration tests (CPTu) is calibrated to evaluate the effective stress friction angle ([Formula: see text]) for undrained conditions for a variety of fine-grained soils ranging from natural lean to plastic clays and clayey silts from marine, alluvial, lacustrine, deltaic, and glaciofluvial origins. Data from 105 clay sites are compiled to examine the CPTu-interpreted [Formula: see text] values in comparison with laboratory benchmark values obtained from undrained consolidated anisotropic (CAUC) and undrained compression (CIUC) triaxial tests made on undisturbed samples. An approximate inversion of the theoretical solution is developed to allow profiles of [Formula: see text] to be evaluated with depth. Five well-documented case studies in Illinois, Louisiana, South Carolina, Ireland, and Massachusetts are presented to illustrate the application of the solution. Lastly, results from 1g chamber tests involving kaolin and kaolinitic–silica mixtures tested by miniature piezocone probes are shown for additional verification.

Assessment of Ground Improvement by Vibro-compaction Method for Liquefiable Deposits from In-Situ Testing Data

Seismic piezocone penetration tests, resistivity piezocone penetration tests, and standard penetration tests (SPT) were conducted to quantitatively assess the effects of soil improvement by vibro-compaction. The differences of piezocone penetration test (CPTU) basis readings, improvement index for densification, electrical resistivity of soils, and state parameters before and after ground treatment were analyzed, and the effect of the increase in stiffness on the site response was also analyzed for the effect of densification. A combination of shear wave velocity, Vs, and cone tip resistance, qc, was used for the interpretation of the changes of coefficient of earth pressure at rest, K0, and mean grain size, D50, before and after compaction. The dissipation process of excess pore pressures during vibro-compaction has been presented to show the effect of drainage. In addition, liquefaction potential was also estimated by CPTU and SPT for its effect of reinforcement. The results showed that the liquefied soil was densified and the use of a combination of in-situ tests could be used for ground improvement needed to mitigate liquefaction.

Interrelationship between Undrained Shear Strength from DMT and CPTU Tests for Soils of Different Origin

Abstract The article presents test results on the use of the flat dilatometer test (DMT) to evaluate changes in undrained shear strength su in soils of various origins. Reference values for the undrained shear strength calculated with Marchetti’s original formula were su values obtained from the piezocone penetration tests. The tests were conducted at eight investigation sites in Poland, where five groups of soils were separated: loess-deluvial, loess-deluvial cemented, young till, aged till, and Pliocene clay. The soils exhibited varied overconsolidation effects. The study results revealed that the factors influencing the relationship between undrained shear strength and the KD coefficient from DMT test were various because of the origin, grain size distribution of the soils and cementation. In order to include the influence of overconsolidation and grain size distribution in calibration of su from DMT, a modified KD1 coefficient was introduced into the formula describing this relationship. The final solution was obtained with multiple linear regression. A relatively high statistical evaluation of this relationship was determined for aged till and deluvial and uncemented loess.

Evaluation of Undrained Shear Strength of Clay Using the CPTU Pore Pressure Method

Difficulties in obtaining high-quality undisturbed soil samples have necessitated the increased use of cone penetration test (CPT) or piezocone penetration test (CPTU) to determine soil properties at geotechnical engineering sites. Undrained shear strength (a key parameter for most clay investigations) traditionally is evaluated by cone tip resistance or effective cone tip resistance. In this paper a method of using the clay's excess pore pressure was used to estimate the undrained shear strength. A correlation of pore pressure ratio and cone factor was discovered and compared with results from the published literature and with those from field vane tests.

Determination of Bearing Capacity of Single Pile based on Seismic Piezocone Penetration Tests

Based on the similar characteristics of installation about the penetrometer of seismic piezocone penetration tests(SCPTu) and the single pile, a theoretical relationship between ultimate bearing capacity of single pile, time-effect of shaft bearing capacity of single pile, excess pore water pressure around the pile during pile driven and the data measured from SCPTu is developed according to the cavity expanded theory, the Terzaghi one-dimensional consolidation theory and effective stress theory. The result of field test in KunShan and the calculated result which used the theoretical relationship mentioned above are compared. The results indicate that the analytical solutions agree well with the in-situ tests, which show that the applications of seismic piezocone penetration tests have wide range in the design of pile foundation.

Undrained Shear Strength and In Situ Horizontal Effective Stress from Piezocone Penetration Test Measurements in Clayey Soils: New Approach

Undrained Shear Strength and In Situ Horizontal Effective Stress from Piezocone Penetration Test Measurements in Clayey Soils: New Approach

Effective Stress Strength Parameters of Clays from DMT

Abstract In this study, an established effective stress limit plasticity solution for piezocone penetration tests (CPTu) in clay developed by the Norwegian Institute of Technology (NTH) for evaluating the effective stress friction angle (ϕ′) is extended to flat plate dilatometer tests (DMT) readings. A nexus between CPTu and DMT is built through spherical cavity expansion solutions for undrained penetration to link the cone tip resistance (qt) and shoulder porewater pressure (u2) from CPTu to the measured contact pressure (p0) and expansion pressure (p1) obtained from DMT in soft to firm intact clays. Data from 49 paired sets of CPTu-DMT soundings in a variety of clays are used to support and validate the links. A variety of soils ranging from lean to plastic clays and clayey silts from marine, alluvial, lacustrine, deltaic, and glaciofluvial origins are subjected to flat DMTs, and the measurements are utilized to evaluate the effective stress friction angle (ϕ′). Data from 46 clays are compiled to examine the DMT-interpreted ϕ′ values in comparison with laboratory benchmark ϕ′ values obtained from CAUC or isotropically consolidated undrained triaxial compression tests on high-quality samples. An approximate inversion of the theoretical solution is derived to allow ϕ′ profiles to be determined with depth. Four well-documented DMT examples, including two natural clay sites and two chamber test series (one pressurized and the other unpressurized), are presented to illustrate the NTH procedures.

A Study on the Improvement Effect and Field Applicability of the Deep Soft Ground by Ground Heating Method

The soft ground in coastal areas should be treated when it needs to be used for the sustainably developed of urban or industrial complex constructions. The ground heating method for soft ground improvement was applied in Eastern Europe in the 1960s, but it was not widely used due to economic and environmental problems. The author developed a device for improving soft ground using an electric heating pipe. This paper investigates the improvement effect and field application of deep soft ground by the ground heating method using the electric heating pipe. Ground heating increases the temperature of the deep soft ground and increases the tip resistance of the static electronic piezo-cone penetration test. Additionally, the pressure of the pore water decreases because the pore water is evaporated due to the ground heating. As a result of the experiment, it was verified that there was an improvement in the effect of deep soft ground by the ground heating method. With ground heating for 96 h, the tip resistance was increased by 61% at a point 0.35 m horizontally away from the electric heat pipe, 22% at 0.97 m, and 2% at 1.31 m. As a result of the field test, it was found that there were no problems in the power supply of the diesel generator and the control panel. It was easy to install the electric heating pipes in the deep soft ground. However, due to boring, the ground was disturbed and water vapor was discharged through this gap. To minimize the discharge of water vapor, it is necessary to drive the electric heating pipe.