Standard Cone Penetration Test Research Articles

Development of the heat flow cone penetration test (HF-CPT)

The heat flow cone penetration test (HF-CPT) provides in-situ values of thermal conductivity (patent pending). The HF-CPT test records include (1) heat flow (HF) measurements acquired by a CPT add-on module, i.e. heating power and temperature versus time and (2) cone penetration test (CPT) measurements, i.e. cone resistance, sleeve friction and pore pressure versus depth and time. The test method requires a short interruption of the continuous CPT penetration phase, to allow stationary HF heating and cooling cycles.
 Values of thermal conductivity are derived similarly to the principles for laboratory thermal needle probes described in common ASTM standards, particularly [1].
 Data processing makes use of an advanced interpretation method that accounts for the short-cylinder effects of the HF module and short timeframe heat fluxes. The novel interpretation method includes inversion of a numerical forward model of the interaction between the heat flow module and the surrounding soil. The interpretation method also integrates standard CPT results, such that both a semi-continuous thermal conductivity profile and a continuous standard CPT profile are obtained.
 Validation of the interpretation method included comparison of thermal conductivity values derived from other test methods, notably laboratory transient plane source tests [1], in-situ thermal needle probe tests (based on [2]) and thermal cone penetration tests [3]. Figure 1 presents an example of validation results for predominantly clay soil. The results are seen to closely match those derived from an in-situ needle probe. As the HF-CPT measurements were taken two metres apart horizontally from the in-situ needle probe measurements, some deviation between the results is to be expected due to heterogeneity of the soil.

Characterizing the in-situ state of sandy soils for liquefaction analysis using resistivity piezocone penetration test

Estimation of in-situ state is an important step in evaluating the liquefaction potential of sandy soil. Due to the difficulty in obtaining high-quality undisturbed samples, the cone penetration test (CPT) is being widely used to determine the relative density, state parameter, and dilatancy index which indicate the in-situ state of the soil. The resistivity piezocone penetration test (RCPTU) can not only measure standard CPT data (cone tip resistance and sleeve friction), but also measure in-situ pore pressure and the electrical resistivity of the soil. In this study, a new RCPTU-based soil state characterization method has been developed to assess the soil in-situ state characteristics associated with the liquefaction potential. New correlations between in-situ state indices, liquefaction resistance, and RCPTU data have been developed for soil state characterization and liquefaction evaluation. The results indicate that the RCPTU-based soil state characterization provides an independent “first principle” method to evaluate the in-situ state of soils. The correlations developed in this study can be used confidently for evaluating the dilatancy behavior or liquefaction susceptibility of sites involving high-risk engineering.

Case study on soft soil improvement using vertical drains—field measurements and numerical studies

This paper presents an interesting case study for a very large ground improvement project in north Egypt using prefabricated vertical drains (PVD) and surcharge. The first 15m of soil at this site is soft silty clay to silty sand over 35m layer of very soft clay. To build a trustable numerical model that can predict the behaviour of the complex situation, a trial area was built, including several types of instrumentations for intensive monitoring of deformations and excess pore water pressures over time. Undisturbed samples were collected all over the soil profile and tested in the lab to determine the soil parameters to be used in the numerical model. An axisymmetric numerical model was built and calibrated using the collected data to predict the soil behaviour and the development of settlements due to the construction works. The analyses were performed using the soft soil model and the soft soil creep model; thus, the numerical investigations allow an evaluation of the long-term effects. The comparisons of the finite element analysis with the measured deformations presented in this paper show a very good match. Moreover, pre and post in situ measurements of standard cone penetration tests with sensors for the measurement of the pore water pressures (CPTu) have been used to calibrate the numerical model. These CPTu tests were used additionally to verify the improvement of the soil shear parameters over the preloading duration. It is shown that a combination of surcharge and vertical drains can be successfully used to improve the soft soil conditions present at the discussed project.

Study of mining tailings geotechnical parameters obtained from SCPTu tests carried on dry and saturated layers

The correct interpretation of in situ and laboratory test results is an important step in the design of mining tailing containment structures. This study aims to analyze the Seismic Cone Penetration Test (SCPTu) results obtained into a mining tailing reservoir composed of two material layers: a thick-dry and a tick-saturated. It is possible to observe that in a same tailing reservoir, the CPTu test interpretation can lead to a classification of each layer as a different soil with specific behavior and properties. This condition demonstrates that tailings with intermediate permeability (10-5 m/s < k < 10-8 m/s) may present partial drainage conditions during a standard cone penetration test (CPTu) (v=20 mm/s), if saturated conditions are verified. The effects of partial drainage can affect test results, and can induce to errors in the prediction of soil behavior and geotechnical parameters. To evaluate the possible effects of partial drainage, in situ test results were compared to laboratory tests results. It was possible to verify that estimated behavior of dry layers, obtained from in situ tests results, present more similarity to the results from laboratory tests. Probably, the partial drainage effects verified through the interpretation of dissipation tests, distorted the estimated behavior of the saturated layer material.

Geotechnical study of a landslide reactivation in clay soils (central Piedmont, NW Italy).

In March 2015, exceptional meteoric events occurred in southern Piedmont caused a remarkable rise of the rivers water level of the Tanaro Basin with flooding and many landslides. The engineering geological study reported here, concerns a triggering of a previous landslide occurred in 1982 in the hills, shaped in the marine sedimentary succession (Lugagnano Clay, lower Pliocene) of the southern Asti Reliefs, near San Martino Alfieri village. Detailed geological, morphological and topographic surveys of this landslide, with the aim to recognize the morphological features linked to the previous landslide and those connected to the triggering of it, have been carried out. The reactivation of the landslide was highlighted by the presence of a main scarp with minor escarpments and tracks. The mechanism activation of the main landslide is due to a rotational movement. To define the engineering geological model of the landslide body, standard cone penetration tests. rotary drilling borings with S.P.T. and geotechnical laboratory tests were performed. Through surveys, both main slip surface and deep-water seepage have been detected. In details, failure mechanism in OC clays was caused by: a) rapid increase in the bulk density or volume weight during rainfall events; b) rise of interstitial pressures along the sliding surface with reduction of normal stress and consequent reduction of the shear strength along this surface (progressive failure); c) reduction of cohesion and friction angle, due to clay softening. The results of the study have highlighted the need, as a primary factor of slopes consolidation, to install sub-horizontal drainage pipes in order both to avoid subsoil imbibition and to control the changes of interstitial pressure. The consolidation works focused on the construction of containment structures with deep consolidation and the execution of drainage works in the landslide area.

Using CPTs to derive thermal properties of soil

A method of utilizing cone penetration tests (CPTs) is presented which gives continuous profiles of both the in situ thermal conductivity and volumetric heat capacity, along with the in situ temperature, for the upper tens of meters of the ground. Correlations from standard CPT results (cone resistance, sleeve friction and pore pressure) are utilized for both thermal conductivity and volumetric heat capacity for saturated soil. These, in conjunction with point-wise thermal conductivity and in situ temperature results using a Thermal CPT (T-CPT), allow accurate continuous profiles to be derived. The CPT-based method is shown via a field investigation supported by laboratory tests to give accurate and robust results.

Determination of Thermal Conductivity of Soil Using Standard Cone Penetration Test

Abstract: The thermal cone dissipation test is a newly-developed method for determining thermal conductivity in situ based on temperature dissipation over time. The standard cone penetration test with pore pressure measurement (CPTu) is used. The cone heats up as it is pushed through the soil, due to the build-up of friction on the cone and rods. The dissipation of this heat can then be measured when penetration of the cone is stopped at intervals, and the thermal conductivity of the soil over that test interval determined. Three thermal cone dissipation tests (TCT) were conducted, the first test in soft clay with a high moisture content, and the second and third tests in clay containing a stiff sandy clay layer. The stiff sandy clay layer showed the more significant temperature increase on cone penetration. Using a previously developed correlation, the thermal conductivity was then calculated for each TCT. The temperature increase of the cone for the duration of each CPTu test was also recorded. While the TCT is a promising new test, it is suggested that further research is necessary to develop and refine the method.

Algorithm for generation of stratigraphic profiles using cone penetration test data

Cone Penetration Test (CPT) data are often used directly in the design of shallow and deep foundations and many other applications. To produce more cost-effective designs, it is advantageous to use CPT data to establish stratigraphic profiles as well. Algorithms to generate a stratigraphic profile using data from an individual CPT sounding and a Soil Behavior Type (SBT) chart as inputs are presented. Two SBT charts from the literature were selected and modified to eliminate ambiguity in soil classification. Novel algorithms were developed for handling the occurrence of thin layers within a stratigraphic profile to account for the fact that the standard CPT cone cannot accurately sense layers with thickness below a certain limit and a representative cone resistance cannot be obtained if the layer is too thin. Likewise, the algorithms prevent the creation of a soil profile with adjacent layers of essentially the same soil by consolidating layers appropriately. The algorithms presented generate a design soil profile, produced using a precise classification based on soil type and state and by elimination of artificial layering, that can be more effectively used in design.

A new soil mechanics approach to quantify and predict land subsidence by peat compression

AbstractLand subsidence threatens many coastal areas. Quantifying current and predicting future subsidence are essential to sustain the viability of these areas with respect to rising sea levels. Despite its scale and severity, methods to quantify subsidence are scarce. In peat‐rich subsidence hot spots, subsidence is often caused by peat compression. We introduce the standard Cone Penetration Test (CPT) as a technique to quantify subsidence due to compression of peat. In a test in the Holland coastal plain, the Netherlands, we found a strong relationship between thickness reduction of peat and cone resistance, due to an increase in peat stiffness after compression. We use these results to quantify subsidence of peat in subsiding areas of Sacramento‐San Joaquin delta and Kalimantan, and found values corresponding with previously made observations. These results open the door for CPT as a new method to document past and predict future subsidence due to peat compression over large areas.

ESTIMATION OF RANDOM FIELD CHARACTERISTIC PARAMETERS OF SOIL LAYERS AT TIANJIN PORT

The environment and conditions for both natural and artificial soilsat different places are similar. Therefore physical and mechanical properties of soil samples are relevant. The relevance can be analyzed with random field theory. To estimate spatial characteristics of physical and mechanical properties of soil in Tianjin Port, tests such as boring in situ and standard cone penetration are employed to acquire enough test data that are essential to the employment of random field theory. Because it can continuously obtain enough data, the standard cone penetration test is the main method to get test data. The data is used to inspect the stationary and ergodicity of this area. Results show that the random field model put up by Vanmarcke can be employed in this research. In this paper, the innovation points include that the method establishing random field model in Tianjin Port is discussed and the characteristic parameters of typical layers in this area are estimated with the improved non-correlation method. The result can lay a solid foundation for reliability analysis in geotechnical engineering in Tianjin Port. This method of estimating characteristic parameters of random field can be used for other areas.

Comparison of Liquid Limit of Soils Resulted from Casagrande Test and Modificated Cone Penetrometer Methodology

In this paper the experimental work in the field of evaluation the liquid limit is described. Two different types of soil were analyzed – loam (intermediate plasticity) and sodium bentonite (high plasticity). Two basic methods were used for the evaluation of the liquid limit – Casagrande percussion (cup) method and cone penetrometer method. Two approaches were applied to the evaluation of liquid limit based on cone penetrometer test (30°/80g cone) – standard method assuming 20mm penetration at liquid limit and new calibration line for cone penetrometer liquid limit - NCCLL (Mohajerani). Experimentally obtained calibration line assumes the influence of depth of cone penetration at liquid limit on undrained shear strength, which is not unique for all types of soils. The paper presents the comparison of results of liquid limit based on the previously mentioned methods. Presented results of laboratory tests show, that bentonite liquid limit based on the standard cone penetration test (using 20mm penetration) is significantly lower in comparison with Casagrande liquid limit. On the other hand was verified very significant consistency of Casagrande liquid limit and liquid limit based on NCCLL (evaluated depth of penetration 29mm). Obtained results indicate the need for further research in this area.

Numerical modeling of large deformations in soil structure interaction problems using FE, EFG, SPH, and MM-ALE formulations

Present design practice for soil structure interaction (SSI) problems most frequently assumes linear elastic properties of the soil and disregards geometrical nonlinearities, treating the displacements as small. However, there are numerous problems that require a more advanced approach. This paper presents an application of such numerical approaches to modeling SSI problems in the presence of large soil deformations. Simulations using Lagrangian finite element, element-free Galerkin, smoothed particle hydrodynamics (SPH), and multi-material arbitrary Lagrangian Eulerian (MM-ALE) approaches were performed for two previously conducted experimental tests: (1) large-scale steel pad penetration into silty clay with sand and (2) standard cone penetration test performed on poorly graded sand. In this paper, the usefulness and the efficiency of the methods was assessed in terms of modeling robustness and computational cost. Results show that to some extent each of the utilized methods is able to capture large deformations. However, the most robust turned out to be SPH and MM-ALE methods as the only two that were successful in simulating both experiments.

원심모형실험용 소형 콘 개발 및 콘 선단저항치 특성에 관한 연구

현장지반의 공학적 특성을 파악하기 위한 콘 관입시험(Cone Penetration Test; CPT)은 원지반의 연속적인 강도 특성을 분석하여 다양한 지반변수를 손쉽게 획득할 수 있다는 점에서 널리 활용되고 있으며, 원심모형실험에서도 널리 활용되고 있다. 본 연구에서는 원심모형실험에서 콘선단저항치를 계측할 수 있는 직경이 10 mm인 소형 콘을 개발하고 원심모형실험에서의 적용성을 평가하였다. 개발된 콘으로 4자유도 로봇을 활용하여 원심모형 가속 상태에서 콘 관입시험을 수행하였다. 이 때, 원심가속도 수준을 4회 변화시켜 다양한 유효응력상태에서 콘 관입시험을 실험을 수행하였다. 그 결과, 얕은 관입깊이의 동일한 유효응력에서 콘 선단저항치는 g-level에 영향을 받으며, 선단저항치가 임계 깊이 도달하는 깊이는 g-level과 상대밀도가 커질수록 깊어짐을 확인하였다. 또한, 각 실험에서 임계 깊이에 도달한 선단저항치와 실내실험에서 획득한 지반물성을 이용하여 기존 경험식과 비교하였다. The standard CPT(Cone Penetration Test), which can be easily performed to investigate in-situ soil engineering properties, has been widely used. CPT are also widely being utilized in centrifuge model tests. In this study, a miniature cone with 10mm diameter was developed and its applicability in the centrifuge was evaluated. The developed miniature cone was equipped with a four degree-of-freedom in-flight robot. A series of cone penetration tests was performed under four centrifuge acceleration levels. As results, the cone resistances measured at the same confining stress within shallow penetration depth were affected by the centrifugal accelerations. The critical depth was proportional to the cone diameter and relative density. Cone resistances results below the critical depth and soil parameters obtained from the laboratory tests were compared with those by previously proposed empirical relations.

The influence of pore pressure gradients in soil classification during piezocone penetration test

The standard cone penetration test (CPT) measures the resistance at the tip (qc) during constant rate of penetration as well as the friction/adhesion along the sleeve (fs). The excess porewater pressures generated as a result of the penetration can also be measured by a piezometer/transducer (u2) located immediately behind the cone (CPTU). The collected data help to identify several physical, hydraulic and mechanical properties of the soil layers. However, the main function of the test is soil classification. Classification has been done by using the qc and fs values at the early stages to be followed by incorporating the concept of soil behaviour type index Ic. Soil behaviour type (SBT) index calculates Ic and is generally calculated by normalised values of tip resistance and sleeve friction: Q and F, respectively. The porewater pressure component in the relationship is accounted for by the coefficient Bq. A clear distinction between the soil classes cannot be made due to limited coverage of the parameters employed. A new parameter “i” which contributes significantly to the classification process by the use of varying porewater pressure values Δuw by depth is introduced in this paper to improve the value of Ic in the classification procedure.

Scale Effects and Field Applications for Continuous Intrusion Miniature Cone Penetrometer

콘관입시험은 현장조사 시험법으로 사용 빈도가 증가되고 있다. 그러나 콘관입시험은 콘크기와 용량 등에 따라 적용 가능한 현장조건이 제한되는 단점이 있다. 소형콘의 감소된 단면적은 시스템 용량을 증대시켜 적용성을 향상시킬 수 있으며, 코일식 롯드를 이용한 연속관입 시스템은 신속하고 경제적인 지반조사를 가능하게 한다. 본 연구에서는 국내 여러 현장에서 연속관입형 소형콘관입시험 시스템의 성능을 표준 콘관입시험 시스템과의 비교시험을 통하여 평가하였다. 소형콘관입시험 장비는 기존의 표준콘관입시험 장비와 비교하여 지반정수 도출 및 지반분류에 동일한 성능을 발휘하는 것을 확인하였으며, 장비의 기동성 및 적용대상 토질 확대 등의 장점을 나타내는 것으로 평가되었다. 크기효과 검증을 위한 현장시험 결과 기존 시험 방법에 비해 콘저항력의 경우는 약 10% 과대평가하는 것으로 나타났다. 차량 형태의 조사장비는 표층이 연약하거나 진입이 어려운 경우에는 조사의 한계가 있으므로, 궤도장치에 탑재된 연속관입형 소형콘관입시험 시스템으로 개선하여 적용성을 확대시켰다. 따라서 개선된 연속관입형 소형콘관입시험 시스템은 연약지반 심도탐지 및 흙분류시 경제적이고 신뢰성 높은 지반조사 방법으로 활용할 수 있다. Cone penetration tests (CPTs) have been increasingly used for site characterizations. However, the site investigations using CPTs are often limited due to soil conditions depending on the cone size and capacity of the CPT system. The small sectional area of a miniature cone improves the applicability of the CPT system due to the increased capacity of the CPT system. A continuous intrusion system using a coiled rod allows fast and cost effective site investigation. In this study, the performance of the continuous intrusion miniature cone penetration test (CIMCPT) system has been evaluated by comparison tests with the standard CPT system at several construction sites in Korea. The results show that the CIMCPT system has a same performance with the CPT system and has advantages on the mobility and applicability. According to field verification tests for scale effect evaluation, the cone tip resistance evaluated by CIMCPT overestimates by 10% comparing to standard CPTs. A crawler mounted with the CIMCPT system has been implemented to improve accessibility to soft ground, and has shown improvement over the truck type CIMCPT system. Therefore, the improved CIMCPT system can be utilized as a cost effective and highly reliable soil investigation methodology to detect the depth of soft ground and to evaluate soil classification.

Waveform Inversion for One-Dimensional Near-Surface Structure in the New Madrid Seismic Zone

Waveform inversion is applied to P and S waveforms selected from microearthquakes of duration magnitude ( M d ) between 1.8 and 2.4 recorded at station PARM in Stahl Farm, Missouri, operated by the Cooperative New Madrid Seismic Network in the upper Mississippi Embayment to resolve the one-dimensional (1D) velocity structure of uppermost near-surface soils. Constrained by vertical seismic profiling (VSP) and standard cone penetration test (SCPT) data at nearby sites, we begin by defining a gradient velocity structure in the soils. A reference velocity model is constructed by grid search in which the observed P and P S wave shapes, ![Graphic][1] travel time, and P / P S amplitude ratio are the controlling factors in the systematic selection from among 136,000 models. A waveform inverse scheme is then implemented to obtain the least spectral misfit and best waveform correlation between synthetic and observed data. Four simultaneous inversions of joint waveforms from P and S wave types are performed. Resolved four 1D final models with associated uncertainties are listed in this article. The uppermost 7 m of near-surface soil exhibit very low velocities, through which V P and V S are in the ranges of 140 m/s to 470 m/s and 95 m/s to 215 m/s, respectively. This noninvasive technique demonstrates that the observed high-frequency reverberations (1–17 Hz) of P , S , and P S waveforms from local microearthquakes can be utilized to provide a view of the near-surface soil structure. Although there are trade-offs between layer thickness and slowness, this method explains much of the high-frequency site response due to microearthquake wave propagation through the very low-velocity, near-surface soils. [1]: /embed/inline-graphic-1.gif

CPT-Based Evaluation of Liquefaction and Lateral Spreading in Centrifuge

Two series of centrifuge model tests were conducted using Nevada sand. Four saturated models placed in a mildly inclined laminar box and simulating a 6-m-thick deposit were shaken inducing liquefaction effects and lateral spreading. The sand was deposited at a relative density, Dr =45 or 75%; two of the 45% models were subjected to overconsolidation or preshaking. The second series involved in-flight measurements of static cone tip penetration resistance, qc , simulating the standard cone penetration test (CPT) 36-mm cone. Values of qc increased with Dr , overconsolidation, and preshaking. A normalized resistance, qc1N , was assigned to each of the four liquefaction/lateral spreading models. Increases in Dr , overconsolidation, and preshaking decreased liquefaction and ground deformation, but relative density alone captured these effects rather poorly. Conversely, qc1N predicted extremely well the liquefaction and lateral spreading response of the four models, confirming Seed’s hypothesis to explain the s...

Hydraulic Conductivity Measurement from On-the-Fly uCPT Sounding and from VisCPT

Detailed profiles of hydraulic conductivity are recovered from the deployment of direct-push permeameters at the Geohydrologic Experimental and Monitoring Site, Kansas. Measurements with thin tapered tips, and with standard cone penetration test (uCPT) tips, show only minor differences, suggesting that tip-local disturbance effects are small, and that routine uCPT measurements are therefore representative of pristine conditions. Permeameter measurements are correlated against closely deployed uCPT measurements, estimates of hydraulic conductivity from uCPT sounding correlations, and from grain size correlations derived from both vision CPT (VisCPT) and from cone metrics. On-the-fly evaluations of hydraulic conductivity require that the tip-local pressure field is both steady and partially drained. Continuous penetration is shown to yield pore pressures sufficiently close to steady to enable conductivities to be directly determined. Cone metrics of cone resistance, sleeve friction, and pore pressure ratio are shown to be sufficient to discriminate between partially drained and undrained behavior, and therefore to define the permissible regime where conductivities may be determined from uCPT sounding data. Estimates of hydraulic conductivities from uCPT sounding data are shown to correlate with independently measured magnitudes of hydraulic conductivity recovered using the permeameter tests. However, most of hydraulic conductivities from the permeameter tests (4.5 cm length screen) are underpredicted, suggesting that storage effects, the inability to reach a steady state, or the effects of dilation may influence the response. Profiles of hydraulic conductivities evaluated from the on-the-fly method also correlate well with the permeameter measurements. Predictions from soil classification and from VisCPT methods are also capable of estimating conductivities, with soil classifications giving the closest correlations of these two for this particular suite of data.