Cone Penetration Resistance Research Articles

Compaction control and related stress–strain behaviour of off-shore land reclamations with calcareous sands

When constructing off-shore land reclamations, one aims to ensure that the final soil mass fulfills certain minimal criteria related to shear strength, stiffness and resistance against liquefaction. In general, these characteristics improve with increasing density of the soil mass, which means that the above criteria are usually condensed into a single one: ‘adequate densification’.Quality control of reclamation constructions therefore focuses on the latter. Technical requirements are written based on one single parameter: the relative density Dr. On the site, this parameter is commonly determined indirectly using correlations with the cone penetration resistance qc, making the CPT the main tool for quality control.The paper presents data gathered during the design and construction of an off-shore land reclamation using calcareous sands. For this specific project, density control had to be done through the use of CPT.Calibration chamber tests were performed to establish the CPT qc–Dr correlation for the specific soil material. This correlation was used to analyse CPT results during construction of the site in order to determine the quality of compaction.In a further stage, an elaborate laboratory study was performed to establish additional correlations between soil parameters and the stress–strain parameters. Furthermore, seismic CPT tests were executed on the site to test the relevance of the laboratory correlations and the ‘relative density approach’ in general.It is shown that off-shore land reclamations have a very erratic stress-history, due to the different processes of depositing the soil material and the various densification methods. This stress-history is of great importance in the stress–strain behaviour of the site. Results also suggest that the CPT does not provide enough data to reliably predict soil stiffness when dealing with crushable materials. Specifically, in situ measurements show that there is no direct correlation between the small strain shear modulus G0 and qc.

Microstructural study of deformation zones during cone penetration in silt at variable penetration rates

During conventional cone penetration testing in silt, the soil will normally be partially drained. If the penetration rate varies, time for drainage is altered and therefore the measured cone resistance and pore pressure will change. This paper studies the change in soil microstructure around the probe during cone penetration carried out at different penetration rates to investigate the failure mechanism and the processes controlling drainage in silt. Backscattered electron images of polished thin sections prepared from frozen samples at the end of penetration were used. Making use of advanced image-processing techniques, the statistical distribution of particle orientations and the local porosity were investigated for zones around the cone tip and shaft. The spatial distribution of the measured microscale parameters in the region near the probe indicates that the soil deformation during a piezometric cone penetration test (CPTU) in silt leads to the formation of both contractive and dilative zones. The macro response of the material, presented by the pore pressure and cone penetration resistance measured during the test, results from the competition between these zones during penetration, which is shown to be dependent on the penetration rate.

Discrete element modelling and cavity expansion analysis of cone penetration testing

This paper uses the discrete element method (DEM) in three dimensions to simulate cone penetration testing (CPT) of granular materials in a calibration chamber. Several researchers have used different numerical techniques such as strain path methods and finite element methods to study CPT problems. The DEM is a useful alternative tool for studying cone penetration problems because of its ability to provide micro mechanical insight into the behaviour of granular materials and cone penetration resistance. A 30° chamber segment and a particle refinement method were used for the simulations. Giving constant mass to each particle in the sample was found to reduce computational time significantly, without significantly affecting tip resistance. The effects of initial sample conditions and particle friction coefficient on tip resistance are investigated and found to have an important effect on the tip resistance. Biaxial test simulations using DEM are conducted to obtain the basic granular material properties for obtaining CPT analytical solutions based on continuum mechanics. Macro properties of the samples for different input micro parameters are presented and used to obtain the analytical CPT results. Comparison between the numerical simulations and analytical solutions show good agreement.

Interpretation of cone resistance and pore-water pressure in clay with a modified spherical cavity expansion solution

A theoretical approach to interpreting the cone penetration resistance and the pore-water pressure measured on the face of the cone during piezocone tests of clays is proposed. The mechanism for the penetration of the piezocone is assumed to be spherical cavity expansion in modified Cam clay critical-state soil. Using large strain theory, the spherical cavity expansion problem is reduced to solving a system of first-order ordinary differential equations for effective stresses in the plastic zone. By taking the normal and shear stresses acting on the cone face to be the ultimate cavity expansion pressure and the effective friction at the cone–soil interface, respectively, the cone resistance was evaluated at force equilibrium. The pore-water pressures induced by cone penetration include components caused by changes in normal and shear stresses, for which the normal term can be predicted by integrating the radial equilibrium equation in terms of total stress. As it is based on an exact constitutive relationship, the present method takes more factors (such as the effects of interface shear and the traditional overconsolidation ratio) into account than other methods of tackling this problem. Comparisons between the predicted and measured values of cone resistance and pore-water pressure at different well-documented sites are in good agreement for most relatively homogeneous low- and medium-sensitivity clay sites.

地震履歴が砂の液状化強度およびコーン貫入抵抗に及ぼす影響に関する動的遠心模型実験

東北地方太平洋沖地震では、若齢の人工造成地盤に液状化被害が多く発生した。これは、堆積・造成年代の異なる地盤における液状化強度の「年代効果」が影響を及ぼした結果であると考えられている。砂の年代効果に関する具体的な作用としては様々なものが考えられるが、本研究では地震履歴に着目した動的遠心模型実験を行った。数多くの地震履歴を与えたケースと地震履歴を与えていないケースの過剰間隙水圧等の変化を分析・比較することにより、地震履歴が液状化強度に及ぼす影響を検討した。実験結果は地震履歴と液状化強度比の関係に加えて、液状化強度比と相対密度、コーン貫入抵抗の関係にも着目して整理した。その結果、地震履歴を受けることで砂の液状化強度が顕著に上昇する傾向と、コーン貫入抵抗とS波速度は砂の相対密度の違いとよく対応する傾向が認められたものの、地震履歴による液状化強度の上昇傾向はコーン貫入抵抗およびS波速度に表れにくいことを明らかにした。

Effect of synthetic and natural water absorbing soil amendment soil physical properties under potato production in a semi-arid region

Effect of synthetic and natural water absorbing soil amendments on soil physical properties, fresh tuber yield and size of potato production was investigated in a field experiment in a semi-arid region in northern China in 2010–2012. Treatments included two different synthetic water absorbing amendments (potassium polyacrylate-PAA, polyacrylamide-PAM) and one natural amendment (humic acid-HA), both as single amendments, and compound amendments (natural combined with a synthetic) and a no amendment control. Soil amendments had highly significant effect (P≤0.01) on soil water holding capacity, soil cone penetration resistance and soil aggregate size fractions, but had no significant effect (P>0.05) on soil bulk density. Soil amendments increased fresh tuber yield by 4.2–32.9%, increased the proportion of tuber size category 1 (>150g) and decreased size category 3 (<75g) in all the three years. The compound amendment, with PAM+HA, showed best effect of all amendment treatments on soil physical properties in potato production, and deserves further research.

The Thixotropic Hardening Behaviour of a Low Plasticity Dredged Marine Silt

An alternative to solve the problem of disposing dredged marine sediments (DMS) in open sea, which could lead to undesirable contamination and destruction of the marine ecosystem, is to reuse the material in reclamation works. For such applications, it is important to determine the time required for strength gain of the relocated DMS. A lab-based study was conducted to simulate and examine the post-consolidation hardening of DMS when placed as a backfill with relation to time. A separate series of tests were also carried out on the DMS being lightly solidified with cement, with the purpose of identifying potential shortening of the waiting period. The DMS sample was prepared at different water contents based on the soil's liquid limit (LL = 54.5 %), i.e. 0.90, 1.25 and 1.81LL. The undrained shear strength was measured using the laboratory vane shear (VS) test. Complementary fall cone (FC) tests were conducted for additional information on the improved remoulded strength and stiffness of the DMS. The results showed that the strength and stiffness (cone penetration resistance) of the relocated DMS could effectively improve with time, though the rest period required is shorter for a sample with lower initial water content. On the other and, light cementation shortened the rest period, and significantly improved the strength and stiffness at dosages as low as 5 % (as per dry weight of the soil). Overall the study gave an overview of the reusability of DMS as a backfill material in reclamation works, whether with or without lightly induced solidification, depending mainly on the limitations of rest period available.

Influence of non-/low plastic fines on cone penetration and liquefaction resistance

Uncertainties prevail at the current liquefaction screening method based on the cone penetration test (CPT) as to whether the existence of fines increases liquefaction resistance or decrease cone penetration resistance. In this study, field-based data are used to evaluate the effects of non-/low plastic fines on liquefaction resistance at the current CPT-based liquefaction assessment method. The first part of this paper examines the effects of the coefficient of consolidation or drainage characteristics of soils containing fines on cone penetration resistance. The coefficient of consolidation is influenced by the fines content and the relative density of the soil. The second part of this paper investigates the contribution of fines content less than 30% by weight on the liquefaction resistance of soils at different relative densities. Fines content over 30% by weight and/or high plasticity of fines can cause additional complications; therefore, it needs different valuation methods, which is beyond the scope of this paper. The liquefaction resistance of sands and silty sands is reinterpreted from the current CPT-based liquefaction assessment method. The trend, which presents the change of liquefaction resistance with fines content at the same relative density, is compared with the available laboratory-based data in the literature. The results show that the interpreted trend is not consistent with the laboratory-based correlations obtained by several previous researchers. Therefore, there will be probably some inaccuracies in estimation of liquefaction potential of silty sand using the current CPT-based liquefaction assessment method.

Numerical Simulation of CPT Cone Penetration in Sand

Numerical simulation of cone penetration in sand is performed by means of a computationally efficient critical state model implemented in an explicit-integration finite element code. Its main advantage, compared to other published studies employing simpler soil models such as the Drucker-Prager, is that sand compressibility can be described with a single set of model parameters, irrespective of the stress level and the sand relative density. Calibration of the constitutive model is based on back-analysis of published centrifuge tests results, and consequently the predictions of the numerical methodology are compared against independent tests. Additional analyses are performed for proposing a new simplified formula to correlate the cone penetration resistance with the in situ sand relative density.

The use of neural networks for CPT-based liquefaction screening

This study deals with development of two different artificial neural network (ANN) models: one for predicting cone penetration resistance and the other for predicting liquefaction resistance. For this purpose, cone penetration numerical simulations and cyclic triaxial tests conducted on Ottawa sand–silt mixes at different fines content were used. Results obtained from ANN models were compared with simulation and experimental results and found close to them. In addition, the performance indices such as coefficient of determination, root mean square error, mean absolute error, and variance were used to check the prediction capacity of the ANN models developed. Both ANN models have shown a high prediction performance based on the performance indices. It has been demonstrated that the ANN models developed in this study can be employed for predicting cone penetration and liquefaction resistances of sand–silt mixes quite efficiently.

In situ dynamic piezocone penetrometer tests in natural clayey soils — a reappraisal of strain-rate corrections

Cone penetration testing with pore pressure measurement (CPTU) is a cost- and time-efficient way of collecting in situ geotechnical parameters of near-surface marine soils for cable and pipeline tracks, offshore foundations, and geohazard identification. The measured dynamic CPTU parameters (cone penetration resistance, sleeve friction, pore pressure) are higher than the measured static CPTU parameters. This mismatch is caused by the different penetration rates used for dynamic and static CPTU tests (dynamic tests have up to 500 times higher penetration rates than the static tests; i.e., with the commonly used 2 cm/s penetration rate). This study presents comprehensive Calypso piston and gravity core as well as dynamic and static CPTU datasets acquired in the landslide-prone Sørfjorden area (Finneidfjord, northern Norway). The fjord-marine sediments at the study site are characterized as normally consolidated to slightly over consolidated clay-dominated soils with embedded layers of sandy silt to sand. The dynamic CPTU results were corrected to match the nearby static CPTU (i.e., distance less than 10 m) using strain-rate factors (SF) derived from three known correction methods. Based on a statistical test and visual comparison of dynamic and static CPTU profiles, the modified inverse sin-hyperbolic correction method is found to be best suited for the strain-rate correction of dynamic CPTU tests, and results in SF less than 1.35 for the corrected cone penetration resistance and up to 2.4 for the sleeve friction. Our data illustrate a positive correlation between penetration rate and penetration depth, which is governed by the consolidation state of the clays. The good agreement between SF-corrected dynamic CPTU data from 34 deployments (acquired within less than 36 h shiptime) with data obtained from static CPTU and laboratory experiments on sediment cores further demonstrates that the MARUM dynamic CPTU device is a powerful tool for characterizing the properties of surficial seafloor sediments in shallow-water environments.

Numerical simulation of cone penetration testing using a new critical state constitutive model for sand

A new perspective on the numerical simulation of cone penetration in sand is presented, based on an enhanced critical state model implemented in an explicit-integration finite element code. Its main advantage, compared to similar studies employing simpler soil models, is that sand compressibility can be described with a single set of model parameters, irrespective of the stress level and the sand relative density. Calibration is based on back-analysis of published centrifuge experiments, while results of the methodology are also compared against independent tests. Additional analyses are performed to investigate sand state effects on cone penetration resistance, in comparison with empirical expressions from the literature.

The cone penetration test in unsaturated sands

Laboratory-controlled cone penetration test results for an unsaturated sand are presented, obtained using a suction-controlled calibration chamber. The cone penetration resistances are found to increase significantly, owing to the presence of suction, when compared with those for saturated or dry states, for a given relative density and net confining stress. Increases of as much as 50% for a relative density of 0·33 and net confining stress of 50 kPa are recorded. When suction is included in the effective stress, the same semi-empirical expressions used for saturated sands are found to link penetration resistance to the relative density and effective confining stress. The expressions may also be used to back-calculate the suction changes in a soil profile when cone penetration resistances for two unsaturated states are known. It is also shown that failure to account for suction influences may lead to significant and non-conservative overestimations of relative density or peak friction angle.

Energy saving scoop type rotary tiller blade for deep tillage

The energy consumption for the land preparation is excessive during the primary and secondarytillage operations; because of the high draft force required. Many researchers were reported that thereverse rotational rotary ti lIer had an advantage for the deep ti IIing on the power req uirement comparedto the conventional rotary tiller. The reverse rotational rotary tiller can be used for deep tillage withless energy requirement. Three types of scoop type rotary tiller blades were fabricated by changingdesign parameters of the horizontal portion of the scoop surface of the blade for reverse rotational inorder to minimize the re-tillage during deep tillage achieving low power consumption. Blades withcutting angles 25°, 35 and 55° were tested with conventional blade (45° cutting angle) at 15.6% soilmoisture conditions.When compared the maximum power and the torque at maximum power, blade with angle 35° showedbest performance, while others were in the order of conventional type (45°»55°&gt;25°. In terms of soiltilth, significantly better performances were shown by the blades with angles 35° and 45° with reducingbulk density and cone penetration resistance values. Blade with angle 35° showed highest backwardthrowing distance as 660 mrn. Blade with angle 55° showed lower backward throwing distance.Blade with angle 35° performed best with lowest power consumption, higher pulverization and backwardthrowing ability and can be recommended for reverse rotation in deep tillage.

State-Based Overburden Normalization of Cone Penetration Resistance in Clean Sand

AbstractInterpretation of experimental and field cone penetration test (CPT) data from across a broad range of stress conditions requires defining the dependence of the measurements on overburden stress and other influencing factors. This paper examines three possible methods for overburden normalization of CPT tip resistance in sand at the same state parameter or same relative state parameter. The three methods for determining state-based normalized tip resistance at a reference overburden stress of 101.3 kPa (1 atm) are evaluated against calibration chamber test data for four well-studied clean sands. The CPT data from the calibration chamber tests are corrected for chamber boundary effects using two different methods to illustrate the effect this step has on derived relationships. The CPT data are further normalized to a common lateral earth pressure coefficient to illustrate the effect of this step. The three methods for state-based overburden normalization were evaluated for bias and dispersion again...

Rapid observations to guide the design of systems for long-term monitoring of a complex landslide in the Upper Lias clays of North Yorkshire, UK

The Whitby Mudstone Formation has one of the highest landslide densities in the UK with 42 landslides per 100 km 2 . Landsliding at Hollin Hill in North Yorkshire, UK is complex and continuing, and includes shallow, retrogressive rotational failure on the upper slope, translation, and flow from the base of the Whitby Mudstone Formation over the scarp slope of the Staithes Sandstone Formation. Surface observations augmented by information relating to lithological, moisture and strength variation with depth allowed rapid initial interpretation of the masses affected by movement. These were provided by a single person operating portable probes providing depth logs of cone penetration resistance and soil moisture based upon dielectric property measurements in conjunction with a sampling auger. The gathered information was used to guide the design of further invasive site investigation and the configuration of permanent systems to monitor changes in dynamic moisture distribution and direct movement. At Hollin Hill, the near-surface materials in the upper 5 m interval are distinctly weathered or destructured, predominantly comprising silty clay in the Whitby Mudstone Formation, and fine silty, clayey sand and silty clay in the Staithes Sandstone Formation. Direct and secondary evidence was observed showing high moisture variation to be related to narrow intervals within the upper 5 m. Cyclic variation in moisture has played a key role in the movement and break-up of sliding materials, especially within the prograding lobes resulting from flow over the Staithes Sandstone Formation. Since these observations, permanent monitoring systems have been installed, including electrical resistivity tomography (ERT) arrays, which have successfully mapped the distribution of the Whitby Mudstone and the Staithes Sandstone, but will also be used in time lapse mode to image the near-surface moisture movement driving the landsliding processes. ERT array installations included a large area, low spatial resolution grid designed to investigate the potential coupling between the upper and lower slope hydrogeological processes and a small area, high spatial resolution grid designed to investigate the hydrogeological processes driving the earth flow.

Experimental study, numerical modeling of and axial prediction approach to base grouted drilled shafts in cohesionless soils

The pressure grouting of drilled shaft tips has become popular worldwide due to its effectiveness in mobilizing a larger portion of the available tip resistance under service displacements. This paper presents experimental and numerical studies on the load transfer mechanism and factors controlling the axial response of base grouted drilled shafts in cohesionless soils. The study found that the increased axial capacity of grout-tipped drilled shafts under service loads and displacements depended mainly on preloading effects and the increased tip area provided by the grouting process. A simple prediction approach for estimating the tip capacity of grouted shafts utilizing cone penetration resistance was suggested based on the results of the study. The validity of the proposed approach was verified by the analysis of full-scale case studies of grouted shafts reported in the literature.

Shallow tillage effects on soil properties for temperate-region hard-setting soils

Shallow tillage (ST; typically <10cm) has a considerable impact on soil physical properties and hence modifies significantly the conditions for root growth and soil biotic activity as compared to mouldboard ploughing (MP; typically ∼25cm). At field capacity in the spring, we measured cone penetration resistance (PR) of the top 40cm soil and sampled intact soil cores (at 0–4 and 14–18cm depths) in 11 field experiments (4–23% clay) after continued ST and MP management for mostly 4–8 years (two experiments >30 years). Bulk soil was sampled from 0 to ∼20cm of the MP soil and from the two layers above (‘ST-upper’) and below (‘ST-lower’) ST primary tillage depth. Soil organic carbon (SOC), water content, bulk density, air-filled pore space (ɛa) and air permeability (ka) at the field-sampled water content were determined. ST increased SOC concentration in the ST-upper soil when compared to MP, whereas no difference between ST and MP was found for the ST-lower soil. When based on equivalent soil masses, the quantity of SOC did not differ between ST and MP. Bulk density and PR of the ST-lower soil were higher than at the same depth of MP soil. PR was generally close to or exceeded the often quoted 1.5MPa critical limit for root growth. Across the 11 field experiments, the untilled ST soil at 14–18cm generally had lower ɛa and ka than the mechanically loosened soil at the same depth for MP. Also the specific air permeability (pore organization=ka/ɛa) was lower for ST than for MP. SOC turned out to be a dominating driver of bulk density across the soils studied. Our results indicate that relatively sandy soils low in SOC display hard-setting behaviour and are little suitable for ST. Our study also identified a pedotransfer function enabling prediction of PR for the upper B-horizon soil at a water content of field capacity for soils with the same geological origin as in this study.

Comparative study of the impact of two mechanical perforation densities on the behavior of a sandy soil

The effects of mechanical perforation densities by extracting soil cores through an aerator Vertidrain with a working width of 1.6 m and equipped with hollow tines spaced of 65 mm, were studied on a sandy soil of a grassy sward in the Golf Course El Kantaoui in Sousse (Tunisia). The mechanical aeration was performed at two densities: 250 and 350 holes/m2. The cone penetration resistance and soil water infiltration were measured. These parameters were performed at initial state before aeration (E0) and then on the 10th, 20th and 30th day after aeration. These results showed that perforation density of 350 holes/m2 had a positive effect on the soil by reducing its cone resistance to penetration compared to the initial state (Rp = 14.8 daN/cm2). At 5 cm depth the decrease in resistance to penetration was 34% and 43% on the 10th and 20th day after aeration, respectively. However, on the 30th day after aeration the soil resistance to penetration tended to grow and its value compared to the initial state decreased only by 21 and 26%, respectively, at 5 and 15 cm of depth only by 10% and 9% with 250 holes/m2 density. The soil water infiltration made a good improvement after aeration compared to the initial state. This parameter increased from 4.8 cm/h to 8.3, 10.9 and 13.1 cm/h with 250 holes/m2 density and to 10, 12.9 and 14.8 cm/h with 350 holes/m2 density on the 10th, 20th and 30th day following the aeration.

Field measurements regarding the influence of the installation method on soil plugging in tubular piles

Soil plugging in open-ended piles leads to an increase in compressive bearing capacity but also influences pile driving resistance. Many different factors affect the tendency for soil plugging, for example, pile diameter, penetration depth and installation method. In this paper, the influence of the installation method on soil plugging is investigated. In situ measurements during the installation of two instrumented tubular piles are carried out to investigate the internal and external stresses acting on the pile during the installation process. Furthermore, the cone penetration resistance inside one pile is measured during the installation, and the accelerations and strains at the pile head are monitored to predict the bearing capacity. The installation method is varied between vibratory and impact pile driving. The results show that a significant increase in horizontal stresses inside the pile occurs during impact driving which leads to the conclusion that a soil plug is formed. During vibratory pile driving, no stress increase was observed.