Calibration Chamber Tests Research Articles

Effect of Penetration Rate on Cone Penetration Resistance in Saturated Clayey Soils

In this paper, the effects of penetration rate on cone resistance in saturated clayey soils are investigated. Shear strength rate effects in clayey soils are related to two physical processes: the increase of shear strength with increasing rate of loading and the increase of shear strength as the process transitions from undrained to drained. Special focus is placed on this second effect. Cone penetration tests were performed at various penetration rates both in the field and in a calibration chamber, and the resulting data were analyzed. The field cone penetration tests were performed at two test sites with fairly homogeneous clayey silt and silty clay layers located below the groundwater table. Additionally, tests with both cone and flat-tip penetrometers in sand-clay mixtures were performed in a calibration chamber to investigate the change in drainage conditions from undrained to partially drained and from partially drained to fully drained. A series of flexible-wall permeameter tests were conducted in the laboratory for various clayey sand mixtures prepared at various mixing ratios in order to obtain values of the coefficient of consolidation, which is required to estimate the penetration rates below which penetration is drained and above which penetration is undrained. A correlation between cone resistance and drainage conditions was established based on the results of the calibration chamber and field penetration tests.

Interpretation of the seismic cone test in granular soils

This paper presents a simple theoretical approach to the interpretation of the seismic cone test in granular soils. In particular it is demonstrated that there is a theoretical justification for using the ratio of elastic stiffness (estimated from the measured shear wave velocity) to the cone resistance to derive fundamental mechanical soil properties. Using the cavity expansion-based correlation for cone resistance and a well-established correlation between the elastic stiffness and soil void ratio and stress level, theoretical correlations are established between the ratio of elastic stiffness to cone resistance and in situ state parameter and soil friction angle. Application to data obtained from field, calibration chamber and centrifuge tests in various granular soils generally confirms the validity of the proposed theoretical approach. Scatter in predicted values is significant, and further validation is required.

Evaluation of relative density profiles of sand fill at a reclaimed site

The determination of relative density is an important part of site characterization for reclaimed sand fill. In practice, a direct determination of the relative density profile is not always possible, and very often one has to resort to indirect methods using in situ tests, such as the cone penetration test. The usefulness of the indirect method is strongly affected by the validity of available correlations. This investigation compares relative density profiles of reclaimed sand fill created from a marine sand by two distinctively different placement methods at the Changi East reclamation site in Singapore as obtained using both the direct and indirect methods. For reclaimed fill, the relative density profile is found to be predominantly influenced by the method of sand placement, although the basic characteristics of the sand also have an effect. Existing correlations developed in calibration chamber tests for indirect evaluation of relative density from the cone resistance in silicate sand are found to provide a slight underestimate of the relative density in direct-dumped fill in Changi, mainly because of the high compressibility of the marine sand. On the other hand, inadequate consideration of overconsolidation and variation in particle size from the specific placement process have led to an overestimate of the relative density in hydraulically placed sand fill in Changi using similarly derived correlations.Key words: in situ density, relative density, sand, land reclamation, cone penetration test, sand placement.

Energy Efficiency for Standard Penetration Tests

The need for standardization of the measured blow count number Nspt into a normalized reference energy value is now fully recognized. The present paper extends the existing theoretical approach using the wave propagation theory as framework and introduces an analysis for large displacements enabling the influence of rod length in the measured Nspt values to be quantified. The study is based on both calibration chamber and field tests. Energy measurements are monitored in two different positions: below the anvil and above the sampler. Both experimental and numerical results demonstrate that whereas the energy delivered into the rod stem is expressed as a ratio of the theoretical free-fall energy of the hammer, the effective sampler energy is a function of the hammer height of fall, sampler permanent penetration, and weight of both hammer and rods. Influence of rod length is twofold and produces opposite effects: wave energy losses increase with increasing rod length and in a long rod composition the gain in potential energy from rod weight is significant and may partially compensate measured energy losses. Based on this revised approach, an analytical solution is proposed to calculate the energy delivered to the sampler and efficiency coefficients are suggested to account for energy losses during the energy transference process.

Finite-Element Analysis of Inclined Piezocone Penetration Test in Clays

A three-dimensional finite-element analysis was performed to analyze the effect of soil anisotropy on the inclined piezocone penetration test in normally consolidated clay. The piezocone penetration was numerically simulated based on a large strain formulation using the commercial finite-element code ABAQUS, and the anisotropic modified cam clay model (AMCCM) was chosen and implemented into ABAQUS through the user subroutine UMAT. For verification purposes, numerical simulations were first performed on previously conducted calibration chamber tests, and the predicted results were compared with the measured values. For different initial stress conditions and different penetration angles, the cone tip resistance profile; excess pore pressure profile at the cone tip; typical stress, strain and excess pore pressure distributions around the cone; and excess pore pressure dissipation at the cone tip are provided. This study shows that when the initial stress state is anisotropic, the soil behavior is different under different angles of penetration.

Cone tip resistance in sand: modeling, verification, and applications

A numerical modeling procedure is presented to evaluate cone tip resistance in sand. The procedure involves a moving boundary simulating cone penetration. The soil is modeled as a Mohr–Coulomb elastic–plastic material with stress-dependent parameters. The procedure is verified by comparing predicted numerical values of cone tip resistance with published experimental measurements from calibration chamber tests. The selected database consists of 59 calibration chamber tests on Ticino sand with different relative densities, overconsolidation ratios, stresses, and boundary conditions. Several applications of the modeling procedure are also presented. The computer program FLAC is used to carry out the analysis.Key words: cone tip resistance, numerical modeling, sand, calibration chamber, Mohr-Coulomb, in situ horizontal stress.

Pore pressure response of saturated soils around a penetrating object

It is known that the excess pore pressure response of saturated soils around a penetrating object varies depending on the location of the pore pressure measuring point. In this work, the pore pressure response of soils measured during the penetration test is analyzed by the finite element analysis based on the coupled theory of mixtures. It is also experimentally investigated using the Louisiana State University calibration chamber test. From this study, it is found that the pore pressure distribution along a penetration object is higher at the face and lower at the shaft. This phenomenon is typically believed to be due to two different mechanisms of excess pore pressure generation. The first is the shear induced pore water pressure and the second is the compression induced pore water pressure. It is shown that the interaction and accompanying dissipation of the shear-induced pore pressure and compression-induced pore pressure play a major role for the excess pore pressure response at the shaft of the penetrating object.

Displacement and strain paths during plane-strain model pile installation in sand

The underlying mechanisms governing the behaviour of displacement piles in sand are not well understood, leading to unreliability in design methods. A series of plane-strain calibration chamber tests has been conducted in order to quantify the penetration mechanism around the pile tip, and the response of the interface layer adjacent to the shaft during further penetration. A series of eight tests is reported, examining the influence of soil type, initial state, pile breadth and the use of a driving shoe. A novel image-based deformation measurement technique has been used to observe the displacement and strain paths, which are found to be relatively independent of soil type. The measured strain paths are similar to predictions made by the strain path method, and contrast sharply with assumptions implicit in cavity expansion solutions. An interface zone adjacent to the pile shaft comprising fine broken soil particles was observed to contract while shearing along the pile–soil interface. This mechanism offers an explanation for the degradation of shaft friction at a given soil horizon with increased pile penetration (‘friction fatigue’), and a subsequent recovery of capacity over time (‘set-up’).

Effect of Pile Installation Method on Pipe Pile Behavior in Sands

Open-ended pipe piles are often used for the foundations of both land and offshore structures because of their relatively low driving resistance. In this study, calibration chamber tests were conducted on model pipe piles installed in sands with different soil conditions in order to investigate the effects of the pile installation method on penetration parameters and bearing capacity. Results of the test program showed that both the hammer blow count necessary to install the piles and the incremental filling ratio (IFR), which is used to indicate the degree of soil plugging in open-ended piles, decreased (1) with increasing hammer weight for the same driving energy, and (2) with increasing hammer weight at the same fall height. The base and shaft load capacities of the piles were observed to increase (1) with increasing hammer weight for the same driving energy, and (2) with increasing hammer weight for the same fall height. It was also observed that the noise level observed during pile driving decreases (1) as the driving energy decreases and (2) as the hammer weight increases for the same driving energy. Model jacked piles were also installed and tested. The jacked piles were found to have higher bearing capacities than identical driven piles under similar conditions, mostly due to the more effective development of soil plugging in jacking than in driving.

High Overburden Stress Effects in Liquefaction Analyses

A reevaluation is presented of two factors that can strongly affect the estimation of liquefaction resistance for clean sands under high effective overburden stresses (σv′): the relation used to normalize penetration resistances to a σv′ of 1 atm (i.e., CN), and the adjustment factor for the effects of σv′ on cyclic resistance ratio (i.e., Kσ). These two factors have been investigated in a number of ways and several relations exist for each of them. An improved CN relation is developed based on cone penetration theory and validation against calibration chamber test data for both cone penetration and standard penetration tests. A relative state parameter index (ξR) is shown to provide a consistent theoretical framework for interrelating the penetration and cyclic loading resistances. It is subsequently shown that the CN and Kσ relations are interrelated through the sand properties and relative density (DR) in ways that have compensating effects on the predicted cyclic resistance. The derived relations prov...

Interpretation of calibration chamber tests involving cone penetrometers in sands

Interpretation of calibration chamber tests involving cone penetrometers in sands

Interpretation of calibration chamber tests involving cone penetrometers in sands

Interpretation of calibration chamber tests involving cone penetrometers in sands

Displacement and strain paths during plane-strain model pile installation in sand

The underlying mechanisms governing the behaviour of displacement piles in sand are not well understood, leading to unreliability in design methods. A series of plane-strain calibration chamber tests has been conducted in order to quantify the penetration mechanism around the pile tip, and the response of the interface layer adjacent to the shaft during further penetration. A series of eight tests is reported, examining the influence of soil type, initial state, pile breadth and the use of a driving shoe. A novel image-based deformation measurement technique has been used to observe the displacement and strain paths, which are found to be relatively independent of soil type. The measured strain paths are similar to predictions made by the strain path method, and contrast sharply with assumptions implicit in cavity expansion solutions. An interface zone adjacent to the pile shaft comprising fine broken soil particles was observed to contract while shearing along the pile–soil interface. This mechanism offers an explanation for the degradation of shaft friction at a given soil horizon with increased pile penetration (‘friction fatigue’), and a subsequent recovery of capacity over time (‘set-up’).

Influence of placement method on the cone penetration resistance of hydraulically placed sand fills

The reclamation for the new airport at Chek Lap Kok in Hong Kong included the placement of a substantial volume of sand fill by various hydraulic placement techniques, which resulted in a wide range of as-placed densities of the sand fill. This paper described the use of cone penetration tests (CPT) on the evaluation of the possible ranges of density achievable by various hydraulic placement methods adopted in the construction of the new airport. The results of the CPT indicated that the placement technique is one of the most important factors in controlling the as-placed density of hydraulically placed sand fill. There is a marked contrast in cone tip resistance (and the associated relative density) profiles for the sand fills formed by subaerial and subaqueous placement methods, in which the cone tip resistance of the sand fill formed by subaerial placement is substantially higher than that of the sand fill formed by subaequeous placement. The results confirm that dense sand fill cannot be formed by subaqueous placement methods. The weakest zone is generally located just beneath the water level where fill is placed by subaqueous discharge.Key words: sand, hydraulic fill, cone penetration test, calibration chamber test, in situ density.

Analysis of calibration chamber plate load tests

The estimation of base resistance is a key step in the design of piles embedded in moderately dense to dense sand. Calibration chamber plate load tests are sometimes used to investigate the base load - settlement relationship of nondisplacement piles in sand. In such tests, the sand specimens are carefully prepared to simulate the installation of nondisplacement piles. In this paper, calibration chamber tests are analyzed using the finite element method; experimental and numerical results are compared. The finite element models are axisymmetric and use a nonlinear, elastic-plastic constitutive model. Plate resistance values predicted using the finite element analysis are shown to be in good agreement with measured values, which validates the proposed numerical model. Questions regarding the existence of calibration chamber size effects have not, to this date, been adequately addressed. Finite element analyses of both pile base resistance and plate resistance for sands with various relative densities and stress states show that size effects are usually small for settlement levels of interest in practice. This suggests that the use of calibration chambers in pile base capacity studies is justified.Key words: calibration chambers, plate load tests, constitutive modeling, size effects, piles, sands.

Undrained shear strength of clean sands to trigger flow liquefaction

This paper attempts to evaluate the undrained shear strength of sand during flow failures, based on both laboratory testing and field observations. In the laboratory, the minimum shear resistance during monotonic loading was taken as the undrained strength, based on the criterion of stability. Triaxial compression, triaxial extension, and simple shear test data on clean sand were examined and it was revealed that the undrained shear strength ratio could be related to the relative density of the material provided that the initial stress, piprime, was less than 500 kPa. Three previous flow failures involving sand layers with relatively low fines contents and reliable cone penetration test (CPT) data were studied. Using existing calibration chamber test results, the Toyoura sand specimen densities in the laboratory tests were converted to equivalent values of CPT penetration resistance. The undrained shear strengths measured in the laboratory for Toyoura sand were compared with those from the case studies. It was found that the behaviour of sand in simple shear in the laboratory was consistent with the field performance observations. Triaxial compression tests overestimated the undrained strengths, and triaxial extension tests underestimated the undrained strengths. From both the simple shear test result and the CPT field data, the threshold value of clean sand equivalent cone resistance for flow failure was detected. Based on these observations, a CPT-based guideline for evaluating the potential for flow failure of a clean sand deposit is proposed. Key words: liquefaction, flow, laboratory testing, in situ test, case histories.

Effects of Placement Method on Geotechnical Behavior of Hydraulic Fill Sands

Recently, large port and airport projects, together with other governmental and private projects in Hong Kong, required the use of large quantities of hydraulically placed marine sand fill. Concerns emerged among engineers about the effects of dynamic or transient loads on these fills, because the geotechnical performance of these sand fills in the past has not been observed and reported. Results of an investigation of the geotechnical behavior of a hydraulic sand placed at five land reclamation sites in Hong Kong are presented and interpreted. The study was conducted to aid in developing guidelines for quality control of hydraulic landfill placement. The work described consisted of field investigations, static and cyclic triaxial testing, and calibration chamber tests to study the cone penetration test versus relative density relationships for marine sands obtained from the reclamation sites. The results of this study clearly indicate that the placement technique is the single most important factor controlling the geotechnical behavior of a given type of sand when placed as a hydraulic fill. The weakest zone is generally located just beneath the water level where fill deposition is placed by pipeline discharge.

Calibration Chamber Size Effects on Penetration Resistance in Sand

Calibration chamber tests provide an effective way to study cone penetration resistance in sands under controlled conditions. Calibration chamber tests are performed in large soil samples with known densities, consolidated to desired stresses, and subjected to known boundary conditions. Results from calibration chamber tests can be used to establish the relationship between cone resistance, soil density, and stress state. However, the penetration resistance measured in a calibration chamber differs from that measured in the free field because of chamber size and boundary condition effects. There has been considerable uncertainty about these effects, precluding use of the results of calibration chamber research with greater confidence. In this paper, a penetration resistance theory recently developed is used to quantify chamber size effect, to investigate the factors it depends on, and to show how to correct calibration chamber test penetration resistance values to free-field conditions. The theoretical results are compared with available experimental results.

Characterization of Sandy Soils Using CPT and DMT

A site investigation campaign using cone penetration test (CPT) and dilatometer test (DMT) was carried out on three sandy soils of Japan. Two of these sites are natural sand deposits and the third one is a sand fill reclaimed about twenty years ago. On two sites, high quality samples were taken using the freezing sampling method so that the measured value of the relative density D r is assumed to be accurate. Seismic cone tests were also performed in order to measure the shear modulus at a very small strain level in the order of 10 –5 . Data from CPT and DMT were related to design parameters using correlations established from calibration chamber tests. The main conclusions obtained in the present study are: 1) existing soil classification methods using CPT and DMT data can be applied to the investigated sites; 2) D r values predicted from relationships linking D r to q t / ( p' v 0 ) 0.5 , where q t is the point resistance from CPT and p' v 0 is the vertical effective overburden pressure, seem to be in good agreement with actual values of D r ; 3) D r can also be well predicted using DMT horizontal stress index K D values, and 4) the ratios of the shear modulus G sc from the seismic cone to q t or E D from DMT, G sc /q t or G SC /E D decrease with increasing values of the relative density D r .

Interpretation of Model Pressuremeter Test Using Automated Clay Calibration Chamber Data

Abstract The details of an automated flexible wall calibration chamber test system developed to perform strain-controlled model pressuremeter testing in cohesive soil are presented. The procedure involved in obtaining uniform speciments by consolidating a slurry of kaolin in two stages is described. The importance of automated control (electro-pneumatic control for this study) to perform second stage K0 consolidation accurately is shown. Typical test results are presented along with the evaluation of undrained strength, initial shear modulus, stress-strain variation, limit pressure, and horizontal stress using various methods of interpretation. Unload-reload loops were performed, and the shear modulus values were compared with the deduced values from the initial loading curve. Interpreting the pressuremeter test data using the Marquardt-Levenburg algorithm is presented. The improvements to the Simplex method are identified along with the effect of the reference state. A new procedure for incorporating the unloading portion in interpreting the pressuremeter test data is developed along with the detailed comparisons.