Numerical simulation of 220Rn activity concentration distributions in calibration chambers

The most widely used in situ testing instrument for tailings storage facility (TSF) is the cone penetration test (CPT), which uses calibration chamber (CC) test data as the preferred method to correlate the soil's state with the CPT acquired data. Many, if not most, mine tailings are different from the soils historically used in CC studies (mainly sands). Moreover, these tests were conducted at denser states than typically found in TSFs. Additionally, CC tests cannot practically be performed for every new soil-specific project. For these reasons, practitioners usually perform numerical simulations to approximate these correlations. One of the most popular techniques for this is the spherical cavity expansion approach. This study compares novel small CC testing of two different silty mine tailings, and their respective spherical cavity expansion simulations. Since these simulations use the NorSand constitutive model, this study also presents the calibration process that includes the triaxial laboratory testing to calibrate the NorSand properties, and the corresponding iterative process to infer the additional plastic and elastic parameters of the model. Finally, an adjustment equation is introduced for the contractive state of these silty materials.

In this study, laboratory Cone Penetration Tests (CPTs) were conducted in the MARUM Calibration Chamber (MARCC) with three lateral boundary conditions: (BC), constant stress, constant strain and the simulated field conditions with constant stiffness. Cuxhaven-Sand was studied in the chamber tests and tip resistance-relative density (qc − Dr ) relationships were generated for each BC. Laboratory experiments were carried out to estimate the mechanical properties of the Cuxhaven-Sand. Multiple numerical analysis have then been undertaken to simulate the calibration chamber results. First, the soil model was calibrated against laboratory soil parameters and a CPT result of the calibration chamber with fixed lateral boundaries, then, a numerical penetration analysis in an infinite soil mass was performed to evaluate the implemented constant stiffness boundary condition in the chamber. Good agreement between experimental and numerical cone resistances demonstrates the possibility of using the advanced small volume MARCC for producing controlled CPT results applicable in true field test conditions.

A walk-in type 222Rn calibration chamber (~ 22 m3) is established at the Centre for Advanced Research in Environmental Radioactivity (CARER), Mangalore University, India which is being used by research groups working on 222Rn in India and other countries as well. In recent times, computational fluid dynamics (CFD) technique is opted as an alternative approach for the prediction of 222Rn concentration profile in the closed domain. CFD simulations were carried out to study the transient build-up and spatial behavior of 222Rn concentration in the calibration chamber. Measurements were performed using active 222Rn measuring devices and results of the CFD predictions and direct measurements were compared. A good agreement was observed between the simulated and experimental results with deviation between the two entities being ~ 3% in the case of transient build up and ~ 8% in the case of spatial distribution of 222Rn concentration.

At the Centre for Metrology MIKES of VTT Technical Research Centre of Finland (VTT MIKES), we have been developing a humidity calibration apparatus for radiosondes within an EMRP Project Metrology for Essential Climate Variables. The minimum air temperature and absolute humidity are $$-80\,^{\circ }\hbox {C}$$ and 2.576 $$\times $$ $$10^{-4} \,\hbox {g}\cdot \hbox {m}^{-3}$$ (corresponding the dew-point temperature $$-90\,^{\circ }\hbox {C}$$ ), respectively. Recent developments for the apparatus extend its pressure operation range down to 7 hPa (abs). When operating in such dry conditions, the efficiency in calibration is highly limited by the time of humidity stabilization in a measurement chamber: Because the water vapor pressure is very low, the adsorption and desorption of water molecules at the chamber walls have a significant effect on the spatial and temporal humidity differences in the chamber. Inhomogeneity in humidity field inside the calibration chamber increases calibration uncertainty. In order to understand how varying parameters such as pressure, temperature, inflow speed and geometry of chamber effect on stabilization time of humidity field, computational fluid dynamics simulations were developed using Comsol software. Velocity and pressure of fluid, water vapor diffusion, temperature as well as adsorption/desorption of water molecules on the chamber walls were included in the simulations. Adsorption and desorption constants for water on the measurement chamber wall were determined experimentally. The results show that the flow speed and the surface area are the dominant parameters affecting the stabilization time of a calibration chamber. It was also discovered that more homogenous water vapor concentration field is obtained at low pressures.

Cone penetrometer tests (CPTs) are used to characterize soil for a variety of geotechnical engineering applications, including earthquake-induced liquefaction triggering assessment. Numerical modeling of CPTs is frequently used to better understand soil behavior, soil-penetrometer interaction, and engineering estimates made from CPT data. However, calibrating and validating numerical CPT simulations with experimental calibration chamber (CC) data can be challenging. Specifically, uncertainties in the interpretation of laboratory strength and compression data compound with uncertainties in the CC testing and the assumptions made when developing the numerical model. This article provides a comprehensive review of uncertainties in the calibration and validation of CPT numerical simulations performed in homogenous sand, homogenous clay, and layered sand-clay soil profiles, comparing numerical results with well-documented experimental calibration chamber tests performed at Deltares. In particular, the Material Point Method (MPM) is used to perform the numerical analyses. A framework is presented to assess how uncertainty in the numerical model output is attributed to each input parameter. It is demonstrated that uncertainties can be explored numerically. Finally, recommendations for future experimental and numerical studies of CPTs are provided.

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Physical modelling of piles has been recognised as an effective tool to investigate the soil–pile interaction phenomenon. To conduct physical modelling tests on piles, different apparatuses such as calibration chambers, geotechnical centrifuges or frustum confining vessels (FCVs) could be employed. This study was designed to introduce the largest modified FCV ever built. To do this, the effects of boundary conditions, size of the apparatus and the bottom pressure on the FCV performance were examined using numerical and experimental approaches. The optimised dimensions of the FCV were determined using numerical simulations; then the modified FCV was built accordingly. The experimental stress distributions along the centreline of the apparatus showed a good agreement with the numerical results. Finally, the ability of the FCV testing method to predict the behaviour of axially loaded piles was examined by comparing static pile loading test measurements with numerical results. Given all results, it was concluded that the modified FCV built in this study could properly model the axially loaded piles' behaviour.

This research focuses on the effects of cone penetration rate and anisotropy on the results of piezocone penetration and subsequent dissipation tests. Finite element analyses, and miniature piezocone penetration and dissipation tests in a calibration chamber were performed, then the results were compared. The anisotropic elastoplastic-viscoplastic; bounding surface model was chosen as a soil model and it was implemented into a computer program, ANCALBR8. The isotropic/anisotropic triaxial compression, creep tests, and oedometer tests were performed to determine the model parameter values and verify the model. The model showed very good agreement with the triaxial test results. The theoretical formulation was based on the theory of mixtures with the soil model in the Updated Lagrangian frame, and it was implemented into a computer program, EPVPCS-S. EPVPCS-S was used for the finite element analyses of piezocone penetration and dissipation tests. Ten piezocone penetration and dissipation tests were conducted under Ko condition using LSU/CALCHAS (Louisiana State University Calibration Chamber System). The K33 (the mixture of 33% kaolin, 67% fine sand) was used for the laboratory tests and the chamber tests as the soil sample. The chamber tests were conducted for normally consolidated and heavily overconsolidated cases at the penetration rates of 0.3 cm/sec and 0.6 cm/sec. The U1 (filter element at the cone tip) and U2 (filter element above the cone base) configurations of miniature piezocone penetrometers were used. The results of the finite element analyses showed good agreement with the experimental results with regard to cone resistance, excess pore water pressure, and dissipation. It was observed that cone resistance, excess pore water pressure, and sleeve friction increased with the increase in penetration rate, but decreased with the increase of OCR for both U1 and U2 configurations. The excess pore water pressures at the cone tip (U1) were larger than those above the cone base (U2). The initial immediate drop of excess pore water pressure was clearly identified. Its magnitude increased with the increase in penetration rate, but decreased with the increase of OCR.

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.

Laboratory-scale cone penetration tests are often carried out to calibrate the response of cone penetration, and in particular cone tip resistance to soil characteristics. However, because of the limited sample size, sample boundaries can often affect the measured cone resistance in laboratory tests. This paper presents numerical simulations using the discrete element method (DEM) to study the effect of boundary condition on cone penetration calibration chamber tests. Numerical simulations were performed under flexible (BC1) and laterally-constrained (BC3) boundary conditions on K0consolidated models at different relative densities and vertical stresses. Additional models were simulated with periodic boundaries (BC5) to model the free-field condition. To track the radial stress variations in different sections of the chamber, scattered representative volume elements (RVE) were embedded in the models. Particle displacements and contact force chains were examined to determine the relation between microscopic variables and macroscopic response of the specimens subjected to cone penetration under different boundary conditions. Larger cone resistances were obtained under BC3 condition than those in BC1 condition. For the chamber-to-cone diameter ratio of 25 adopted in this study, the influence of the lateral boundary was found to be negligible in loose to medium-dense assemblies, while the effect of chamber boundary amplified in dense to very dense samples with increasing relative density and reduced with increasing vertical stress. This was attributed to the higher radial stress induced along the cone penetration path in laterally-constraint BC3 models. Based on these findings, a correction factor is proposed to better estimate free-field penetration resistance from calibration chamber experiments.

In this paper, Hardening Soil model with small-strain stiffness (HSsmall) and DeltaSand model are used as constitutive soil models to simulate the Cone Penetration Test (CPT) using the Material Point Method (MPM). Both models are formulated within the double hardening framework, in which independent yield surfaces represent mechanical behavior of soil under deviatoric and volumetric loadings. DeltaSand is a new advanced state-dependent constitutive model in which the relative density is incorporated in the formulation to represent the mechanical behavior of soil under deviatoric and volumetric loading in different stresses and relative densities. The numerical simulations are compared with CPTs in Cuxhaven Sand in a calibration chamber. Both constitutive soil models are compared with each other and DeltaSand is found to be capable to capture the soil behavior during quasi-static CPT.

In this paper, Hardening Soil model with small-strain stiffness (HSsmall) and DeltaSand model are used as constitutive soil models to simulate the Cone Penetration Test (CPT) using the Material Point Method (MPM). Both models are formulated within the double hardening framework, in which independent yield surfaces represent mechanical behavior of soil under deviatoric and volumetric loadings. DeltaSand is a new advanced state-dependent constitutive model in which the relative density is incorporated in the formulation to represent the mechanical behavior of soil under deviatoric and volumetric loading in different stresses and relative densities. The numerical simulations are compared with CPTs in Cuxhaven Sand in a calibration chamber. Both constitutive soil models are compared with each other and DeltaSand is found to be capable to capture the soil behavior during quasi-static CPT.