Early Stages Of Consolidation Research Articles

Consolidation of sensitive clays: a numerical investigation

Consolidation of sensitive clay layers, which have significant compressibility at different stress states, is investigated via a nonlinear one-dimensional consolidation approach with a piecewise linear e ~ log10σ′ model. The behaviour of sensitive clays during consolidation and the limitations of conventional consolidation theory are addressed. It is shown that (1) the sensitive clay layer can be divided by the preconsolidation pressure into two zones, that is, high- and low-compressibility zones. The progressive destruction of particle cementation bonding through the soil layer is shown by the moving front of the interface between these two zones; (2) the excess pore pressure dissipation primarily takes place in the low-compressibility zone, which results in a small settlement during the early stages of consolidation; (3) conventional consolidation theory highly overestimates the settlement and gives a poor prediction of effective stress distribution.

Effects of Latency on Bone Formation during the Consolidation Period of Rabbit Mandibular Distraction

Objective: To investigate the effect of latency on bone formation during the consolidation period in mandibular distraction osteogenesis in rabbits.Materials and Methods: Thirty young adult Japanese white rabbits were divided into 4 groups. Nine animals each were allocated to groups A, B and C, where bilateral mandibular corticotomy was performed and an external distraction device fixed. Three animals were used as controls for each experimental group (group D). Latency periods of 0 days (group A), 5 days (group B), and 10 days (group C) were observed before the start of distraction. Distraction was carried out at a rate of 0.25 mm every 12 hours to lengthen the mandible for 10 days. The rabbits were sacrificed at 3 stages — immediately after completion of distraction, after 5 days of early consolidation, and after 10 days of late consolidation — in all groups. The distracted mandibles were examined using haematoxylin and eosin stain for histology at various stages. The bone mineral densities were examined using peripheral quantitative computed tomography after 10 days of consolidation.Results: Histological study showed that the 10-day latency group exhibited good bone formation when compared with the 0- and 5-day latency groups during the early stages of consolidation. However, bone mineral densities of the experimental groups showed no statistically significant differences after 10 days of consolidation.Conclusion: A change in latency does not alter the properties of the regenerate bone in rabbit mandibular distraction osteogenesis after a period of consolidation.

Laser Induced Breakdown Spectroscopy

This review describes the fundamentals, instrumentation, applications and future trends of an analytical technique that is in its early stages of consolidation and is establishing its definitive niches among modern spectrometric techniques. The technique has been named Laser Induced Breakdown Spectroscopy (LIBS) and its main characteristic stands in the use of short laser pulses as the energy source to vaporize samples and excite the emission of electromagnetic radiation from its elements and/or molecular fragments. The emitted radiation is analyzed by high resolution optics and the intensities are recorded, usually by fast triggered solid state detectors. Together, these devices allow producing and registering a wide ranging emission spectrum of the short-lived phenomenon induced by the laser pulse. The spectrum contains qualitative and quantitative information which can be correlated with sample identity or can be used to determine the amount of its constituents. This review is divided in four parts. First, the relevant historical and theoretical concepts associated with LIBS are presented; then the main practical aspects of the several experimental and instrumental approaches employed for implementation of the technique are critically described; the applications related in the literature, including those making use of chemometrics, are classified and exemplified with relevant and recently published work. Finally, an attempt to portray an overall evaluation and future perspectives of the technique are presented.

Effect of recombinant human tissue inhibitor of matrix metalloproteinase-1 in rabbit mandibular distraction osteogenesis: A histological and immunohistochemical study

Bone matrix metalloproteinases are capable of degrading bone matrix during the remodelling, and their degradation activities can be down regulated by the tissue inhibitors of matrix metalloproteinases. This study evaluated the influence of exogenous tissue inhibitor of matrix metalloproteinase-1 on the expression of matrix metalloproteinases and endogenous tissue inhibitor of matrix metalloproteinases in mandibular distraction osteogenesis. Fifteen New Zealand white rabbits were assigned to three groups: a negative control; a sham control group implanted with a collagen sheet; and an experimental group implanted with recombinant human tissue inhibitor of matrix metalloproteinase-1 impregnated in a collagen sheet. Rabbits were sacrificed at 6 weeks, 12 weeks and 24 weeks of consolidation. Major expression of matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases was observed at the early stage of consolidation, only positive signals of tissue inhibitors of matrix metalloproteinases were observed at 24 weeks. The addition of recombinant human tissue inhibitor of matrix metalloproteinases-1 did not affect bone maturation and remodelling. An equilibrium of bone formation and resorption was reached at 24 weeks of consolidation in the rabbit mandible. No obvious influence of recombinant human tissue inhibitor of matrix metalloproteinase-1 on bone remodelling of mandibular distraction osteogenesis was noted.

Expression of nerve growth factor and vascular endothelial growth factor in the inferior alveolar nerve after distraction osteogenesis

The objective of this study was to evaluate changes occurring in the inferior alveolar nerve (IAN) subsequent to mandibular distraction osteogenesis, with regard to the expression of nerve growth factor (NGF) and vascular endothelial growth factor (VEGF). Unilateral mandibular distractions (0.5 mm each, twice per day for 10 days) were conducted on 8 mongrel dogs. Two animals were killed at 7, 14, 28 and 56 days after completion of distraction. The distracted IAN and contralateral control nerve were then harvested and analysed histologically and immunohistochemically. Signs of acute nerve injury, including demyelination, were observed in the distracted IAN on the 7th and 14th day after distraction. At 56 days, the histological features of the distracted IAN were similar to those of the control nerve. The levels of NGF and VEGF expression were significantly elevated on the 7th and 14th day after distraction. NGF was expressed in most of the distracted nerve tissues, but VEGF was primarily detected in Schwann cells and the neurovasorum. VEGF expression had returned to normal but NGF expression was still profoundly elevated 28 days after distraction. NGF expression returned to normal levels at 56 days after distraction. NGF and VEGF appeared to have been elicited from the Schwann cells and damaged nervous tissues, and they may play important roles in the initial healing of damaged nerves. VEGF expression returned to normal more quickly than did NGF expression. This may indicate that hypoxic conditions within the distracted nerve had recovered to normal during the early stages of consolidation. Micro-vessels in the distracted nerve may have recovered more rapidly than did the nerve tissue itself.

NMDA receptor-dependent processes in the medial prefrontal cortex are important for acquisition and the early stage of consolidation during trace, but not delay eyeblink conditioning

Permanent lesions in the medial prefrontal cortex (mPFC) affect acquisition of conditioned responses (CRs) during trace eyeblink conditioning and retention of remotely acquired CRs. To clarify further roles of the mPFC in this type of learning, we investigated the participation of the mPFC in mnemonic processes both during and after daily conditioning using local microinfusion of the GABA(A) receptor agonist muscimol or the NMDA receptor antagonist APV into the rat mPFC. Muscimol infusions into the mPFC before daily conditioning significantly retarded CR acquisition and reduced CR expression if applied after sufficient learning. APV infusion also impaired acquisition of CRs, but not expression of well-learned CRs. When infusions were made immediately after daily conditioning, acquisition of the CR was partially impaired in both the muscimol and APV infusion groups. In contrast, rats that received muscimol infusions 3 h after daily conditioning exhibited improvement in their CR performance comparable to that of the control group. Both the pre- and post-conditioning infusion of muscimol had no effect on acquisition in the delay paradigm. These results suggest that the mPFC participates in both acquisition of a CR and the early stage of consolidation of memory in trace, but not delay eyeblink conditioning by NMDA receptor-mediated operations.

Internal Behavior of Clayey Ground Improved by Vertical Drains in 3D-Consolidation Process

In order to establish a precise method for predicting the residual settlement, including the secondary consolidation, of clayey ground improved by vertical drains, a new consolidation test apparatus was developed. In this test apparatus, the consolidation of a hollow cylindrical body, in which the pore water flows radially toward the center, can be simulated by installing a vertical drain at the center of the specimen. The radial distributions of the radial displacement and excess pore water pressure in the specimen during the three-dimensional consolidation process also can be measured in this test apparatus. The radial displacements in the specimen were obtained by measuring the intensity of the magnetic field induced by a small magnet buried in the specimen by magnetometers set in the consolidation ring surrounding the specimen and in the vertical drain installed at the center of the specimen. From the measured results on the radial displacements in the specimen, it was found that during the three-dimensional consolidation process not only the vertical displacement but also the radial displacement occurs inside the specimen. The radial displacement developed toward the center of the specimen in the early stage of consolidation and then returned toward the outside in the later stage of consolidation but did not completely return to the original position at the end of consolidation. The mechanism of the three-dimensional consolidation by the vertical drain, which caused these behaviors, was clarified based on the test results on the radial distributions in the radial displacement and the excess pore water pressure in the specimen.

Modeling of hot isostatic pressing and hot triaxial compaction of Ti–6Al–4V powder

The accuracy of a hybrid continuum–micromechanical model for predicting the rate-dependent consolidation of metal powder was established using measurements from hot isostatic pressing (HIP) and hot triaxial compaction (HTC) experiments. The experiments were performed with PREP® Ti–6Al–4V powder encapsulated in thin-walled containers and yielded relative density vs time and height vs relative density data for direct comparisons with model predictions. The model was found to underpredict the densification rate in HIP, primarily during the early stages of consolidation, and the degree of consolidation during HTC. Adjustments to the values of the strain-rate sensitivity or a state variable representing the geometric structure of powder compacts resulted in good agreement between hybrid model predictions and measurements. The physical basis for discrepancies between predictions and measurements and justification for the postulated/required parameter adjustments were attributed to two factors: (1) differences in microstructure between the unconsolidated powder and the fully consolidated material used in the compression testing to obtain the material coefficients for the model; and (2) interparticle bonding characteristics/particle sliding effects not taken into account in determining the material properties for the model.

Cold isostatic pressing of composite powders — Experimental investigation: C.D. Turner, M.F. Ashby. (Cambridge University, Cambridge, UK) Acta Materiallia, vol 44, no 11, 1996, 4521–4530

To improve the design of optimum consolidation cycles for powder processing, it is important to be able to predict the final shape of the product. When components are solidified from metal powders by isostatic pressing, substantial shape changes can occur due to the constraint of the can. This effect can be modelled in terms of a new constitutive law for the plastic yielding of powder aggregates. It is found that in the early stages of consolidation, the shape is controlled by the container and the powder has no influence. The container deforms into shapes it would achieve if it were empty. This suggests that the initial design of a container can be carried out with an empty can under external pressure.

The analysis of shape change during isostatic pressing

To improve the design of optimum consolidation cycles for powder processing, it is important to be able to predict the final shape of the product. When components are solidified from metal powders by isostatic pressing, substantial shape changes can occur due to the constraint of the can. This effect can be modelled in terms of a new constitutive law for the plastic yielding of powder aggregates. It is found that in the early stages of consolidation, the shape is controlled by the container and the powder has no influence. The container deforms into shapes it would achieve if it were empty. This suggests that the initial design of a container can be carried out with an empty can under external pressure.

Estimation of Soil Parameters Based on Monitored Movement of Subsoil under Consolidation

This paper presents a numerical procedure in which the soil parameters affecting the two dimensional consolidation are back-calculated from the data monitored in the field. By using a combination of finite element method and mathematical programming technique, the procedure allows to seek the unknown soil parameters which minimize the differences between calculated and measured quantities. Young's modulus, Poisson's ratio, and permeability coefficient in multiple soil layers are the soil parameters determined by the procedure. The validity of the proposed procedure is verified by calibrating the performance of the procedure being applied to hypothetical case studies. The applications to practical projects provide the interesting results such as the changing trend of soil parameter values during consolidation process. By applying the procedure at the early stage of consolidation, one may be able to predict the future settlements with a good accuracy.

One-Dimensional Consolidation Under Linear Loading

Abstract A nonlinear theory of consolidation under linear loading is formulated for various load-increment ratios. Variable coefficients of permeability and volume decrease and constant coefficient of consolidation are assumed during consolidation. The results obtained for a very small load-increment ratio very closely follow those of Schiffman's linear loading theory. A hydraulic loading odometer having provisions for applying linear loading and multipoint pore-pressure measurement is developed. Laboratory linear loading tests on kaolin and Calcuttta silty clay under a load-increment ratio K of 0.25 indicate that the experimental pore pressures dissipate at a faster rate than predicted by both non-linear and Schiffman theories. Improved agreement between experiment and theories are observed for K = 4. A quasi-preconsolidation effect is observed during early stages of consolidation. The void ratio effective stress relationship based on base pore pressures and isochrones obtained during slow rate of linear loading tests very closely follows the curve determined conventionally.

An Inverse Problem Approach to the Prediction of Multi-Dimensional Consolidation Behavior

ABSTRACT This study intends to give theoretical bases for the observational procedure of predicting multi-dimensional consolidation behavior, in which the observations of deformations and/or excess pore water pressures raised in the early stages of consolidation are utlized for the prediction of those behavior in the successive future stage. The developed procedure is based on the Biot’s linear elastic consolidation theory and is applicable to inhomogeneous soil mass with anisotropic soil properties concerning both elasticity and permeability. For the purpose of practical use the procedure is introduced in two ways, one is under constant load condition and the other, under gradual load application. Furthermore, taking field engineering practice into consideration, the method is presented for two cases, one is the case when excess pore water pressure behavior can be observed and the other, not observed. The numerical simulations using finite element analyses and some actual field observations show the high applicability of the proposed procedure.

Back analysis techniques for slope stabilization works: a case record

Back analysis techniques for two aspects of slope stabilization works are discussed in the context of the re-alignment of the A606 road over landslipped slopes in Leicestershire. Stability analyses of the existing slopes enabled strength parameters to be selected for earthworks and slope stabilization design; analyses of individual segments of the landslide enabled the degree of curvature of the residual strength envelope to be established, the consequences of which are important for design. The observed rate of drainage achieved by trench drains excavated in the lower part of the landslide was used to assess the likely rate of consolidation of the same area beneath the road embankment. This analysis overestimated the rate of consolidation during the early stages of consolidation by a factor of about four, apparently as a result of the effects of stress relief in reducing pore pressures immediately after excavation of the drains. The road embankment was successfully constructed over the landslide, and the movement and pore-pressure observations are reported. Movements were generally small, of the order of 2 cm, consistent with the high factor of safety (≃1·50) achieved during construction. Des techniques d'analyses de revers pour deux aspects de travaux de stabilisation de pente sont discutées dans le contexte du redressement de la route A606 dans le Leicestershire, sur des pentes qui ont subit des glissements de terrain. Des analyses de stabilité des pentes existantes ont permis de sélectionner des paramètres de résistance pour le projet des terrassements et de stabilisation de pente; les analyses de segments isolés du glissement de terrain ont permis d'établir le degré de courbure de l'enveloppe de résistance résiduelle, dont les conséquences sont importantes pour le projet. Le taux de drainage observé, réalisé par des drainages de fossé excavés dans la partie inférieure du glissement de terrain a été utilisé afin d'évaluer le taux probable de consolidation de la même surface sous le remblai routier. Cette analyse a surestimé le taux de consolidation pendant les premières phases de consolidation par un facteur d'environ quatre, ceci est apparemment aux effets de décharge de contrainte en réduisant la pression interstitielle immédiatement aprés l'excavation des drains. Le remblai routier fut construit avec succés sur le glissement de terrain, et le mouvement et les observations de pression interstitielle qui furent faits sont rapportés. Les mouvements furent généralement faibles, de l'ordre de deux centimètres, compatibles avec le Facteur de Sécurité élevé (≃ 1·50) atteint pendant la construction.