Primary Consolidation Research Articles

지하수위 저하에 따른 고속철도 토공노반 침하특성에 관한 연구

지하수위 하강에 따른 침하량은 1차 압밀 침하량에 비해 비교적 작기 때문에 잔류침하량 산정시 별도로 고려하지 않는다. 그러나 고속철도 콘크리트 궤도에서의 허용잔류침하량은 30mm로 작기 때문에 예기치 못한 과도한 지하수위 하강으로 인하여 허용잔류침하량을 초과할 수 있다. 본 연구에서는 응력-간극수압 유한요소 해석을 통하여 지하수위 변동에 따른 침하 영향을 분석하여 해석결과와 실측자료를 비교하였다. 그 결과 허용잔류침하량을 만족하기 위한 탄성계수 범위를 제시 하였으며 설계 시 지하수위 저하 영향이 반영되는 것이 타당하다고 판단된다. Unlike the primary consolidation settlement, the settlement of ground water lowering is not considered separately because of relatively small residual settlement. But the allowed residual settlement (30 mm) of the concrete track in the high-speed railway may be exceeded due to unexpected excessive ground water lowering. This study analyzed the effect of the settlement according to the ground water level change using finite element analysis of stress-pore pressure coupling model, and compared the analysis results with the measured data. As a result, the range of elasticity modulus satisfying the allowable settlement was proposed, and it is suggested that settlement due to ground water level changes should be reflected in the design.

Groundwater-derived land subsidence in the North China Plain

Land subsidence usually bears strong relationship to abstraction of underground fluid. Land subsidence occurs commonly in the North China Plain (NCP) and has become a major environmental factor hindering regional sustainable development. This paper focuses on issues associated with mechanism of land subsidence in the NCP. The analysis shows that multi-layer aquifer systems with deep confined aquifers and the thick normally consolidated or unconsolidated compressible clay layers are the key of geological and hydrogeological conditions favorable for the development of land subsidence in the NCP. Groundwater withdrawal results in an increase in the distribution of effective stress within the strata and the compression of the aquifers and the confining layers, and then triggers land subsidence. In the middle-east plain of the NCP, the land subsidence volume approximately represents the amount of water released from compression of deep aquifers and aquitards in that land subsidence is primarily caused by excessive groundwater withdrawal in deep aquifer system. The percentage of water released from compression of aquifers and aquitards in deep groundwater abstraction is significant but distinct in Cangzhou City and in the whole middle-east plain. This is due to the difference in local lithological structure and recharge and discharge conditions of deep groundwater system. The hysteresis of land subsidence is also discussed in typical areas and the results reveal that the time for completing the primary consolidation ranges from less than one year to tens of years, and that the rate of secondary compression tends to increase with the moisture content.

Effect of salt grain additions on fibrous peat consolidation

Peat has been considered a problematic geotechnical material, with extremely high water content, low shear strength and high compressibility. Although initially high, fibrous peat undergoes dramatic reductions in permeability under compression, with secondary compression (creep) accounting for a large proportion of the settlement under loading. The key to accelerating the whole consolidation process for fibrous/hemic peats is to create a means of accelerating water flow from micropores (within the cellular structure) or humus contained in the peat. This paper presents the results of preliminary laboratory trials performed using the hydraulic consolidation (Rowe) cell apparatus to investigate a novel approach involving the addition of salt grains to fibrous peat towards accelerating its rate of primary consolidation and reducing its creep rate. Under similar loading conditions, salt-treated specimens were found to have reduced rate and magnitude of creep settlement, explained by larger volumes of micropore water expelled during primary consolidation.

Reply to the discussion by Grimstad et al. on “Viscous behaviour of clays in one-dimensional compression”

We, the authors of this paper, wish to express our appreciation to Grimstad, Degago, and Boumezerane for their time and effort in studying our paper and preparing the Discussion. We view their Discussion to be equally important as our paper. Their comments address (i) the uniqueness of the void ratio at end of primary consolidation, eEOP, (ii) the creep deformation of individual particles, and (iii) the concept of isotache. Themain focus of the paper is to identify different deformation modes involved in one-dimensional (1D) creep compression. One of the main findings of our study is that creep compression deformation at the contacts causes compression of the large interaggregate pores, which is a continuation of primary consolidation. During primary consolidation, most of the excess pore pressure generated by the total stress change has dissipated. The eEOP is proposed and used as a reference state to illustrate the continuation of the collapse of the large interaggregate pores. Our experimental data illustrate that the normal consolidation line (NCL) is unique, implying the uniqueness of eEOP based on the assumption that the time required for consolidation is small, i.e., the time-dependent deformation during consolidation and the excess pore pressure induced by the time-dependent deformation are insignificant. We concur that time-dependent deformation occurs in the entire compression process involving primary and secondary compression. One can argue the uniqueness of the coefficient of consolidation and the NCL if the time-dependent deformation dominates in the primary consolidation. The major challenge is that the 1D consolidation test is not an element test, and the response of the test sample is dependent on the initial and imposed boundary conditions. The intrinsic properties are very difficult to determine from the test results without any assumptions. In soft geomaterials such as soft clay and peat, it is challenging to separate or decouple the creep deformation process from the consolidation. In such cases, we propose the use of nondestructive methods such as microcomputer tomography scanning and nuclearmagnetic resonance imaging tomonitor the evolution of the soil structure at a microlevel during 1D compression. We also agree that the creep deformation of individual particles is very small in normally consolidated clay at low stress levels. However, this mode of deformation becomes dominant in heavily overconsolidated clay (clay shale) and sand at high stress levels. The concept of isotache is one of empirical correlations used in modeling the time-dependent behaviour of soils. However, it has some limitations in explaining the behaviour observed in relaxation tests in which the strain rate in one direction is zero.

Discussion of “Viscous behaviour of clays in one-dimensional compression”

Wong and Varatharajan hypothesize that the time-dependent or creep deformation under one-dimensional constant effective stress involves creep deformations of individual particles and creep shear deformation at interaggregate contacts. They have conducted different experiments on reconstituted kaolinite clay samples to investigate certain creep mechanisms. In the rheological model they tend to advocate, an implicit assumption made is that the creep strain starts at end of primary (EOP) consolidation and the void ratio at EOP, eEOP, is unique. Consequently, the authors interpreted their test data with this assumption and ended up asserting that “... the creep compression behaviour of claymay be uniquely related to its eEOP ...”. This is in contradiction to the opening statement of their Introduction where they state that creep deformation occurs in the entire compression process involving primary consolidation and secondary compression. The authors’ attempt to investigate the effect of drainage path on resulting void ratio, by conducting tests with top and radial drainages, is too limited to appreciate and be conclusive about this important effect. However, Degago et al. (2009) interpreted experimental data by Feng (1991) and showed that EOP tests on 127 and 508 mm thick samples, under similar loading and drainage boundary conditions, yielded a nonunique eEOP. Differences in eEOP can further be demonstrated by differences in vertical deformation of a soil element located closest to and farthest from a drainage boundary. Tests by Feng (1991) configured in such a way revealed that soil elements closer to the drainage boundary have lower eEOP values when compared with elements farthest from the drainage boundary (Degago et al. 2011) The authors tried to demonstrate unique EOP values by comparing multiand singlestage tests. The discussers do not see how the authors “proof” for unique eEOP values holds true. In Figs. 4 and 7, the authors plot log (that can be reformulated into inverse of strain rate over stress) versus strain after EOP. The inclination of this line is the reciprocal value of C (for a remolded sample in practice a constant value is expected) and the shift in vertical direction as plotted by the authors is close to log( ), which comes from multiplying the inverse of strain rate with stress. If the authors had instead presented a plot of the inverse of the rate of void ratio change versus void ratio for the different stress levels, the plot would have shown a unique relation between void ratio, rate of change in void ratio, and effective stress level as stated in the isotache concept (Suklje 1957). This demonstrates that the isotache concept also holds for the tests conducted and presented by the authors. This, thus, implies that that eEOP cannot be unique, but depends on the experienced strain rate, i.e., time it takes to reach “EOP”, and the position of the material with respect to the drainage boundary. In conclusion, the discussers believe the primary aim of such laboratory tests is to enable proper characterization of the field behavior of soils and in this aspect the extension from laboratory to field condition is observed to follow isotache formulation (Leroueil 2006) — this implies that creep occurs during the entire soil compression process and eEOP cannot be unique and therefore cannot be considered as a soil parameter.

Geotechnical Investigations of Coal and Iron Mine Refuge for Backfilling in Opencast Mine: A Comparative Study

All opencast mines should be restored and reclaimed with proper technology to reduce stability issues and environmental problems. Proper backfilling of mines using the waste materials from waste dumps could be a viable solution as it reduces mining subsidence, minimize spontaneous combustion, enhance reclamation, restore mined out surface land and create a safe working atmosphere. While taking a particular material for backfilling, assessment of the material's short term and long term geotechnical properties and likely response after the placement to determine the fill's ability to be act as stowing material is imperative. Important properties for the insitu fills are strength, deformability, capability to dissipate pore pressure, primary and secondary consolidation characteristics, durability and leachabilityetc. In this paper, the geotechnical properties of the coal and iron mine wastes have been investigated as to assessing and comparing their suitability for backfilling in opencast mines.

Discussion of “Large-strain elastic viscoplastic consolidation analysis of very soft clay layers with vertical drains under preloading”

where vs ′ and vf ′ are the effective vertical stress reached before the removal of surcharge and final effective vertical stress, respectively. According to the observed ground surface settlements in Fig. 9 and the pore-water pressure measurements in Fig. 10, end of primary (EOP) consolidation was probably reached near 610 days when the 20 kPa surcharge was removed. The post-surcharge secondary settlement is computed using (Terzaghi et al. 1996, p. 110)

Proximal Femoral Allograft in Two-Stage Revision for Failed Septic Hip Arthroplasty

Infection after hip prostheses is a potentially devastating complication, and a serious medical and surgical challenge, especially when associated with Paprosky type III femoral bone loosening. Treatment is difficult and options are limited. We report on a 2-stage revision of 15 patients undergoing femur reconstruction with massive allografts. Materials and methods: This was a prospective study which included 15 patients (10 men and 5 women) with infected hip prosthesis, associated with Paprosky type III femoral proximal massive bone loss. The median age of patients was 64 years with a preoperative functional status score of 6. The average number of procedures to the same hip after the first arthroplasty was 6. All patients benefited from a 2-step surgery with massive allografts and locking prosthesis. The average follow-up time was 36 months. Results: Infection was monomicrobial in 14 cases; and was polymicrobial in 4 cases. Methicillin-resistant Staphylococcus epidermidis was the main bacteria (n = 10). The average C-reactive protein level before the second procedure was 2.3 ± 3.4. It was normalized in 8 cases. We recorded 13 cases of primary consolidation without another surgery, 3 cases of relapse, 2 traumatic dislocations and 2 fractures of the allograft. Conclusion: Hip prosthesis infection is a potentially catastrophic complication with significant negative ramifications for both the patient and the healthcare system. Massive allografts use in Paprosky III femoral defect remains very attractive for bone stock restoration and hip function improvement.

Coefficient of consolidation by end of arc method

One of the most important issues in geotechnical engineering is excess pore pressure caused by clay soil loading and consolidation. Regarding uncertainties and complexities, this issue has long been the subject of attention of many researchers. In this work, a one-dimensional consolidation apparatus was equipped in a way that pore water pressure and settlement could be continuously read and recorded during consolidation process under static loading. The end of primary consolidation was obtained using water pressure changes helping to present a new method for determining the end of primary consolidation and consolidation coefficient. This method was then compared with two classical theory methods of lg t and \(\sqrt t \). Using Terzaghi’s theory, the way of pore pressure dissipation for lg t, \(\sqrt t \) and the new method was found and compared with experimental results. It is concluded that the new method has better results.

Modeling stone column installation in an elasto-viscoplastic soil

The majority of numerical studies investigating stone column performance have used “wished-in-place” columns (no installation effects) in conjunction with elastoplastic soil models (no viscous effects). In the first part of this paper, cylindrical cavity expansion (CCE) is used in conjunction with the PLAXIS 2D elasto-viscoplastic soft soil creep (SSC) model to evaluate the effect of creep on column installation. Creep leads to lower post-installation lateral earth pressure coefficients (K) than if primary consolidation was considered alone, although the values of K/K0, which decay with distance from the column center, are nevertheless greater than 1·0. In the second part of this paper, two sets of unit cell analyses have been carried out to investigate the effect of accounting for column installation on subsequent settlement performance. The results indicate that “primary” settlement improvement factors are larger than “total” settlement improvement factors and that the relative differences between them increase when installation is taken into account.

Bending of a rectangular plate resting on a fractionalized Zener foundation

The long-term performance of plates resting on viscoelastic foundations is a major concern in the analysis of soil-structure interaction. As a powerful mathematical tool, fractional calculus may address these plate-on-foundation problems. In this paper, a fractionalized Zener model is proposed to study the time-dependent behavior of a uniformly loaded rectangular thin foundation plate. By use of the viscoelasticelastic correspondence principle and the Laplace transforms, the analytical solutions were obtained in terms of the Mittag-Leffler function. Through the analysis of a numerical example, the calculated plate deflection, bending moment and foundation reaction were compared to those from ideal elastic and standard viscoelastic models. It is found that the upper and lower bound solutions of the plate response estimated by the proposed model can be determined using the elastic model. Based on a parametric study, the impacts of model parameters on the long-term performance of a foundation plate were systematically investigated. The results show that the two spring stiffnesses govern the upper and lower bound solutions of the plate response. By varying the values of the fractional differential order and the coefficient of viscosity, the timedependent behavior of a foundation plate can be accurately captured. The fractional differential order seems to be dependent on the mechanical properties of the ground soil. A sandy foundation will have a small fractional differential order while in order to simulate the creeping of clay foundation, a larger fractional differential order value is needed. The fractionalized Zener model is capable of accounting for the primary and secondary consolidation processes of the foundation soil and can be used to predict the plate performance over many decades of time.

Viscosity and secondary consolidation in one-dimensional loading

Viscosity and secondary consolidation effects are observed in one-dimensional compression, but it remains unresolved if viscous effects occur during the primary consolidation phase and consequently whether the end of the primary consolidation (EOP) line is unique and the H2 scaling law applies. Dynamical systems soil mechanics suggests that viscosity and secondary consolidation each have a separate physical basis. Viscous behaviour is due to strain rate dependence of the coefficients of friction at interparticle contacts as they slide against each other in simple friction, and occurs during both primary consolidation and secondary consolidation. Secondary consolidation is the continued deformation of the soil structure after excess pore pressure has dissipated, as small numbers of particles move at random shear strains, in a Poisson process, to new final positions. The near constant C(αe)/Cc ratio is due to the form of the equation that expresses this ratio and because very few particles move to new positions during secondary consolidation. Strain rates for typical geotechnical problems being pseudo-static, viscous effects in the field are small, and the current design practice of using the EOP curve and C(αe) to calculate compression settlements appears reasonable. Empirical evidence suggests that adsorbed water layers control strain-rate-related effects.

Settlement Rate–Settlement Method for Radial Consolidation (SRSM–RC)

Abstract The settlement rate–settlement method for radial consolidation (SRSM–RC) is proposed for evaluating the coefficient of radial consolidation cr and end-of-primary (EOP) settlement δp. The SRSM–RC explicitly relates cr and δp to the intercept and slope of the linear settlement rate–settlement (dδt/dt-δt) relationship observed theoretically over the entire Ur range of the Barron theory; δt is the settlement at time t and Ur is the degree of radial consolidation. The SRSM–RC computes cr independently of any specific Ur value and can simultaneously compute δp without the need to use the secondary compression range. The SRSM–RC does not require a complete record of compression–time data; a minimum of four representative data points at any stage of primary consolidation are required to estimate cr by the SRSM–RC. Experimental results on radial consolidation of several clayey soils obtained from literature are used to validate and compare the SRSM–RC with existing methods. The validity of the method is also evaluated by matching the experimental compression–time data with the theory.

Health insurer market power and primary care consolidation

This paper analyzes how health insurance market concentration impacts the market structure of primary care physicians. In more concentrated insurance markets, physicians are found to work in larger practices and their practices are more likely to have a hospital with an ownership interest. Physicians are also less likely to report being in a competitive physician market, consistent with practice consolidation. Our results suggest that consolidation in insurance markets impacts the competitive structure of physician markets.

Evaluation of the Oedometer Tests of Municipal Landfill Waste Material

Abstract The aim of the ongoing research is (i) to develop a new biodegradation landfill technique so that the landfill gas production could be controlled and the utilisation of the landfill gas could economically be optimized, (ii) to plan the energy utilisation of the landfill including individual and combined solutions (solar, wind, geothermal energy, energy storage using methanol etc.). [1, 2, 3] After summarizing the previous measurements made on the ongoing research, the first results of the oedometer tests are presented. The compression curves were determined, the measured data are evaluated by two simple models, the parameters are identified, the reliability of the parameters is tested. The simple models make possible the separation of the three major components of the settlement: the immediate settlement, the creep settlement and the primary consolidation settlement. The degradation induced strains were not considered since the tests were short term. Using these components, three different oedometric moduli are defined. The identified parameters are presented and compared with the parameters previously identified from some CPTu dissipation test data, and with the parameters measured by some recent seismic tests. The parameters are used to estimate the settlement of the landfill.

Filtration of core–shell colloids in studying the dewatering properties of water-swollen materials

The properties of filter cakes formed by the deposition of suspended particles play important roles in numerous filtration applications. As the properties of suspensions of biological/organic origin differ markedly from classical filtration properties derived from inorganic suspensions, organic polymer particles with core–shell morphology have been synthesized and applied in dead-end filtration experiments. These particles, with a dense polystyrene core and a water-swollen gel-like poly(acrylic acid) shell, have been made with varying shell–core volume ratios and particle sizes. Filtration results show that the specific filter cake resistance is more dependent on the volume fraction of the shell than on particle size, and that the filter cakes exhibit pressure-dependent compressibility with a linear correlation with shell volume fraction. Furthermore, the primary consolidation of the filter cakes was investigated and linked to the particle properties, again exhibiting dependency on both shell fraction and applied pressure.

Vacuum distribution with depth in vertical drains and soil during preloading

The vacuum consolidation method which was proposed by Kjellman in 1952 has been studied extensively and used successfully since early 1980 throughout the world, especially in East and Southeast Asia. Despite the increased successful use, different opinions still exist, especially in connection to distribution of vacuum with depth and time in vertical drains and in soil during preloading of soft ground. Porewater pressure measurements from actual cases of field vacuum and vacuum-fill preloading as well as laboratory studies have been examined. It is concluded that (a) a vacuum magnitude equal to that in the drainage blanket remains constant with depth and time within the vertical drains, (b) as expected, vacuum does not develop at the same rate within the soil at different depths; however, under ideal conditions vacuum is expected to become constant with depth in soil after the end of primary consolidation, and (c) there exists a possibility of internal leakage in vacuum intensity at some sublayers of a soft clay and silt deposit. A case history of vacuum loading with sufficient subsurface information is analyzed using the ILLICON procedure.

Analysis on the Influence of the Primary Consolidation Settlement of the e~p Curves and the Soil Bulk Density of the Soft Soil Foundation

In general, primary consolidation settlement of soft foundation is calculated by layerwise summation method considering the design load in seawall engineering design, and the total settlement is obtained by multiplying a settlement correction coefficient which is difficult to select. In this paper, one seawall engineering case is enumerated, the impact on the thickness of compressible stratum and the primary consolidation settlement is studied by considering the changes of the e~p curves of the soft soil foundation. The results indicate that the thickness of the compressible stratum changes obviously for different stress ratio owing to the difference of the soil bulk density of the compressible soil, and the primary consolidation settlement has corresponding change tendency according to the shape of the e ~ p curves and the soil bulk density of the compressed soil. At last, this paper suggests that a designer can weaken the weight of settlement correction coefficient based on the analysis of the influence of primary consolidation settlement with different e ~ p curves of the soft soil foundation in future design.

Regional differences in primary school consolidation and public finance

Regional differences in primary school consolidation and public finance

Effect of Autologous Plasma, Ascorbic Acid and Glucose Local Infusions on Pelvic Fracture Healing in Experiment

The efficacy of reparative osteogenesis stimulation by local infusion of autologous plasma in combination with ascorbic acid and glucose solutions was experimentally demonstrated in ani- mals (dogs) using the models of transverse acetabular ( n =20) and iliac shaft fracture ( n= 6). Either intraarticular or intraosseous solution infusions via injection system with automatic drug pump were performed from 2nd to 5th day after transverse osteotomy, reposition and stable external fixation. Fixator was dismounted on 21st postoperative day. In control series of experiment (intraarticular and intraosseous infusion of saline) fibrocartilagenous junction was formed and bone deformity due to secondary bone fragments displacement was noted after device removal. In experimental series primary pelvic bone fragments consolidation was observed in 14 days after operation and no displacement of fragments occurred after external fixation device removal.