Secondary Consolidation Research Articles

Subsidence and carbon loss in drained tropical peatlands

Abstract. Conversion of tropical peatlands to agriculture leads to a release of carbon from previously stable, long-term storage, resulting in land subsidence that can be a surrogate measure of CO2 emissions to the atmosphere. We present an analysis of recent large-scale subsidence monitoring studies in Acacia and oil palm plantations on peatland in SE Asia, and compare the findings with previous studies. Subsidence in the first 5 yr after drainage was found to be 142 cm, of which 75 cm occurred in the first year. After 5 yr, the subsidence rate in both plantation types, at average water table depths of 0.7 m, remained constant at around 5 cm yr−1. The results confirm that primary consolidation contributed substantially to total subsidence only in the first year after drainage, that secondary consolidation was negligible, and that the amount of compaction was also much reduced within 5 yr. Over 5 yr after drainage, 75 % of cumulative subsidence was caused by peat oxidation, and after 18 yr this was 92 %. The average rate of carbon loss over the first 5 yr was 178 t CO2eq ha−1 yr−1, which reduced to 73 t CO2eq ha−1 yr−1 over subsequent years, potentially resulting in an average loss of 100 t CO2eq ha−1 yr−1 over 25 yr. Part of the observed range in subsidence and carbon loss values is explained by differences in water table depth, but vegetation cover and other factors such as addition of fertilizers also influence peat oxidation. A relationship with groundwater table depth shows that subsidence and carbon loss are still considerable even at the highest water levels theoretically possible in plantations. This implies that improved plantation water management will reduce these impacts by 20 % at most, relative to current conditions, and that high rates of carbon loss and land subsidence are inevitable consequences of conversion of forested tropical peatlands to other land uses.

Fastest Rapid Loading Methods of Vertical and Radial Consolidations

Fastest curve-fitting procedures are proposed for vertical and radial consolidations for rapid loading methods. In vertical consolidation, the next load increment can be applied at 50–60% consolidation (or even earlier if the compression index is known). In radial consolidation, the next load increment can be applied at just 10–15% consolidation. The effects of secondary consolidation on the coefficient of consolidation and ultimate settlement are minimized in both cases. A quick procedure is proposed in vertical consolidation that determines how far cv is calculated from the true cv, where cv is coefficient of consolidation. In radial consolidation no such procedure is required because at 10–15% the consolidation effects of secondary consolidation are already less in most inorganic soils. The proposed rapid loading methods can be used when the settlement or time of load increment is not known. The characteristic features of vertical, radial, three-dimensional, and secondary consolidations are given in terms of the rate of settlement. A relationship is proposed between the coefficient of the vertical consolidation, load increment ratio, and compression index.

Long-Term Consolidation Settlement Prediction of D-Runway in Tokyo International Airport

In the construction of the D-runway in Tokyo International Airport (Haneda Airport), “the settlement prediction and management system (HSAP)” which can efficiently evaluate the consolidation settlement of artificial reclamation was developed. The reclamation history data base which reflected the actual construction until July, 2009 and the reclamation plan after that was made. The actual measurement and the calculation value were compared and the various consolidation parameters were identified. Moreover, the long-term consolidation test and constant strain rate consolidation test were executed, and the secondary consolidation parameter was set based on the isotache model's concept. Based on the prediction result of the residual consolidation settlement, the filling height of the D-runway at the start of in-service period was decided to be 0.70m, which is required from the aviation operation.

Experiment Research on Deformation Properties under Unloading of Soft Clay

In this study, many experiments are developed to analyze the deformation properties under unloading of soft clay. There are many settlement deformation analyses about soft soil ground in the past. Now we need analyze the rebound deformation in many engineering. Deformation properties under unloading of soft clay have been studied through large numbers of tests. The soft clay’s rebound defamation existed critical unload ratio, When its unload ratio is less than critical unload ratio, rebound deformation doesn’t happen; But rebound deformation would happen if unload ratio is more than critical unload ratio; The soft clay deformation after unloading is divided into three parts included primary rebound, secondary rebound and appending secondary consolidation deformation.

Experiment Research on Deformation Properties under Unloading of Soft Clay

In this study, many experiments are developed to analyze the deformation properties under unloading of soft clay. There are many settlement deformation analyses about soft soil ground in the past. Now we need analyze the rebound deformation in many engineering. Deformation properties under unloading of soft clay have been studied through large numbers of tests. The soft clay’s rebound defamation existed critical unload ratio, When its unload ratio is less than critical unload ratio, rebound deformation doesn’t happen; But rebound deformation would happen if unload ratio is more than critical unload ratio; The soft clay deformation after unloading is divided into three parts included primary rebound, secondary rebound and appending secondary consolidation deformation.

Working Hypothesis, Special Laboratory Tests, Working Tools, Analysis of the Monitoring of a Pilot Embankment Built on Soft Clay in Santos with Wick Drains and its Application to the Final Design

Routine in-situ and laboratory investigations carried out for the basic design failed to provide reliable values for compressibility and consolidation parameters of soft clay layers at the site of a terminal to be built in Santos. A pilot embankment was designed and built divided in three equal areas, two with wick drains in a square mesh at spacings of 1.2 m and 2.4 m respectively and one with no drain. The basic working hypothesis adopted by the authors was that, in the field, primary and secondary consolidation occur simultaneously. High quality standard and special (long term and relaxation) oedometer tests provided reliable values of Cc , Cr and σ’p and the OCR value of 2.1 as equivalent to the end of secondary consolidation allowing to estimate the total primary and secondary compressions of one of the most compressible layers (layer 6). No of the shelf tool is available to backanalyze the measured compression of a soft clay layer based on the adopted hypothesis. The first tool tested, the ε vs. log(σ’v) Bjerrum type abacus with lines of equal values built from the oedometer tests results, proved to be non applicable. The second tool tested, the same type of abacus extrapolated from the first one for the field conditions through Taylor and Merchant’s theory also proved to be non applicable. Both the third tool tested, the fitting of a theoretical Taylor and Merchant type curve to the measured compression curve in the area with no drain and the fourth tool tested, the fitting of a theoretical curve obtained through a method tailored by the authors designated “Primary Barron + secondary pseudo Taylor and Merchant” to the measured compression curves in the areas with wickdrains proved to provide excellent conformity of the theoretical and measured curves. The cv and ch field values thus obtained are of the same order of magnitude as the laboratory values and show the same trend to decrease when the effective stress increases, contradicting the current creed based on backanalysis through Asaoka’s method, i.e. considering that secondary consolidation only starts after primary consolidations ends, that field cv and ch values are commonly 10 to 100 times higher than laboratory values. Based on their results the authors conclude that the excellent conformity of the theoretical and the measured curves obtained with the working hypothesis they adopted, the results of the laboratory tests they performed and the tools they used for the back-analysis, leads to the conclusion that the working hypothesis, the laboratory tests and the tools proved to be very efficient and trustworthy in leading to reliable compressibility and consolidation parameters of the soft clay, and will be equally efficient and trustworthy when used for the final design of the improvement of the foundation soft clay layer

Compressive Behavior During the Transition of Strain Rates

ABSTRACT The application of a strain-rate-dependent model, for example, an isotache model, is very useful and highly effective for predicting the settlement due to consolidation, including secondary consolidation. In the isotache model, compression curves are not only determined by pressure, but also by strain rate. The validity of this model has been experimentally confirmed by many researchers using different types of oedometer tests, such as constant rate of strain (CRS) tests, incremental loading (IL) tests, etc. However, considerable scatter has been observed in the test results, which show the effects of the strain rate, and questions arise as to whether such scatter is caused by the heterogeneity of the soil samples or by the incompletion of the model. To avoid the heterogeneity of the tested samples, special CRS tests, in which the strain rate is not kept constant but is varied during the tests, were carried out on intact and reconstituted Osaka clay samples. The effects of the strain rate on the compressive behavior of these clays were carefully evaluated in terms of visco-plastic strain, assuming that the total strain consists of visco-plastic strain and elastic strain. It was confirmed that the stress and the visco-plastic strain relation of clay samples strongly depends on the visco-plastic strain rate. However, the effects of the strain rate, under a given constant visco-plastic strain rate, do not become constant when the visco-plastic strain rate becomes very small. The reason is assumed to be due to the development of structures under a constant small visco-plastic strain rate. The development of structures may restrict the applicability of the isotache model to the compressive behavior of clay.

Use and misuse of the isotache concept with respect to creep hypotheses A and B

Time-dependent settlements of thick in situ clay layers are normally analysed based on results of thin laboratory specimens. However, the time used to complete primary consolidation is significantly different for laboratory specimens and in situ soil layers. Two totally different cases, referred to as creep hypotheses A and B, have been used as a basis of discussion to assess the effect of creep during the primary consolidation phase. Several laboratory and field experiments have been conducted to study the effect of soil layer thickness on the time-dependent compressibility of a soil layer. Some of these tests seemed to support hypothesis A, others hypothesis B, and in some cases showed a behaviour between the two. As a result this question has continued to be a controversial topic among researchers, and remains to be an issue that needs to be resolved. In this study, some relevant experimental investigations from the literature are thoroughly studied and critically reviewed, and also explained consistently using the isotache concept. This work indicates that the isotache approach can capture the main characteristics of the time-dependent compressibility of clays during both the primary and secondary consolidation phases. It is also shown that the misuse of the isotache concept, as reported in the literature, may give a confusing picture of reality. Based on the considered data, it is demonstrated that the measured time-dependent compressibility of clays agrees well with hypothesis B.

Colonization in action: genetic characteristics of Daphnia magna Strauss (Crustacea, Anomopoda) in two recently restored ponds

New habitats are an interesting tool to monitor colonization processes in the light of changes in genetic structure and evolutionary potential of populations. Cladocerans are cyclical parthenogens that offer the possibility to track genetic changes during the colonization process due to the alternation of sexual and asexual phases. The locally called “malladas” are shallow and temporary peridunal ponds in Eastern Spain that were silted in the 1960s and have been recently dug to their original basin. We here describe the colonization process in two of these newly restored ponds by the cladoceran Daphnia magna during their first 3 years. This colonization process followed three critical steps: population founding by the initial colonists, arrival of secondary immigrants and consolidation of the population structure. We found a low number of genotype colonists followed by the establishment of secondary immigrants and a slight decrease in gene flow with time. We discuss the importance of dispersal, founder effects, natural selection, inbreeding depression and genetic drift during the colonization process in the light of the most recent literature.

Study on Secondary Consolidation Behavior of Soft-Clay Sediment from Lakes in Yinchuan

There are many soft-clay sediment foundations in Yinchuan area, most of which are made of soft-clay silt from lakes. Its secondary consolidation deformation occupies a large proportion of its total deformation, and displays a greater volume of settlement after work completion, which seriously influence the normal use of buildings. The orthogonal experiments are designed to study the influence of factors such as current stress, dry density and OCR on the secondary consolidation behavior of soft-clay sediment of lake in Yinchuan. The regulation and mechanism of secondary consolidation is revealed. Some useful conclusions are reached to provide reference for projects design and construction.

Temperature responsive flocculation and solid–liquid separations with charged random copolymers of poly(N-isopropyl acrylamide)

Temperature-responsive random copolymers based on poly(N-isopropyl acrylamide) (PNIPAM) with 15mol% of either acrylic acid or dimethylaminoethyl acrylate quaternary chloride were prepared. The effect of the charge and its sign were investigated in the solid–liquid separation of silica and alumina mineral suspensions. The results were compared to PNIPAM homopolymer of similar molecular weight. PNIPAM copolymers of the same charge as the particles (co-ionic PNIPAM) act as dispersants at both 25°C and 50°C. Flocculation occurs when counter-ionic PNIPAM facilitates selective aggregation and rapid sedimentation of minerals at both 25°C and 50°C. Adsorption and desorption studies showed that, unlike non-ionic PNIPAM, little desorption of the counter-ionic copolymers from the oxides occurred after cooling a suspension from 50°C to below the lower critical solution temperature. Thus, incorporation of counter-ionic charge into the temperature sensitive polymer PNIPAM was found to reduce the sediment bed consolidation upon cooling when compared to PNIPAM homopolymers. The lack of secondary consolidation upon cooling is attributed to attractive inter-particle forces, such as conventional polyelectrolyte flocculation mechanisms (bridging, charge neutralization or charge patch) which persist at both 25°C and 50°C when counter-ionic PNIPAM is used. On the other hand, it was possible to obtain rapid sedimentation with the counter-ionic PNIAPMs even when they were added to the suspension already at 50°C, a process which has not been possible with neutral PNIPAM homopolymers.

Abstract 3463: Treatment of young children with localized medulloblastoma by chemotherapy alone: Final results of the prospective multicenter trial HIT 2000 confirming the prognostic impact of histology

Abstract Background: This study was designed to confirm the previously observed favorable survival rates and prognostic factors in young children with non-metastatic medulloblastoma (MB) treated by postoperative chemotherapy alone. Methods: Patients diagnosed between January 2001 and December 2005 and younger than 4 years received three cycles of postoperative systemic multiagent chemotherapy and intraventricular methotrexate. In case of complete remission, treatment was terminated after two additional cycles of chemotherapy. Otherwise secondary surgery, radiotherapy and consolidation chemotherapy were recommended. Results: The 5-year event-free survival (EFS) and overall survival (OS) (±SE) rates of 45 patients were 57 ± 8% and 80 ± 6% (median follow-up: 4.5 years, median age: 2.5 years). Nineteen patients with desmoplastic / nodular MB variants had better EFS and OS (5-year rates: 90 ± 7% and 100 ± 0%) compared to 23 patients with classic MB (30 ± 11% and 68 ± 10%; p< 0.001 for EFS, p=0.008 for OS). Five-year EFS and OS rates of 3 children with anaplastic MB were 33 ± 27%. Desmoplastic / nodular histology was an independent prognostic factor for EFS. Twenty-nine of 30 (97%) patients without postoperative residual tumor remained in continuous complete remission. Conclusions: Our results confirm histology of MB variants as a strong prognostic factor in this age-group. Sustained tumor control and favorable survival rates can be achieved by this chemotherapy regimen in young children with desmoplastic / nodular MB variants. For children with non-desmoplastic / non-nodular MB variants, where predominantly local relapses lead to less favorable survival rates, local radiotherapy has been introduced after chemotherapy since 2006. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3463. doi:10.1158/1538-7445.AM2011-3463

Analytical solutions for advective–dispersive solute transport in double‐layered finite porous media

AbstractAnalytical solutions for advection and dispersion of a conservative solute in a one‐dimensional double‐layered finite porous media are presented. The solutions are applicable to five scenarios that have various combinations of fixed concentration, fixed flux and zero concentration gradient conditions at the inlet and outlet boundaries that provide a wide number of options. Arbitrary initial solute concentration distributions throughout the media can be considered via explicit formulations or numerical integration. The analytical solutions presented have been verified against numerical solutions from a finite‐element‐based approach and an existing closed‐form solution for double‐layered media with an excellent correlation being found in both cases. A practical application pertaining to advective transport induced by consolidation of underlying sediment layers on contaminant movement within a capped contaminated sediment system is presented. Comparison of the calculated concentrations and fluxes with alternative approaches clearly illustrates the need to consider advection processes. Consideration of the different features of contaminant transport due to varying pore‐water velocity fields in primary consolidation and secondary consolidation stages is achieved via the use of non‐uniform initial concentration distributions within the proposed analytical solutions. Copyright © 2010 John Wiley & Sons, Ltd.

Field Performance of PVD Combined with Reinforced Embankment on Peaty Ground

This paper describes the field performance of prefabricated vertical drains (PVD) used in combination with reinforced embankments on peaty ground. A large-scale field test of PVD adopted in combination with an embankment reinforced using galvanized steel grid was conducted on peaty ground in Hokkaido, Japan. Although the site was characterized by extremely soft peaty ground, a stable, high embankment 11.8 m in thickness was successfully constructed through the combination method. A consolidation-accelerating improvement from the PVD and a reinforcement effect from the steel grid were clearly observed, and settlement of the PVD-improved peat layer corresponded roughly with Barron's solution with consideration to well resistance. However, it was necessary to make the coefficient of consolidation nine times as large as that seen in the results of oedometer testing. The surcharge embankment allowed a reduction of the coefficient of secondary consolidation for the overconsolidated peat layer (overconsolidation ratio: approx. 1.13) to approximately 60% that of the normal consolidated layer.

Posttraumatic arthrodesis of the subtalar joint – outcome in workers compensation and rates of non-union

Regardless of the simple surgical technique, the success of the subtalar arthrodesis is limited by the rate of non-unions of the arthrodesis. The functional outcome of workers compensation is known to be poorer compared to patients without pending litigation. The aim of this study was to quantify the rate of non-unions and to determine risk factors leading to failure of the osseous consolidation after arthrodesis of the subtalar joint. The outcome assessed is a general health assessment with the SF-36 questionnaire and more illness specific with the AOFAS hindfoot score. Secondly, the influence of the health insurance status of the patients with or without worker's compensation on the outcome was tested. The inclusive criterion was an arthrodesis of the subtalar joint with and without autologous cancellous bone grafting and screw osteosynthesis. This cohort study included the clinical course of 115 patients with posttraumatic osteoarthritis from 2000 to 2006. The average age of the patients (n=115) was 47±11.0 years, 83% of the treated patients were men. 68% of the patients suffered of secondary osteoarthritis after calcaneal fracture. The time interval from trauma to presenting at the physician due to therapy resistant pain was in the average 5.5±9.9 years. After primary arthrodesis (n=101) of the subtalar joint osseous consolidation was proved in 55% cases, consolidation was questionable in 21% and the rate of no consolidation with revision was remarkable high with 24%. The duration of osseous consolidation was proved by plain projection radiography or computer tomography and clinical reduction of pain. For primary arthrodesis osseous consolidation was reached after 6.4±6.3 month, after secondary arthrodesis osseous consolidation was reached after 9.4±13.1 month. After revision surgery 57% of the arthrodesis healed, 12% the osseous consolidation was questionable, and the failure rate was still 12%. The outcome measures of the patients with SF-36 and the more functional related AOFAS hindfoot score showed poor outcome rates after subtalar fusion in posttraumatic osteoarthritis. The AOFAS hindfoot score was 47±24 points after primary arthrodesis and 46±17 points after secondary arthrodesis of the subtalar joint. The patients regained their former ability to work only in 30% after fusion of the subtalar joint. If revision surgery was necessary 8% of the patients got back to their work prior to the injury.

The sedimentary structure of Upper Pleistocene–Holocene deposits in Venice and its effects on the stability of the historic centre

The results of a recent study (Geologia e Progettazione nel centro storico di Venezia”, Secondo Convegno Nazionale: La riqualificazione delle città e dei territori, Venezia 7 dicembre 2007, Quad. IUAV 54, Il Poligrafo ed. 2008) focused on Venice’s historic centre have led to the identification of a peculiar sedimentary structure (multistorey sandbody). This structure was created during the Upper Pleistocene by the multiple overlapping of sandbodies corresponding to stream channels, all of which crossed the area where the city now lies. The erosion and deposition events responsible for these stratigraphic conditions are the effects of both climatic variations during the Wurmian glaciation and changes in the fluvial regime. The sedimentary structure was completed during the Holocene by the deposition of sand in fluvial and tidal channels on top of the previous Pleistocene stream channel sediments. The deposits of this structure are heteropic with those of the rhythmic succession (cyclothemic organization) belonging to the alluvial plain of the Upper Pleistocene and the Holocene lagoon facies of tidal plain found in the surrounding area. The geological model of the city is able to explain the mechanical behaviour of the soil in the western and eastern areas of the historic centre where the losses in elevation are considered at present as a consequence of the urban development in the last centuries, since the vertical movements due to groundwater exploitation of the deep aquifers have more than likely ended. According to a methodology known as operational facies concept, which first determines the facies relationship, then discriminates the intervals with lithological variability and finally fits together the information coming from the terrain properties, it can be inferred that the losses in elevation are related to the evolution of the deformation processes acting nowadays in the urban settlement. The results of the aforementioned study reveal, in fact, that these processes are provoked by the residual component of a long-term secondary consolidation and by the geochemical subsidence which occurs between salt water intrusion and clay containing organic matter and peat.

A general framework for modeling long-term behavior of earth and concrete dams

Many problems are linked with the long-term behavior of both earthdams and concrete dams. They range from hydraulic fracturing to alkali-silica reaction (ASR) and to repair work in concrete dams, from seismic behavior to secondary consolidation in earthdams. A common framework for the simulation of such systems is shown, based on the mechanics of multiphase porous media. The general model is particularized to specific situations and several examples are shown.

Expression of reversion-inducing-cysteine-rich protein with Kazal Motifs (Reck) during mouse endochondral ossification

on final consolidation are achieved with daily administration of 40 μg/kg of PTH1-34. Our results suggest the existence of a natural window of treatment efficacy in mouse peaking 18 d. after fracture. Healing processes are anticipated and enhanced from early teriparatide administration. Further applications of the study could be the treatment of osteoporotic or secondary fractures, consolidation delays and non-unions. Disclosure of Interest: None declared

Ramifications of high in-situ temperatures for laboratory testing and inferred stress states of unlithified sediments – A case study from the Nankai margin

The recovery of drill cores involves changes in pressure and temperature conditions, which inevitably alter the mechanical properties of unlithified sediments. While expansion from unloading after core recovery is well studied, the effects from cooling on standard geotechnical tests are commonly neglected. Along the central portion of the Nankai margin sediments were recovered from high in-situ temperatures of up to 110 °C during IODP Leg 190. So far, the interpretation of the consolidation state of the Lower Shikoku Basin facies (LSB) entering the accretionary Nankai margin is ambiguous. Results from laboratory consolidation tests at room temperature show high pre-consolidation stresses. These were interpreted as hardening caused by cementation, while the field-based porosity vs. depth trend points towards normal consolidation. As an explanation for this discrepancy, the change of the mechanical properties by cooling from in-situ to laboratory conditions is proposed. In this paper, the results of a thermo-mechanical model are compared to published field data. This comparison suggests that the observed hardening is at least partially an artefact from cooling during core recovery, and that the strata may be considered normally consolidated to slightly overconsolidated. The latter can be explained by minor cementation or the influence of secondary consolidation. The results suggest that cooling from high in-situ temperatures may be important for the interpretation of the consolidation state of other sedimentary successions elsewhere.

Swelling behavior of expansive soils

Volumetric changes (usually swell) of expansive soils in presence of water are undesirable from stability reasons. Swell and Swelling pressure of an expansive soil is primarily dependent on the initial dry unit weight or void ratio and also on the moisture content. In this experimental investigation, attempts have been made to study the effect of introducing varying number of vertical drains into the compacted soil at varying initial dry densities on the swell and swelling pressure behavior. Both percent swell and the swelling pressure are significantly influenced by the presence of vertical drains (facility of water availability). The percent swell versus time relationship could be identified as a rectangular hyperbola, facilitating the prediction of ultimate percent swell. This is advantageous to predict the swell from the data obtained from the initial stages of the swell test and the experiment could be terminated without continuing till equilibrium conditions are reached. This concept was also extended to predict swelling pressure determined by constant volume method. Irrespective of the presence or absence of drains, the density effect on rate of secondary swelling and consolidation behavior of swollen sample was found to be almost the same for all testing conditions used in this study.