Primary Consolidation Research Articles

The long-term effects of school consolidation on human capital formation

ABSTRACT This study investigates the long-term effects of school consolidation on human capital formation. We explore the implementation of a large-scale primary school consolidation programme in rural China aimed at improving the quality and efficiency of education. Using a difference-in-differences strategy, we find that exposure to the programme significantly increases the number of years of schooling completed by rural children. The effect changes with exposure duration to the RPSC programme and is stronger for children from areas with low economic development, areas with low educational inputs, and families with low parental education. Moreover, we provide evidence that improvements in input-based and output-based school quality are important mechanisms by which the programme affects educational attainment. Finally, the results of further analysis alert us to the adverse effects of the programme on noncognitive skills such as agreeableness and emotional stability, as well as on labour supply time in adulthood.

Retrospective evaluation of large settlements of a very soft clay: Alameda, California

The Harbor Bay Isle residential project in Alameda, CA, USA, comprises some 600 acres (243 ha) reclaimed from the margin of San Francisco Bay underlain by very soft (C c ∼ 1), high-water-content clay (e 0 > 2): San Francisco Bay Mud. Settlements of as much as 2.5 m developed from about 7 m (varying across the site) of sandfill surcharge, with records over some 43 years extending through primary consolidation and into secondary consolidation (creep). Iterative numerical modelling using large-strain theory (implemented in the Microsoft Excel software program), constrained by in situ void ratios and oedometer trends, achieved close matches with settlement histories over the full 43 years for the three locations considered, each of which displayed a markedly different history from the others. The presence or absence of a dried ‘crust’ was found unimportant; instead, the proportion of subunits within the Bay Mud controlled the evolution of settlements. Subunits within Bay Mud, evident in modern cone penetration test soundings (which were not available during the reclamation works), exist across the region and have systematically different states and properties. Further, while ageing is a factor, depositional conditions of the Bay Mud have produced a residual fabric that presents as a component of the pre-consolidation pressure.

Testing Procedures on the Assessment of the Effects Temperature on Residual Shear Strength of Soils

Testing Procedures on the Assessment of the Effects Temperature on Residual Shear Strength of Soils

Interfragmentary screws in Danis and Weber type B ankle fractures: is it necessary to maintain the stability of the joint?

OBJECTIVE: This study aimed to investigate whether the presence or absence of an interfragmentary screw significantly impacts surgical time, bleeding, consolidation, complications, and overall recovery in patients with Weber type B ankle fractures. METHODS: A cross-sectional analytical study was conducted, involving 47 patients with Weber type B ankle fractures between January 2022 and January 2023 at San Francisco General Hospital in Quito. Patients with multi-fragment fractures were excluded. and two groups were established: patients with interfragmentary screws and those without. Variables such as surgical time, bleeding, complications, and consolidation time were assessed using JASP 0.16.0.0 software and statistical tests. RESULTS: Out of all patients, 53.19% were treated with interfragmentary screws, while 46.80% were not. No statistically significant differences were observed between the two groups. Complications occurred in 7 out of 25 patients with interfragmentary screws and in 4 out of 22 patients without them, with average follow-up periods of 82.81 and 76.8 days, respectively. Consolidation time was similar in both groups, with no statistical differences. CONCLUSION: Although interfragmentary screws are beneficial for achieving primary consolidation, this study suggests that they may not be universally necessary, especially when precise anatomical reduction is accomplished. Anatomical reduction remains pivotal in fracture management. While interfragmentary screws can provide compression, their use may increase costs, recovery time, and complications.

Primary and secondary consolidation characteristics of a high plasticity overconsolidated clay in compression and swelling

For a reliable prediction of the time-development of soil deformations, a detailed characterization of both primary and secondary deformations is required. Nevertheless, in the current engineering practice the estimation of the primary and secondary deformations relies on the assumption of a constant coefficient of consolidation and a constant creep index respectively. However, high plasticity overconsolidated clays have reportedly complex stiffness and permeability relationships that challenge the validity of those assumptions. Analytical solutions of the one dimensional consolidation have been proposed, accounting for variation in permeability and oedometer modulus. Nevertheless, the methods assume a simplified log-linear and linear relationship with void ratio and effective stress for the two parameters, respectively. One-dimensional oedometer and constant rate of strain testing were employed to investigate the time-deformation development of a particular high plasticity overconsolidated clay. A dependency of the time until the end of primary deformations on the stress path was observed, with the majority of the unloading steps extending well beyond the 24 h typical duration of a load increment. It was revealed that the coefficient of consolidation generally increases during consolidation, and it may vary by more than one order of magnitude at the early stages of the consolidation process. This variation has been attributed to a transient effect noticed in the permeability, which has not been previously reported. The linear relationship between primary and secondary deformation indices was confirmed as an upper bound. In an effort to better characterize the time dependent behaviour a new index, the primary time deformation index, was defined as the slope at the inflection point of the time-curves. This parameter was found to be linearly related to the creep index, presenting thus a potential of better predictions of the duration and magnitude of consolidation deformations for the engineering practice.

Analysis of long-term settlement of road embankment on peat ground during its service period

Roads on peat grounds are subject to stringent requirements in terms of controlling the residual settlement during their service period in order to minimize the post-construction maintenance work. This paper addresses the applicability of the Finite Element Method (FEM) by incorporating a time-dependent model for peats to an evaluation of the residual settlement. The applicability of isotach viscoplasticity, used to describe the peats’ behavior under variable-rate compression, was confirmed in laboratory tests. Long-term consolidation test results and a model simulation revealed the particular importance of two mechanisms in the residual settlement in peat grounds, namely, the stress-dependency of the coefficient of consolidation, cv, and the viscosity-induced secondary consolidation. A model peat ground, capturing these mechanisms, was implemented for the FEM and applied to a case history of a high-standard road construction in Hokkaido, Japan. The viscoplastic parameters determined from standard oedometer tests successfully reproduced the observed long-term settlement in a peat-dominated section of the expressway. The analysis was extended to address the settlement in the peat ground with the installation of prefabricated vertical drains (PVDs). The results indicate that the delayed primary consolidation due to the stress-induced cv reduction can be significantly alleviated, while the settlement arising from the secondary consolidation over a longer term is little affected by the PVDs. These insights point to the importance of untangling the two mechanisms of long-term settlement for the sake of making accurate predictions of the residual settlement in different time scales.

Autologous Transplantation May Still Effectively Treat Relapsed Diffuse Large B-Cell Lymphoma in Selected Patients.

Treating relapsed and refractory diffuse large B-cell lymphoma is still challenging for clinicians, but the available CAR-T and bispecific antibodies have revolutionized therapy. Autologous stem cell transplantation was the most effective treatment modality previously. The authors reported data from a single center over ten years. The retrospective study included 116 patients, with 53 relapsed cases, 39 primary refractory cases, 19 who had CNS involvement, and 5 who had received primary consolidation transplants. The median duration of follow-up was 46 months. The median event-free survival was 75 months, and the median overall survival was 105 months for all cases. Five-year overall survival was 59%, and event-free survival was 54%. Pretreatment prognostic factors at diagnosis had no effect on the outcome of transplantation. The authors found no difference between survival in relapsed or refractory cases, and the number of salvage lines or the germinal center/activated B-cell type also did not influence the results. Complete metabolic response before transplantation confirmed by 18FDG PET/CT strongly affected survival. The pre-transplant creatinine and CRP levels significantly influenced the long-term outcome. The number of stem cells infused did not affect survival, but engraftment within nine days did result in a longer survival. These data support the finding that the response to salvage therapy did facilitate the identification of a better prognostic group who may still benefit from autologous transplantation.

Electronic structure of the atom in virtual reality: integrated lesson of chemistry and informatics

The article discusses the possibilities of using virtual reality systems in an informatics lesson in conjunction with such a discipline as chemistry. It substantiates the conduct of an integrated lesson in chemistry and informatics. The lesson on the theme "Electronic structure of the atom in virtual reality" is given. At the motivational-target stage of the lesson, such methodological techniques as "Quoting the statements of famous people" and "Photography" are used. At the stage of knowledge actualization, repetition of information about the virtual reality system was organized; how to properly put on a virtual reality helmet and controllers; the basic safety rules for being in virtual reality are discussed. Also at this stage, students repeat information about the structure of atoms. At the stage of learning new material, the purpose and interface of the Abelana's Atom Maker VR virtual reality application, which is involved in the integrated lesson, are described. At the stage of primary consolidation, tasks in chemistry are proposed, which should be implemented in the virtual reality application Abelana's Atom Maker VR. Reflection of educational activity is carried out using the "10 opinions" technique. Homework includes watching a video on the basis of which a similar task formulated by the teacher is performed.

A Comparative Case Study on Drainage Consolidation Improvement of Soft Soil under Vacuum Preloading and Surcharge Preloading

Based on an improvement project of soft soil ground in Zhuhai City on the Pearl River Delta, a comparative study on vacuum preloading and surcharge preloading was performed. The ground and stratified settlements, excess pore water pressure, and the degrees of consolidation of soft soil are analyzed, along with the horizontal displacement and soil strength. The results show that surcharge preloading results in smaller secondary consolidation settlements than vacuum preloading. Primary consolidation settlement quickly increases with increasing excess pore water pressure of less than −40 kPa in vacuum preloading, while also increasing between 20 kPa and 25 kPa in surcharge preloading. The sharp increase in the strata permeability coefficient will induce the increase in strata consolidation degree and has little effect on the ground consolidation degree. The surcharge preloading can be given priority to reduce the settlement foundation in the service stage.

Land Subsidence Phenomena vs. Coastal Flood Hazard—The Cases of Messolonghi and Aitolikon (Greece)

Land subsidence in coastal and delta cities often results in infrastructure and residential building damages, while also increasing the area’s flooding vulnerability. The coastal cities of Messolonghi and Aitolikon are typical examples, as they are built on top of old stream deposits near the coast. In the last several years, the gradual subsidence of the sites, combined with the impact of climate change, resulted in multiple floods. The rush of seawater over the lowlands has also been reported. Persistent scatterer interferometry (PSI) is a remote-sensing technique that can provide a reliable and cost-effective solution, as it can be used to identify and monitor soil displacements. In this study, a novel parallelized PSI (P-PSI) processing chain, developed by the Operational Unit Center for Earth Observation Research and Satellite Remote Sensing (BEYOND) of the National Observatory of Athens, as well as the Copernicus EGMS product were used to identify these displacements. The results were examined in correlation with other potential factors such as the overexploitation of the underground water, the natural compaction of the clay soil layers, the primary and secondary consolidation due to the external construction loading, the oxidation of the organic soils, tidal gauge data, precipitation data, and ground truth data. In Messolonghi, various deformation rates were recorded, with maximum mean values of −5 mm/year in the eastern part, whereas in Aitolikon, the maximum values were around −4.5 mm/year. The displacements were mostly attributed to the primary consolidation due to the building loads. Deformation patterns and their correlation with precipitation could also be witnessed. It was evident that the increased precipitation rates and sea level rise played a leading role in the constant flooding.

Effect of the Organic Matter Content on the Mechanical Properties of Soils Stabilized with Xanthan Gum

The aim of this paper is to study the effect of the organic matter (OM) content on the effectiveness of the soil stabilization process using the biopolymer xanthan gum. Five different artificial soils with an organic matter content in the range of 1.5 to 7.7% are subjected to unconfined compressive strength (UCS) and oedometer tests to evaluate their strength, stiffness and compressibility, respectively. These results are complemented by an analysis of SEM images. The results from the UCS tests show a positive effect of the stabilization process in terms of strength and stiffness in a range of an OM content of 1.5 to 5.5%, but a detrimental effect for a higher OM content (7.7%) is observed. Due to the hydration of the biopolymer’s hydrogels, the compressibility tends to increase in specimens stabilized with xanthan gum. This effect is amplified for higher OM contents. The results of oedometer tests also show that the stabilization with xanthan gum brings about a significant decrease in the coefficient of consolidation, inducing an increase in the primary consolidation time.

Improved analysis and design for surcharging

Surcharging or preloading is one of the oldest and most widely used in situ ground improvement techniques to strengthen weak compressible clays and to remove undesirable settlements prior to erection of permanent infrastructure. Recently, the ground improvement technique has been adopted in combination with many other techniques. The current design methodology for surcharging based on the concept of average degree of consolidation is inadequate, as all the primary consolidation settlement to be induced by the permanent load is not eliminated by the surcharging process. The problem is quantitatively analysed using Terzaghi's one-dimensional consolidation theory. The proportion of residual primary consolidation settlement is quantified, and the starting time of the re-occurrence of primary consolidation on exertion of the permanent load is determined. The effect of a change in surcharging duration on the proportion of residual settlement is quantified. The results are presented in design charts to facilitate application of the results by practicing geotechnical engineers.

Coupling Numerical Analysis Method for Primary and Secondary Consolidation of Soft Soil Foundation

Soft clay is widely distributed in our country, and this type of soil usually has the character of large compressibility and poor permeability, so the foundation composed mainly of soft clay is prone to primary and secondary consolidation coupling settlement deformation after the completion of construction. In this paper, secondary consolidation deformation is redefined in the improved time logarithmic coordinate system, and the calculation formula of secondary consolidation deformation is given. Then an extended unified hardening model is introduced, and by applying this model, the effect of time can be transformed to the increment of equivalent stress. The numerical governing equations are established in combination with the seepage consolidation theory. Thus the coupling analysis of primary and secondary consolidation of soft clay foundation can be realized. By means of a finite element case analysis and verification of subgrade construction and post-construction deformation, it is found that the effective calculation of primary and secondary consolidation deformation can be accomplished smoothly based on the extended unified hardening model, and meanwhile the permeability coefficient and secondary consolidation parameters are able to effectively control the primary consolidation deformation and secondary consolidation deformation of soft clay foundation. The research is valuable to develope the prediction method of soft clay foundation deformation and improve the prediction accuracy of soft clay foundation deformation in engineering, and it is of great significance to solve complex geotechnical engineering problems.

Effect of clay with high water adsorption capacity on process of secondary consolidation of peat

Introduction. Primary consolidation of peat, underlying an embankment, is completed 3 to 5 years after its filling. It is followed by secondary consolidation, caused by removal of bound moisture from micropores. At this stage, the settlement rate depends on the degree of peat decomposition, temperature, content of various chemicals in the pore water, vibration effects, and other factors. To reduce the embankment deformation, caused by the secondary consolidation, peat is either modified by binding compounds, having filling agents, or other actions are taken to accelerate the settlement process for a short term and to decelerate it thereafter using temporary surcharge, electroosmosis and other actions.
 
 Materials and methods. The authors studied the effect of peat dehydration using clayey materials with high water adsorption capacity, such as bentonite and saponite waste generated by the diamond mining industry. 100 days oedometer tests were carried out. In the course of testing, vertical cylindrical elements, made of the above materials, were installed in the specimens. These cylindrical elements occupied about 10 % of the specimen volume.
 
 Results. Bentonite inclusions, formed without any peat extraction, had a powerful effect on development of deformations. Intensive dehydration of peat led to a 2–4 times increase in the coefficient of secondary consolidation сαε. Following 25 to 30 days of intensive settlement, the value of the cαε coefficient went down by an average of 1.5 times relative to its initial value. The effect of elements, made of saponite-containing waste, turned out to be different. The value of the cαε coefficient increased by 11 to 15 %, but 20 to 30 days later it went down by an average of 2 times relative to the initial value. Higher resistance of elements to vertical loading served as the factor preventing the development of settlement.
 
 Conclusions. Clay has a high water adsorption capacity, and its intrusion into peat results in accelerated water migration from micropores and boosts the rate of secondary consolidation. In addition to peat dehydration, secondary consolidation was accelerated by mechanical compaction in the process of adding clay into specimens followed by clay swelling.

One-Dimensional Computational Model of Gyttja Clay for Settlement Prediction

One of the most important subjects of geomechanics research is finding mathematical relationships which could correctly describe behavior of the soil under loading. Safety of every engineering structure depends strongly on accuracy and correctness of this description. As laboratory tests show, macroscopic properties of soil are complicated. Therefore, working out appropriate load-settlement relationships is considered to be a very difficult geomechanics tasks to solve. A majority of constitutive models proposed to date concern mineral soils and there is very little research related to modelling organic soil behavior under loading. In case of organic soils, due to their very complicated and composite structure, constitutive models are often formulated empirically based on laboratory tests of particular soils. The authors of this paper propose a 1-D rheological structure which accounts for complex behavior of soil related to the settlement process. The model simulates immediate reversible elastic settlement and plastic soil deformation as well as primary and secondary (creep effect) consolidation. Material parameters of the model were determined by a curve fitting procedure applied for a natural scale settlement test of plate foundation. The test was carried out in soil conditions connected with Eemian geological structure of Warsaw, i.e., Eemian glacial tunnel valley in Warsaw called Żoliborz Glacial Tunnel Valley filled with organic soils being up to 20 metres thick. This area has lately become an object of interest of investors as a site for building construction.

THE EFFECT OF ADDED NICKEL SLAG TO COMPRESSION AND SHEAR STRENGTH ON LATERITE SOIL SOUTH KALIMANTAN

Laterite soil is an embankment soil that is often used because it is easy to find and is widely found in South Kalimantan. However, this land has many shortcomings to be used as embankment soil. This is because the lateritic soil has a clay content and a high Plasticity Index (PI) value. So the quality is still questionable to be used as landfill. To overcome this, it is necessary to improve or stabilize the lateritic soil. In this study, the lateritic soil was stabilized by the addition of slag nickel This study aims to determine the physical characteristics of laterite soil after being given a mixture of nickel slag addition, this study also aims to determine the effect of the percentage of nickel slag on primary consolidation (Sc) of laterite soil. As well as knowing the effect of the percentage of nickel slag on the parameters of shear strength in the form of cohesion (c) and shear angle (f). Consolidation and shear strength specimens were made with 90% of the optimum moisture content. The variations of the nickel slag mixture used in this study were 0%, 5%, 10%, 15%, and 20% of the weight of the soil used. Based on the results of data analysis, the addition of a mixture of nickel slag in each sample variation can reduce the plasticity index value of the lateritic soil. In addition, the addition of nickel slag also affects the value of the primary consolidation settlement value (Sc) of the laterite soil. The addition of the percentage of nickel slag also affects the parameters of the shear strength of the soil, for the cohesion value (c) of the laterite soil experiences a value that decreases with the increase in the percentage of nickel slag. Meanwhile for the shear angle (φ) of the laterite soil, the value increases with the increase in the percentage of nickel slag.Keywords: laterite soil, nickel slag, plasticity index, consolidation of laterite soil, shear strength of laterite soil

One-dimensional cyclic loading tests on saturated and unsaturated sand-clay mixtures

A series of one-dimensional cyclic loading tests are carried out on three different proportions of Sydney sand – kaolin mixtures, at various initial degrees of saturation. The settlement of the samples throughout the tests is accurately monitored. The effects of the degree of saturation and frequency of the cyclic load on the evolution of the settlement during the tests are thoroughly investigated for each mixture. The settlement patterns are compared to those of saturated samples to highlight the effect of soil suction on the behaviour. The results show that soil settlement decreases while the time required for the completion of the primary consolidation increases with the decrease in the degree of saturation of the soil. This trend is more pronounced in soils with higher kaolin content. The loading frequency, however, seems to have negligible effects on the settlement behaviour of unsaturated soils under cyclic loading. The result of the study provides valuable data for future simulations and validations of various constitutive models.

Numerical analysis of time-dependent negative skin friction on pile in soft soils

The generation of negative skin friction (NSF) induces the additional axial force on the pile, which exerts a detrimental load rather than a beneficial one. However, the effect of soil creep on the long-term development of NSF has remained poorly understood. The study uses numerical analysis to investigate this effect. First, an elasto-viscoplastic model with an enhanced time integration algorithm is successfully implemented into a finite element code. Next, the two-dimensional axisymmetric pile-soil interaction model is established and properly calibrated with a known field case. Finally, parametric studies are conducted to examine different degrees of creep effect on the variation in NSF and neutral plane (NP) within the primary and secondary consolidation periods. According to the findings, a high creep coefficient of the soil results in an increase in NSF and descending trend of the NP. The creep induced delay of NSF is observed attributed to the increase in excess pore pressure during the early stage of consolidation. The NP position varies drastically at the commencement of consolidation when taking creep into consideration. Lastly, the study proposes an exponential prediction model to reflect the time dependence of the location of the NP.

Study of Energy Dissipation in a Two-Phase Soil System

The dependence of energy dissipation coefficient on filtration properties and on creep characteristics of soil skeleton is examined. The study was carried out on the basis of the general solution of the joint task of creep and consolidation theory for a two-phase soil system obtained on the basis of the generalized model of bulk forces, taking into account the interaction of soil phases, changes over time in the general stress state at any point of the soil and additional pressures in pore water, and incomplete transfer of external pressure to the pore water. Interactions between phases are taken into account in the solution of the one-dimensional joint task of the theory of creep and consolidation, and the creep kernel is taken in the form of an exponential function. The formula for the deformation of two-phase soils is presented as the sum of two syllables due to primary and secondary consolidation of the soil. The strain formula uses experimentally obtained values of filtration characteristics and creep parameters of the soil skeleton. Using the formulas obtained, hysteresis loops under sinusoidal stress changes can be plotted and the energy expended per deformation cycle and the dissipation coefficient for two-phase soil can be obtained.

Experimental study on consolidation characteristics of deep clayey soil in a typical subsidence area of the North China Plain

Land subsidence is an important environmental problem in the North China Plain (NCP). A typical subsidence area mainly located on adjoining areas of Beijing and Hebei provinces was selected to study the consolidation characteristics of deep clayey soil. Clay samples were collected from 14 boreholes at different depths, and the compression and consolidation behavior of the soil was analyzed by high-pressure oedometer tests. Results show that the deformation amount and deformation stabilization time in the primary consolidation stage increase with the load but decrease with the sampling depth. The nonlinear compression model of e-log(p) does not fit well for deep normally-consolidated clayey soil, the log(e+ec)–logp model fit the shallow clayey soil better than the deep clayey soil, and the hyperbolic model fits almost all soil samples well. Based on statistical theory, the soil consolidation equation CE_NCP was established for calculating the relationship between the degree of consolidation and the time factor in subsidence areas. The equations were fitted with the data obtained from high-pressure consolidation tests to obtain three parameters a, b and c, which are applied to the consolidation calculations for soil samples at depths of 0–100 m, 100–200 m, 200–300 m and 300–400 m, respectively. The applicability of CE_NCP equation was evaluated by comparing it to the analytical solution of Terzaghi’s consolidation equation, results showing that CE_NCP equation is more suitable for the calculation of the consolidation in the study area than the Terzaghi’s analytical solution. Eventually, the CE_NCP equation was successfully used to estimate the degree of consolidation in a subsidence area of Lang Fang City in the NCP.