Dredger Fill Research Articles

Consolidation Theory Selection of Dredger Fill

Consolidation Theory Selection of Dredger Fill

Anisotropy Study on the Process of Soil Permeability and Consolidation in Reclamation Areas: A Case Study of Chongming East Shoal in Shanghai

Anisotropic permeability is of great significance for assessing the consolidation and drainage mode of soil layers in reclamation areas, as well as for preventing and controlling ground settlement after project construction. This paper analyzes the anisotropic permeability of the inland and nearshore soil layers in Chongming East Shoal, Shanghai, and the formation mechanism of anisotropic permeability through permeability and scanning electron microscope (SEM) tests. The results highlight that compared with dredger fill and sandy silt, the horizontal permeability coefficient of underlying soft clay (USC) is significantly higher than its vertical permeability coefficient, which is more significant in nearshore USC. Interestingly, the upper clay (21.5 m) in the thickest clay layer shows greater anisotropic permeability than the lower clay (41.5 m). Due to the instability of seepage channels, the USC anisotropic permeability increases in a fluctuating manner as the hydraulic gradient increases. Microstructural parameters are used to reveal the mechanism of anisotropic permeability, which shows that a simple soil skeleton and structure, strong particle orientation, decreased particle abundance, increased particle roundness, decreased particle contact area, and increased pore area all contribute to the enhancement of permeability. Moreover, micro-parameters have been proposed to evaluate anisotropic permeability in terms of the effective seepage-pore area. This approach addresses the constraint of water films on the permeability efficiency of USC particles.

The Influence of Different Curing Environments on the Mechanical Properties and Reinforcement Mechanism of Dredger Fill Stabilized with Cement and Polypropylene Fibers.

An effective method widely used in geotechnical engineering to solve the shrinkage and cracking issues in cement-stabilized soil (CS) is evenly mixing randomly distributed fibers into it. Dredger fills stabilized with cement and polypropylene fibers (PFCSs) are exposed to rainwater immersion and seawater erosion in coastal areas, influencing their mechanical performance and durability. In this study, direct shear and consolidation compression tests were conducted to investigate the influence of different curing environments on the mechanical properties and compressive behavior of PFCSs. Dominance and regression analyses were used to study the impact of each factor under different curing regimes. The reinforcement mechanism of different curing environments was also explored using scanning electron microscopy (SEM) imaging. The results show that the cohesion and elastic modulus of the specimens cured in seawater were reduced compared with those cured in freshwater and standard curing environments. The best fiber content for the strength and compressive modulus of PFCSs was determined to be 0.9% of the mass of dredged fill. The results of value-added contributions and the relative importance of each factor in different curing environments show that the overall average contribution of cement content in the seawater curing environment is reduced by 6.79% compared to the freshwater environment. Multiple linear regression models were developed, effectively describing the quantitative relationships of different properties under different curing conditions. Further, the shear strength was improved by the coupling effect of soil particles, a C-S-H gel, and polypropylene fibers in the PFCSs. However, the shear strength of the PFCSs was reduced due to the structural damage of the specimens in the freshwater and seawater curing environments.

Chloride Transport Characteristics of Concrete Exposed to Coastal Dredger Fill Silty Soil Environment

In contrast to the marine environment, coastal regions encompass substantial saline soils characterized by complex corrosive chemical compositions. This poses notable challenges to the durability of concrete structures erected in coastal dredger fill silty soil environments. This research undertook concrete chloride corrosion assessments in both a dredger fill silty soil environment and a simulated solution environment. The findings demonstrated a progressive escalation in the free chloride concentration within concrete specimens, as the exposure duration was extended from 60 to 120 d, and discernible convection zones were observed with depths ranging from 6 to 8 mm. The investigation revealed a diminishing trend in the apparent chloride diffusion coefficient, corresponding to the elongation of exposure time and the augmentation of burial depth. Paradoxically, the burial depth and exposure duration exhibited converse effects on the apparent surface chloride concentration. Empirical formulations were derived to express the apparent surface chloride concentrations and apparent chloride diffusion coefficients as dependent on the exposure time and burial depth variables. These models exhibited an excellent goodness of fit, reaching up to 0.96. Notably, concrete specimens interred at a depth of 0.0 m displayed a favorable likeness to the simulated solution environment throughout the 60 d exposure period.

Permeability of High Clay Content Dredger Fill Treated by Step Vacuum Preloading: Pore Distribution Analysis

In this study, the step vacuum preloading method was used to reinforce high clay content dredger fill in the laboratory. The pore structures and permeability characteristics of dredger fill under different vacuum pressures were tested. The correlation between the pore structure parameters and permeability coefficient was analyzed using the grey T’s correlation analysis method. The research results indicate that the pore ratio, large pore (the diameter with a range of 4–40 μm) content, and permeability coefficient of dredger fill decreased with the increase in vacuum pressures, but the decrease rates of the pore ratio were different at various sampling locations. The contents of micropores (the diameter with a range of <0.04 μm) and small pores (the diameter with a range of 0.04–0.4 μm) increased with the increase in vacuum pressure. The results of the correlation analysis showed that a large pore content had a strong correlation with the permeability coefficient and could be used to describe the permeability characteristics of soil. The research results can provide reference for the improvement of the reinforcement method and for the evaluation of the reinforcement effect of dredger fill in engineering practice.

Dynamic properties of dredger fill involved coupling action of initial stress and principal stress rotation

GCTS hollow cylinder apparatus was used to perform a series of tests on dredger fill from Tianjin under different initial stress states. This cyclic loading mode can simulate the rotation of the principal stress direction induced by wave loading. The effects of the initial intermediate principal stress parameter, initial shear stress and initial orientation angle of principal stress on softening index of dredger fill were investigated. A stiffness softening model which can consider different initial stress states was established. The test results show that when two of the three initial stress parameters remain unchanged, the softening index decreased with the increase of any other parameter. Among them, the initial orientation angle of principal stress has a great influence on stiffness softening. Based on the regression analysis of the test data, the relationship between the generalized shear strain ratio and the number of cycles under different cyclic shear stress amplitudes is proposed. Subsequently, the dynamic strength characteristics of the dredger fill were studied. It is found that the dynamic strength decreased significantly with the increasing initial angle of the principal stress, which can be accurately described by the model proposed in this article.

A settlement prediction model for shallow dredger fill improved by vacuum preloading

To investigate the settlement behaviour under alternate vacuum preloading, a series of laboratory tests considering different influencing factors, such as vacuum pressure and alternating criterion, were conducted. Based on experimental data, a new settlement prediction model, which can synthetically reflect the effects of vacuum pressure, alternating criterion, and improvement time, was proposed. The prediction model took into account the influence of improvement depth and variations in vacuum pressure. The model was validated using several case studies and laboratory tests. Comparisons between the proposed model and layer-wise summation method results indicate that the calculated results of the proposed model are closer to the actual settlement with errors consistently less than 10%. The proposed model can conveniently and accurately predict the ultimate settlement of high water content dredger fill improved by vacuum preloading method.

Study on the Safety Analysis of Dredger Fill Sea Sand Reused in Embankment Slope near the Yangtze River

In view of the shortage of sand and gravel aggregates, the sea sand in coastal areas is used as roadbed filler in road restoration of tunnel project by the Yangtze river. The basic mechanical performance tests were carried out to demonstrate the particle gradation and consistency limit of dredger fill sea sand. Triaxial test and direct shear test were performed to analyze the stress-strain relationship of sea sand shear strength in riverside environment and the law of shear displacement under vertical pressure. The road performance was analyzed by testing the compaction characteristics and deformation resistance of dredger fill sea sand. The riverside slope is always damaged by water flow, therefore, the stability of the dredger fill sea sand road slope under the measures of wrapping soil was analyzed. Based on the analysis of existing measures to improve the safety of sea sand used in road, the technology of sea sand solidified by alkaline coupling agent is proposed.

Rapid Treatment Using Vacuum-surcharge Preloading with Dynamic Consolidation Method: Laboratory Model Test

This study presents an experimental investigation of reinforcement effect of dredged fill obtained from the Oufei project of Wenzhou, China using improved method of vacuum-surcharge preloading with dynamic consolidation by five parallel laboratory model tests: four model tests with different tamping energy combinations and a control group of vacuum-surcharge preloading method. The water content after treatment of the vacuum-surcharge preloading method was close to the optimal water content obtained from standard compaction test. The treatment of improved method of vacuum-surcharge preloading with dynamic consolidation can improve reinforcement effect and shorten consolidation time. The tests with higher tamping energy have a higher range of improvement. Under the condition of the identical level of tamping energy, compared with the drop height, the weight of hammer plays a greater role in foundation reinforcement, embodying concretely in water discharge, crater depth, and dissipation of pore water pressure, water content, vane shear strength, and porosity. The findings from this study may benefit the engineering application and further research of the combined method.

Study on the Solidification Effect of Dredger Fill by Microbial-Induced Calcium Precipitation (MICP).

This paper puts forward a new soft soil reinforcement technology-microbial-induced calcite precipitation (MICP) technology-which considers the problem of dredger fill soft-soil reinforcement in Dalian Taiping Bay. In this paper, the calcium carbonate content (CCC) and unconfined compressive strength (UCS) of microbial solidified dredger fill (MSDF) samples were determined using laboratory experiments. The microstructure and chemical composition of MSDF samples were studied by SEM-EDS and XRD. The failure and reinforcement mechanism of MSDF under different experimental conditions (ambient temperature, cementation solution concentration, and clay content) were investigated. The results showed that there was a certain residual strength after the peak strength of MSDF. With the increase of ambient temperature, the number of microorganisms increased, but the activities of urease, CCC, and UCS decreased. The UCS and CCC increased with the increase of cementation solution concentration, while they first increased and then decreased with the increase of clay content. The clay content enhanced the compactness of MSDF samples but reduced the soil permeability and weakened the mineralization. There were significant differences in the morphology of microbial-induced precipitation caused by different concentrations of cementation solution.

Improved calculation method for consolidation of dredger fill treatment using prefabricated vertical-horizontal drains

Prefabricated vertical-horizontal drains (PVHDs) with high efficiency have been applied to accelerate the consolidation of dredger fill foundations. Considering the nonlinear characteristics of soil, the horizontal and vertical drainage paths and the penetration degree of horizontal drainage pipes, an improved consolidation calculation method for dredger fill foundations treated by PVHDs was developed. Sensitivity analysis was carried out on the parameters of the PVHDs system, and the effectiveness of the proposed method was verified by field tests. It is found that the parameters C c/C k, loading ratio (Δp/σ'), and penetration degree (ρ) jointly control the rate of the consolidation process. The average settlement consolidation degree (Us ) calculated by the proposed method agrees well with the field test values. By increasing ρ from 0.2 to 1.0, the consolidation time can be reduced by half when Us reaches 90%.

Study of the sorting pattern of dredger fill under artificial disturbance based on the concealment degree.

This paper focuses on the sorting pattern of silt deposited at estuaries under artificial disturbance based on the concept of bidirectional concealment, which is introduced for such silt with similar particle size, low disturbance exposure angle, and difficult sorting. By establishing the relationship among the absolute concealment (Δi), the drag force coefficient ({C}_{mathrm{D}}), and the lift force coefficient ({C}_{mathrm{L}}) of highly concealed silt particles under disturbance and considering the concepts of disturbance intensity, disturbance direction, and particle concealment degree, the contribution equation for the effective depth (Y) of artificial disturbance in the deposited slurry is introduced, and the mechanical equation for the internal disturbance of silt is established. On this basis, the motion initiation probability for fine particles ({varepsilon }_{{d}_{i}}) is calculated using the Shields parameter (Thetac), and the theoretical model of plastic sandy silt sorting under artificial disturbance is derived from the Markov chain-based three-state transition. The method proposed in this paper can explain the bedload gradation of sandy silt under internal physical disturbance. The calculated data in this paper agrees well with that of the flume test on uniform sandy silt and the related sediment particle theories. Therefore, the clay particle transport pattern model in slurry under artificial disturbance based on the bidirectional concealment degree can explain the gradation changes of flow-plastic sandy silt under artificial disturbance, thus providing a theoretical basis for the research on the sorting of flow-plastic sandy silt under artificial disturbance.

Geotechnical properties of marine dredger fill with different particle size

To get a macroscopic understanding of the geotechnical engineering properties of typical marine dredger fill in coastal areas of Shandong Province, China, the mineral composition, particle size distribution, cation exchange capacity (CEC), consolidation characteristics, and strength characteristics of dredger fill in four regions, namely Rizhao, Dongying, Weifang, and Yantai, were studied and the correlation between typical indicators of dredger fills in different regions were analyzed. The results show that the difference in soil particle size distribution in Shandong province is related to the regional sedimentation type and dynamic effect and there is a significant correlation between some typical soil indicators. Vane shear strength test and consolidation test results show that the silt in Weifang has good drainage and shear strength indicating it is suitable as dredger fill. For the mucky clay in Rizhao, pharmaceutical vacuum preloading method is recommended to improve soil strength and the reasonable loading size should be less than 200 kPa. The purpose of this paper is to study typical geotechnical properties of four types of dredger fill, find and verify the correlation between some of geotechnical properties, to provide an objective scientific reference basis for the treatment of dredger fill in coastal area from the perspective of dredging and filling engineering.

Experiment and Mechanism Analysis on the Solidification of Saline Dredger Fill with Composite Slag Solidifying Agent: A Case Study in Caofeidian, China

Most areas of Caofeidian (Tangshan Caofeidian New District in Hebei Province, China) were formed by land reclamation, where the dredger fill has a high water content and a high salt content. The solidification of Caofeidian’s dredger fill is difficult because of salinisation, as well as environmental and economic factors. This article proposes a composite slag solidifying agent. The optimal proportion of various additives was determined by an unconfined compression test and orthogonal design. Next, a microanalysis was carried out by SEM and XRD tests to characterise the solidification mechanism of the composite slag solidifying agent. The results reveal that the composite slag solidifying agent can substantially improve the unconfined compressive strength of Caofeidian’s saline dredger fill by imparting a good microstructure: a compact overall structure was obtained and few voids were observed in the solidified soil. The optimal proportion was determined as 10% slag + 1.0% quicklime + 0.8% sodium silicate + 1.5% gypsum powder. In addition, the composite slag solidifying agent can effectively reduce the content of soluble salts in saline dredger fill and substantially improve the engineering characteristics of solidified soil.

Study on Solidification Mechanism of Microorganism Induced Dredger Fill Soft Soil Mineralization

Study on Solidification Mechanism of Microorganism Induced Dredger Fill Soft Soil Mineralization

An EVP Double‐Yield Nonstationary Flow Surface Model for Soft Clay

According to experimental findings, soft clay has compression and shear creep. The goal of the study is to develop an elastic‐viscoplastic (EVP) model for the viscous behavior of soft clay. The new EVP model is deduced from the associated flow rule, Yin’s double‐yield surface theory, and the critical state soil mechanics. The nonstationary flow surface model with double‐yield surface, compared to other existing models, considers the compression and shear creep properties of soft clay. The model parameters can be identified from two sorts of tests (i.e., the general triaxial tests and triaxial rheological tests). Different types of soft clay, such as Tianjin Coastal clay, Shantou dredger fill, and silted soil in front of dam, were tested to verify the accuracy of the constructed model. All comparisons of computed and experimental findings revealed that the new EVP model accurately reflected the time‐dependent behaviors of soft clay in both shear and compression creep.

Study on Solidification Effect of Dredger Fill by Micp Method Under Different Experimental Conditions

Study on Solidification Effect of Dredger Fill by Micp Method Under Different Experimental Conditions

Vacuum Preloading Combined with Electroosmotic Dewatering of Dredger Fill Using the Vertical-Layered Power Technology of a Novel Tubular Electrokinetic Geosynthetics: Test and Numerical Simulation

Abstract A novel tubular EKG material in electroosmotic field test combined with a vacuum preloading method was first conducted in a reclamation project in Ningbo, China, by using a vertical-layere...

Engineering characteristics of coral reef and site assessment of hydraulic reclamation in the South China Sea

Calcareous soil is a peculiar geotechnical medium which is utilized as land filler for engineering activities, such as the Maldives, Middle East, and South China Sea (SCS). Since the hydraulic dredged calcareous soil has a wide grain size distribution, irregular particle shape, crushable particles, high porosity, and poor uniformity, ground-improvement was conducted to improve the bearing capacity and reduce foundation settlement. In this paper, the geological conditions, material characteristics, and mechanical behavior of dredger fill site on a coral reef in the SCS were studied. The densification of soil using deep vibro-compaction combined with impact rolling was investigated. An innovative method of sprinkling water during impact rolling was put forward to improve rolling efficiency and soil compactness. A set of modified in-situ measurement and calculation methods suitable for the compactness of calcareous soil were put forward. Based on in-situ test results, the relationship between the soil bearing capacity and blow count of dynamic penetration test was established. It was suggested that the two-point parallel and arranged in equilateral triangles vibro-flotation method is effective for the reinforcement of hydraulic dredged calcareous soil, and after vibro-flotation, the loose soil on the ground surface should be compacted with a 25 kJ three-side impact roller for 20 passes and then compacted with 25 t smooth vibratory roller until there are no visible wheel tracks. In addition, the methods of ground improvement, in-situ test, and foundation evaluation were proposed to contribute to coral reef engineering designers. This paper also provides new insights for coral reef foundation filling and improvement around the world.

Strength and structural variations in dredger fill subjected to vacuum dynamic consolidation

Laboratory vacuum dynamic consolidation tests were performed to study the effect of dynamic impact loads on the shear strength characteristics of dredger fill. The results revealed that the shear strength increased with the increase in the number of blows. The relationship between the increase in the shear strength and the soil structure was analyzed through scanning electron microscopy and mercury intrusion porosimetry. The structure collapsed progressively and the larger inter-aggregate pores were affected the most. Considering pore evolution, the pore size distribution was primarily unimodal, and the variations in porosity and shear strength with the blow count were the same. Thus, the shear strength of dredger fill is influenced by its structure. On average, five blows ensure high compaction efficiency.