Mucky Clay Research Articles

Investigation of the microscopic properties of natural structured clay

Conducting quantitative research on the microstructure of soft clay can reveal the essence of its soil mechanical behavior, which is of important practical significance for geological disaster risk assessment and prevention. To quantitatively investigate the microscopic properties of natural structured clay, soft clay soils from various sedimentary environments in the Hangzhou Estuarine Bay area were chosen as the research subject in this study. Subsequently, a comprehensive investigation into the microstructure of clay was conducted, involving X-ray phase analysis and SEM imaging analysis. The results revealed the following: (1) In comparison to the deep clay deposited in fluvial-lacustrine environments, the shallow mucky clay in marine sediments had a higher clay mineral content, accounting for 48%. Illite makes up the majority of it, with minor levels of kaolinite and montmorillonite being present. (2) The shallow mucky clay in the Hangzhou Estuarine Bay area had a typical agglomerate-flocculated structure. In contrast, the deeper clay showed a flocculated structure with less uniform particle sizes, strong stacking randomness, poor directional alignment of soil pores, and tends to form arrangements where edges are adjacent to faces or edges are adjacent to other edges. (3) Compared to the deep clay deposited in fluvial-lacustrine environments, the marine-deposited shallow mucky clay displayed orderly pore arrangements, strong directional alignment, significant pore shape variability, and minimal pore size changes between adjacent pores. The microstructure of soil plays a crucial role in determining the physical, mechanical, and other engineering properties of the soil. This study provides insightful information about the relationship between clay microstructure and geotechnical characteristics in Hangzhou and the surrounding areas.

Enhancing hydraulic fracturing for in-situ remediation in low-permeability soils: A comprehensive investigation of fracture propagation

Enhancing the complexity of the hydraulic fractures to provide a wide channel for the injection of the agent is crucial for remediating low-permeability contaminated sites. This study involved a physical simulation experiment of large-scale true triaxial hydraulic fracturing in undisturbed soil, as well as field fracturing tests, to investigate fracture initiation mechanisms and the influence of different factors on fracture propagation. The study revealed a unique failure mode for low-permeability soils characterized by impact splitting, involving simultaneous tensile and shear failure. Three typical fracture propagation patterns emerged: (1) horizontal fracture, (2) parallel fracture, and (3) complex fracture. Silty clay predominantly exhibited horizontal fractures, while mucky clay facilitated the formation of complex fractures dominated by multiple transverse fractures. As the vertical stress difference coefficient increased from 1.0 to 1.5, the pressure on the fracture surface enhanced the connection between hydraulic fractures and natural fractures. Hydraulic fracturing in low-permeability soils necessitated large displacements and high-viscosity fracturing fluids to sustain fracture propagation. The field fracturing test results underscored that soil type and in-situ stress were the primary factors governing hydraulic fracture initiation and propagation. Identifying the optimal fracturing location was critical for achieving the maximum stimulated formation volume.

High-resoultion shallow anomaly characterization using cross-hole P- and S-wave tomography

Cross-hole seismic tomography is a high-precision method that can obtain the velocity structure between boreholes. At present, single-component geophones are mainly used for P-wave velocity estimation. However, S waves have a shorter wavelength than P waves, incurring a high-resolution tomography image. In this paper, we apply three-component cross-hole seismic tomography to shallow geological survey. First, three-component geophone is used to collect cross-hole seismic data. Secondly, the apparent velocity polarization method is used to separate the P and S wavefields from the recorded three-component waveform data. Then, a damped least-squares traveltime tomography is used to calculate the cross-hole P- and S-wave velocity structures. Finally, the distribution of Poisson's ratio between the boreholes is derived from the inverted P- and S-wave velocities. Numerical model experiments show that this method can solve some typical shallow subsurface problems, such as the detection of karst features and boulders. The proposed method is used to detect an underground air-raid shelter located in Hangzhou, Zhejiang Province, China, and the P- and S-wave velocities and the Poisson's ratio are obtained with high precision. The tomography image of the air-raid shelter agrees well with its known location. and the calculated Poisson's ratio distribution shows that the air-raid shelter may be partially filled with mucky clay. Three-component cross-hole seismic tomography achieves a high data acquisition efficiency and can simultaneously obtain shallow subsurface stratum velocities and Poisson's ratio with high precision. Thus, this technique can be used for shallow-subsurface surveys.

Micropore Structure and Fractal Characteristics of Clays Due to Freeze-Thaw and Compression Based on Mercury Intrusion Porosimetry

The artificial ground freezing method has been widely used in shield end reinforcement and connecting channel reinforcement of urban subway tunnel in water-rich soft soil. Accurate quantification of micropore change and redistribution due to freeze-thaw is important to understand frost heave and thaw settlement of soft soils including mucky clay and silty clay. This paper presents Mercury Intrusion Porosimetry (MIP) data for mucky clay and silty clay specimens before and after freeze-thaw and compression. MIP tests were conducted on the soil samples of undisturbed soil, frozen-thawed soil, compressed soil and compressed frozen-thawed soil. The pores of clays were divided into five groups according to the diameter, including 1) macro pore, 2) medium pore, 3) small pore, 4) micro pore, 5) ultramicro pore. Micro pores and ultramicro pores account for more than 80% of clays’ total pore volume and pore surface area. The pore distribution characteristics of mucky clay and silty clay were studied, and the pore volume and pore surface area distributions’ capacity dimension was estimated. The particle contact, pore changes of clays due to freeze-thaw and compression were analyzed quantitatively. Total pore volume and pore surface area of clays increased due to freeze-thaw, and decreased due to compression correspondingly. The distribution of clays’ pore volume and pore surface area have statistical self similarity, and it is effective to quantify the microstructure changes of clays due to freeze-thaw and compression by estimating capacity dimension, which can provide a new way to reveal the internal micro-pore change of clays due to freeze-thaw and compression quantitatively.

Influence of Lateral Multistage Unloading Intensity on Mechanical Properties of Reconstituted Coastal Soils Containing Silty Particles

The unclear understanding of the mechanical behavior of soil under unloading conditions is a significant reason for the frequent occurrence of accidents and difficulties in the deformation control of foundation pit engineering in coastal areas. This paper discusses the effect of multistage unloading intensity on the mechanical properties of reconstituted coastal soils containing silty particles through a series of laboratory tests, namely, the CU triaxial, bender-element, and permeability tests. Results indicate that, with an increase in unloading intensity, the shear strength and stiffness parameters decrease, while permeability slightly increases. The effect of unloading intensity on the mechanical properties of silt and mucky silty clay is more pronounced. Additional consideration should be given to the effect of a single excavation depth on the mechanical properties of fine-grained soil in foundation pit engineering in order to ensure the stability of the surrounding soil and the safety of adjacent structures.

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.

Morphologic analysis of hysteretic behavior of China Laizhou Bay submarine mucky clay and its cyclic failure criteria

Morphologic analysis of hysteretic behavior of China Laizhou Bay submarine mucky clay and its cyclic failure criteria

Shear modulus degradation of China Laizhou Bay mucky clay under cyclic loading at an offshore wind turbine site

Shear modulus degradation of China Laizhou Bay mucky clay under cyclic loading at an offshore wind turbine site

Dynamic properties of the mucky clay improved with the steel slag and the rubber particles

To make full use of advantages of waste steel slag and old rubber particles, the steel slag and rubber particles were mixed into the mucky clay to form the mucky clay-steel slag-rubber particles admixtures (MCSRA) to improve the engineering properties of mucky clay. Dynamic tests have been carried out by resonant column apparatus to investigate the influence of steel slag content, rubber particle content, rubber particle size and confining pressure on small-strain dynamic shear properties of MCSRA. The results showed that the dynamic properties of MCSRA were significantly improved compared with those of the mucky clay. It also revealed that as steel slag content increased, the shear modulus increased and the damping ratio decreased. In addition, as rubber particle content and rubber particle size increased, the shear modulus decreased and the damping ratio increased, and as confining pressure increased, the shear modulus increased and the damping ratio decreased. Moreover, an improved dynamic model was built based on the Hardin-Drnevich model to describe the dynamic performance of MCSRA. By comparing the dynamic characteristics of MCSRA with those of the mucky clay-steel slag admixtures, the Fujian standard sand and the Nanjing fine sand, the MCSRA could be applied to replace the mucky clay improved with the steel slag and Nanjing fine sand in some practical engineering.

Stability Control of Staged Filling Construction on Soft Subsoil Using Hyperbolic Settlement Prediction Method: A Case Study of a Tidal Flat in China

An improved method, which combines in situ measured settlement data, hyperbolic method, and deep lateral displacement rate, is presented in this study to predict the consolidation and stability of the ground, which can be used in conducting staged filling construction on soft subsoil. A case history of a highway embankment construction in a tidal flat with thick mucky clay is studied in Xia Pu, China. Preloading with the prefabricated vertical drain method is adopted to accelerate the consolidation of a subgrade. The field behavior of soft ground under filling load is observed through in situ monitoring sensors in four typical sections. The final ground settlement in each stage is determined using the field monitoring data based on the hyperbolic settlement prediction method. For each stage of graded filling load, the ground settlement with a strain consolidation degree of 95% is defined as the standard settlement, and the corresponding settlement time is set as the standard settlement time. The preloading period is estimated according to the standard settlement time. The deep lateral displacement rate of the ground is monitored to control the stability of the foundation and recommended to guide the embankment construction. Results indicate that the presented method can predict the preloading time of graded filling, reduce the frequency of observation, and ensure the consolidation and stability of the ground.

Deformation Prediction and Deformation Characteristics of Multilayers of Mucky Clay under Artificial Freezing Condition

Artificial ground freezing method, is a popular technique applied in coastal soft soil area for underground engineering construction. This method can bring some side effects, like frost heave and thaw settlement, due to the water migration in soil during freezing-thawing process. A self-designed one-dimensional freezing apparatus is used to study the deformation performance of the reconstituted soft clay from Shanghai 4th layer during freezing-thawing process. Test results show that total frost heave amount increases with decreasing boundary freezing temperature while it remains with the variation of initial water content in the test. The deformation of multilayers during freezing process reveals compression phenomenon due to the water migration in the soil samples. The compression area is the main part contributed to thaw settlement. Besides, a prediction model is established with void ratio as a variable to connect frost-heave model with thaw-settlement model. FDM (Finite Difference Method) method is used for computation through compiling code in MATLAB software. Comparison shows that compression phenomenon is necessary to be considered when calculating thaw settlement. This study provides valuable reference to the deformation control of soil in the construction of artificial ground freezing.

Applicability of cavity-throat connecting model for estimating the hydraulic conductivity of fine-grained soils: a geometrical and mathematical approach

Determining the hydraulic conductivity of low permeable fine-grained soils is difficult and time-consuming. This work develops a new method with an eye to the pore morphology to correlate hydraulic conductivity with pore-size distribution (PSD) parameters obtained from mercury porosimeter data. In order to realize this method, calculating percolation loss along the flow paths in pore channels and quantifying the spatial morphology of pore channels by proposing a cavity-throat connecting model is necessary. In order to establish the standard process of the new method, a kind of sedimentary mucky clay with regular dual-structural PSD has been collected. The samples are divided into three series: (a) vibrated with variable frequencies; (b) frozen at variable temperatures and unfrozen, making the freezing-thawing effect as the variable; and (c) remolded with different water contents. The PSD of freeze-dried samples at the end of each process is obtained by mercury intrusion porosimetry. After that, the method is demonstrated with application to 12 series of fine-grained soils. Deduced from mercury porosimeter data, the volume-based PSD curves of fine-grained soils are bimodal, due to the presence of inter-aggregate and intra-aggregate pores. Two important hypotheses have been proposed: (i) one is that in the smaller pore scales, the experimental extrusion curve controlled by the hysteresis loop has a really approximate part compared to the theoretical overall retraction curve, making the experimental extrusion curve characterize the pore cavity size approximately, and (ii) the pore system consists of a series of multistage cavity-throat connections. Accumulating the effects of single connection on the percolation can be used to measure the overall effects of pore system on the percolation. Based on fluid-driven path analysis of percolation, the pore system is quantified by a series of cavity-throat connections and the percolation loss has been derived to estimate the hydraulic conductivity. The permeable parameter (κ) representing the overall effects of pore connections on the hydraulic conductivity (K) is suited to correlate the microstructure and hydraulic conductivity by the linear relationship with the fixed slope in semilogarithmic coordinate for the fine-grained soils. It is the destruction and recombination of cavity-throat connections that are dominant during the treatments like freezing, remolding, and reinforcing.

Failure Investigation at a Collapsed Deep Open Cut Slope Excavation in Soft Clay

Collapse of a 7.08-m-deep open cut excavation for the bank of a navigation lock in sensitive soft clay in Zhejiang, China, is presented in this paper. Cone penetration tests, field vane shear tests (VSTs), and traditional laboratory tests have been performed to investigate the soil properties after the collapse. According to the test results, the soft soil layers of mucky clay and muck have been found to be disturbed because of the effects of the boring holes. For bored concrete piles, the stresses release due to the cut slope, thus its shear strength is much lower than that measured from laboratory tests. The shear strength reduction technique based on a finite-element method program has been used to study the excavation behavior and overall factor of safety (FOS) of the excavated slope considering geometries of original design, later adopted schemes and soil properties associated with various test types. The computed FOS values obtained from VST results are lower than the corresponding recommended values and just a little higher than the limited value. Thus the excavated slope may easily collapse triggered by additional vehicles and surface surcharge loads. The reasons of excavation collapse can be explained as the misuse of soil properties for designers, and inadequate construction process management. The investigation of the failure provides experiences and lessons for the design and construction of similar projects in sensitive soft clay.

Leaning pagodas in China: laboratory test and analysis of subsidence under frequent earthquakes

The inclination of ancient pagodas leads to a non-uniform stress distribution on the soil below. This non-uniform stress threatens the structural stability of the ancient pagodas, and the degree of damage depends on the soil properties. This paper researches the residual strain under the ancient pagodas in China to simulate the non-uniform stress state under frequent earthquake conditions using a dynamic triaxial test apparatus. The non-uniform stress state was expressed by the consolidation stress ratio. The frequent earthquakes were indicated by the dynamic stress ratio and cyclic interval vibration loading. To describe the foundations of the ancient pagodas in China, two types of soil, the mucky clay (Q4) and the paleo-clay ( $${\text{Q}}_{3}^{\text{al}}$$ ), were tested. The relationship between the two different soils and the consolidation and dynamic stress ratios were determined by measuring the deformation and accumulated deformation. Additionally, mathematical models to estimate the residual strains of the soils were established and verified. The results indicate that the soil strain increment of mucky clay, which increases with the consolidation stress ratio and dynamic stress ratio, is an important parameter for evaluating the leaning pagodas’ stability in soft soil regions when subjected to frequent earthquake. The soil strain increment of paleo-clay, however, is inversely proportional to the consolidation stress ratio and no apparent relationship is found with the dynamic stress ratio. More research needs to be done on the subsidence of paleo-clay.

Dynamic Behaviors of Mucky Clay Material under Cyclic Loads

A series of consolidated-undrained (CU) triaxial compression tests and dynamic triaxial tests on mucky clay material were performed in the present paper, and the dynamic behaviors of mucky clay material for different dynamic stress amplitudes and initial static deviator stresses were studied. It is indicated that both the accumulated strain and the pore water pressure increase rapidly with increasing number of cycles. While after a certain number of cycles, the accumulated strain tends to be stable and there is enough time for the equilibrium of pore water pressure. Results also show that the influences of dynamic stress amplitudes and initial static deviator stresses on the accumulated plastic strain and pore water pressure of the mucky clay material are significant.

The deformation characteristics of saturated mucky clay under subway vehicle loads in Guangzhou

Since the long-term performance of subway tunnels is largely determined by the deformation of the soil around them, the study for the soil deformation characteristics under subway vehicle loads is important, especially in soft soil area. Based on a series of dynamic cyclic triaxial tests, the deformation characteristics of saturated mucky clay in Guangzhou were studied. The result shows that the failure cyclic stress amplitudes (CSA) and failure cyclic stress ratio occur when recoverable strain and accumulative plastic strain reaches approximately 0.22 and 15 %, respectively. Accordingly, the development of cyclic plastic strain is categorized into three types: steady state, rapid growth and instantaneous failure. When the stress level is below the failure CSA, the development of recoverable strain is nearly linear with accumulative plastic strain. To prevent and control engineering geological hazards induced by subway vehicle loads, vibration amplitudes of mucky clay around the subway tunnel axis must be closely monitored. More attention must be paid to soil deformation at the early operation stages of a subway line when mucky clay is sensitive to external loads. The strength of soil of the shallow ground should be considered as the basic parameters for study and design. The results of this paper can contribute to the design and maintenance of subway tunnels, as well as the prevention and control of tunnel axis deformation.

Artificial ground freezing of fully saturated mucky clay: Thawing problem by centrifuge modeling

In the construction of cross passages in subway tunnels in soft soils having high water content and large void ratio, Artificial Ground Freezing (AGF) has been preferred due to its unique advantages as both a structural support and a water barrier. Compared to the freeze process, the thaw response is much more complicated and less research work has been documented, particularly in applicably predicting long-term settlement. It is mainly because of the variability in the redistribution of water released from melting ice crystals and the re-consolidation or over-consolidation circumstances during freeze. This paper is based on centrifuge modeling experiments to investigate the thaw settlement of the saturated mucky clay surrounding the subway tunnel. The experimental results demonstrated the significance of replicating the prototype self-weight stress condition in a model to evaluate the thaw settlement of Shanghai mucky clay after artificial ground freezing. The water content profiles of model soils presents that there was still serious water content re-distribution even after freeze–thaw. It indicates the potential reason of differential settlement along subway tunnel around AFG construction site. Great increase in permeability of mucky clay also makes clear sense for additional large thaw settlement after artificial ground freezing. More importantly, field self-weight stress condition extended the influence area of moisture migration and aggravated the pore size to be concentrated in coarser field. All the discussion revealed that the advantages of centrifugal modeling in thaw problem by providing field self-weight. Additionally in the further computation model development, large strain thaw consolidation theory should be applied to prognosticate the long-term settlement of thick soft mucky clay after artificial ground freezing construction. Finally the scaling laws generally used in thaw processes were also checked in this paper in consideration of lacking references on thaw problem in centrifuge models.

Centrifuge experimental study of thaw settlement characteristics of mucky clay after artificial ground freezing

Artificial ground freezing (AGF) plays a significant role in the construction of subway tunnel cross passages, underground commercial streets and underground pumping stations, etc. especially under adverse hydro-geological conditions. Associated with the properties of high water content and large void ratio in saturated Shanghai mucky clay, large thaw settlement has arisen after AGF construction. The thawing response is much more complicated compared to freezing and less research work has been documented in the AGF method partly due to the long-period and variability in the redistribution of water released from melting ice crystals and the rewetting of the soil aggregates in clay. This paper presented a series of centrifuge model tests to derive the thawing function development and predict the thaw settlement. The results show that the thawing rate was distinct and larger than the conventional results of small sample tests without stress acting. The thawing front advanced much faster compare to the development in natural frozen soil. An improved gray prediction model emphasizes that a simple analytical result with new thaw front function is much consistent with the experimental and prediction results. All the discussions demonstrate that small scale specimen thaw test at 1g is not capable to directly apply into full scale prediction of the thaw settlement in thick soft saturated clay after artificial ground freezing construction, in which self-weight dominates the process of consolidation. This could motivate, in the near future of computation model development, that the large strain thaw consolidation theory should be applied to prognosticate the long-term settlement of thick soft mucky clay after artificial ground freezing construction.

Research on the thermal conductivity and moisture migration characteristics of Shanghai mucky clay. I: Experimental modeling

With the development and exploitation of geothermal energy ground source heat pump (GSHP) sys- tems are being utilized all over Shanghai due to its unique energy advantages. A model experiment is designed and carried out to simulate an alternately-running GSHP sys- tem in summer and winter. It aims to study the character- istics of thermal conductivity and moisture migration of saturated soft clay (Shanghai mucky clay) with respect to thermal balance during the operation of a GSHP system by a series of laboratory modeling experiments. Thermal conductivity is an essential thermo-physical parameter for designing a GSHP system and is calculated (1.3680 W/(m C)) rather than obtained via the expensive and time consuming in situ thermal response test. The value mea- sured in laboratory experiments (1.1200 W/(m C)) by transient probes did not comply well with in situ data. The Thermal conduction and moisture migration characteristics of Shanghai mucky clay indicate it is a geo-material with good heat storage but poor heat release based on a com- parison between summer and winter conditions. All results provide reference for further discussion regarding the environmental effect of thermal balance surrounding a GSHP system. They are essential and valuable for the development of GSHP systems in Shanghai.

Changes of the pore distribution of silty clay under the subway train loads

Vibrations induced by the passage of subway trains are a major concern in urban areas. These vibrations can cause annoyance to people. Meanwhile, they can cause the settlement of tunnels by loading on the structured soft soil around the tunnel. It is known that the engineering behaviors of soft soil are determined by its microstructure. Therefore, the changes of pore distribution under characteristic dynamic loads were studied in this paper through a series of dynamic triaxial tests and mercury intrusion porosimeter tests. It is worth mentioning that the low-order fundamental frequency should be paid more attention to the similar research. Under the dynamic loads, the silty clay and mucky silty clay samples were all compacted. The volume of large pores (pore radius >400 nm) significantly decreased, while the volume of medium and small pores (pore radius <400 nm) increased due to the transformation of large pores. The changes of pore distribution can be well reflected by the fractal dimensions in thermodynamic model.