Soft Marine Clay Research Articles

The Practice and Development of T-Bar Penetrometer Tests in Offshore Engineering Investigation: A Comprehensive Review

In recent years, the development of marine hydrocarbon resources has led to an increased demand for research on the marine soil bearing capacity and cyclic loading effect in marine engineering design. Because of the difficulties and high costs involved in obtaining high-quality soil samples from offshore sites, in situ testing techniques have become the preferred method of determining design parameters in offshore geotechnical engineering projects. This paper provides a review of the current state of marine penetrometer deployment technology used in offshore engineering investigations and presents a summary of the T-bar penetrometer test for measuring marine soft clay. The existing literature research on penetration mechanisms, numerical simulations, laboratory experiments, and field tests of the T-bar penetrometer in the field of marine geotechnical engineering are analyzed. Finally, the potential difficulties, challenges, and prospects of the T-bar penetrometer tests are discussed.

Thermal Triaxial Tests to Evaluate Improvement of Soft Marine Clay through Thermal Consolidation

Abstract This paper presents an experimental study on the thermomechanical behavior of marine clay from the Santos Basin off the coast of Brazil. The aim of the study is to assess the gain in undrained shear strength of reconstituted, normally consolidated (NC) clay specimens after drained thermal consolidation using a thermal triaxial device. The motivation behind performing these tests is that relatively few studies in the literature have focused on understanding the changes in shear strength of NC clays after a heating-cooling cycle, a path encountered in using heat to improve the properties of soft clays. Furthermore, the high-plasticity marine clays evaluated in this study have a pronounced thermal creep different from that observed in previous non-isothermal tests on clays. Consolidated isotropic undrained triaxial compression tests were performed on specimens consolidated to effective stresses of 100 kPa, 200 kPa, and 400 kPa and then sheared conventionally at room temperature as well as after drained heating-cooling cycles with maximum temperatures of 40°C and 55°C. The results were analyzed according to critical state soil mechanics after drained thermal consolidation, which was well suited to explain the improvement in undrained shear strength. The results have potential implications on the development of techniques that can promote thermal improvement of deep-water offshore anchors installed in soft soil.

Load-Settlement Characteristics of Stone Column Reinforced Soft Marine Clay Deposit: Combined Field and Numerical Studies

Foundations supporting infrastructure built on soft and compressible marine soil are unlikely to sustain due to possibility of undrained shear failure or excessive settlement of the supporting soil. This necessitates the importance of implementing an adequate ground improvement strategy. Among different techniques, soft soil reinforcing by the installation of stone columns is one of the most successful methods in terms of long-term stability of foundations. To investigate the load-settlement characteristics of such reinforced soil, a group of closely spaced stone columns was constructed at a location along the eastern coast of Australia. The site geology revealed thick layers of soft, compressible marine clay deposit. These stone columns were loaded by constructing earthen embankment and the resulting load-settlement characteristics were measured by an array of sensors. A two-dimensional plane strain analysis was performed using finite element modeling simulations. Comparison of numerical results with the field data demonstrated accuracy of the numerical model. Additional studies were carried out to investigate the efficiency of the model. This paper integrates the new findings from the full-scale field study and advanced numerical simulations while drawing pertinent conclusions.

Preparation of anti-washout cement-stabilized marine soft clay for scouring protection of wind power pile foundations

This study aims to prepare an anti-washout grout using marine soft clay to stabilize the wind power pile foundations. The cement, hydroxypropyl-methyl cellulose ether (HPMC), and sodium silicate were chosen as the main materials to modify the marine soft clay, and the fluidity, bleeding rate, setting time, rheology, anti-washout characteristics, and compressive strength were investigated. The results showed that high cement content, HPMC, and sodium silicate decreased the workability of grout while enhancing the washout resistance. The addition of HPMC and sodium silicate would increase the yield stress and plastic viscosity of the grout. The sodium silicate content was the key factor influencing the early strength, while the cement content and HPMC affect the later strength. The microstructures including the morphology of C-S-H gels and the content of ettringite and calcium hydroxide significantly changed with the addition of sodium silicate, and Friedel’s salt was observed through the microstructure analysis. This study can provide effective guidance for the utilization of marine soft clay, the preparation of anti-washout grout, and the control of pile foundation stability.

A Vertical Electro-Osmosis Method to Improve the Bearing Capacity of Piles in Marine Soft Clay

A vertical electro-osmosis method was proposed to improve the bearing capacity of piles in marine soft clay foundations. A top-down electro-osmosis test was conducted by setting an anode and cathode at the top and bottom of the pile, respectively, while the settings of bottom-up electro-osmosis were set in the opposite way. At the same time, a pile without electro-osmosis was also set up for comparison. The variation law of water content, water discharge volume, soil pressure, and surface settlement of soil around the pile during electro-osmosis was tested and analyzed. A direct shear test and static load test were carried out to study the effects of vertical electro-osmosis on the shear strength of soil and the bearing capacity of the pile. The experimental results show that vertical electro-osmosis can significantly improve the bearing capacity of the pile and the shear strength of soil around the pile. The bearing capacity of the piles in the top-down electro-osmosis test was 16.7% higher than that in the bottom-up electro-osmosis test, and the amount of water discharged was 41.69% higher. Compared with the horizontal electro-osmosis around the pile, the vertical electro-osmosis had a faster drainage speed, better soil consolidation, and a slightly smaller increase in the bearing capacity of the pile. Because vertical electro-osmosis is easy to implement on concrete piles, the new method proposed in this study has a broad application prospect.

Undrained deformation behavior of marine clay under two-way cyclic loading

In offshore engineering, marine clays, which are widespread in the southeastern coastal areas of China, may be subjected to two-way cyclic stresses. To experimentally investigate the effects of the two-way cyclic stress with low-stress amplitude on the cyclic behavior of soft marine clay, a series of triaxial tests is performed on intact marine clay from Zhoushan covering various values of the cyclic stress ratio (CSR) and confining pressure (p′0). Several useful conclusions are inferred: First, the double-amplitude axial strain (ε DA), dynamic axial modulus (E), and energy dissipation (W) increase with the CSR. Second, under the same CSR, the value of ε DA is independent of p′0. The values of E and W increase with increasing p′0 during cyclic loadings, whereas the normalized modulus and normalized energy are independent of p′0. Third, an allowable CSR is proposed based on the strain behavior and energy concept. Based on the experimental results, two equations are established to predict the dynamic axial modulus and double-amplitude axial strain.

Near-field vibrations in railway track on soft subgrades for semi high-speed trains

For the development of a high-speed rail network in urbanised areas, ground vibration and associated damage to surrounding structures are major concerns. The problem becomes critical especially in areas with soft soil deposits due to amplification of vibration during Rayleigh wave propagation. In the present study, near field ground vibrations from a high-speed rail ballasted track are predicted for an area which contains predominantly soft marine clay deposits. A two-dimensional finite element model coupled with infinite boundaries is developed in ABAQUS. Using the finite element model, the vibration in terms of peak particle velocity (PPV) and root mean square (RMS) velocity is determined for different train speeds and soil profiles, at varying distances from the track centre. Different soil profiles are considered in this study by varying the thickness and depth of the soft clay layer. From the results, it was observed that maximum ground vibration happens when the train speed is close to the Rayleigh velocity of the soft clay layer. Further, the safe limits for residential and sensitive structures are determined for different conditions based on peak particle velocity. Considering human discomfort during vibration propagation, the vibration level in decibel scale is determined for different track configurations.

P-y based approach to predicting the response of monopile embedded in soft clay under long-term cyclic loading

Offshore wind turbines (OWTs) are subjected to environmental loadings such as those induced by waves or wind typically comprising up to millions of cycles (i.e., high-cycle loading). To evaluate the performance of OWTs during a lifetime cycle, this study proposed a p-y based approach to predict monopile response subjected to a long-term cyclic loading. A cyclic loading may cause an accumulation of strain and a built-up of excess pore water pressure under undrained conditions, accompanied by a corresponding reduction of stiffness and shear strength in soft marine clay. In the proposed procedure, the cyclic degradation and strain accumulation of soft clay is considered by a generalized empirical model given the soil reaction calculated from p-y analysis for a prescribed loading condition on the pile. Afterward, the response of pile subjected to a long-term cyclic loading is predicted by modifying the preselected p-y curve by p-multiplier and y-multiplier to take account for the cyclic degradation and strain accumulation, respectively. The proposed approach is validated by three centrifuge tests on a monopile in soft clay. The simulation results are in good accordance with the measurements in terms of pile displacement and bending moment versus number of applied cycles. Therefore, the proposed approach is feasible to predict the long-term pile response subjected to high-cycle loading. Moreover, it is easily implemented in the widely used p-y approach.

Optimization of synergy between cement, slag, and phosphogypsum for marine soft clay solidification

Ground granulated blast furnace slag (GGBS) and waste gypsum are cost-effective and environment-friendly substitute materials for Portland cement. This work aims to investigate and optimize the synergy of ordinary Portland cement (OPC), GGBS, and phosphogypsum (PG) in solidifying marine soft clay. The soft clay is treated with the ternary blending designed, and NaOH (NH), Na2SO4 (NS), calcium aluminate cement (CA), and γ-nano-Al2O3 (NA) are used as additives to it. The effectiveness of the ternary blending and the additives is evaluated using unconfined compressive strength (UCS), consolidation, and durability tests, and the associated mechanisms are revealed by pH evaluation, X-ray diffraction (XRD), and scanning electron microscopy (SEM) tests. A high-efficiency ternary cement (TC) is developed by blending OPC, GGBS, and PG in the optimum ratio of 5:3:2. TC solidified clay (TCSC) exhibits better strength performance than cement or binary cement (OPC–GGBS/PG) solidified clay, due to the combined action of pozzolanic reaction and ettringite formation. The single additives, particularly NH and NS, can dramatically improve the early strength of TCSC, whereas the composite additives NS/CA and NS/NA finally result in greater strength gains. Besides, the lower compressibility and stronger sulfate resistance also verify TCSC as a preferable reinforced material over cement solidified clay, and these mechanical properties can be further improved using the composite additives. The increased basicity and the more effective role of ettringite explain the improved mechanical performance. In particular, the NS/CA and the NS/NA induce ettringite to grow in clustered and oriented patterns, providing effective pore filling and structural support, respectively.

A Case Study of Deep DNAPL Contamination in Marine Soft Clays

Aquifers in China’s southeast coastal areas are protected by the overlying marine soft clays formed in Holocene transgression. However, a fundamental understanding of the characteristics of DNAPL (dense nonaqueous phase liquid) contamination in marine soft clays is limited. The study was conducted on the site of a former pharmaceutical factory in Shanghai, where serious 1,1,2-trichloroethane (DNAPL) contamination was detected up to the depth of 22.0 m below the existing grade. Partitioning calculation method was used to identify the presence of pure phase, and the results showed that pure 1,1,2-trichloroethane was accumulated at the interface of the upper soft silty clay and lower soft clay. The vertical transport was believed to be the pure DNAPL displacing pore water following the principle of two-phase flow, rather than the convection and diffusion of aqueous phase. The contamination (NAPL-soil interaction) impacted the soil properties slightly, and this effect could not account for the deep contamination. Soil structure analysis showed that these clays contained a proportion of large interaggregate pores, providing pathways for the transport of pure DNAPL. Considering their flocculated structure, the marine soft clays are not capable to perform as a barrier to prevent the downward migration of pure DNAPL.

Parametric Study on Analyzing the Effect of Soil–Cement Strength on the Uplifting Behavior of HSCM Piles Installed in Marine Soft Clay

The Helix-Stiffened Cement Mixing (HSCM) pile is a composite pile constructed by grouting the soil–cement during the installation of the helical pile. A series of 3-D Finite Element Method (FEM) models were developed to investigate the uplifting behavior of HSCM piles installed in marine soft clay. The uplifting behavior of HSCM piles was compared to the Stiffened Deep Cement Mixing (SDCM) piles and the difference was discussed. The FEM results showed that the uplifting ultimate bearing capacity of the HSCM piles and SDCM piles increased with the soil–cement-strength-to-clay-adhesion ratio (Cref/su) until the ratio reached 20 and 40, respectively. The failure mode influenced the uplifting behavior of HSCM piles. At Cref/su ∈ 40,80, the HSCM pile incurred damage at the pile–soil interface, which gradually shifted to the steel pipe and soil–cement interface as the Cref/su was further decreased. Based on the FEM results, the empirical formula for estimating the uplift ultimate bearing capacity of HSCM piles under different failure types was proposed, which provided reliable guidance for designing HSCM piles.

Undrained cyclic behavior of under-consolidated soft marine clay with different degrees of consolidation

In certain land reclamation projects, soft marine clay with various consolidation degrees (U) under a foundation exhibits different mechanical properties when subjected to cyclic loadings. Compared with normally consolidated soft marine clay, under-consolidated soft marine clay has poor engineering properties and exhibits a larger deformation when it is subjected to cyclic loadings. Therefore, the cyclic behavior of soft marine clay with different consolidation degrees needs to be examined. In this study, a series of triaxial tests were conducted to investigate the cyclic behavior of soft marine clay with various consolidation degrees. The undrained shear strength, permanent strain, and stress-strain hysteretic loops were analyzed. Some useful conclusions were obtained. First, the undrained shear strength of the specimen decreased, and the permanent strain increased with a decreasing consolidation degree. Second, compared with the normal consolidated sample (U = 1), the stress-strain hysteretic loops of the under-consolidated specimen (U < 1) had a larger envelope area, indicating that the deformation behavior of the under-consolidated soil exhibited more distinctive viscoelastic and hysteretic characteristics. Finally, in the low consolidation range (U = 0.5–0.85), the deformation resistance of the clay rapidly increased as the consolidation degree increased. By contrast, in the near-normal consolidation range (U = 0.85–1), the deformation resistance of the clay did not significantly increase. Based on these results, the critical consolidation degree for soft marine clay was found to be 0.85, which can be used as a standard reference, considering the need for rapid construction in actual projects.

Energy-based evaluation of undrained cyclic behavior of marine soft clay under multidirectional simple shear stress paths

Energy-based evaluation of undrained cyclic behavior of marine soft clay under multidirectional simple shear stress paths

One-Dimensional Solar Energy Thermal Consolidation Model Testing and Analytical Calculation for Marine Soft Clays

There are significant energy and financial expenditures associated with the current thermal drainage consolidation approach used to treat the marine soft clay foundation. Especially for some reclaimed lands in remote areas where a large amount of stable electricity is not readily available. In view of the problem, this paper aims to investigate a novel treatment method by using solar energy thermal consolidation. The model testing was conducted to assess the treatment effect of the foundation. Results from two groups of one-dimensional surcharge preloading consolidation model experiments, conducted under conditions of both solar heating and ambient temperature, were presented. The advantage of the solar heating approach was demonstrated by a comparison of the two tests. An analytical calculation method was proposed for predicting the consolidation behavior on the basis of the temperature variation caused by solar energy in the marine soft clays, and good agreement was observed. The outcomes reveal that solar heating can improve the consolidation effect of soil deep in the foundation. The foundation temperature can be raised by 15 °C in winter, and the variation range can exceed 10 °C. The settlement increases by 16% compared with the ambient temperature group.

The Impact of Scour on Laterally Loaded Piles Bored and Socketed in Marine Clay

The majority of long-span bridges and offshore construction in deep water are supported by bored pile foundations. Pile foundations under water will be susceptible to scour, which will pose a significant danger to their safe operation. A three-dimensional finite element (FE) numerical analysis was conducted to examine the influence of scour on the responses of laterally loaded drilled piles in marine clays. First, the FE numerical model was calibrated using field test data of a drilled pile that did not include scour in soft marine clay. The findings of numerical modeling reveal that scour decreases the ultimate lateral capacity of socketed drilled piles, with the percentage of reduction being strongly related to scour types and depth, but moderately related to scour hole width and slope angle. Finally, a semi-empirical formula for calculating the effects of scour on the lateral capacity of socketed drilled piles following scour is presented. This method may be utilized fast and effectively to calculate scour’s effects.

Salinity effects on the strength and morphological indices of soft marine clay

This study evaluates the strength behaviors and morphological characteristics of Lianyungang marine clay under the effect of porewater salinity. Soil at higher salinity was found to have increased internal friction angle and undrained shear strength. The difference in undrained shear strength enlarges as the confining pressure increases. Different stress paths were exhibited with soil at different salinities. Soil morphology analysis including scanning electron microscopy (SEM) and Image-Pro Plus (IPP) were employed to investigate the underlying mechanism of the enhanced strength behaviors of soft marine clay with increased salinity. Aggregated soil fabric was observed at higher salinity and contributed to enhanced strength. The results demonstrate that the aggregated soil structure is the primary mechanism responding to the enhanced strength behavior of marine clay under relatively high salinity (6%). Quantitative relationships were developed between the strength parameters and morphological characteristics of soil, i.e., area of particles, roundness of particles, area of pores, pore orientation, and fractal dimension of pore distribution, in the forms of empirical equations, and are expected to serve as the references for prediction in undrained behaviors of soft marine clays with known soil index.

Axial Behavior of Pressure Grouted Helical Piles Installed in Marine Soft Clay Based on Full-Scale Field Tests

Axial Behavior of Pressure Grouted Helical Piles Installed in Marine Soft Clay Based on Full-Scale Field Tests

Large-strain rheological consolidation analysis of multi-layered marine soft clays exhibiting natural structural characteristics

The destruction of marine soft clays’ macropore structure results in large-strain deformation during consolidation, as well as the potential to alter rheological deformation characteristics. A sectionalised regimes rheological model was adopted to describe the structural characteristics under the isotache framework, which led to a nonlinear variation of geometrical boundaries and material properties during consolidation. A semi-analytical theory combining numerical and analytical methods was developed, and the solutions for excess pore water pressure, degree of consolidation, and settlement were derived and computationally programmed. Using parametric analysis, the effects of rheological and structural characteristics on the consolidation behaviour of soft clay were discussed compared to the solutions of other theories. The coefficient of secondary consolidation in the transitional regime has an impact beginning in the middle of primary consolidation. The proposed solutions for degree of consolidation are smaller than the small-strain solutions during the early period of primary consolidation but change larger as consolidation progresses.

Undrained cyclic shear strength and stiffness degradation of overconsolidated soft marine clay in simple shear tests

In offshore engineering, overconsolidated marine clays are frequently encountered, which may be subjected to simple shear loading conditions (e.g. soil beneath a gravity-type foundation). The corresponding monotonic and cyclic behaviours of overconsolidated clay are of vital importance for offshore foundation design. Therefore, in this study, the undrained shear behaviour of soft marine clay is experimentally investigated through a series of monotonic and cyclic simple shear tests. The shear strain, pore water pressure, stiffness, and shear strength are presented and discussed by considering the effects of the overconsolidated ratio (OCR) and cyclic stress ratio (CSR). Consequently, an OCR-independent linkage is established between cyclic and monotonic shear strengths. In addition, a new empirical model considering the influences of both OCR and CSR is proposed. It predicts the evolutions of shear stiffness and strain with the number of cycles for soft clay specimens when the CSR is sufficiently large to induce cyclic failure. Furthermore, the datasets of shear modulus (G) and residual pore pressure (Δur) of different CSRs converge to a narrow band, which is dependent on the OCR. The peak of negative Δur is rarely affected by CSR but increases with increasing OCR.

Influence of cyclic deviator stress and consolidation degree on permanent strain of “under-consolidated” marine sediment

Rapid rates of clay sedimentation produce a highly hazardous marine foundation condition: “under-consolidated” marine sediments. Numerous traffic infrastructure facilities have been constructed on this type of clay. In this study, a series of original cyclic oedometer tests were performed to investigate the drained long-term permanent strain of soft marine clays. The stress–strain relationships and permanent strain accumulations of the clay specimens were evaluated and compared under different cyclic stress ratios (CSR s) and consolidation degrees (U s). First, when CSRs increased, the total strain also increased; however, its rate of increase decreased at higher CSR values. Thereafter, we derived a new threshold value as the upper boundary of the CSR for pavement designs on soft clay foundations. When the CSR was below this threshold value, the accumulated permanent strain increased rapidly with an increase in the CSR; when the value was surpassed, the strain accumulated slowly and was approximately linear as the CSR increased. Finally, equations for predicting the long-term permanent strain of under-consolidated clays were established. The findings of this study will serve as a useful technical reference for researchers and engineers in the field of land reclamation, thereby helping ensure the safety and durability of current and future public infrastructure facilities constructed on such lands.