Saturated Soft Clay Research Articles

Study on Reinforce Saturated Soft Clay Foundation with Dynamic Consolidation by Drainage

Dynamic consolidation method has been widely used in improving soft land, but always inefficient to saturated soft clay land, which is hard to improve, and even leads to rubber soil. Dynamic and drain consolidation method will deal with it well, with drainage system, pore-water can be expelled instantly from saturated soft clay as impacting. The pore-water pressure and earth pressure test in construction, the standard penetration test, plate loading test, geotechnical test after construction, which are all effective methods for effect testing. There is a comprehensive detection through different depth of soil layer with different detecting means on construction site. The results show that improving saturated soft clay land with dynamic and drain consolidation method has obtained good effect, and the fruit can be guidance for such construction in the future.

Design and Test of Self-Draining Pile

putting out a new pile type, that is, making the precast concrete pile with a vertical side channel and pouring the yellow sand, which lead to the pile had the self-draining function, reduce the soil squeezing effect of precast concrete pile construction in saturated soft clay, that is, the design principles and methods of self-draining pile. Indoor model test showed that the self-draining piles could reduce the pore water pressure, and its effect was obviously, its role is equivalent to sand wells, sand bags wells or plastic drain board, which meet the requirements of the construction technique.

Constitutive model of saturated soft clay with cyclic loads under unconsolidated undrained condition

An equivalent visco-elastic model of saturated soft clay was studied under unconsolidated undrained (UU) condition, which can be used to evaluate the stability of ocean foundation. Cyclic triaxial compression and extension tests were conducted to study the parameters of the model. Results showed that the relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain were nearly unique, when the initial octahedral shear stress ratios of specimens were equal to 0.3, 0.5 and 0.7. The relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain determined from the cyclic triaxial compression tests were basically the same as those determined from the cyclic triaxial extension tests. Furthermore, the relationships were not related to the initial stress condition, the test stress state and the octahedral cyclic shear stress ratio. The relationships determined from the cyclic triaxial tests under no deviatoric stress were basically the same as those determined from the cyclic triaxial tests under deviatoric stress. The change of the octahedral cyclic accumulative strain with the number of cycles was unique under different tests stress states. An equivalent visco-elastic constitutive model of saturated soft clay under UU condition was initially established.

Centrifuge Model Test Study of Static and Cyclic Behavior of a Pile Foundation for an Offshore Wind Generator

Abstract The use of large-diameter piles as foundations for offshore wind-driven generators has become increasingly common in recent years. These piles are usually located in saturated soft clay and experience a wide variety of static and dynamic loads. A new approach was described to simulate different types of loads on a large-diameter pile under high g levels in centrifuge model tests by simplifying the complex horizontal load combinations to which such a pile is typically subjected. A series of centrifuge model tests was conducted to assess the influence of several factors. An image-based measurement system, together with a transducer-based measurement, was used to obtain a comprehensive understanding of the response of the soil. The horizontal load-induced bending moment of the pile exhibited a nearly triangular distribution. A critical load, which can be estimated as approximately half of the ultimate load, was found to exist, beyond which the rate of displacement of the pile increased significantly with increasing load. The pile-induced deformation of the soil, concentrated within zones on both sides of the pile, gradually increased as the load increased and became nearly constant when the load was close to the ultimate load. Significant separation occurred between the pile and the neighboring soil in the upper part of the pile. The critical and ultimate loads of the pile were significantly dependent on the behavior of the soil in the upper layer, the depth, and the diameter of the pile.

Microstructure Distribution of Soft Clay under Conditions of Stratigraphic Profiling Variation

Base on the microscopic structure is characterized by anisotropy of microstructure that inherent in the process of saturated soft clay with sedimentary primary anisotropy or external force caused by induced anisotropy, biological changes along with the trend of the minimum potential energy. By studying the spindle rotation stress characteristics of the soil of the microscopic distribution, the pore characteristics of saturated clay sourced from microstructure pictures in Pearl River Delta region of south China is analyzed considering the microstructure in different stress conditions. Microstructure distribution of soft clay under conditions of section profiling variation including the anisotropy ratio law of pore characteristics are focused to study saturated clay. It is found that major-minor axis status induced the directional property of saturated soil in the process of consolidation by vacuum preloading. And porosity shapes factors which are small indicate directional property would be probability entropy which is able to calculating the chaos of overall arrangement, and it will be a lower value because of directional property. It is apparently inconsistent with the pore distribution of saturated clay which results from the cut section of different point of angle. And horizontal joint and large pore space constitute one of the saturated clay structure characteristic, which related to different pressures.

Accumulated Deformation Behavior and Computational Model of Water-Rich Mudstone Under Cyclic Loading

With the rapid development of Chinese railway systems, a large number of railway tracks have been built on or across soft soils and soft rocks, resulting in problems such as accumulated deformation and settlements of the tracks (Zhang et al. 2009) and severe mud pumping in railway tunnels which are built through soft soils (Zhu and Li 2001). Such problems are a big challenge to the safety and efficiency of train operation. Investigations on the characteristics of long-term deformation of geotechnical materials under cyclic train loading are of great interest in engineering practice. Sangrey and Henkel (1969) conducted triaxial cycling tests for saturated soft clay and demonstrated the existence of a critical stress state for soils. Yasuhara and Yamanouchi (1983) performed a triaxial drained test on soft soils under cyclic loading. Muhanna (1994) reported that the permanent deformation of soils was proportional to the cyclic loading number and stress level. Jafari et al. (2004) conducted a systematic study on the fatigue behavior of artificial rock joints that were subjected to cyclic shearing. Bagde and Petros (2005, 2009) analyzed the fatigue behavior of intact sandstones under dry and saturated conditions with dynamic uniaxial cyclic loading. Erarslan and Williams (2012) studied the stress–strain characteristics of Brisbane tuff disc specimens under a diametral compressive sinusoidal cyclic loading with an increasing magnitude. Chinese researchers have also conducted extensive research in this area. Several cyclic triaxial tests have been conducted with different soil types. Systematic studies have been conducted to evaluate the characteristics of cyclic deformation and identify their influencing factors (Cai and Cao 1996; Tang et al. 2003; Gong et al. 2009). Several empirical models based on the results of cyclic loading tests have been developed to describe the cyclic cumulative deformation behaviors of different geotechnical materials. Monismith et al. (1975) proposed an exponential model for the cumulative plastic deformation of clay under cyclic loading. Li and Selig (1996) improved Monismith’s model by adding soil static strength parameters. Based on these models, Chai and Miura (2002) proposed a computational formula to predict the cumulative deformation of road subgrade soil under traffic loading. This formula, which takes into account the original state of soil, is expressed as

Undrained deformation behavior of saturated soft clay under long-term cyclic loading

Subgrade soils of traffic infrastructures are subjected to large numbers of load applications at a stress level below their shear strength. It is therefore of great practical relevance to study the deformation behavior of soft clay under long-term cyclic loading. In this study, a series of monotonic triaxial tests and long-term cyclic (50,000 cycles) triaxial tests have been carried out to investigate the undrained deformation behavior of undisturbed soft clay from Wenzhou, China. The stress–strain hysteretic loop, resilient modulus and permanent strain of the tested samples were found significantly dependent on CSR and confining pressure. With an increase of CSR and confining pressure, the resilient modulus decreases more significantly with increasing number of cycles and the accumulation rate of permanent strain increases. Furthermore, the shape of the stress–strain hysteretic loop almost remains unchanged and the resilient modulus tends to a steady value after a large number of cycles. Based on the experimental results, two equations are established for the prediction of long-term resilient modulus and permanent strain. Finally, a new critical value of 0.65 is suggested for CSR. When CSR>0.65, the resilient modulus for large number of cycles is reduced to a so called “asymptotic stiffness” and the accumulation rate of permanent strain significantly increases.

Attenuation-type and failure-type curve models on accumulated pore water pressure in saturated normal consolidated clay

Based on dynamic triaxial test results of saturated soft clay, similarities of variations between accumulated pore water pressure and accumulated deformation were analyzed. The Parr’s equation on accumulated deformation was modified to create an attenuation-type curve model on accumulated pore water pressure in saturated normal consolidation clay. In this model, dynamic strength was introduced and a new parameter called equivalent dynamic stress level was added. Besides, based on comparative analysis on variations between failure-type and attenuation-type curves, a failure-type curve model was created on accumulated pore water pressure in saturated normal consolidation clay. Two models can take cycle number, coupling of static and dynamic deviator stress, and consolidation way into consideration. The models are verified by test results. The correlation coefficients are more than 0.98 for optimization of test results based on the two models, and there is good agreement between the optimized and test curves, which shows that the two models are suitable to predict variations of accumulated pore water pressure under different loading cases and consolidation ways. In order to improve prediction accuracy, it is suggested that loading cases and consolidation ways should be consistent with in-situ conditions when dynamic triaxial tests are used to determine the constants in the models.

Research on Engineering Characteristics of Negative Friction Resistance for Large-Diameter Caisson Pile

The negative frictional resistance for large-diameter caisson pile is very important to the stability of pile foundation. Lots of engineering projects speak volume for the signal influence of negative frictional resistance on foundation pile. Therefore, it is very necessary to analyze the generation mechanism of the negative frictional resistance on the large-diameter caisson pile and the mechanics characteristics for pile-soil in the coastal under consolidated soil environment. Base on the generation conditions and basic characteristics of negative frictional resistance, the generation conditions and generation mechanisms of negative frictional resistance for large-diameter caisson pile are analyzed on condition of under consolidation for saturated soft clay. Based on the linear softening model for the pile lateral face and hardening model for the tip of the pile, the analytical solution for negative frictional resistance based on the elastic theory was proposed. According to the one-dimensional consolidation theory, the analytical equations are attained when the pile-surrounding soil and pile-end soil is in different conditions. At last, the rationality of analysis process is verified by an engineering case.

The Deformation Characteristics of Soft Clay under Cyclic Loading

Through the undrained dynamic triaxial experiment, the deformation characteristics of saturated soft clay under cyclic loading are investigated. The cyclic loading was simplified as sine wave. It is found that under different dynamic stress, the deformation patterns of specimen in this experiment can be divided into three kinds, such as dense compressed, tensile break-up and shear failure type. In the process of vibration, the deformation forms of samples can also be divided into three types by dynamic stress amplitude, such as stable, destructive and critical type. The dynamic stress amplitude corresponding to the critical type is called critical dynamic stress. With the dynamic elastic strain increasing gradually, the dynamic elastic modulus decreases and rigidity softening occurs. Furthermore, dynamic elastic modulus and dynamic elastic strain curve decrease while the cyclic number is increasing. Finally, to establish the equation of the relationship between dynamic elastic modulus and dynamic elastic strain, the factor of cycle number should be considered.

The Deformation Characteristics of Soft Clay under Cyclic Loading

Through the undrained dynamic triaxial experiment, the deformation characteristics of saturated soft clay under cyclic loading are investigated. The cyclic loading was simplified as sine wave. It is found that under different dynamic stress, the deformation patterns of specimen in this experiment can be divided into three kinds, such as dense compressed, tensile break-up and shear failure type. In the process of vibration, the deformation forms of samples can also be divided into three types by dynamic stress amplitude, such as stable, destructive and critical type. The dynamic stress amplitude corresponding to the critical type is called critical dynamic stress. With the dynamic elastic strain increasing gradually, the dynamic elastic modulus decreases and rigidity softening occurs. Furthermore, dynamic elastic modulus and dynamic elastic strain curve decrease while the cyclic number is increasing. Finally, to establish the equation of the relationship between dynamic elastic modulus and dynamic elastic strain, the factor of cycle number should be considered.

A field study of the behavior of small-scale single rammed aggregate piers, testing methodology and interpretation

This paper presents the measured behavior of small-scale single rammed aggregate piers as a function of the piers’ slenderness ratio. For this purpose, loading tests at the site were carried out on two groups of single rammed aggregate piers with a constant diameter of 135 mm and variable lengths of 350–1000 mm, and two groups with a constant length of 1000 mm and various diameters of 105–185 mm. The testing area consisted of relatively uniform saturated soft alluvial clay overlain by a 1-m-thick wet soft-to-stiff silt layer. Results show that when length and diameter change, the pier load and top settlement variations at the design limit, in terms of the slenderness ratio, are not in the same direction while other design limit parameters’ variations are. The variations of design limit parameters in the two modes of change to pier length and diameter including the applied load, top settlement, stiffness modulus and pier modulus, in terms of the slenderness ratio, make a linear function while the variations of load and settlement ratio show an exponential function. Interpretations of the test results are particularly focused on the load-settlement behavior and variations of design limit parameters as a function of pier slenderness ratios.

Coupled Numerical Analysis of Tunnel Excavation in Saturated Soft Clay under High Groundwater

A coupled numerical simulation of a river-crossing shield tunnel excavation in saturated soft clay with high groundwater has been performed using a three-dimensional finite difference model, which takes into account variation of soil permeability with stress, anisotropy of permeability, reduction effect of joints on segment bending stiffness and the hardening process of synchronized grouting material. Groundwater seepage conditions around the tunnel, bending moment, axial forces and strength safety factor of tunnel segment as well as deep soil displacement during tunnel diving are investigated numerically. The analyses provide valuable information concerning the mechanical behavior of tunnel segment and hydrological field in soil around tunnel during advancing. The result also is benefited to control groundwater for river-crossing tunnel in soft clay under high water table.

Cone Penetration Test–Based Ultrasonic Probe for P-Wave Reflection Imaging of Embedded Objects

An ultrasonic P-wave reflection imaging probe is developed and utilized to noninvasively image the geometry of a deep foundation supporting a bridge pier. The source ultrasonic transducer emits compressive waves into saturated soil that subsequently transmits to and reflects back from an embedded object, and the receiver transducer measures the reflections that are used to construct an image. The components of the system, including the custom transducer probe and data acquisition hardware, were integrated with the [email protected] cone penetration testing truck. Some fundamentals of propagation of ultrasonic waves in soil are presented first, including transducer directivity, effects of unsaturation, the size of the internal scale of the soil, and transducer coupling. The system components are then presented, followed by field testing. The probe successfully imaged a pile foundation in very soft saturated clay but not in stiffer and/or unsaturated soils. The probe could be very useful for nondestructive quality assurance of structural elements constructed in situ in soft saturated soils.

Creep failure of geomaterials and its numerical simulation

It is shown that creep failure of geomaterials can be simulated by a non-linear three-component elasto-viscoplastic model. The model is described in the case of a single stress variable and the isotach viscous property type, although the model can be applied to more general three-dimensional stress conditions and viscous property types other than isotach. Various trends of viscous behaviour, including stress relaxation and creep deformation with and without creep failure, are illustratively simulated to show that creep failure is one specific aspect of the whole viscous behaviour that can be simulated by a single model. Creep failures observed in drained triaxial compression tests on compacted moist cement-mixed gravelly soil and saturated soft clay are simulated.

Model Test and Study on Pile Foundation in Transversely Isotropy Clay

To further verify the feasibility of theoretic calculation, according to similarity theory, the principles and methods of pile foundation-soil interaction in saturated soft clay are determined. It studies acceleration interaction of each test point on the soil surface under the same largest shock force with different frequency on the top of the pile. The results of experiment show that the acceleration interaction trend of each point changes with the change of shock frequency, it shapes like a down N with the shock frequency of 5Hz, like an M with the shock frequency of 10Hz, like a down V under the shock frequency of 15Hz～30Hz. With the shock frequency of 40Hz and 50Hz, it likes a plane curve (hyperbolic curve) shape.

Attenuation-Type and Failure-Type Curves of Cyclic Accumulated Deformation Models in Saturated Normal Consolidated Clay

Based on dynamic triaxial test results of saturated soft clay, influence factors and variations on accumulated deformation were analyzed. The Parr’s equation on accumulated deformation was modified to create an attenuation-type curve model on accumulated deformation of saturated normal consolidation clay. In this model, dynamic strength was introduced and a new parameter called equivalent dynamic stress level was added. Besides, based on comparative analysis on variations between failure-type and attenuation-type curves, a failure-type curve model was created on accumulated deformation of saturated normal consolidation clay. The two models can take cycle number, coupling of static and dynamic deviator stress, consolidation way into consideration. The models were verified by test results. The correlation coefficients are more than 0.96 for optimization of test results based on the two models, and there is good agreement between optimized and test curves, which show that the two models are suitable to predict variations of accumulated deformation under different loading cases and consolidation ways. In order to improve prediction accuracy, it is suggested that loading cases and consolidation ways should be consistent with in-situ conditions when dynamic triaxial tests being used to determine the constants in the models.

Dynamic Stress-Strain Relationship of Saturated Clay by Dynamic Triaxial Test

Subgrade diseases are exposed more and more serious with raising speed of existing railway in wide range. Fro the complexity of dynamic stress-strain relationship of soil, dynamic triaxial test was used to analyze .the dynamic mechanics behavior under cyclic train load for saturated soft clay in Yangtze Delta region. Compaction coefficient, confining pressure, dynamic shear strsss ratio, inputing stimulus and loading frequence were taken into account in test. The results show that the dynamic stress-strain curves of soil specimen are provided with prominent hysteretic characteristics and area surrounded by hysteretic curves gradually augment and slope of hysteretic curve decreases with the increase of dynamic shear train amplitude. The strong correlation exists between dynamical stress and strain.

Study on the Variation Regularity of Shear Strength of Saturated Soft Clay under Cyclic Loading

The stiffness and shear strength of soft clay attenuate under long-term cyclic loading, resulting in reduced foundation bearing capacity of road. The variation regularity of undrained shear strength of saturated soft clay which is normally consolidated or over consolidated under cyclic loading was studied with two-way vibration triaxial test, and some useful results are obtained.

Finite Element Analysis on Instantaneous Deformation and Consolidation Deformation of Saturated Soft Clay Foundation

Deformation analysis of foundation is an important research field in geotechnical engineering, especially analysis on instantaneous deformation and consolidation deformation of saturated soft clay foundations. In this paper, a computation model of instantaneous deformation and consolidation deformation was built on the basis of Biot Consolidation Theory and consideration of mechanism of instantaneous deformation and consolidation deformation and consideration of interrelation of both deformations. A method was proposed to determine initial pore water pressure in soil. Nonlinearity of soil deformation under drainage conditions was considered by combining Duncan-Zhang model with compaction curve of soil, and failure soil elements were processed by Mohr-Coulomb Failure Criteria. By numerical simulation, a nonlinear axi-symmetric FEM program was complied to solve foundation deformation and applied in calculation of soft ground tank settlement. Results show that the method presented in this paper is efficient and suitable to analyze instantaneous deformation and consolidation deformation.