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1.
Soils are classified as sandy soils and clayey soils in most soil classification systems, and appropriate equations are used for practical design, depending on soil type, to represent each soil behavior. Sand-clay mixtures, however, need a special standard to evaluate their specific behaviors since they are categorized as intermediate soils or transitional soils and typically show intermediate properties. In this article, a series of cyclic triaxial tests were conducted on specific sand-fines mixtures with three fine types and various fine contents. The behaviors of various soil mixtures (silica sand with Iwakuni natural clay, Tottori silt, and Kaolin clay) were investigated by considering a concept of granular void ratio expressed in terms of sand structure. The cyclic shear strengths of the soil mixtures were also evaluated by increasing the fine content but no more than the threshold fine content. In the results, the cyclic deviator stress ratio decreased in dense soils whereas it increased in loose soils by increasing the fine content. In addition, a simple equation was proposed to predict the liquefaction resistance of sandy soils by evaluating the cyclic deviator stress ratio with a concept of equivalent granular void ratio.  相似文献   

2.
Abstract

Liquefaction is a phenomenon developed in loose and saturated layers of sands subjected to dynamic or seismic loading, and often leads to excessive settlement and subsequent failures in structures. Several methods have been proposed to improve soil resistance against liquefaction, among which use of stone columns is one of the most applicable methods. In this research, the effect of stone columns with different geometries and arrangements on the liquefaction behaviour of loose and very loose saturated sands subjected to vibration is investigated using shaking table. Results of the experiments show that when using stone columns in sand layers, the level of maximum settlement is significantly reduced. Further, the presence of stone columns significantly reduces pore water pressure ratio. This further indicates that stone columns have a positive effect and reasonable performance, even in relatively strong earthquakes, provided that the number and cross-section of the columns are sufficient. In addition, stone columns reduce the pore water pressure dissipation time. Moreover, by increasing cross-sectional area and the number of columns, both pore water pressure and settlement decrease. Stone columns in loose sand have a greater effect on the reduction of pore water pressure compared to that of very loose sand.  相似文献   

3.
A stress path with continuous rotation of the principal stress direction and continuous alteration of amplitude of deviatoric stress difference under the interaction of wave and earthquake loading was proposed based on the characteristics of the stress path under wave and earthquake loading, respectively. Using a GDS dynamic hollow cylinder apparatus, a series of cyclic triaxial-torsional coupling shear tests were performed on Nanjing saturated fine sand via the stress path mentioned previously under different relative densities, effective initial confining pressures, plastic fines contents, and loading frequencies to study the development of excess pore water pressure (EPWP) of saturated sand under the interaction of wave and earthquake loading. It was found that the development of EPWP follows the trend of fast-steady-mutative-drastic, which is different from that under the cyclic triaxial test or wave loading. The number of cycles causing initial liquefaction (NL) of saturated sand increases remarkably with relative densities. However, the relationships between NL and effective initial confining pressures, plastic fines content, or loading frequencies are more complex.  相似文献   

4.
Abstract

This article presents a study of liquefaction resistance behaviour of sand using a cyclic triaxial test. The site investigation was performed, and frozen undisturbed specimens were taken from the Izumio site in Osaka, Japan. According to the evidence in 1995 Kobe Earthquake, the first two sand layers are vulnerable to undergo liquefaction. The effect of deviatoric stress on liquefaction resistance was focused on in this study. The excess pore pressure ratio, hysteresis loop, and effective stress path from the cyclic triaxial tests were reported. A multispring element model was employed to simulate the soil behaviour under cyclic loading. The results showed that applied deviatoric stress could influence the liquefaction resistance of sandy soil samples. The plots of the cyclic stress ratio versus the number of cycles to generate liquefaction known as a liquefaction resistance curve can be then constructed and compared with other sands.  相似文献   

5.
Vacuum preloading is often used to improve the geotechnical properties of dredged slurry. Although the performance of this method has improved with rapidly developing technology, soil columns usually formed on the drainage boundary induce the decrease of permeability around the boundary, thereby limiting the further development of this method. To address this issue, this paper proposes a method for pretreating the slurry combined with sand prior to vacuum consolidation. This method partially replaces the fine particles with sand to reduce the formation of soil columns. Two groups of vacuum preloading tests were performed to investigate the effect of sand content and sand grain size on the vacuum consolidation of dredged slurry. The test results revealed that for a given sand grain size, increasing the sand content of the sand–slurry mixture increased the pore water drainage and accelerated the dissipation of pore water pressure, thereby increasing the vane shear strength. In contrast, for a constant sand content, the samples containing coarse sand exhibited increased pore water drainage and accelerated dissipation of pore water pressure, thereby increasing the vane shear strength of the soil.  相似文献   

6.
The maximum shear modulus of soil is a principal parameter for the design of earth structures under static and dynamic loads. In this study, the statistical data of the maximum shear moduli of reclaimed ground in the Songdo area on the western coast of Korea were evaluated using various field and laboratory tests, including the standard penetration test (SPT), piezocone penetration test (CPTu), self-boring pressure meter test (SBPT), down-hole seismic test (DHT), seismic piezocone penetration test (SCPTu) and resonant column test (RCT). Soils were classified variously by using a conventional unified soil classification system and classification charts for CPTu data. For the soils containing mostly sand and silt, the soil classifications using the classification charts for CPTu data show good agreement with the unified soil classification. Based on the statistical analysis on various maximum shear moduli, new site-specific empirical correlations between the shear moduli and SPT and CPTu values were proposed. Predictions of the maximum shear moduli using the proposed correlations were compared with the data obtained from the DHT, which is comparatively exact in evaluating the maximum stiffness of soils. The good agreement confirmed that the proposed correlations reasonably predicted the maximum shear moduli of soils in western coastal area of Korea.  相似文献   

7.
The foundations of nearshore and offshore structures are always subjected to long-term cyclic loading which is often a one-way, with low amplitude and a large number of cycles. Hence, the long-term dynamic behaviour of shoreline soils and sediments should be understood to avoid excessive deformation and liquefaction. As one of the most problematic soft soils in Melbourne, Coode Island Silt (CIS) at the northern shoreline of Port Phillip Bay contains a considerable but variable amount of sand. This paper explores the dynamic response of CIS containing different sand content subjected to a large number of cycles. To determine the liquefaction potential, and the effect of sand content on the resilient modulus and permanent strain of CIS, a series of long-term cyclic triaxial tests at a sinusoidal loading frequency of 1 Hz is performed. Based on the test results, it is found that CIS with varying sand content up to 30%, does not liquefy under the cyclic stress ratios and frequency applied in this study. Also, a sand content of 10% causes CIS to degrade more under cyclic loading. In the end, an empirical model to predict the permanent strain of CIS with a variable sand content is calibrated.  相似文献   

8.
Based on the analytical solutions for wave-induced soil response in an unsaturated anisotropic seabed of finite thickness, an elliptical, i.e., noncircular rotation stress path is proven to be a more common state in a soil element with the cyclic shear stresses due to the traveling linear wave. The influence of an elliptical stress path on the characterization of failure strength is analyzed using three new parameters representing the shape, size, and the orientation of the ellipse. A series of cyclic rotational shear tests on the reconstituted specimens of Chinese Fujian Standard Sand have been performed to investigate the effect of elliptical stress path. A strength function in term of failure cycles is derived to quantify the failure strength of a given sand within a seabed subjected to regular wave loading. The results provide a basis for the evaluation of liquefaction potential of seabed but also point to a unique backbone cycle shear strength curve for soil under principal stress rotation.  相似文献   

9.
未胶结钙质砂静力和循环强度的单剪试验研究   总被引：1，自引：1，他引：0  
王晓丽  裴会敏  王栋 《海洋工程》2018,36(6):124-129
通过等体积的单调和循环单剪试验研究南海未胶结钙质砂的静、动力反应,讨论应力水平和相对密实度对钙质砂静、动力强度的影响,并与典型的石英砂性质进行比较。在单调单剪试验中,中密和密实钙质砂在100～400 k Pa范围的初始竖向应力下都表现出应变硬化的性质,有效内摩擦角随剪应变增大。在循环单剪试验中,钙质砂的反应与相对密实度和初始竖向应力密切相关,但中密和密实钙质砂中的等效孔压都能达到初始竖向应力的85%～90%,此时剪应变突增,试样发生破坏。与相近密实度的石英砂相比,钙质砂抵抗液化的能力更强。提出了南海钙质砂动强度的归一化表达式,建立了不排水静强度、不排水动强度和循环次数之间的关系。  相似文献   

10.
现代黄河水下三角洲砂土液化模式   总被引：1，自引：1，他引：1  
根据实际勘探资料及室内土工试验结果，按极限平衡理论和线性波动理论等，分析了现代黄河水下三角洲砂土在地震和波浪动力因素的作用下发生液化的可能性，并根据其液化过程实质是孔隙水压力产生、发展和消散的过程，总结出砂土液化模式应包括四个阶段；（１）压密阶段：孔隙水压力升高至砂土本身强度，使颗粒产生相对位移；（２）初始液化阶段：孔隙水压力升至土层所受侧向压力，产生较大应变；（３）完全液化阶段：孔隙水压力升至土层上覆有效应力，产生喷水冒沙现象；（４）塌陷形成阶段：孔隙水压力消散。  相似文献   

11.
In recent years, interest in understanding the mechanisms of mechanical instability of porous media, leading to catastrophic failure has been continuously revised to include, new porous media parameters generating the phenomenon of liquefaction under static or dynamic loadings. Results from experimental test programs have concluded too many physical concepts based on material intrinsic properties, initial states, and other characteristics. Despite the great progress on the subject, these concepts do not allow a unified treatment of such porous media. The assessment of critical shear strength of sandy soils as porous media under undrained conditions is a major challenge in stability analysis. Such strength serves to evaluate the occurrence of flow deformation under liquefaction phenomena. The determination of the critical undrained strength is essentially fundamental for the design of soil structures such as earth dams, bridge supports, building foundations as well as soil densification process to avoid catastrophic failure due to soil instability manifested by failure or large displacement such as settlement. In this work, experimental program on reconstituted loose and medium dense specimens of terrigenous silica sands with different specified fine contents was carried out to analyze its mechanical behavior under undrained conditions. The present article is an attempt to experimentally describe mechanical behavior and theoretically justify such response of loose and medium dense sand by means of critical state soil parameters.  相似文献   

12.
Analysis of wave-induced liquefaction in seabed deposits of silt   总被引：1，自引：0，他引：1  
The dynamic stress introduced in half elastic space by wave loading is characterized by the equation between the magnitude of half cyclic axial stress and cyclic torsion shear stress and the principal stress,whose direction rotates continuously and compression stress on seabed can be calculated by the use of small amplitude wave theory.With relationship curves of saturated silt of liquefaction cycles and cyclic stress ratios obtained by cyclic triaxial-torsional coupling shear tests and curve fitting method to different data points of relative density,it is suggested that the cyclic stress ratio corresponding to constant liquefaction impedance be taken as the critical cyclic stress ratio which implies liquefaction.There exists a linear relationship between critical cyclic stress ratio and relative density under different relative densities.Empirical formula for critical cyclic stress ratios of seabed liquefaction induced by wave loading under different relative densities is established.The possibility of seabed silt liquefaction and its influence factors are analyzed based on the small-amplitude wave theory and the data acquired in laboratory tests.  相似文献   

13.
This paper has identified six major factors causing property changes in surrounding soils during and after installation of deep mixing columns: soil thixotropy, soil fracturing, cement penetration and diffusion, cementation, consolidation, and heating. Laboratory tests were performed to investigate the effects of soil thixotropy, soil fracturing, and cementation in a soft marine clay, Ariake clay. Laboratory tests were conducted to evaluate property changes in surrounding clays due to installation of deep mixing columns. Test results showed that an influential zone of property changes existed in surrounding clay ranging from the edge of the columns to the distance of about twice the radius of the columns. Within this influential zone, water content decreased as samples neared the columns, while pH values and electric conductivity increased. Test results also showed that undrained shear strengths of the surrounding clays decreased during mixing but regained after a 7-day curing period and continued increasing during 28 days in this study.  相似文献   

14.
This paper has identified six major factors causing property changes in surrounding soils during and after installation of deep mixing columns: soil thixotropy, soil fracturing, cement penetration and diffusion, cementation, consolidation, and heating. Laboratory tests were performed to investigate the effects of soil thixotropy, soil fracturing, and cementation in a soft marine clay, Ariake clay. Laboratory tests were conducted to evaluate property changes in surrounding clays due to installation of deep mixing columns. Test results showed that an influential zone of property changes existed in surrounding clay ranging from the edge of the columns to the distance of about twice the radius of the columns. Within this influential zone, water content decreased as samples neared the columns, while pH values and electric conductivity increased. Test results also showed that undrained shear strengths of the surrounding clays decreased during mixing but regained after a 7-day curing period and continued increasing during 28 days in this study.  相似文献   

15.
Deep cement mixing (DCM) technique is a deep in-situ stabilization technique by mixing cement powder or slurry with soft soils below the ground surface to improve their properties and behavior. Some of DCM treated soft soil grounds are approximately in a plane-strain condition; for example, a fill embankment on DCM improved ground. In this study, a plane-strain physical model was created with instrumentation and used to investigate the bearing capacity and failure mode of a soft soil improved by an end-bearing DCM column group. This study focuses on the observed wedge-shaped shear failure of the model ground and attempts to give an account of the failure. Two different methods are used to calculate the bearing capacity of the model ground, and the computed values are compared with the measured ones. It is found that the simple Brom's method gives a better estimate of the bearing capacity of the present model ground. It is also found that measured data of pore water pressures at different locations in the soft soil indicate coupling between failure of columns and consolidation of the soft soil. This study has presented the first time that a wedge-shaped block failure was observed for pattern of DCM treated soil ground.  相似文献   

16.
The central Alborz mountain range, located in northern Iran, neighboring the Caspian Sea and where the two Persia and Eurasia plates meet, is known as a seismologically active area. In this regard, investigation of the behavior of saturated sand deposits located in this area may be of particular interest. Saturated sand deposits are subjected to instabilities owing to liquefaction or volume change due to earthquake shakings. A particular type of saturated sand deposits is Anzali sand which is abundant in Anzali port and other cities located in this area in northern Iran. This type of sand is a representative for most sands found in this area, i.e., the southern coastal line of Caspian Sea. This research is solely focused on the volume change behavior of marine deposits of Anzali area, often characterized as Anzali sand, in terms of the settlement of a model footing located on the surface of the sand by the aid of a transparent laminar shear box apparatus. Effects of a number of factors such as the frequency of the cyclic loading, the initial density of the sand, and the sample preparation method have been investigated. Observations indicated that the density index and the frequency of loading which are proportional to the energy of an earthquake have direct effects on the accumulation and amount of the final settlement of Anzali sand.  相似文献   

17.
Abstract

Liquefaction of loose saturated soil deposits is a hazardous type of ground failure occurring under earthquake excitations. Therefore, an accurate estimation of liquefaction potential is extremely important in geotechnical engineering. In the current study, a new model is proposed which estimates the level of strain energy needed for liquefaction initiation. A compiled database containing cyclic tests gathered from previously published works was used to develop new models to predict liquefaction potential. M5′ algorithm was used to find the best correlation between parameters. It was shown that not only the derived formulas are acceptably accurate but also they feature a very simple structure in comparison with available formulas in the literature. The proposed equations are accurate, physically sound and uncomplicated. Furthermore, safety factors were given for different levels of risk, which can be useful for engineering practice. In addition, the influence of different predictors on the liquefaction potential was evaluated and also the significance of input variables was assessed via sensitivity analysis. Finally, a new model was introduced for preliminary estimation of liquefaction potential.  相似文献   

18.
A remarkable combined dry jet mixing (DJM) and prefabricated vertical drains (PVDs) method was used to enhance the performance for soft ground improvement. In the combined method, PVDs are first installed and then DJM columns are installed between the PVDs at larger spacing. This combined method improves the effectiveness of the ground improvement and creates a more economical solution. This paper presents a case study of the combined method for marine clay improvement in Lianyugang of China. The excess pore water pressure in soils created by the installation of DJM columns with and without PVDs was monitored and compared. In situ standard penetration tests were conducted in the DJM columns and before-and-after piezocone penetration tests were performed in soils surrounding the columns. Long-term settlement monitoring under embankment loading was carried out for the ground improved by combined method and DJM method alone. The field tests, settlement monitoring and economic benefit analysis results demonstrated that the DJM-PVD method is technologically sound and cost-effective as compared with the conventional DJM method.  相似文献   

19.
Based on the vertical equal strain assumption, there are many consolidation theories of soft soil incorporating vertical drains. Because the influence of many factors is often ignored and the flow of the pore water usually happens in three-dimensional directions, analytical solutions could not be accurate enough. Because of the amount of computer storage and the computing time needed, two-dimensional finite element analysis is used to model the stone column improving the soft foundation. The embankment load is transferred to a column because of the soil arching effect. When the embankment is constructed, the settlement accounts for 64% of the total settlement, which shows that the column can reduce the post-construction settlement. The stone column's bulge is confined to a length about one to two times the diameter of the stone column away from its top, and the column at the toe would bears the shear stress to some extent.  相似文献   

20.
Abstract

The study of the unsaturated soils is a very complex field to which several researches in laboratory and on site are directed these last years. An experimental study aims to quantify the influence of the Skempton coefficient B characterizing the degree of saturation on the behavior of the granular sand to the liquefaction resistance of sand. The study is based on undrained triaxial tests performed on natural Chlef sand carried out at an initial relative density Dr = 50% under a confining pressure of 50, 100 and 200?kPa for Skempton coefficient B?=?10 to 92%. The results of the tests show that an increase of confining pressure leads to an increase of the shear stress of the samples. For the lower value of the degree of saturation results of our findings indicate an increase of the resistance to liquefaction; our results are in good agreement with others observed in several research projects conducted with other sands. The increase of Skempton coefficient B induces an increase of pore water pressure and a decrease of the shear strength. The pore pressure (u) increases with an exponential manner with the increase of the degree of saturation; while the residual shear strength (Rs) decreases with logarithmic manner with the increase of degree of saturation (B).  相似文献   

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