首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 375 毫秒
1.
To study the relationship between nano-MgO and soil shear property, the nano-MgO was evenly mixed in the soil to perform the triaxial consolidation draining shear test. Then the microscopic soil granules on the shear planes were observed through the scanning electron microscope. The soil water content was 10% and soil dry density was 1.5?g/cm3, different dosages of nano-MgO, i.e., 0, 2, 4, and 6% were put into the soil samples. The result of triaxial consolidation draining shear test showed that, under low confining pressure and more nano-MgO dosage, the stress–strain relationship of nano-MgO-modified soil turned from hardening to softening. The incorporation of nano-MgO can effectively improve the soil failure strength and cohesive force, and the increasing dosages of nano-MgO had a positive effect on soil shear strength and cohesive force, but little effect on internal friction angle. The analysis of scanning electron microscopy showed that the dosage of nano-MgO can reduce the void ratio of soil and reinforce the cementation between soil granules to change the shear property of soil.  相似文献   

2.
Abstract

River-dredged sludge has a high water content and minimal bearing capacity and strength. Adding cement, fly ash, and slag to dredged sludge as a combined curing agent can quickly reduce its water content and improve its strength. This study experimentally investigates the solidification effectiveness of different proportions of curing agents using methods including electron microscopy, particle size analysis, water ratio limit, and water content and direct shear tests. The water content and shear strength of different combined curing agents are obtained at different ages. We find that an optimum curing agent combination exists. With increases in fly ash and slag content, test results indicate that the water content of solidified sludge first decreases and then increases, whereas the shear strength first increases and then decreases, allowing an optimal combination curing agent to be obtained. When using industrial waste residue as curing agent, it is necessary to consider the negative effects of the curing agent to better control the dosage so as to achieve better curing effect.  相似文献   

3.
Abstract

This study investigated the penetrability of high volume fly ash cement suspensions prepared with and without superplasticizer into sandy soil having different relative densities with 30%, 60%, 73%, and 83% through permeation grouting. Class C fly ash was used due to its pozzolanic activity and fineness. Due to engineering characteristics and cost, cementitious grouts are the most commonly used grout in both waterproofing and ground strengthening. Fly ash-cement grouts have relatively constant and low viscosity values for a reasonable period after preparation, exhibit limited or negligible bleed capacity and set and develop satisfactory strength within a relatively short period. Modeling of grouting of soil was done in laboratory and improvements in physical and mechanical properties of grouted soil were analyzed. Unconfined compressive strength, shear strength and permeability characteristics of grouted soil were studied as a result. Unconfined compressive strength values of grouted sand with high volume fly ash ranged between 410 and 1107?kPa. Morover, cohesion values were comparable to microfine cement grouting ranging from 373 to 511?kPa. Furthermore, permeability values were also approximately equal to the permeability of impervious liners, which is around 1?×?10?7?cm/s. The findings support the applicability of grouting in different applications.  相似文献   

4.
Abstract

The coastal area of Fujian Province in China is rich in both sea sand and sea mud. However, sea sand and sea mud are both unsuitable as direct filler materials for seawalls due to their poor geotechnical properties. To turn waste into a useful product, a mixture composed of sea sand and sea mud is proposed as a filler material for seawalls. The strength, compressibility, moisture sensitivity, and permeability of the mixture are investigated experimentally. The results show that when the mass ratio of sea sand to limed sea mud is 1:2, the mixture exhibits good engineering properties and can serve as a filler material for general engineering purposes in dry environments. To apply the mixture under saturated conditions, both cement and lime are used to improve the engineering properties of the mixture. The improvements in the properties increase with both the binding agent content and the curing time, and the improvement with the addition of cement to the mixture is better than that with the addition of lime. The engineering requirements of seawalls can be satisfied by adding cement, and the cement content can be chosen according to considerations of the construction period and engineering costs.  相似文献   

5.
Environmental friendly earth fill was produced by recycling dredged marine sediment and phosphate tailing. The properties of the marine sediment and tailing were tested. Composite soil samples of different mix ratios were prepared. The optimum moisture contents, basic physical properties, compression characteristics, and shear strength characteristics under the optimum moisture contents were tested and analyzed. The results indicated that the optimum moisture content decreases with increasing phosphorus tailing content and that composite soil is preferable over both marine sediment and phosphate tailing because of its higher dry density, lower compressibility, and higher shear strength. When the phosphorus tailing content is in 50–65%, the dry density is maximized and the void ratio is minimized, indicating the best ratio. The coefficient of compressibility is in 0.07–0.12?MPa?1. When the phosphorus tailing content is 50%, the compression index and coefficient of compressibility are minimized, whereas cohesion is maximized. The internal friction angle increases with increasing phosphorus tailing content. The optimum phosphorus tailing content is 50%; at this phosphorus tailing content, the compacted composite soil can be reutilized as good earth fill. The results demonstrate the properties and optimal conditions of composite soil composed of mud and silty sand.  相似文献   

6.
ABSTRACT

Electro-osmosis is a foundation treatment method for clay that is not widely used because of its nonuniform consolidation effect and high cost. To overcome these limitations, this study investigates fracture grouting. To determine the optimal grouting method, anode grouting, polyurethane grouting, and fracture grouting were first compared in one-dimensional electro-osmosis consolidation tests using self-made model boxes under an equal electric potential gradient, and then different solution concentrations were tested. By comparing the current, drainage rate, and coefficient of energy consumption during the electro-osmosis process, as well as moisture content, electrical conductivity, and shear strength after the tests, the moisture and shear strength of clay after electro-osmosis were found to be significantly improved by adding chemical reagents at the fracture. In addition, the optimum concentration of fracture grouting was determined to be 1.5%, and the shear strength after testing of clay that had been treated with sodium hydroxide was found to be higher than that of the control group. However, the effects of fracture grouting in the early stage were clearer than the effects of fracture grouting at later stages.  相似文献   

7.
Abstract

The mechanical characteristics of calcareous silt interlayers play an important role in the stability of island-reef foundations. Direct shear and consolidation tests were performed to study the relationship between the mechanical properties and the physical parameters of calcareous silt. Based on the consolidation test results and analysis of the settling examples, different calculation methods for soil settling were compared. The results show the following. (1) The relationship between the cohesion and water content of calcareous silt can be represented by an M-shaped curve. The water contents corresponding to the two peaks of the M-type curve increase with increasing dry density. (2) When the dry density is less than 1.33?g/cm3, increasing the density significantly improves the internal friction angle of calcareous silts. When the dry density of the calcareous silt is greater than 1.33?g/cm3, the internal friction angle is affected by both the dry density and the water content. (3) The shear strength decreases when the water content exceeds the optimum level. (4) The compressive modulus of calcareous silt is larger than that of terrigenous silt. Specifically, it decreases with decreasing dry density and increasing water content. (5) The stepwise loading method should be used to estimate the soil settling before fill engineering construction.  相似文献   

8.
Abstract

Evaluation of the strength of cement-treated clay with a broad range of mix ratios and curing periods was conducted using unconfined compression tests (UCTs). The influence of cement content, total water content, and curing period on the unconfined compressive strength of cemented clay are investigated. It is found that, at constant total water content, higher cement content results in higher unconfined compressive strength, while the total water content has an opposite effect. A power function can be used to correlate the unconfined compressive strength with the cement content or the total water content. For a fixed mix ratio, the unconfined compressive strength of cement-stabilized clay increases with the curing period, the effect of which can be characterized by a semi-log formula. Also, a strength-prediction model that considers both mix ratios and curing periods for cement-admixed marine clay is developed and validated; the model can capture the effect of clay type by considering the plastic index of untreated soils. It is also proved that the proposed framework for strength development is also applicable for other cement types.  相似文献   

9.
Abstract

To achieve the rapid dewatering of dredged sludge, the flocculation–vacuum-preloading method was tested indoors. In this study, the optimal mixing ratio of six flocculants was determined through the settling column test, and then the proposed method was tested. The water drainage and settlement were monitored during the test, while the soil moisture content and shear strength were measured after the test. The results show that all the flocculants had an optimal mixing ratio, and the addition of 0.8% FeCl3 or 0.08% anionic polyacrylamide (APAM) in the sludge can better accelerate solid–liquid separation of the sludge. After the test, the water content in the sludge decreased from 140% to 60%. Compared with general vacuum preloading, the use of the proposed method increased the water drainage by 46.5% and 56.8% and decreased the soil volumes by 60.5% and 82.4% for FeCl3 and APAM, respectively. Moreover, the corresponding shear strength was increased from 10 to 14 and 17?kPa. In addition, the use of APAM increased the solidification rate of heavy metals in the sludge to more than 80%, effectively inhibiting the migration of heavy metals.  相似文献   

10.
Abstract

In this study, the mechanical behaviour of nano magnesia–cement-reinforced seashore soft soil (NmC3S) was evaluated and characterised by the direct-shear testing of seashore soft soil (3S), cement reinforced seashore soft soil (C3S) and NmC3S. The comparison among these three types of soils indicates that NmC3S has greater shear strength and deformation modulus than C3S and 3S. The shear stress of both C3S and NmC3S increase significantly prior to a shear displacement of 1.0?mm, followed by a sharp decline before reaching the critical state. The failure displacement increases as the applied normal stress increases. NmC3S demonstrated greater friction angle than both C3S and 3S; however, the magnitude of its cohesion lies between that of C3S and 3S. Moreover, a mathematical model that describes the shear stress–displacement curve was proposed, which can effectively model the strain-hardening and strain-softening curves of these three types of clays. Finally, a generalised formula for capturing the stress–displacement behaviour of these three materials is presented with the explanations for the physical meaning of each parameter.  相似文献   

11.
Abstract

As a part of the environmental impact assessment studies, geotechnical properties of sediments were determined in the Central Indian Basin. The undrained shear strength and index properties of the siliceous sediments were determined on 20 box cores of uniform dimension collected from various locations in five preselected sites. The maximum core length encountered was 41 cm and most of the sediments were siliceous oozes consisting of radiolarian or diatomaceous tests. The shear strength measurements revealed that surface sediments deposited in recent times (0–10 cm) have a shear strength of 0–1 kPa; this value increases with depth, reaching 10 kPa at 40 cm deep. Older sediments have greater strength because of compaction. Water content varies in the wide range of 312–577% and decreases with depth. The clay minerals such as smectite and illite are dominant and show some control over water content. Wet density, specific gravity, and porosity do not indicate any notable variation with depth, thereby indicating a uniform, slow rate of sedimentation. The average porosity of sediments is 90.2%, specific gravity 2.18, and wet bulk density 1.12 g/cm3. Sediments exhibit medium to high plasticity characteristics, with the average plasticity index varying between 105% and 136%. Preliminary studies on postdisturbance samples showed an increase in natural water content and a decrease in undrained shear strength of sediments in the top 10- to 15-cm layer.  相似文献   

12.
ABSTRACT

Strength and stiffness properties of materials are widely studied and used in civil engineering practice. However, most studies are based on unconfined conditions, which are different from real status of soil. This study investigated the primary yielding and yield locus for cement-stabilized marine clay. In this study, two types of cement-stabilized soils were studied through isotropic compression, triaxial drained shearing, unconfined compression, and bender element testing. Specimens with 20–50% of cement content and 7–90 days of curing period were used for the tests. Stress–strain behavior and primary yielding were evaluated, followed by construction of the primary yield locus. The characteristics of the primary yield locus and its development with curing time then were studied. The results showed that the properties of the primary yield locus were dependent on the type of stabilized soil, but were independent of the cement content and curing period. Thus, the approach provides a way to estimate the primary yield stress and drained stress path before primary yielding for cement-stabilized soil under confined condition. An empirical function was used to fit the primary yield locus. The primary isotropic yield stress was correlated to unconfined compressive strength or maximum shear modulus. Three indirect methods were proposed to predict the primary yield stress for cement-stabilized marine clay. The results showed that the primary yield stress can be estimated with reasonable accuracy.  相似文献   

13.
Compacted sand–bentonite mixtures have been used as a good alternative hydraulic barrier material to compacted clays. This study presents the results of a laboratory investigation on the strength characteristics of cement-stabilized sand–bentonite (CSB) mixtures and the effects of adding small amounts of fibers and metakaolin to the mixture material for strength improvement. The strength characteristics of the mixture materials were examined using unconfined compressive strength (UCS) tests and splitting tensile strength (STS) tests, with emphasis on evaluating the effects of different proportions of bentonite, fibers, and metakaolin within the CSB mixtures with a constant value of cement content. The test results indicated that the maximum improvements in UCS and STS were all attained in the CSB mixture with 10% bentonite content, and the inclusion of fibers and metakaolin of 1% each within the same CSB mixture led to an increase in UCS of about 40 and 70%, respectively. The addition of fibers also increased the ductility of the mixture material and was more effective for the improvement of tensile strength compared to that of metakaolin. The contribution of metakaolin to early-age strength (i.e., 3 and 7 days) of CSB mixture was found to be small due to the relatively low cement content in the mixture.  相似文献   

14.
Abstract

A nonlinear mathematical model for estimating the water content dependent undrained shear strength of clayey soils was developed. Three types of clay mixtures (kaolinite, bentonite, and kaolinite-bentonite) were considered. The shear strength of the given soil samples was determined via torvane tests. Experimental results were compared with three numerical results: (i) the analytical function fit, (ii) modeling without the water content effect, and (iii) modeling with the water content effect using the Mohr-Coulomb (M-C) model. There was good agreement among the experimental, analytical, and numerical results with and without the water content effect in the fully softening zone. However, there was a large difference between the numerical results obtained from the developed model with and without the water content effect in the flow zone with a high liquidity index, because the shear strength may decrease significantly to low value in the case of an abrupt increase of the water content. The greatest advantage of the developed model is that it can simulate the reduction of the shear strength and shear band development under the high water content condition, which may trigger a large mobile mass movement.  相似文献   

15.
Abstract

The use of soft clay and dredged marine clays as the construction material is challenging. This is because the high water content, high compressibility and low permeability of the clay causing the instability of ground and structure. This detrimental effect of soft clay can be improved by the cement solidification process, which is relatively cheap and efficient. This paper mainly focuses on the study of improvement on the mechanical behavior of cement mixed marine clay. The soil is reconstituted by using ordinary Portland cement of 5%, 10%, 15% and 20% by its mass. The study reveals that cementation of clay significantly improves the peak and residual strength of soil. Similarly, the primary yield stress of the soil is also improved from 16 to 275?kPa as cement content increases from 5% to 20%, respectively. By using statistical tools, the relationships between various parameters are established, which are very important to define the mechanical behavior of the clay. This study reveals that the yield surface of the solidified marine clay is not a smooth elliptical surface. Rather it is composed of two linear surfaces followed by a log-linear surface which can be modeled by using simple parameters obtained from triaxial tests.  相似文献   

16.
Abstract

By application of the limit equilibrium method associated with Coulomb failure mechanism, the effect of variation of undrained shear strength with depth on seismic bearing capacity was evaluated. The approach followed in this study to take into account seismic forces is pseudo-static. It is also assumed that the occurrence of an earthquake does not have any effects on the values of soil cohesion. Two different marine soil deposits exhibiting linear and bilinear variations of undrained shear strength with depth were considered. The undrained bearing capacity factor has been computed as a function of dimensionless parameters of λ1B/c0, λ2B/c0, and Zt/B. The results of this paper have been compared with solutions reported in the literature, and the consistency of the results confirmed the ability of Coulomb failure mechanism and its corresponding limit equilibrium method formulation in static condition. Furthermore, the pseudo-static bearing capacity of shallow foundations on heterogeneous marine deposit is addressed. Finally the results of this study presented in the form of table and design charts.  相似文献   

17.
ABSTRACT

In this paper, a series of mini-drum centrifuge experiments on motion of submarine debris flow, which are able to correctly reproduce the self-weight stresses and gravity-dependent processes, are presented. These tests were performed using artificial submarine clay with high water content, from 93 to 149%. The extremely low shear strength made the debris material behave as idealistic lubricating material when it was deposited, resulting in a linear relationship between water content and runout distance of strongly coherent debris flow. On the other hand, the dilation of the flow body and hydroplaning was observed for weakly coherent debris flow, which further increased the mobility of flow body. A densimetric Froude number Frd was used to indicate the threshold of hydroplaning, which occurs if the Frd is greater than 0.2. Finally, two simple analytical models based on prototype debris flow under 1?g condition was used to validate the experiment results, which further prove the effects of soft marine clay on the high mobility of submarine debris flow. On the other hand, when the water content exceeded 120%, the experiment results deviated from the analytical solution due to the effects of hydroplaning.  相似文献   

18.
Beach sands located above the sea water level exist in an unsaturated, rather than a fully saturated or dry state. Within the unsaturated zone, a steep excavated surface can be sustained for some unknown but finite time, and some slopes may remain stable for extended time periods due to capillary forces. These observations clearly indicate small but nonzero values for attraction strength (tensile strength and cohesion) in unsaturated beach sands, especially apparent but not confined to settings where there are low stress levels. Thus, experiments were carried out to quantify the magnitude of attraction strength in moist sands (D r ?=?30%) and to examine the variation of these values as a function of moisture content and presence of a small amount of fines. Tensile strength, which is significantly different from zero, increases with increasing moisture content and fines. However, the influences of fines on the tensile strength are substantially dependent on the water content. Apparent cohesion strength is also identified in moist sands. A simple relationship between tensile strength and apparent cohesion is proposed using the obtained data. This study would help to further understand the phenomenon of stability of beach sands.  相似文献   

19.
Abstract

Marine soft clay with a high salt concentration is widely distributed in coastal areas. In this study, cement-based composites consisting of cement, silica fume, plant ash and NaOH were used as a substitute for ordinary Portland cement, and the effect of salt (sodium chloride) on the strength development of clay was investigated by unconfined compressive strength (UCS) testing and scanning electron microscopy (SEM). With the addition of sodium chloride (NaCl), the amount of cementitious materials decreased, and the salt (sodium chloride) was considered to consume the cement-based composites. The consumption effect could be quantitatively evaluated by the consumption index of salt (CIS) and the clay-water/cement ratio hypothesis. The relationship between the CIS and curing period and an UCS prediction model of clay stabilized with cement-based composites with different salt contents and curing times were established. The CIS gradually decreased with increasing curing time and cement-based composites content. The accuracy of the prediction model was evaluated by a comparative analysis between the measured strengths and predicted strengths; the deviation was mostly within 10%. SEM analyses were employed to describe the changes in the microstructure of the specimens and the influencing mechanism of salt on clay stabilized with cement-based composites.  相似文献   

20.
ABSTRACT

Natural Ariake clays are characterized by high sensitivity. In this study, the mechanism and the factors controlling undrained shear strengths of both undisturbed and remolded Ariake clays are discussed. A series of unconfined compressive tests were performed on undisturbed samples of natural Ariake clays. The remolded undrained shear strength is predicted using a quantitative expression derived from extensive data of remolded undrained shear strength for a number of soils compiled from resources in the literature. The sensitivity of natural Ariake clays derived from the ratio of half of unconfined compressive strength for undisturbed samples to remolded undrained shear strength is found to be affected by both natural water content and normalized water content that is defined as the ratio of natural water content to liquid limit. The smaller the natural water content, the higher the sensitivity is at the same normalized water content. At the same natural water content, the larger the normalized water content, the higher the sensitivity is.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号