Increase Of Internal Friction Angle Research Articles

Method for predicting dynamic shear strength in soils – Part II: Validation of the new criterion using an innovative test device

This publication series describes the phenomenon of dynamic strengthening of soils. This part presents a literature review, based on which a new tester was designed. It allows shearing of soils in a wide range of speeds, it is not susceptible to the scale effect, wall effect and the bulldozing effect, as well as it has shear kinematics adequate to the modelled process. Comparison of the test device with direct shear tester showed a substantial decrease of cohesion and increase of internal friction angle of cohesive soils with the new tester. Four different cohesive and non-cohesive soils have been investigated in this study. Dynamic shearing tests have confirmed that cohesive soils may increase shear strength by up to almost 3 times compared to quasi-static shearing. Non-cohesive soil (quartz sand) did not exhibit distinct increase of shear strength. Validation of the new criterion proved it can be used to describe the shear strength – shear speed relationship of agricultural soils. The proposed model correlated with experimental data at R2 over 0.85 for cohesive soils and over 0.64 for sand.

Dynamic Analysis of Embankments Reinforced with Micro-Piles

Application of micro-piles to stabilize unstable slopes has been widely considered in recent years. A micro-pile is a small-diameter (typically less than 300 mm), drilled, and grouted as non-displacement pile that is typically reinforced. The main objective of this study is to evaluate the influence of the micro-pile group on increasing safety factor as well as finding the optimum position of micro-piles across the embankments slopes. In this study, numerical analyses were performed to investigate the efficiency of micro piles on the behavior of embankments using ABAQUS Finite Element code. The analyses have been carried for plane strain conditions and under earthquake loads. Based on acquired results, it was implied that using micro pile groups on the lower part of embankment slope is the optimal approach to reinforce embankments. This can increase the embankment safety factor by 33% in static mode and by 34% in dynamic mode. The impacts of the parameters of micro pile inclination angle, diameter, length, micro-pile spacing, and the type of soil on safety factor in dynamic mode have been investigated. Results show that increasing the length and diameter of the micro piles increase the safety factor. By increasing the micro pile angle in respect to vertical axis up to 30°, safety factor increases but any additional increase of the angle decreases the factor. Furthermore, by increasing the spacing of micro piles up to 4 times the diameter, causes improving the safety factor, but more space has a negative impact. By strengthening the type of the adhesive soil (simultaneous increase of embankment adhesion from 8 KPa to 16 KPa and elasticity module from 30 MPa to 60 MPa), embankment safety factor increases by 40%. Furthermore, by strengthening the sandy soil (simultaneous increase of internal friction angle from 32 to 40 and soil elasticity module from 20 MPa to 45 MPa), the safety factor of embankment increases by 41 percent.

Experimental Study on Engineering Properties of Large-Thickness Loess in Dongzhiyuan Area

In this paper, the engineering properties of collapsible loess with large thickness in Dongzhiyuan Area is analyzed in detail through consolidation test, triaxial shear test, maximum dry density test, static penetration test, standard penetration test and site wave velocity test. The results show that: (1) the engineering properties of Malan loess in the upper part of collapsible loess in Dongzhiyuan Area are not so satisfying. With the increase of the depth, the void ratio of the loess becomes increasingly smaller while the cohesive force and internal friction angle increase gradually. The bearing capacity of the foundation increases, indicating that the engineering properties of the foundation soil become better. (2) At the same time, the static lateral resistance and point resistance of the foundation soil become increasingly larger, which is very beneficial to the friction piles in the large-thickness collapsible loess area.CLC number: TU443 Document code: A

Experimental Study on Stress and Strain Characteristics of Solidified Clay under Seawater Condition

This paper presents the results of a laboratory study on the stress-strain relationship of solidified clay formed in seawater corrosion condition. An automatic triaxial apparatus was used and the axial stress and strain was monitored continuously. The dry density was 1.0g/cm3, the cement contents were 4, 6, 8 and 10% by weight of dry soil particles, and the curing time was 28, 60 and 90 days respectively. Test results indicate that the stress strain relationship of cemented clay was affected by soil density, cement content and curing period. A behaviour of strain hardening to strain softening occurred with the increase of cement content. Strong structure will form in cemented clay when the admixture content is 10% or more. The increase in strength of the solidified foundation is resulted from the increase in internal friction angle and cohesive force. The cohesive force increases obviously with the increase of the cement content and the curing age, but the change of internal friction angle is not pronounced after reaching a certain value.

Influence of Sample Size on the Shear Strength of Structural Plane

The indoor experimental research of structural planes is often limited, whereas that of rock mass is practically extensive. Therefore, using a small structure to simulate the mechanical properties of reactions in a large structural plane is worthy of further study. Then studies for the effects of size on the shear strength of structural planes have important significance. This paper uses samples with a variety of sizes in the direct shear test of structure planes under varying values of normal stress. The results show that, the corresponding shear deformation is small and the shear capacity of the structural plane generally declines after reaching the peak shear stress. Cohesion c was small when the height of the specimen was not over half of its length. If the height is below half of the specimen length, then the internal friction angle increases. When the specimen size is small, the effect of cohesion was limited. The internal friction angle decreases with an increase in size.

정수압에 의존하는 항복기준의 강도정수 비교연구

이론적 연구를 통하여 정수압의 영향을 받는 항복기준인 Mohr-Coulomb 항복기준과 Drucker-Prager 항복기준의 강도정수를 <TEX>${\pi}$</TEX>-평면에 대해 일치시킴으로써 강도정수간의 상관관계를 분석해 보았다. Drucker-Prager 강도정수 <TEX>${\alpha}$</TEX>와 k를 Mohr-Coulomb 강도정수인 c와 <TEX>${\phi}$</TEX>를 이용하여 표현하였는데 k는 c, <TEX>${\phi}$</TEX>의 함수로 표현되었고 <TEX>${\alpha}$</TEX>는 <TEX>${\phi}$</TEX>만의 함수로 표현되었다. Drucker-Prager 강도정수 <TEX>${\alpha}$</TEX>값은 흙의 내부마찰각이 커짐에 따라 증가함을 알 수 있었는데 Drucker-Prager 항복기준을 나타내는 원이 Mohr-Coulomb 항복기준에 외접 및 내접하는 경우의 <TEX>${\alpha}$</TEX>값을 나타내는 <TEX>${\alpha}_c$</TEX>와 <TEX>${\alpha}_i$</TEX>값에 대하여 평균값인 <TEX>${\alpha}_{av}$</TEX>의 값은 내부마찰각에 비례하였는데 내부마찰각이 <TEX>$10^{\circ}$</TEX>인 경우 약 0.07이었으며 내부마찰각이 <TEX>$45^{\circ}$</TEX>인 경우 약 0.29이었다. 또한, <TEX>${\alpha}_c/{\alpha}_i$</TEX>값은 내부마찰각에 비례하였는데 내부마찰각이 <TEX>$10^{\circ}$</TEX>인 경우 약 1.12이었으며 내부마찰각이 <TEX>$45^{\circ}$</TEX>인 경우 약 1.62이었다. Mohr-Coulomb 강도정수가 Drucker-Prager 강도정수 k에 미치는 영향을 살펴보았는데 본 연구에서 가정한 흙의 점착력 중 최소값이 10kPa인 경우를 제외하고 흙의 내부마찰각의 영향을 거의 받지 않고 전체적으로 흙의 점착력에 영향을 받음을 알 수 있었다. 일정한 점착력에 대하여 내부마찰각이 증가함에 따라 일축압축시 및 일축인장시의 Mohr-Coulomb 항복기준에 의한 축차응력인 <TEX>$S_{c0}$</TEX>와 <TEX>$S_{t0}$</TEX> 그리고 두 값의 평균값인 <TEX>$S_{0(ave)}$</TEX>값은 감소하였다. 또한 내부마찰각이 증가할수록 Mohr-Coulomb 항복궤적을 나타내는 육각형이 더욱 불규칙해져 <TEX>$S_{0(ave)}$</TEX>로부터 <TEX>$S_{c0}$</TEX>와 <TEX>$S_{t0}$</TEX> 사이의 편차가 내부마찰각이 증가함에 따라 커짐을 알 수 있었다. In this theoretical study, the strength parameters of the Drucker-Prager yield criterion and Mohr-Coulomb yield criterion were set to equal values, in order to analyze the correlation among the parameters. The Drucker-Prager strength parameters <TEX>${\alpha}$</TEX> and k were represented by the Mohr-Coulomb strength parameters c and <TEX>${\phi}$</TEX>. Specifically it can be seen that k is function of c, <TEX>${\phi}$</TEX> and <TEX>${\alpha}$</TEX> is function of <TEX>${\phi}$</TEX> alone. Drucker-Prager strength parameter <TEX>${\alpha}$</TEX> increases as the internal friction angle of soil increases. <TEX>${\alpha}_{av}$</TEX> which is the average of <TEX>${\alpha}_c$</TEX> and <TEX>${\alpha}_i$</TEX> was proportional to internal friction angle in which <TEX>${\alpha}_c$</TEX> and <TEX>${\alpha}_i$</TEX> are <TEX>${\alpha}$</TEX> values corresponding to the circles of the Drucker-Prager yield cirteria circumscribes and inscribes the Mohr-Coulomb yield criterion respectively. The values of the <TEX>${\alpha}_{av}$</TEX> was 0.07 and 0.29 which correspond to the internal friction angle of <TEX>$10^{\circ}$</TEX> and <TEX>$45^{\circ}$</TEX> respectively. In addition, value of <TEX>${\alpha}_c/{\alpha}_i$</TEX> was proportional to internal friction angle of soil and the values of <TEX>${\alpha}_c/{\alpha}_i$</TEX> 1.12 and 1.62 which corresponds to internal friction angle of <TEX>$10^{\circ}$</TEX> and <TEX>$45^</TEX><TEX>{\circ}$</TEX> respectively.The influence of the Mohr-Coulomb strength parameters on the Drucker-Prager strength parameter k was investigated and it was found that k was mainly influenced by the cohesion of the soil, except in the case of the minimum assumed value of c of 10kPa. The deviator stresses, <TEX>$S_{c0}$</TEX> and <TEX>$S_{t0}$</TEX>, which correspond to the cases of the Mohr-Coulomb yield criterion under uniaxial compression and uniaxial tension, respectively, and <TEX>$S_{0(ave)}$</TEX>, which is the average value of <TEX>$S_{c0}$</TEX> and <TEX>$S_{t0}$</TEX>, decrease as the internal friction angle increases. Furthermore, the hexagon, which represents the Mohr-Coulomb yield locus, becomes more irregular, and the deviations of <TEX>$S_{c0}$</TEX> and <TEX>$S_{t0}$</TEX> from <TEX>$S_{0(ave)}$</TEX> also increase, as the internal friction angle increases.

Experimental study on the microstructure and mechanical behaviors of leachate-polluted compacted clay

The intent of this article is to investigate the microstructure characteristics and macroscopic mechanical behaviors of leachate-polluted compacted clays. X-ray diffraction, scanning electron microscope, and mercury intrusion porosimetry were used to observe the mineral component, microstructure of the compacted clays polluted by different concentrations of landfill leachate. One-dimensional swelling test, direct shear test, and permeability test were conducted to measure and analyze the swelling properties, shear strength, and permeability of leachate-polluted compacted clays. Results indicated that the leachate pollution caused a decrease in smectite content of compacted clays. Aggregate structure was destroyed by leachate pollution, causing an increase in the relative porosity of the smaller pores and a decrease in that of the larger pores. However, the total porosity increased with the leachate concentration because of the decrease in swelling deformation of compacted clay. Leachate pollution caused a significant increase in cohesion and a slight increase in internal friction angle of the compacted clays. Moreover, the permeability of the leachate-polluted compacted clays decreased with the increase in time and leachate concentration.

Impact Analysis of Support Structure of Unsymmetrical Loading Deep Foundation Pit Adjoining Highway

The air shaft deep foundation pit 6 is influenced by subgrade unbalance loading of highway 312, specifically its deep horizontal displacement of supporting piles and subgrade settlement of expressway 312 under unsymmetrical load effect. This paper carries out construction monitoring and numerical simulation analysis and gives a detailed study on the influenced factors of support structure deformation. Calculation results show that subgrade unsymmetrical load has a great influence on deep horizontal deformation of supporting piles. The maximum horizontal displacement at the bias side is about three times more than non-bias side’s; when the distance of subgrade to foundation pit is the same as the depth of excavation, the influence of subgrade on pit can be ignored; as the cohesion and internal friction angle increases, the horizontal displacement of fender piles decreases. However, enlarging the embedded depth of supporting piles has no significant influence on the stability of foundation pit.

Experimental Study of the Relationship between Matric Suction and Strength of Unsaturated Residual Clay in Xiamen under Different Drying-Wetting Cycle Paths

To discuss the relationship between matric suction and strength under different drying-wetting cycle paths of residual clay, soil water characteristic curve was determined by the filter paper method. The shear strength, unconfined compressive strength and matric suction were obtained during desorption and adsorption at the drying and wetting cycle. The experimental results show that the matric suction of soil specimens subjected to different drying and wetting cycle paths are different although at the same water content. Contributions of internal friction angle and cohesion to shear strength are different at different matric suction. In the low matric suction stage, matric suction mainly contribute to shear strength by affecting the cohesion, yet in the high matric suction stage by increasing both the internal friction angle and cohesion; in the transition matric suction stage, the contribution of cohesion decreases while the contribution of internal friction angle increases. Furthermore, the unconfined compressive strength of specimens subjected to the drying and wetting cycle path of desorption first and then adsorption is reduced and increase with the opposite path.

Experimental Study on Deformability and Shear Strength of Solidified Dredged Soil

To protect the marine environment, a kind of new composite curing agent was used to solidify dredged soil. The compression test and direct shear test were conducted to make experimental study on solidified soil of 2 curing time and 4 curing agent content, and to analyze the effects made by curing time and curing agent upon soil shear strength and soil compression modulus. The results show the increase of curing time raises compression modulus and soil cohesion to some extent but affects soil internal friction angle slightly. The rise of curing agent content makes a significant growth of compression modulus and cohesion. The compression modulus and cohesion of 7%-curing-agent solidified soil are respectively 1.57 and 15.8 times those of plain soil. But curing agent impacts slightly on the increase of internal friction angle. The maximum growing rate of internal friction angle is just 18.2%.

이차원 개별요소 수치해석을 통한 화강풍화토의 평균입자크기와 전단강도의 관계 규명

본 연구에서는 개별요소법을 적용하여 화강암 기원의 풍화토에서 입자 크기와 입자크기 분포 특성 중 최대입경/최소입경의 비가 강도정수에 미치는 영향을 살펴보았다. 입자크기와 입도분포가 변화할 때의 전단강도 특성 변화를 규명하기 위하여 개별요소법 수치해석을 실시하였다. 점착력이 0.25MPa, 내부마찰각이 <TEX>$29^{\circ}$</TEX>인 강도특성을 갖는 기준시료를 수치해석적으로 구현한 후, 간극률을 기준시료와 동일하게 유지하면서 입자의 크기와 입도분포를 바꾸어 가며 점착력과 내부마찰각의 변화를 살펴보았다. 수치해석결과 평균입자의 크기가 커질수록 점착력의 현저한 감소가 관찰되었으며, 내부마찰각의 변화는 미미하지만 증가하는 경향을 보였다. 이러한 연구결과는 입도만을 이용하여 간편하게 화강풍화토의 강도정수 산정 시 활용될 수 있을 것으로 판단된다. 특히 풍화상태가 점이적으로 변화하는 화강풍화토의 경우, 현장시험과 실내시험을 통하여 일부 구간에서 측정된 입도-강도 자료가 있을 때, 이러한 시험들이 수행되지 않은 구간에 대해서도 입도분포를 통해 간편하게 강도특성을 규명할 수 있을 것으로 여겨진다. We have carried out a series of numerical experiments to study the effect of average particle size on the mechanical properties of granite-derived weathered soils. A distinct-element method was adopted to study the changes in macro-scale mechanical properties with particle size and maximum-to-minimum particle size ratio. The numerical soil specimen with cohesion values of 0.25 MPa and internal friction angle of 29 degrees was prepared for reference. While keeping the porosity values constant, we varied particle size and size distribution to study how cohesion and internal friction angle changes. The experimental results show that the values of cohesion apparently decrease with increasing particle size. Changes in the values of internal friction angles are small, but there is a trend of increase in internal friction angle as the average particle size increases. This study demonstrates a possibility that the results of numerical experiments of this type may be used for rapid estimation of mechanical properties of granite-derived weathered soils. For example, when mechanical properties obtained through in situ tests and particle size data obtained through lab analysis are available for a site, it is expected that the mechanical properties of weathered granite soils with varying degrees of weathering (thus, varying particle size) may be estimated rapidly only with particle size data for that site.

Predicting flow mode in cylindrical hopper

Most of the problems associated with industries handling solids are related to hopper flow. Hoppers may develop slow and sluggish zones, commonly known as stagnant zones, leading to funnel flow which reduces the efficiency of the process. Modelling can be used to predict the hopper flow based on material properties and hopper design. We have simulated the flow in a cylindrical hopper and validated it by performing 3D experiments. Further the model is used to investigate the effect of material properties and hopper design. It was found that stagnant zone size increases with increase in internal friction angle and decrease in ability of granular material to transfer load. It is also observed that stagnant zone size decreases as hopper angle is increased. Optimum hopper angle can be calculated from the simulation to minimise hopper height. This model can further be used for predicting flow for more complex conditions.

Gravel Content Effect on the Shear Strength of Clay-Gravel Mixtures

Gravel content is an important factor affecting the mechanical properties of clay-gravel mixtures. To study the effects of gravel content on the shear strength of clay-gravel mixtures, constant-strain-rate drained triaxial compression tests were conducted for various mixtures. The gravel contents were 30%, 40%, 50% and 70%. The confining pressures were varied from 50kPa to 300kPa. Test results indicate that the deviator stress at failure under the same confining pressure increases with the increase in gravel content. As the gravel content in the mixtures is between 30% and 50%, the shear strength is jointly attributed by clay and gravel. An increase in gravel content results in slight increases in both the cohesion intercept and internal friction angle. At gravel content of up to 70%, the shear strength of the mixture is controlled by that of the gravel, and the cohesion intercept and the internal friction angle increase sharply.

Bearing Capacity of Two-dimensional Reinforced Composite Foundation

The bearing performance of both vertically and horizontally reinforced composite foundation formed by horizontal reinforcement setded on top of granular piles, which can restrict the failure of granular piles, was studied. With the consideration of restriction of horizon- tal reinforcement and the shear force between the pile and the interpile soil, the bearing capacity formula of composite foundation rein- forced with single-layer horizontal reinforcement and vertical piles was derived according to limit equilibrium condition.lt can well consid- er the effect of horizontal reinforcement, vertical piles and soil' s gravity on composite foundation bearing capacity. A case study was given and the influence of different parameters on bearing capacity of composite foundation was discussed.The results show that the bearing ca- pacity of such composite foundation increases with increase of internal friction angle, cohesion of soils and the friction angle between the pile and the interpile soil. Besides, the bearing capacity increases to a certain level with the existence of horizontal reinforcement on top of granular piles.