• Title/Summary/Keyword: Confining pressure effect

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The Effect of Confining Pressure on Modulus of Soils at Low Confining Pressures (낮은 구속응력 단계에서 지반의 탄성계수에 대한 구속응력의 영향)

  • 권기철
    • Journal of the Korean Geotechnical Society
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    • v.20 no.4
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    • pp.57-63
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    • 2004
  • The range of stresses experienced in subgrade soils and subbase materials in pavement under working stress conditions is below about 150㎪. Therefore, the deformational characteristics of soils at low confining pressures are important properties in the analysis and design of pavement system. Subgrade soils and subbase materials were collected from the actual pavement projects for testing. To evaluate the effect of confining pressure on modulus of those materials at low confining pressures, RC and FFRC tests were performed. Interestingly, the relationship between modulus of soils and confining pressure is more appropriate in linear space than in logarithm space at low confining pressure. Based on those results, new model fur evaluating the effects of confining pressure on modulus at low confining pressures was proposed.

Mechanical properties of tailings with dipping interlayers under high confining pressure

  • Qinglin, Chen;Zugui, Li;Zeyu, Dai;Xiaojun, Wang;Chao, Zhang
    • Geomechanics and Engineering
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    • v.31 no.6
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    • pp.557-571
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    • 2022
  • Landslides are often triggered by weak interlayers initiated in tailings dam foundations, and hazards gradually occur. This is serious for landslides in high tailings dams due to their high potential energy. Tailing samples with a fine-grained interlayer at a set dip angle were prepared. Consolidated undrained (CU) triaxial shear tests were carried out by using a high-pressure triaxial apparatus. The results were compared with the results under a low confining pressure. Four reasons were summarized for high tailings dams more prone to instability than low dams. The shear strength of the samples with dipping interlayers decreases with increasing dip angle. An obvious straight drop in the stress path after the peak occurs in samples with dipping interlayers at an angle of 60°. The effect of the interlayer on the mechanical behaviour of tailings is very sensitive, especially for the sample with a dipping interlayer at an angle of 60°. Shear slipping along the interlayer should be given more attention in tailings dams. Compared with the results under low confining pressure, the stress decreases continuously for the samples with dipping interlayers at large angles under high confining pressure. The positive pore pressure, which reduces the effective stress, occurred in tailings samples under high confining pressure. The residual strength of tailings under high confining pressure is smaller than that under low confining pressure. These factors increase the dam break risk and the disaster impact for high tailings dams.

Strength Characteristics of Clay Soil by Preconsolidation Pressure (선행하중(先行荷重)에 의한 점토(粘土)의 강도특성(强度特性))

  • Chon, Yong-Baek;Shin, Young-Gi
    • Journal of the Korean Society of Industry Convergence
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    • v.6 no.3
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    • pp.185-192
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    • 2003
  • This study consolidation undrain Triaxial Compression Tests using constant confining pressure in clay that receive preconsolidation stress that is different and, void ratio, pore water pressure coefficient, shear strength compare with another thing theory and studied analyzing change relation of elastic modules. The summary of analysis is follows: If preconsolidation stress increases in same confining stress in relation of preconsolidation stress and deviator stress, deviator stress is proportional and increased. Can know that excess void pressure is proportional and decreases in size of preconsolidation stress in same confining stress state if preconsolidation stress increases preconsolidation stress and relation of excess void pressure. Also, over consolidated state can assume that this is thing by Dilatancy's effect though excess void pressure decreased remarkably. Preconsolidation stress and relation of stress path can know that shear strength degree increases preconsolidation stress increases, and specially, preconsolidation stress was appear in stress path form of overconsolidated state case of clay that receive at 300, 400, 500kPa in 100, 150kPa's deviator stress.

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Undrained Behavior on Saemangeum Dredged Sands (새만금 준설모래의 비배수 거동)

  • Jeong, Sang-Guk;Kang, Kwon-Soo;Yang, Jae-Hyouk
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.6 no.1
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    • pp.193-203
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    • 2002
  • The results of an experimental study on Saemangeum dredged sands are presented. Undrained triaxial compression tests were performed with there different initial relative densities, namely 18, 34, and 50%, intend to evaluate undrained Behavior. All undrained triaxial compression tests were performed under static loading conditions. Undrained triaxial compression tests were exhibited complete static liquefaction, zero effective confining pressure and zero stress difference at lower confining pressures. As confining pressures were increased, the effective stress paths indicated increasing resistance to static liquefaction by showing increasing dilatant tendencies. The fines and larger particles create a particle structure with high compressibility at lower confining pressure. The effect of increasing relative density was to increase the resistance of the sand against static liquefaction by making the sand more dilatant.

Numerical simulation of the effect of confining pressure and tunnel depth on the vertical settlement using particle flow code (with direct tensile strength calibration in PFC Modeling)

  • Haeri, Hadi;Sarfarazi, Vahab;Marji, Mohammad Fatehi
    • Smart Structures and Systems
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    • v.25 no.4
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    • pp.433-446
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    • 2020
  • In this paper the effect of confining pressure and tunnel depth on the ground vertical settlement has been investigated using particle flow code (PFC2D). For this perpuse firstly calibration of PFC2D was performed using both of tensile test and triaxial test. Then a model with dimention of 100 m × 100 m was built. A circular tunnel with diameter of 20 m was drillled in the middle of the model. Also, a rectangular tunnel with wide of 10 m and length of 20 m was drilled in the model. The center of tunnel was situated 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m and 60 m below the ground surface. these models are under confining pressure of 0.001 GPa, 0.005 GPa, 0.01 GPa, 0.03 GPa, 0.05 GPa and 0.07 GPa. The results show that the volume of colapce zone is constant by increasing the distance between ground surface and tunnel position. Also, the volume of colapce zone was increased by decreasing of confining pressure. The maximum of settlement occurs at the top of the tunnel roof. The maximum of settlement occurs when center of tunnel was situated 15 m below the ground surface. The settlement decreases by increasing the distance between tunnel center line and measuring circles in the ground surface. The minimum of settlement occurs when center of circular tunnel was situated 60 m below the surface ground. Its to be note that the settlement increase by decreasing the confining pressure.

Study on the mechanical properties test and constitutive model of rock salt

  • Zhao, Baoyun;Huang, Tianzhu;Liu, Dongyan;Liu, Yang;Wang, Xiaoping;Liu, Shu;Yu, Guibao
    • Geomechanics and Engineering
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    • v.18 no.3
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    • pp.291-298
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    • 2019
  • In order to study the mechanical properties of rock salt, triaxial compression tests under different temperatures and confining pressure are carried out on rock salt specimens, the influence of temperature and confining pressure on the mechanical properties of rock salt was studied. The results show that the temperature has a deteriorative effect on the mechanical properties of rock salt. With the increase of temperature, the peak stress of rock salt decreases visibly; the plastic deformation characteristics become much obvious; the internal friction angle increases; while the cohesion strength decreases. With the increase of confining pressure, the peak stress and peak strain of rock salt will increase under the same temperature. Based on the test data, the Duncan-Chang constitutive model was modified, and the modified Duncan-Chang rock salt constitutive model considering the effect of temperature and confining pressure was established. The stress-strain curve calculated by the modified model was compared with the stress-strain curve obtained from the test. The close match between the test results and the model prediction suggests that the modified Duncan-Chang constitutive model is accurate in describing the behavior of rock slat under different confining pressure and temperature conditions.

Development of Design Method of Compression(SSC) Anchor (압축헝 앵커의 설계법 개발)

  • 임종철;홍석우;이태형;이외득
    • Journal of the Korean Geotechnical Society
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    • v.15 no.1
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    • pp.63-78
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    • 1999
  • For the design of compression anchor, three things should be considered. The first is a resistance force by skin friction, the second is a tension strength of tendon, and the third is a compressive strength of grout. Especially, compressive strength of grout is the most important design parameter of compression anchor. When compression anchor is pulled out from the ground, the compressive strength of grout increases by confining pressure of ground($\sigma_{tg$). Here, $\sigma_{tg$ is the confining pressure which is produced by earth pressure at rest and by lateral expansion of grout. We call this phenomenon of increase of confining pressure "poisson effect". In this paper, the design method of compression anchor called SSC anchor and the computer program for the design are developed through compression tests of anchor body grout.ody grout.

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Frictional effects on the cyclic response of laterally loaded timber fasteners

  • Allotey, Nii;Foschi, Ricardo
    • Structural Engineering and Mechanics
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    • v.21 no.1
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    • pp.1-18
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    • 2005
  • Foschi's connector model is used as a basic component in the development of nonlinear analysis programs for timber structures. This paper presents the extension of the model to include the effect of shaft frictional forces. The wood medium is modeled using the Foschi embedment model, while shaft friction is modeled using an elastic Coulomb-type friction model. The initial confining pressure for the case of driven fasteners is accounted for by a lateral shift of the load-embedment curve. The model is used to compute the cyclic response of both driven and inserted fasteners. The results obtained from the cases studied indicate that initial confining pressure and friction do not have a significant effect on the computed hysteretic response, however, they significantly affect the computed amount of fastener withdrawal. This model is particularly well-suited for modeling the hysteretic response of shear walls with moderate fastener withdrawal under lateral cyclic or earthquake loading.

Effects of Gradation on Dynamic properties of Sands (모래의 입도가 동적 특성에 미치는 영향)

  • 송정락;김수일
    • Geotechnical Engineering
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    • v.3 no.2
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    • pp.7-16
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    • 1987
  • The dynamic properties of soils are affected by parameters like, gradation characteristics, void ratio, confining pressure, etc. . This study mainly investigated experimentally the effect of gradation on the dynamic properties of sands with the effect of void ratio and confining pressure. Test results showed that shear modulus/damping ratio was increased/decreased with the decrease of void ratio and with the increase of confining pressure. When the fine content increased, shear modulus/damping ratio was decreased/increased. This study explained this phenomenon by the concept of the "effective number of contacts" and the "dead space".ot;dead space".uot;.

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Liquefaction Behaviour of Saturated Silty Sand Under Monotonic Loading Conditions (정적하중 상태에서 포화된 실트질 모래의 액상화 거동)

  • Lee Dal-Won
    • Journal of The Korean Society of Agricultural Engineers
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    • v.48 no.4
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    • pp.67-74
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    • 2006
  • This study was carried out to investigate the liquefaction behaviour of saturated silty sand under monotonic loading conditions. The undrained soil tests were conducted using a modified triaxial cell and specimens were prepared using the moisture tamping method. Undrained triaxial compression tests were performed at different confining pressures, void ratios and overconsolidation ratios and the samples were sheared to axial strains of about 20% to obtain monotonic loading conditions. It is shown that increasing confining pressures, void ratios and overconsoildation ratios increases the deviator stress, but it has no effect on increasing the dilatant tendencies. It is shown that complete static liquefaction was observed regardless of increases in the confining pressure, void ratio and overconsolidation ratio. Therefore, the confining pressure, void ratio and overconsoildation ratio does not provide significant effects on the liquefaction resistance of the silty sand. The presence of fines in the soil was shown to greatly increase the potential for static liquefaction and creates a particle structure with high compressibility for all cases.