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Bearing capacity of under-reamed piles in clay using lower bound finite element limit analysis 粘土中扩孔桩承载力的下界有限元极限分析
IF 1.9 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2022-03-06 DOI: 10.1080/19386362.2022.2044102
M. Majumder, Debarghya Chakraborty
ABSTRACT In this study, bearing capacity of under-reamed piles in non-homogeneous clay is estimated numerically. A detailed parametric study is carried out for different length to shaft diameter ratio (Lu /D), bulb position (hb /Du ), under-ream angle (β) and constant m indicating the increase of undrained cohesion, number of bulbs (nb ), bulb spacing (s) and pile–soil adhesion factor (αs ). The bearing capacity of the under-reamed pile is presented through design charts and expressed by a dimensionless factor Ncu. Ncu increases significantly with increases in nb, Lu /D and m and moderately with increases in β and αs . For m > 0, Ncu decreases moderately with the increase in hb /Du . For two bulbs, m > 0, the optimum bulb spacing is found at 1.25–1.75Du . For one bulb, Ncu increases in the range of 67.52–162.84% than the pile without bulb. For two bulbs, Ncu increases in the range of 129.41–250.40% than the pile without bulb.
摘要在本研究中,对非均质粘土中扩底桩的承载力进行了数值估算。对不同的长径比(Lu/D)、球头位置(hb/Du)、扩底角(β)和常数m进行了详细的参数研究,表明不排水粘聚力、球头数量(nb)、球顶间距(s)和桩土粘附系数(αs)的增加。扩底桩的承载力通过设计图表表示,并用无量纲因子Ncu表示。Ncu随nb、Lu/D和m的增加而显著增加,随β和αs的增加而适度增加。当m>0时,Ncu随hb/Du的增加而适度下降。对于m>0的两个灯泡,最佳灯泡间距为1.25–1.75Du。对于一个灯泡,Ncu比没有灯泡的灯泡增加了67.52–162.84%。对于两个灯泡,Ncu比没有灯泡的桩增加129.41–250.40%。
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引用次数: 1
Stability analysis of embankment dams with defective internal geomembrane liners 土工膜衬砌内部有缺陷的路堤坝稳定性分析
IF 1.9 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2022-02-28 DOI: 10.1080/19386362.2021.2014676
Sarper Demirdogen, M. Gunaratne
ABSTRACT Internal geomembranes are alternatives to traditional clay cores and upstream geomembranes. In this research, numerical analysis is performed to assess the impact of leakage through 2-D geomembrane defects such as slits, tears and faulty stitches. Five possible applications of internal geomembranes and an upstream geomembrane were modelled to compare their performance with that of clayey cores. The results show that use of upstream or internal geomembranes significantly decreases the pore pressure developed at the downstream slope thus improving its stability. The effects of leakage through both internal and upstream geomembranes on the stability of embankment slopes under steady state and drawdown at a rate, conditions were analysed. Stability of the downstream slope reduces significantly due to defective geomembranes depending on the defective seam locations. Drawdown simulations show that internal geomembranes can cause instability in steep upstream slopes of dams.
内部土工膜是传统粘土芯和上游土工膜的替代品。在这项研究中,进行了数值分析,以评估通过二维土工膜缺陷(如裂缝、撕裂和错误缝合)泄漏的影响。对内部土工膜和上游土工膜的五种可能应用进行了建模,以将其性能与粘土芯的性能进行比较。结果表明,上游或内部土工膜的使用显著降低了下游边坡产生的孔隙压力,从而提高了边坡的稳定性。分析了通过内部和上游土工膜的渗漏对稳定状态下路堤边坡稳定性的影响,以及在一定速率和条件下的水位下降。由于存在缺陷的土工膜(取决于缺陷接缝位置),下游边坡的稳定性显著降低。压降模拟表明,内部土工膜会导致大坝上游陡坡的不稳定。
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引用次数: 4
Evaluation of seepage failure by heave in homogeneous cohesionless soils using finite element method 用有限元法评价均质无粘性土的隆起渗流破坏
IF 1.9 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2022-02-25 DOI: 10.1080/19386362.2022.2042965
S. Koltuk, T. Fernández-Steeger
ABSTRACT Commonly, the base stability of sheeted excavation pits against seepage failure by heave is evaluated by using Terzaghi’s failure plane, which is based on the results of the two-dimensional model tests. However, seepage flows in excavation pits are three-dimensional, and stress levels are relatively high compared to those existing in the model tests. In this study, hydraulically-mechanically coupled, axisymmetric finite element (FE) analyses are performed to investigate the seepage failure by heave in circular-shaped sheeted excavation pits constructed in homogeneous cohesionless soils. The results of FE analyses are compared with those obtained from the well-known failure approach of Terzaghi. The FE analyses show relatively different failure zones compared to Terzaghi’s failure plane. However, the difference between the critical potential differences obtained from the FE analyses ΔH failure(FEM) and Terzaghi’s approach ΔH failure(Terzaghi) is negligible. The maximum and minimum ratios of ΔH failure(FEM)/ΔH failure(Terzaghi) are 1.07 and 0.96, respectively.
摘要:一般采用基于二维模型试验结果的Terzaghi破坏面来评价板状开挖基坑地基抗隆起渗流破坏的稳定性。然而,开挖坑内渗流是三维的,与模型试验相比,应力水平相对较高。本文采用水力-力学耦合轴对称有限元分析方法,研究了均匀无粘性土中圆形板形基坑的渗水破坏。将有限元分析结果与著名的Terzaghi破坏方法进行了比较。与Terzaghi的破坏面相比,有限元分析显示出相对不同的破坏区域。然而,从有限元分析ΔH失效(FEM)和Terzaghi方法ΔH失效(Terzaghi)中得到的临界电位差之间的差异可以忽略不计。ΔH失效(FEM)与ΔH失效(Terzaghi)的最大、最小比值分别为1.07和0.96。
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引用次数: 1
Investigation into small-strain shear modulus of sand–gravel mixtures in different moisture conditions and its correlation with static stiffness modulus 砂砾石混合料在不同水分条件下的小应变剪切模量及其与静刚度模量的相关性研究
IF 1.9 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2022-02-13 DOI: 10.1080/19386362.2022.2033482
Nahid Allahyari, M. Maleki
ABSTRACT The effects of gravel content, relative density and confining pressure on small-strain shear modulus of sand-gravel mixtures under different moisture conditions were experimentally investigated. The specimens were prepared considering three compaction states, different gravel contents and different moisture contents and tested using the bender element device at three levels of confining pressure. The specimens were then sheared in order to derive triaxial stress-strain curves. The results showed that the maximum shear modulus of mixtures increased with increasing the moisture content, while an increasing-decreasing trend was observed for the pure sand. The maximum shear modulus (Gmax) is more influenced by relative density and confining pressure than moisture content. Then the correlation between Gmax and secant stiffness modulus corresponding to 50% of maximum deviatoric stress (E50), was investigated. The results indicated that the increase in E50 leads to a decreasing trend in Gmax/E50 for different moisture contents and compaction states.
摘要试验研究了砾石含量、相对密度和围压对不同水分条件下砂砾混合料小应变剪切模量的影响。试样的制备考虑了三种压实状态、不同砾石含量和不同含水量,并使用弯曲元件装置在三个围压水平下进行了测试。然后对试样进行剪切,以得出三轴应力-应变曲线。结果表明,混合料的最大剪切模量随着含水率的增加而增加,而纯砂的最大剪切模数则呈增加-减少的趋势。相对密度和围压对最大剪切模量(Gmax)的影响大于含水率。然后,研究了Gmax与对应于50%最大偏应力(E50)的割线刚度模量之间的相关性。结果表明,不同含水量和压实状态下,E50的增加导致Gmax/E50呈下降趋势。
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引用次数: 2
Unsaturated behaviour of gypseous sand soils using a modified triaxial test apparatus 用改进的三轴试验装置研究石膏砂土的非饱和特性
IF 1.9 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2022-02-11 DOI: 10.1080/19386362.2022.2033483
Mustafa M. Abdalhusein, A. Akhtarpour, Mohammed Mahmood
ABSTRACT This paper presents laboratory experiments on the effect of matric suction on the compressibility of unsaturated gypsum sand soil. The samples were obtained from Al-Najaf city in Iraq with gypsum contents of 14%, 22%, and 29%. Two series of laboratory tests were conducted. The first one is loading-path likes when a building is constructed on these soils in a specific degree of saturation (specific matric suction). Four matric suctions were adopted; 100, 60, 30, and zero percentages of initial matric suction under two confining stresses; 100 kPa and 200 kPa. Also, two saturated tests (CD) were performed under the aforementioned confining stresses. The second method is wetting-path, likes when a structure has been constructed and the degree of saturation of a foundation soil increases (decreasing in matric suction). The results from both paths revealed that the volumetric strains were increased by decreasing the matric suction and increasing the gypsum content..
摘要本文通过室内试验研究了基质吸力对非饱和石膏砂土压缩性的影响。样品取自伊拉克Al-Najaf市,石膏含量分别为14%、22%和29%。进行了两个系列的实验室试验。第一个是在特定饱和程度(特定基质吸力)下在这些土壤上建造建筑物时的加载路径。采用四种基质抽吸法;两种围应力下的初始基质吸力百分比分别为100、60、30和0;100kpa和200kpa。并在上述围应力条件下进行了两次饱和试验。第二种方法是润湿路径,比如当一个结构已经建成,地基土的饱和程度增加(基质吸力减少)。两种路径的结果都表明,减小基质吸力和增加石膏含量会增加体积应变。
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引用次数: 1
Settlement and pore pressure behaviour and predictions of test embankments on an organic clay 有机粘土上试验路堤的沉降和孔隙压力特性及预测
IF 1.9 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2022-01-31 DOI: 10.1080/19386362.2022.2030129
B. Vesterberg, M. Andersson
ABSTRACT Two test embankments were built on an organic clay at the Lampen test site in Sweden and movements and pore pressures were measured over a period of six years. Well-established 2D and 1D constitutive models, were used to predict the settlement and pore pressures. The predictions suggest, with model parameters based on laboratory test results for carefully taken and handled standard piston samples, that creep should be included to provide better agreement with the in situ measured settlements and pore pressures. A comparison between the predictions and the measured settlements and pore pressures showed that it is important to study the trend over time and at different depths, and not just settlements at a few times at the ground surface. The 2D model including creep agreed relatively well with the measured total settlements and with pore pressures at different depths, but the settlement-time relationship was not qualitatively well described.
摘要在瑞典兰彭试验场的有机粘土上建造了两个试验路堤,并在六年内测量了位移和孔隙压力。已建立的二维和一维本构模型用于预测沉降和孔隙压力。预测表明,模型参数基于仔细采集和处理的标准活塞样品的实验室测试结果,应包括蠕变,以更好地与现场测量的沉降和孔隙压力相一致。预测与实测沉降和孔隙压力之间的比较表明,研究不同深度随时间的变化趋势很重要,而不仅仅是地表几次的沉降。包括蠕变的二维模型与测量的总沉降和不同深度的孔隙压力相对一致,但沉降-时间关系没有得到很好的定性描述。
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引用次数: 4
Vibration mitigation of pile groups by coupling a wave-based vibration analysis and genetic algorithm 基于波动分析和遗传算法的群桩减振研究
IF 1.9 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2022-01-21 DOI: 10.1080/19386362.2021.2025305
A. Farahani, M. Samadzad, R. Rafiee-Dehkharghani
ABSTRACT This paper presents a coupled wave-based/genetic algorithm approach for vibration mitigation in a structure built on a pile group. The wave-based method considers the structure and foundation as a whole waveguide system in which the equations of wave propagation at waveguides and wave refraction at discontinuities are solved analytically using Timoshenko beam theory. These solutions are then assembled and solved numerically within a single system matrix. To model the ground, the viscoelastic soil around the piles is modelled using spring-dashpot elements. The wave-based method is used to evaluate a fitness function within a genetic algorithm procedure, and the resulting coupled tool is used for finding the optimal geometric characteristics of a pile group. The obtained results highlight the efficiency of the wave-based approach to be used in heuristic optimization algorithms such as genetic algorithm. In addition, it is observed that the optimal layout of the pile group depends significantly on loading frequency and soil properties.
摘要:本文提出了一种基于波/遗传耦合算法的群桩结构减振方法。基于波的方法将结构和基础视为一个整体的波导系统,利用Timoshenko光束理论解析求解波导处的波传播方程和不连续处的波折射方程。然后将这些解决方案组装起来,并在单个系统矩阵中进行数值求解。为了模拟地基,采用弹簧-阻尼单元对桩周粘弹性土进行了建模。在遗传算法过程中,采用基于波浪的方法来评估适应度函数,并使用得到的耦合工具来寻找群桩的最优几何特征。结果表明,基于波浪的方法在遗传算法等启发式优化算法中的应用是有效的。此外,观察到群桩的最优布置受荷载频率和土体性质的显著影响。
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引用次数: 4
One-dimensional compression creep change under temperature and suction effects 温度和吸力作用下的一维压缩蠕变变化
IF 1.9 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2022-01-13 DOI: 10.1080/19386362.2021.2025306
Hachimi Dahhaoui, N. Belayachi, Abdeldjalil Zadjaoui, T. Nishimura
ABSTRACT The impact of temperature and unsaturation on the creep behaviour of bentonite is an important topic for environmental geotechnics as in the case of waste storage and energy geostructures. This paper presents an experimental study on the one-dimensional creep of Maghnia bentonite (MB), using two high-pressure oedometer cells, allowing to impose temperature and suction conditions for an unsaturated medium . The characteristics of these two cells and the protocol developed in the framework of this experimental study are briefly presented. The findings highlight a new perspective on the hypothesis (A) which distinguishes between primary and secondary consolidation, and hypothesis (B), which is governed by structural viscosity. The results indicated that the creep behaviour followed the principle of hypothesis (A) under temperature effect, while it followed hypothesis (B) principle under the suction effect. The void ratio variability under secondary compression depends not only on the vertical stress, but also on the temperature and the first load level . Moreover, as soil suction descreases, the normalized void ratio become higher. The creep coefficient (Cαe) increased as temperature and vertical stress increased, while they decreased as the suction increased.
温度和不饱和对膨润土蠕变行为的影响是环境岩土工程的一个重要课题,如在废物储存和能源土工结构的情况下。本文提出了一项实验研究的Maghnia膨润土(MB)的一维蠕变,使用两个高压计细胞,允许施加温度和吸力条件的非饱和介质。简要介绍了这两种细胞的特点和在本实验研究框架内制定的方案。这些发现突出了对假设(a)和假设(B)的新观点,假设(a)区分了初级和次级固结,假设(B)由结构粘度控制。结果表明,温度作用下的蠕变行为遵循假设(A)原则,吸力作用下的蠕变行为遵循假设(B)原则。二次压缩下孔隙率的变化不仅与竖向应力有关,还与温度和第一次荷载水平有关。随着吸力的减小,归一化孔隙比增大。蠕变系数(Cαe)随温度和垂直应力的增大而增大,随吸力的增大而减小。
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引用次数: 0
Dynamic response of underreamed batter piles subjected to vertical vibration 纵向振动作用下空心桩的动力响应
IF 1.9 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2022-01-10 DOI: 10.1080/19386362.2021.2025304
M. Bharathi, R. Dubey, S. Shukla
ABSTRACT This paper presents the dynamic vertical response of a vertical and two batter piles with an underreamed bulb. Batter angles (i.e. inclination to the vertical) of 10 and 20 degrees have been considered. The dynamic vertical tests were conducted using a mechanical oscillator-motor assembly by varying the intensity of exciting force level with a change in eccentricity setting of the oscillator. The dynamic response was recorded in terms of operating frequency and acceleration response. The test data were analysed to estimate the dynamic vertical responses of the piles in terms of resonant frequency, f y ꞌ; peak vertical displacement amplitude, dyꞌ and axial strain εy , and they were compared. For all three piles, with an increase in intensity of exciting force level, the resonant frequency decreased, whereas the peak vertical displacement and axial strain increased.
摘要:本文研究了带扩孔球桩的一竖桩和两竖桩的竖向动力响应。已经考虑了10度和20度的击球角(即垂直倾斜)。利用机械振子-电机组合装置,通过改变振子偏心设置,改变激振力水平的强度,进行了动态垂直试验。动态响应记录为工作频率和加速度响应。对试验数据进行分析,估计桩的竖向动力响应,以共振频率为单位;峰值垂直位移幅值、dy * *和轴向应变ε * *,并进行了比较。随着激振力水平强度的增加,三桩的共振频率减小,竖向位移峰值和轴向应变峰值增大。
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引用次数: 1
Effect of potential swell pressures on anchored sheet pile walls 潜在膨胀压力对锚定板桩墙体的影响
IF 1.9 Q2 ENGINEERING, GEOLOGICAL Pub Date : 2022-01-10 DOI: 10.1080/19386362.2022.2026063
Ö. Bilgin
ABSTRACT Design of retaining walls usually specifies cohesionless soils as backfill material behind the wall; however, local soils which may be expansive are sometimes used due to economic reasons. In addition, the in-situ retaining walls, such as anchored sheet pile walls, are installed in existing soils that may be expansive. Retaining walls installed in expansive soils are subjected to additional lateral pressures during swelling and anchor forces can also increase if the walls are anchored. In this study, the effect of potential swell pressures of expansive soils on the anchored sheet pile walls were modelled and investigated. The swell pressure magnitudes were determined using empirical correlations based on plasticity index. Stress distribution due to the potential swell pressure capacity of expansive soils was proposed. The effect of potential swell pressures on the wall penetration depth, bending moments, and anchor forces are investigated and presented in this paper. The findings of the study show that expansive soil swell pressures have the potential to significantly affect anchored sheet pile walls.
摘要挡土墙的设计通常指定无粘性土作为墙后回填材料;然而,由于经济原因,有时会使用可能具有膨胀性的当地土壤。此外,现场挡土墙,如锚定板桩墙,安装在可能具有膨胀性的现有土壤中。膨胀土中安装的挡土墙在膨胀过程中会受到额外的侧向压力,如果对挡土墙进行锚固,锚固力也会增加。在本研究中,对膨胀土的潜在膨胀压力对锚定板桩墙的影响进行了建模和研究。使用基于塑性指数的经验相关性来确定膨胀压力大小。提出了膨胀土潜在膨胀压力作用下的应力分布规律。本文研究并提出了潜在膨胀压力对壁渗透深度、弯矩和锚固力的影响。研究结果表明,膨胀土膨胀压力有可能对锚定板桩墙产生重大影响。
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引用次数: 0
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International Journal of Geotechnical Engineering
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