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1.
Discrete element modelling of deep penetration in granular soils 总被引：1，自引：0，他引：1
This paper presents a numerical study on deep penetration mechanisms in granular materials with the focus on the effect of soil–penetrometer interface friction. A two‐dimensional discrete element method has been used to carry out simulation of deep penetration tests on a granular ground that is under an amplified gravity with a K0 lateral stress boundary. The numerical results show that the deep penetration makes the soil near the penetrometer move in a complex displacement path, undergo an evident loading and unloading process, and a rotation of principal stresses as large as 180°. In addition, the penetration leads to significant changes in displacement and velocity fields as well as the magnitude and direction of stresses. In general, during the whole penetration process, the granular ground undergoes several kinds of failure mechanisms in sequence, and the soil of large deformation may reach a stress state slightly over the strength envelope obtained from conventional compression tests. Soil–penetrometer interface friction has clear effects on the actual penetration mechanisms. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
2.
An analytical model to simulate the penetration of the piezocone penetrometer in cohesive soils is presented here. The elasto-plastic coupled field equations of the saturated cohesive soils (given by Voyiadjis and Abu-Farsakh) is used in this analysis. The numerical simulation of the piezocone penetration is implemented into a finite element program. The analytical model is used to analyze the miniature piezocone penetration tests (PCPT) conducted at LSU calibration chambers. Simulation of the piezocone penetration is done for two cases. In the first case, the soil–penetrometer interface friction is neglected, while in the second case, the soil–penetrometer interface friction is taken into consideration. The constraint approach is used to model the soil–piezocone interface friction in which the Mohr–Coulomb frictional model is used to define the sliding potential. Analysis is done for three different soil specimens with different stress histories. The results of the numerical simulations are compared with the experimental measurements of the miniature piezocone penetration tests (PCPT) in cohesive soil specimens conducted in LSU calibration chambers. The resulting excess pore pressure distribution and its dissipation using the numerical model are compared with some available prediction methods. © 1998 John Wiley & Sons, Ltd. 相似文献
3.
Dynamic penetrometers have been used for offshore oil and gas industry applications such as pipeline feasibility studies and anchoring systems, and military applications including naval mine countermeasures and terminal ballistic studies. The main challenge of using dynamic penetrometers is the interpretation of their test results in order to deduce the mechanical properties of the penetrated soil via empirical or theoretical relations. Recently, a robust numerical method based on the Arbitrary Lagrangian–Eulerian (ALE) technique has been developed for analysing dynamic penetration problems and used to investigate a smooth penetrometer free falling into a uniform layer of clayey soil. Numerical as well as experimental results indicate that the penetration characteristics, including the impact energy, total time, and total depth of penetration, depend on the mechanical properties of the soil including its stiffness and strength parameters as well as the geometry of the penetrometer and its initial impact energy. In this study, the ALE method is employed to study the effect of shear strength increasing with depth (a common condition of seabed deposits) on the penetration characteristics of a free falling penetrometer. Conducting more than two thousand numerical simulations has shown that there is an approximate quadratic relation between the final embedment depth of a FFP penetrating into a non-uniform clay soil and the combined kinetic energy on contact with the soil and subsequent loss in potential energy of the penetrometer. 相似文献
4.
Field tests are widely used for soil characterization in geotechnical applications in spite of implementation difficulties. The light penetrometer is a well-known testing tool for fine soils, but the physical interpretation of the output data in the case of coarse granular materials is far less evident. Indeed, the data are considerably more sensitive in this case to various parameters such as fabric structure, particle shapes or the applied impact energy. In order to achieve a better understanding of the penetration process into a coarse granular material, a numerical study was performed by means of contact dynamics simulations. The penetration of a moving tip in a sample composed of irregular grain shapes was studied and the influence of the driving velocity and input energy on the penetration strength was analyzed. The results show that the latter grows with both the penetration rate and energy, despite the strong fluctuations occur due to a jamming–unjamming process in which the contact network connectivity evolves intermittently in correlation with the penetration strength. This analysis suggests that the time-averaged data provided by a penetrometer is reliable information from which the bulk strength properties of coarse granular materials can be evaluated. 相似文献
5.
近年来,随着全球海洋开发战略的逐步开展,越来越多的工程建设和试验研究将在海洋中进行,为了掌握海底的土体环境,静力触探（CPT）技术在国内外海洋工程领域中的运用变得更加重要。本文根据国内外大量文献中相关海洋原位测试技术的报道,对海洋静力触探的国内外发展历程进行总结,重点阐述和研究了一种适用于海底淤泥质土的球型全流触探仪。分析结果表明,球型全流触探仪在海洋岩土工程勘察中具有很好的应用前景,且集测量数据精确可靠、试验方法多样化、理论解析丰富全面等优点于一身;利用球型全流触探仪能够有效避免较大的实测数据修正,贯入机理清晰严谨,开展循环贯入试验可以评价土的重塑特性,变速率贯入试验在评价应变速率和现场土体强度以及测试中土体固结状态之间的关系上具有优势;结合现场试验,对比分析传统CPT和球型全流触探仪的试验结果,并考虑海底软土的性质,摸索出一种可停靠球型探头新形式。 相似文献
6.
动力触探杆长修正系数试验研究 总被引：4，自引：0，他引：4
动力触探是一种应用广泛的原位测试技术,其动探杆长最大可达到上百米,在实际应用中需要进行杆长修正,目前规范中关于动力触探杆长修正问题,给出了以牛顿弹性碰撞理论和弹性杆波动理论为基础的两种修正方法,依据两种理论得出的修正系数是截然不同的。动力触探试验成果应该如何进行杆长修正,是限制该方法应用的重大问题。针对动力触探杆长修正问题,提出了室内模型试验,并依据砂砾石和均质砂两种地基土进行不同杆长的重型动力触探模型试验,杆长分别为2.0、8.9、16.4、23.4、30.0、36.0 m。通过试验,得到重型动力触探杆长修正系数。分析认为,重型动力触探杆长修正规律符合牛顿弹性碰撞理论,且与地基土材料特性无关。 相似文献
7.
T型触探仪近年来在国外的海洋软土地基原位测试中得到了广泛应用,但贯入速率、地基土强度的各向异性与渐进软化等因素对于贯入阻力的影响没有得到系统的研究。在大型有限元软件ABAQUS平台上进行二次开发,针对基于Tresca屈服准则的理想弹塑性模型进行了相应改进,使之可以比较合理地反映上述因素的影响,进而对软土中T型触探仪的贯入机制进行了比较系统的数值分析。计算结果表明,贯入速率、地基土强度的各向异性与强度软化效应对于T型触探仪的贯入阻力系数影响较大。通过与有关极限分析上限解的对比分析,在一定程度上验证了有限元分析结果的合理性。 相似文献
8.
This paper outlines the development as well as implementation of a numerical procedure for coupled finite element analysis of dynamic problems in geomechanics, particularly those involving large deformations and soil-structure interaction. The procedure is based on Biot’s theory for the dynamic behaviour of saturated porous media. The nonlinear behaviour of the solid phase of the soil is represented by either the Mohr Coulomb or Modified Cam Clay material model. The interface between soil and structure is modelled by the so-called node-to-segment contact method. The contact algorithm uses a penalty approach to enforce constraints and to prevent rigid body interpenetration. Moreover, the contact algorithm utilises a smooth discretisation of the contact surfaces to decrease numerical oscillations. An Arbitrary Lagrangian–Eulerian (ALE) scheme preserves the quality and topology of the finite element mesh throughout the numerical simulation. The generalised-α method is used to integrate the governing equations of motion in the time domain. Some aspects of the numerical procedure are validated by solving two benchmark problems. Subsequently, dynamic soil behaviour including the development of excess pore-water pressure due to the fast installation of a single pile and the penetration of a free falling torpedo anchor are studied. The numerical results indicate the robustness and applicability of the proposed method. Typical distributions of the predicted excess pore-water pressures generated due to the dynamic penetration of an object into a saturated soil are presented, revealing higher magnitudes of pore pressure at the face of the penetrometer and lower values along the shaft. A smooth discretisation of the contact interface between soil and structure is found to be a crucial factor to avoid severe oscillations in the predicted dynamic response of the soil. 相似文献
9.
为研究结构性砂土静力触探的宏微观力学特性,在10 g重力场中生成一个净砂地基;将一个考虑胶结厚度的微观胶结接触模型引入到净砂地基中以生成结构性砂土地基;用一定速率移动探杆以模拟结构性砂土中的静力触探过程,其中,探杆由4面刚性墙组成。结果表明,随着贯入深度的增加,锥尖贯入阻力逐渐增大,增长速度逐渐减慢,在达到临界深度后贯入阻力在某一定值附近波动;锥尖部位有明显的力链集中现象,力链的集中程度和范围会随着贯入深度的增加而逐渐提高和扩大;静力触探过程中,探杆两侧的土体经历了明显的加载和卸载过程,且土体主应力方向发生偏转;离探杆越远,主应力偏转速度越慢,最终偏转角越小;不同深度处平均纯转动率（APR）的变化趋势基本相同,而APR最大值会随着土体深度而逐渐增加;探杆的贯入会使土颗粒间胶结发生破坏,胶结的破坏形式主要有拉剪破坏和压剪破坏两种,而拉剪破坏数目要比压剪破坏数目多。 相似文献
10.
Derek Elsworth 《国际地质力学数值与分析法杂志》2013,37(14):2135-2153
Rate effects are examined in the steady pore pressure distribution induced as a result of penetration of standard and ball penetrometers. The incompressible flow field, which develops around the penetrometer is used to define the approximate soil velocity field local to the penetrometer tip. This prescribes the Lagrangian framework for the migration of the fluid saturated porous medium, defining the advection of induced pore pressures relative to the pressure‐monitoring locations present on the probe face. In two separate approaches, different source functions are used to define the undrained pore fluid pressures developed either (i) on the face of the penetrometer or (ii) in the material comprising the failure zone surrounding the penetrometer tip. In the first, the sources applied at the tip face balance the volume of fluid mobilized by the piston displacement of the advancing penetrometer. Alternately, a fluid source distribution is evaluated from plasticity solutions and distributed throughout the tip process zone: for a standard penetrometer, the solution is for the expansion of a spherical cavity, and for the ball penetrometer, the solution is an elastic distribution of stresses conditioned by the limit load embedded within an infinite medium. For the standard penetrometer, the transition from drained to undrained behavior occurs over about two orders of magnitude in penetration rate for pore pressures recorded at the tip (U1) and about two‐and‐a‐half orders of magnitude for the shoulder (U2). This response is strongly influenced by the rigidity of the soil and slightly influenced by the model linking induced total stresses to pore pressures. For the ball penetrometer, the transition from drained to undrained behavior also transits two‐and‐a‐half orders of magnitude in penetration rate, although it is offset to higher dimensionless penetration rates than for standard penetration. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
11.
着陆器足垫垂直冲击模型试验研究 总被引：1，自引：0，他引：1
着陆器着陆过程中会产生巨大的冲击作用,影响其内部精密仪器的正常工作。因此,研究着陆器足垫与土体相互作用对着陆器软着陆具有重要意义。基于对着陆过程的研究,将问题分解为垂直冲击和水平滑动两个方向的运动,并通过力的平衡和动量定理建立了垂直冲击的动力模型。利用独立研发的垂直冲击模型试验装置,探讨了冲击过程中土体密实度、冲击速率和冲击质量等对足垫刺入深度、最大轴力和最大加速度等的影响。分析结果表明,足垫刺入深度和最大轴力都随着冲击能量的增大而增大,并且逐渐趋于平稳。土体越密实、冲击质量越小,足垫加速度峰值则越大。试验结果还与动力模型进行了对比,结果表明,动力模型能合理地反映出着陆器在垂直冲击阶段的动力特性。 相似文献
12.
西部地区河床深厚覆盖层勘探取样及工程特性是水电工程地质勘察中常遇技术难题,动力触探(dynamic penetration test,DPT)因操作简单、适用土类多而成为西部地区河床覆盖层原位测试首选方法.现行规范仅给出了20 m杆长范围的修正方法,但对超此范围重型、超重型动力触探杆长适用性及修正问题,长期以来业内则颇多争议却少有研究.鉴于此,利用现场试验与数值模拟相结合,通过对动力触探试验杆上各测点应变现场实测并得到各测点应力分布,再利用LS-DYNA软件进行反演分析并确定相关计算参数,而后进行杆长25 m、40 m、60 m、80 m、120 m的数值模拟计算得到了杆长适用范围及修正系数.试验研究方法及成果可供类似问题研究与深厚覆盖层地区工程勘察借鉴或参考. 相似文献
13.
Recently, two novel binders, one by-product-based binder named as GM and one phosphate-based binder named as KMP, have emerged that can stabilize soils spiked with mixed lead and zinc contaminants. However, field evaluations of the stabilization of actual soils that contaminated with mixed zinc (Zn) and inorganic chloride (Cl?) using GM and KMP have not been performed yet. This study presents a pilot-scale field test to evaluate the performance of GM and KMP to stabilize these inorganic contaminants in soils at two locations in an abandoned industrial plating plant site. The field soils were stabilized and cured for 1, 3, 7, and 28 days and tested for dry density, dynamic cone penetration, soil pH, and leachability. Laboratory unconfined compression tests were performed, and the relationship between unconfined compressive strength and dynamic cone penetrometer index was assessed. The results showed that the strength of both the GM- and KMP-stabilized soils after 28-day curing improved significantly, and the leached Zn and Cl? concentrations were well below the corresponding remediation limits. In general, the KMP-stabilized soil demonstrated superior performance in terms of higher dry density, unconfined compressive strength, average dynamic cone penetration resistance, lower dynamic cone penetrometer index in the early curing stage (7 days), and lower leached Zn concentration under all curing times. In contrast, the GM exhibited superior immobilization of Cl? in the contaminated soil irrespective of the curing time. The results demonstrate that GM and KMP are promising binders for treating Zn- and Cl?-contaminated soils at plating and other industry sites with similar contaminants.
相似文献14.
Rozbeh B. Moghaddam William D. Lawson James G. Surles Hoyoung Seo Priyantha W. Jayawickrama 《Geotechnical and Geological Engineering》2017,35(5):2147-2162
This study analyzes blowcount data from instrumented Texas Cone Penetration (TCP) tests. TCP hammer efficiency, rod length influence on the hammer efficiency, and overburden pressure correction factors for the TCP blowcounts (NTCP) are explored. Results are compared to published correction factors for the standard penetration test (SPT). The final dataset analyzed for this study consisted of 293 TCP tests from which 135 tests were instrumented. TCP hammer efficiency values for automatic trip hammers ranged from 74 to 101% with an average of 89%. Analyses showed a statistically-significant relationship between the TCP hammer efficiency and the rod length below ground surface. Statistical models were developed for undifferentiated soils, and corresponding rod length correction factors for the TCP test (CR-TCP) were obtained ranging from 0.90 to 1.00. In a second analysis, the relationship between the overburden pressure and NTCP was explored and a mathematical expression for the overburden correction factor for the TCP blowcount value (CN-TCP) was determined. This work represents the first study where corrections to NTCP are explored, and the outcome of this research benefits the geotechnical engineering community using the TCP test and its associated foundation design method. 相似文献
15.
A solution is developed for the build‐up, steady and post‐arrest dissipative pore fluid pressure fields that develop around a blunt penetrometer that self‐embeds from freefall into the seabed. Arrest from freefall considers deceleration under undrained conditions in a purely cohesive soil, with constant shear strength with depth. The resulting decelerating velocity field is controlled by soil strength, geometric bearing capacity factors, and inertial components. At low impact velocities the embedment process is controlled by soil strength, and at high velocities by inertia. With the deceleration defined, a solution is evaluated for a point normal dislocation penetrating in a poroelastic medium with a prescribed decelerating velocity. Dynamic steady pressures, PD, develop relative to the penetrating tip geometry with their distribution conditioned by the non‐dimensional penetration rate, UD, incorporating impacting penetration rate, consolidation coefficient and penetrometer radius, and the non‐dimensional strength, ND, additionally incorporating undrained shear strength of the sediment. Pore pressures develop to a steady peak magnitude at the penetrometer tip, and drop as PD=1/xD with distance xD behind the tip and along the shaft. Peak induced pressure magnitudes may be correlated with sediment permeabilities, post‐arrest dissipation rates may be correlated with consolidation coefficients, and depths of penetration may be correlated with shear strengths. Together, these records enable strength and transport parameters to be recovered from lance penetrometer data. Penetrometer data recorded off La Palma in the Canary Islands (J. Volcanol. Geotherm. Res. 2000; 101 :253) are used to recover permeabilities and consolidation coefficients from peak pressure and dissipation response, respectively. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
16.
Coupled theory of mixtures for clayey soils 总被引：4，自引：0，他引：4
In this work, elasto-plastic coupled equations are formulated in order to describe the time-dependent deformation of saturated cohesive soils (two-phase state). Formulation of these equations is based on the principle of virtual work and the theory of mixtures for inelastic porous media. The theory of mixtures for a linear elastic porous skeleton was first developed by Biot (Theory of elasticity and consolidation for a porous anisotropic solid, Journal of Applied Physics, 1955, 26, 188–185). An extension of Biot's theory into a nonlinear inelastic media was performed by Prevost (Mechanics of continuous porous media, International Journal of Engineering Science, 1980, 18, 787–800). The saturated soil is considered as a mixture of two deformable media, the solid grains and the water. Each medium is regarded as a continuum and follows its own motion. The flow of pore-water through the voids is assumed to follow Darcy's law. The coupled equations are developed for large deformations with finite strains in an updated Lagrangian reference frame. The coupled behavior of the two-phase materials (soil-water state) is implemented in a finite element program. A modified Cam-clay model is adopted and implemented in the finite element program in order to describe the plastic behavior of clayey soils. Penetration of a piezocone penetrometer in soil is numerically simulated and implemented into a finite element program. The piezocone penetrometer is assumed to be infinitely stiff. The continuous penetration of the cone is simulated by applying an incremental vertical movement of the cone tip boundary. Results of the finite element numerical simulation are compared with experimental measurements conducted at Louisiana State University using the calibration chamber. The numerical simulation is carried out for two cases. In the first case, the interface friction between the soil and the piezocone penetrometer is neglected. In the second case, interface friction is assumed between the soil and the piezocone. The results of the numerical simulations are compared with experimental laboratory measurements. 相似文献
17.
冲击压路机已大量用于各种原位地基土以及填土的压实处理,压实深度明显大于传统压路机和平板压实设备。但冲击压路机在冲击碾压过程中的能量传递过程、土中应力和位移的分布情况等尚不清楚。为探讨冲击碾压加固地基的机制和加固效果的主要影响因素,研制了冲击碾压模拟试验设备。该设备主要由模型箱、模型冲击轮、简易缓冲装置以及支架与牵引系统四部分组成,其中核心组成部分是具有不同外接圆尺寸大小和质量的三边形模型冲击轮。模型冲击轮可通过牵引系统中电机的牵引作用,在试验土体表面沿直线滚动,对土体施加冲击碾压作用。采用该设备进行了不同尺寸的模型冲击轮冲击碾压砂土的模型试验,并采用直径为2.5 cm的小型静力触探仪对冲击碾压加固效果进行检测。结果表明：该试验设备可用于实现对非圆形冲击轮冲击压实土体过程的模拟,同时显示冲击轮尺寸对冲碾加固效果的影响与冲碾遍数有关,且该影响在不同深度的土体中会有不同的响应,增大冲击轮的尺寸可以在土体的浅层深度范围内获得更好的加固效果。 相似文献
18.
This paper presents numerical simulations of Cone Penetration Test (CPT) in water-saturated soft soils taking into account pore pressure dissipation during installation. Besides modelling interaction between soil skeleton and pore fluid, the problem involves large soil deformations in the vicinity of the penetrometer, soil–structure interaction, and complex non-linear response of soil. This makes such simulations challenging. Depending on the soil’s permeability and compressibility, undrained, partially drained or drained conditions might occur. Partially drained conditions are commonly encountered in soils such as silts and sand–clay mixtures. However, this is often neglected in CPT interpretation, which may lead to inaccurate estimates of soil properties. This paper aims at improving the understanding of the penetration process in different drainage conditions through advanced numerical analyses. A two-phase Material Point Method is applied to simulate large soil deformations and generation and dissipation of excess pore pressures during penetration. The constitutive behaviour of soil is modelled with the Modified Cam Clay model. Numerical results are compared with experimental data showing good agreement. 相似文献
19.
采用离散元商业软件PFC2D对7种重力场下静力触探试验进行了对比分析试验,以研究高、低重力场下静力触探试验的异同点。数值试验结果表明：不同重力场下土体受静力触探贯入主要影响区域不同,低重力场下主要是上部土体受到影响,高重力场下主要是下部土体受到影响;归一化贯入阻力的最大值和稳定值、归一化球应力和偏应力的最大值均与重力加速度的倒数呈线性关系,均随重力加速度倒数的增加而增大;土体经历了明显的加载、卸载过程,重力加速度越小,加载、卸载现象越明显,同一重力加速度下上部土体加载、卸载程度大于下部土体。 相似文献
20.
黄土在应力作用下迂水时力学强度迅速下降 ,产生大范围的快速沉陷。这就是黄土的湿陷性 ,是黄土的诸多特性之一。鉴于对黄土湿陷性以往用各种实验室试验指标进行评价 ,这里提出运用动力触探和静载荷试验进行黄土湿陷性原位评价的一种简便的新方法。该方法的试验程序是 ,先用轻便可变动能触探仪在天然状态和饱水状态下进行触探试验 ,而后在触探孔完成静载荷压缩性试验。运用中国黄土高原黄土原位动力触探和静载荷试验测得的资料 ,详细分析了天然状态的黄土对探头阻力 qdnat,饱水状态的黄土对探头阻力 qdsat,实验室测得的湿陷性指数s压缩曲线参数 (即触探极限压力 ppf,触探蠕变压力ppl 和触探载荷模量Epn)的关系。结果证明所提出的方法适用于原位判定黄土的湿陷性。 相似文献