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1.
The excess pore water pressure distribution (u) induced by the penetration of a piezocone into clay and its dissipation behaviour have been investigated by laboratory model tests, theoretical analysis and numerical simulation. Based on the results of the tests and the analysis, a semi-theoretical method has been proposed to predict the piezocone penetration-induced pore pressure distribution in the radial direction from the shoulder of the cone. The method can consider the effect of the undrained shear strength (su), over-consolidation ratio (OCR) and rigidity index (Ir) of the soil. With a reliably predicted initial distribution of u and the measured curve of dissipation of pore water pressure at the shoulder of the cone (u2), the coefficient of consolidation of the soil in the horizontal direction (ch) can be back-fitted by analysis of the pore pressure dissipation. Comparing the back-fitted values of ch with the values directly estimated by a previously proposed method indicates that the previously proposed method can be used reliably to estimate ch values from non-standard dissipation curves (where u2 increases initially and then dissipates with time). 相似文献
2.
饱和软黏土中足尺静压桩挤土效应试验研究 总被引：12，自引：0，他引：12
饱和软黏土地基中静压桩挤土效应是岩土工程中常见的问题。监测土体侧向位移、孔隙压力、地面隆起随压桩过程变化的规律是很多研究者希望实施的计划。在饱和软黏土地基中进行了3根足尺静压桩的压入试验,重点监测了沉桩时的侧向位移随深度和距桩轴不同距离、地面隆起量随桩的贯入深度和距桩轴不同距离、孔隙压力随桩的贯入深度和时间的变化规律,并分析了超静孔隙水压力最大值沿径向和深度的变化特性。由测试结果可知,最大的侧向位移发生在距地表0.75L附近,地面隆起从桩贯入开始迅速发展,并在桩压入到6 m左右时达到最大值,测点处超静孔压增量的最大值发生在桩端到达该点所在水平面时,而超孔压的最大值沿径向有滞后性。 相似文献
3.
Finite element cavity expansion analysis investigating the effect of penetration rate on piezocone tests in clay is presented. A coupled analysis was performed, in which the rate of cavity expansion was linked to the penetration rate of the cone and the cone angle, using the assumption that the deformation was wholly radial, and took place only between the cone tip and the cone shoulder. The soil was modelled using modified cam clay with two sets of parameters and varying values of overconsolidation ratio (OCR). The influence of penetration rate on the stress and pore pressure distributions was examined. For slower penetration rates, the excess pore pressure at the cone shoulder is lower since consolidation is permitted coincident with penetration. The radial profiles of post‐penetration voids ratio demonstrate that partially drained penetration is permitted by volume change in the near field, in addition to radial movement in the far field. The radial distribution of excess pore pressure after slow penetration differs from the undrained case, with a relatively low radial gradient existing at the cone face. As a result, the dissipation curves after slow penetration lag behind those following fast penetration. The cone velocity is made dimensionless by normalizing with the coefficient of consolidation and the cone diameter. ‘Backbone’ curves of normalized velocity against normalized tip resistance and excess pore pressure capturing the transition from undrained to drained penetration are derived. The normalized pore pressure backbone curve is unique, whilst the normalized tip resistance shows a small dependency on OCR. These backbone penetration curves are compared with centrifuge model piezocone tests conducted at varying rates, and subsequent dissipation tests. The numerical and experimental results suggest that the value of consolidation coefficient operative during the dissipation phase is 2–4 times higher than the virgin compression value due to changes in the operative soil stiffness, as demonstrated from the stress paths of individual soil elements. The use of multi‐rate penetration tests to deduce values of consolidation coefficient is discussed, in light of these differences. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
4.
Fine-grained marine sediments containing large undissolved gas bubbles are widely distributed around the world. Presence of the bubbles could degrade the undrained shear strength (su ) of the soil, when the gas pressure ug is relatively high as compared with the effective stress in the saturated soil matrix. Meanwhile, the addition of bubbles may also increase su when the difference between ug and pore water pressure uw becomes smaller than the water entry value, causing partial water drainage from the saturated matrix into the bubbles (bubble flooding) during globally undrained shearing. A new constitutive model for describing the two competing effects on the stress-strain relationship of fine-grained gassy soil is proposed within the framework of critical state soil mechanics. The gassy soil is considered as a three-phase composite material with compressible cavities, which allows water entry from the saturated matrix. Bubble flooding is modelled by introducing an additional positive volumetric strain increment of the saturated clay matrix, which is dependent on the difference between pore gas and pore water pressure based on experimental observations. A modified hardening law based on that of the modified Cam clay model is employed, which in conjunction with the expression for bubble flooding, can describe both the detrimental and beneficial effects of gas bubbles on soil strength and plastic hardening in shear. Only two extra parameters in addition to those in the modified Cam clay model are used. It is shown that the key features of the stress-strain relationship of three fine-grained gassy soils can be reproduced satisfactorily. 相似文献
5.
Mengmeng Lu Shanyong Wang Scott W. Sloan Buddhima Indraratna Kanghe Xie 《国际地质力学数值与分析法杂志》2015,39(1):51-62
By incorporating the nonlinear variation of a soil's compressibility and permeability during the process of consolidation, an analytical solution for the radial consolidation of vertical drains has been developed for a general time‐variable loading. The general solution was verified for the cases of instantaneous loading and ramp loading. Detailed solutions were further derived for two special loading schemes: multistage loading and preloading–unloading–reloading. The nonlinear consolidation behavior of a vertical drain subjected to these two types of loading schemes was then investigated by a parametric study. The results show that the loading rate, the ratio of the compressibility index to the permeability index (Cc/Ck), and the initial stress state have a significant influence on the consolidation rate. A smaller value of Cc/Ck, a larger initial stress, or a fast loading rate always leads to a rapid consolidation rate. During the unloading period, a negative excess pore water pressure may occur, and a slower unloading rate may reduce this negative value. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
6.
本文介绍了对以饱和粘性土为介质的模型槽中所进行的孔压静力触探(CPTU)试验,通过对试验数据的分析,得出探头贯入时周围土体的轴向附加应力和径向附加应力的变化及分布,锥尖、侧壁摩阻力以及超孔隙水压力的变化,以及停止贯入后孔压消散过程中探头周围土体的超孔压变化,从这些方面来探讨土中应力场的变化,附加应力的影响范围,临界深度现象以及超孔隙水压力的变化规律。 相似文献
7.
Wang Jun Wu Lei Cai Yuanqiang Guo Lin Du Yunguo Gou Changfei Ni Junfeng Gao Ziyang 《Acta Geotechnica》2021,16(4):1161-1174
In certain field conditions such as offshore projects under wave loads or embankments under traffic loads, both the vertical and horizontal stresses are variable. However, previous investigations rarely considered the variation in horizontal stress. To better understand the characteristics of natural saturated soft clay, a series of monotonic and cyclic triaxial tests with a K0-consolidation state were carried out under a variable confining pressure (VCP) stress path. The development of axial strain, pore water pressure and effective stress path is analysed. The results show that with the increase in η (the ratio of the variation in the mean effective principal stress to that of the deviatoric stress), the undrained shear strength (qf) decreases continuously. The pore water pressure generation is slightly improved under a stress path with increasing confining pressure. Based on the test results, a unified formula was established to predict the pore water pressure under VCP stress paths. The unique p–q–e relationship of normally consolidated clay in monotonic VCP triaxial tests was also demonstrated. Under VCP stress paths, the amplitude of the pore pressure increases, and the effective stress path tilts more sharply to the right. Moreover, a unified formula was established that can provide a good reference for predicting effective stress paths under cyclic VCP triaxial tests.
相似文献8.
Interplay between stress permutations and overpressure to cause strike‐slip faulting during tectonic inversion 
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下载免费PDF全文 Field data from an orogenic foreland and an orogenic belt (the Mesozoic rocks of southern England and the Umbria‐Marche Apennines of Italy respectively) indicate the following. Firstly, stress evolution during the tectonic cycle, between maximum compressive stress (σ1) being vertical during extension and least compressive stress (σ3) being vertical during contraction, can involve phases when the intermediate compressive stress (σ2) is vertical, promoting strike‐slip deformation. Secondly, variations in the relative magnitudes of the stress axes are caused by variations in overburden and tectonic forces. Thirdly, overpressure can develop because of compaction during burial, and, as overburden is reduced during uplift and erosion, the vertical stress (σV) reduces but fluid pressure (Pf) remains approximately constant. Brittle deformation, including transient strike‐slip faults, reverse‐reactivated normal faults and normal‐reactivated thrusts, is preferentially developed in overpressured areas because high Pf promotes faulting. 相似文献
9.
考虑固结的透水管桩沉桩全过程有限元模拟 总被引：1，自引：0，他引：1
运用透水管桩技术加快沉桩后桩周土体内超静孔隙水释放,进而消除沉桩施工中超静孔压的不利影响。基于有限元数值计算法,利用ABAQUS有限元软件建立透水管桩模型,实现透水管桩贯入过程以及桩周土体固结过程模拟。对比CEM圆柱孔扩张理论验证数值计算结果;阐述透水管桩贯入过程中位移场以及超静孔压场变化规律;对比分析静压桩和透水管桩桩周土体固结性状,结果表明透水管桩能加速超静孔压消散,短期内实现桩基承载力的快速提升。 相似文献
10.
This paper includes a numerical study of the behaviour of micropiles used for the reinforcement of saturated soil. Analysis is carried out using the (u–p) formulation (displacement for the solid phase and pore‐pressure for the fluid phase) implemented in a three‐dimensional finite element program. The soil behaviour is described by means of a cyclic elastoplastic constitutive relation which was developed within the framework of the bounding surface concept. The paper is composed of three parts. The first one is concerned with a presentation of the numerical model; the second includes analysis of the seismic behaviour of a single micropile; the last part deals with the group effect under seismic loading. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
11.
This paper compares the compression and uplift capacity of a strip foundation from numerical coupled analyses using the Modified Cam Clay (MCC) soil model. The focus is on the failure mechanism and pore pressure development in the soil. Triaxial compression and tension tests were first modelled to develop a rigorous understanding of the pore pressure responses; then, the compression and uplift of a strip foundation were modelled. The results show that the balance of excess pore pressures due to the changes in mean total stress and deviatoric stress during the compression and uplift of a strip foundation are different, although the ultimate undrained capacities are identical. Furthermore, the resistance and excess pore pressure responses during uplift differ from those in compression under the K0-consolidated condition because of the elastic unloading. Although the failure mechanisms have identical shape and size between undrained compression and uplift, the pore pressure distribution in the soil is different and affects the load–displacement behaviours under partially drained compression and uplift. 相似文献
12.
Cheng Wei Chen Ren-peng Hong Peng-yun Cui Yu-jun Pereira Jean-Michel 《Acta Geotechnica》2020,15(10):2741-2755
In thermal-related engineering such as thermal energy structures and nuclear waste disposal, it is essential to well understand volume change and excess pore water pressure buildup of soils under thermal cycles. However, most existing thermo-mechanical models can merely simulate one heating–cooling cycle and fail in capturing accumulation phenomenon due to multiple thermal cycles. In this study, a two-surface elasto-plastic model considering thermal cyclic behavior is proposed. This model is based on the bounding surface plasticity and progressive plasticity by introducing two yield surfaces and two loading yield limits. A dependency law is proposed by linking two loading yield limits with a thermal accumulation parameter nc, allowing the thermal cyclic behavior to be taken into account. Parameter nc controls the evolution rate of the inner loading yield limit approaching the loading yield limit following a thermal loading path. By extending the thermo-hydro-mechanical equations into the elastic–plastic state, the excess pore water pressure buildup of soil due to thermal cycles is also accounted. Then, thermal cycle tests on four fine-grained soils (natural Boom clay, Geneva clay, Bonny silt, and reconstituted Pontida clay) under different OCRs and stresses are simulated and compared. The results show that the proposed model can well describe both strain accumulation phenomenon and excess pore water pressure buildup of fine-grained soils under the effect of thermal cycles.
相似文献13.
随着海洋岛礁工程的大力推进,吹填珊瑚砂地基的密实加固问题开始备受关注。利用自主研发的室内振冲器开展了珊瑚砂饱和砂土地基的室内振冲模型试验研究,深入分析了振冲过程中动孔隙水压力、水平动土压力等动参量的响应规律,探讨了振冲后沉降变形、相对密实度的变化特征。结果表明：松散珊瑚砂地基的密实度在经过两次双点振冲反复加固后均提升至中密。其中相对密实度在振冲点位处的提升效果较其余位置更为明显,并且中层或深层区域的加固效果优于表层区域。在超孔隙水压力方面,其最大值出现在振冲珊瑚砂地基过程中的贯入阶段,并且在留振开始时出现衰减现象。珊瑚砂地基在振冲器上拔过程中超孔隙水压力发生断崖式下跌。在第2次贯入时,超孔隙水压力比的峰值较首次出现显著下降。超孔隙水压力比等值线云图表明,振冲过程中的超孔隙水压力比等值线呈现平行分布。珊瑚砂浅层水平土压力随振冲器的贯入与拔出均呈现增加态势,深层水平土压力则呈现减少态势。 相似文献
14.
可液化场地微型桩的地震响应分析是确保工程安全和优化抗震设计的前提。应用动态离心机试验和三维有效应力数值分析方法,研究了微型单桩桩台的侧向变形和加速度、不同埋深桩身弯矩、可液化场地的加速度及超孔隙水压力等响应特征。首先开展了相对密实度为57%饱和土层、输入波是频率为1 Hz和峰值加速度为1.516 m/s2正弦波的微型桩40 g动态地震响应离心机试验,进而应用基于多重剪切机构塑性模型和液化前缘状态面概念的三维有效应力分析方法,反演了试验结果,并进行了对比分析,结果表明,数值模拟与离心机试验结果吻合,液化场地特性控制着建于其中微型桩的地震响应特征,微型桩桩台的水平变形和残余变形可达78、30 mm,桩身最大弯矩和最大残余弯矩呈现向桩身底部迁移特点,同时表明,基于动态土工离心机试验和数值分析相结合的研究方法,分析可液化场地微型桩地震响应特性是有效可行的,研究结论为可液化场地微型桩的抗震设计提供了可靠的依据和参考。 相似文献
15.
为了探究静压沉桩与CPTU贯入力学机制,开展了饱和黏土中静压沉桩及CPTU贯入的离心模型试验,获得了静压沉桩与CPTU贯入过程中土压力、超孔压和贯入阻力的变化规律。同时,将静压桩和CPTU压入过程视为一系列球孔的连续贯入,应用圆孔扩张解答,建立了静压沉桩和CPTU贯入过程中锥头阻力、侧阻力与超孔压的预测方法。通过离心模型试验和理论预测结果的对比分析表明：随着桩体的压入,桩周土体的超孔压和土压力均逐渐增大,当桩头通过监测点时,超孔压与土压力均达到最大值;在饱和黏土中,CPTU锥头阻力、锥侧摩阻力和锥头超孔压与锥头贯入深度总体上呈线性关系。预测方法估算沉桩和CPTU贯入引起的土压力、超孔压与模型试验结果相符,较好地反映了饱和黏土中静压沉桩和CPTU贯入的力学机制。 相似文献
16.
盾构施工会对周围土体产生扰动,形成超孔隙水压力,引起工后固结沉降。运用应力释放理论推导与衬砌相邻的土体初始超孔隙水压力计算公式。假定扰动范围边界呈圆弧状,确定初始超孔隙水压力的分布范围;同时运用应力传递理论,推导分布范围内任一点土体的初始超孔隙水压力计算公式。通过对实测资料的分析可知,计算值与实测值吻合较好。算例分析表明,与衬砌相邻的土体初始超孔隙水压力呈近似圆形（顶部小、底部大）;随着到衬砌的径向距离增加,土体初始超孔隙水压力呈凹曲线形状;隧道底部的等值线最密,即变化最快;隧道顶部上方土体、不同深度处土体初始超孔隙水压力,以隧道轴线处为最大,呈现类似Peck曲线形状。 相似文献
17.
《Journal of Structural Geology》2004,26(6-7):1275-1291
The Indarama lode gold deposit is hosted by vertically-dipping basalt in the Late Archaean Midlands Greenstone Belt of Zimbabwe. Major deformation events at 2.68 and 2.58 Ga established a complex array of fractures. A limited range of orientations of this fracture network opened towards the end of the younger deformation event, creating a lode pattern where 92% of mineralised veins dip at less than 50°, mainly to the E and W, and most strike directions are represented. A clustered distribution of poles to the quartz–carbonate veins indicates a constrictional stress field at the time of vein opening where σ1 and σ2 were near horizontal, (directed NNW–SSE and ENE–WSW, respectively), and σ3 was near vertical. 3-D Mohr circle analysis demonstrates that σ2 was approximately 67% of σ1 (the stress ratio) and that the driving pressure ratio (R′) was approximately 0.4, reflecting the role of fluid pressure, mean stress, and the maximum shear stress in controlling conditions of fracture opening. 相似文献
18.
Field studies have shown that the driving of a displacement pile into cohesive soil generates large excess pore pressures in the vicinity of the pile. These pore pressures are often larger than the effective overburden pressure and facilitate the installation of the pile. The subsequent increase in bearing capacity of the pile is largely controlled by the dissipation of the excess pore pressures and a consequent increase in the effective stresses acting on the pile. The paper presents a closed formanalytical solution for the radial consolidation of the soil around a driven pile, assuming that the soil skeleton deforms elastically. This assumption is examined in the light of the predicted effective stress changes in the soil and is shown to lead to, a realistic model for the decay of pore pressure near the pile with time after driving. Although the solution may be applied to any initial distribution of excess pore pressure, attention is focussed on that due to the expansion of a cylindrical cavity in an ideal elastic, perfectly plastic soil. The resulting logarithmic variation of excess pore pressure with radius is considered to be close to that generated around a pile as a result of driving. In addition to giving estimates of the time needed for a driven pile to achieve its maximum strength, the solution may also be used in the analysis of pressuremeter tests to provide in-situ measurements of the coefficient of consolidation of the soil. 相似文献
19.
Consolidation of sensitive clays: a numerical investigation 总被引：1，自引：1，他引：0
Consolidation of sensitive clay layers, which have significant compressibility at different stress states, is investigated via a nonlinear one-dimensional consolidation approach with a piecewise linear e ~ log10σ′ model. The behaviour of sensitive clays during consolidation and the limitations of conventional consolidation theory are addressed. It is shown that (1) the sensitive clay layer can be divided by the preconsolidation pressure into two zones, that is, high- and low-compressibility zones. The progressive destruction of particle cementation bonding through the soil layer is shown by the moving front of the interface between these two zones; (2) the excess pore pressure dissipation primarily takes place in the low-compressibility zone, which results in a small settlement during the early stages of consolidation; (3) conventional consolidation theory highly overestimates the settlement and gives a poor prediction of effective stress distribution. 相似文献
20.
随着全套管振动取土灌注桩施工工艺的发展,灌注桩在工程中的应用越来越广泛,但关于灌注桩套管高频振动贯入机制,特别是套管贯入引起的挤土效应研究还不全面。全面介绍了套管高频振动贯入全过程的有限元-无限元耦合模型的建立过程后,对地表隆起、土体侧移及超孔隙水压力等挤土效应的变化规律进行了详细研究。研究结果表明：水平向的挤土位移随套管贯入深度的增加而增大,竖向挤土位移随着套管贯入深度的增加,浅层土表现为隆起量增大,而深层土表现为下沉量增大;最大挤土位移与套管贯入深度存在滞后效应;浅层土体的隆起为水平向应力加载引起竖向应力增加所致,且隆起分界面深度随着动力荷载幅值增大而增大,随振动频率的增大而减小;超孔隙水压力随套管贯入深度增加而增大,随径向距离增大呈指数型衰减。 相似文献