共查询到20条相似文献，搜索用时 797 毫秒
1.
In situ dissipation tests provide a means of evaluating the in situ coefficient of horizontal consolidation and horizontal
hydraulic conductivity of soft clays. Dissipation tests by means of piezocone (CPTU), dilatometer (DMT), self-boring pressuremeter
(SBPT) and BAT permeameter (BAT) were utilized in the characterization of the coefficient of horizontal consolidation and
horizontal hydraulic conductivity of Singapore marine clay at Changi in a land reclamation project. Dissipation tests were
carried out prior to reclamation as well as after ground improvement with vertical drains to compare the changes in the coefficient
of horizontal consolidation and horizontal hydraulic conductivity prior to and after ground improvement. Tests were carried
out in a vertical drain area as well as in an adjacent untreated control area after 23 months of surcharge loading, for comparison
purposes. The purpose of this research is to determine the horizontal consolidation parameters of Singapore marine clay prior
to reclamation as well as after 23 months of surcharge loading with and without vertical drains by means of in situ dissipation
tests. 相似文献
2.
In-situ testing of Singapore marine clay at Changi 总被引：2，自引：0，他引：2
The Changi East Reclamation Project in the Republic of Singapore comprises of the ground improvement of marine clay with the installation of prefabricated vertical drains and subsequent surcharge placement. Prior to the commencement of land reclamation works, a series of in-situ tests were conducted in marine conditions with the use of various in-situ testing equipment. The In-Situ Testing Site was located in the Northern area of the project where the thickest compressible marine clay layers existed. The in-situ tests carried out were with the field vane, piezocone, flat dilatometer, self-boring pressuremeter and BAT permeameter. In-situ tests were conducted to determine the undrained shear strength and overconsolidation ratio of the marine clay. In-situ dissipation tests provide a means of evaluating the in-situ coefficient of horizontal consolidation and horizontal hydraulic conductivity of soft soil and were used to estimate these properties of Singapore marine clay at Changi. 相似文献
3.
A. Arulrajah M. W. Bo H. Nikraz A. S. Balasubramaniam 《Geotechnical and Geological Engineering》2007,25(6):647-656
In situ dissipation tests provide a means of evaluating the in situ coefficient of consolidation due to horizontal flow and
hydraulic conductivity in horizontal direction in marine clays formation. Dissipation tests by means of piezocone were utilised
in the characterisation of the coefficient of consolidation due to horizontal flow and the hydraulic conductivity in horizontal
direction of Singapore marine clay at Changi. Piezocone dissipation tests were carried out prior to reclamation as well as
after ground improvement with vertical drains to compare the changes in the coefficient of consolidation due to horizontal
flow and hydraulic conductivity in horizontal direction prior to and after ground improvement. The quasi-static piezometric
pressures from the dissipation tests were compared with piezometric pressures from piezometers to determine their possibility
of future use as an alternative to piezometers. Post-improvement CPTU dissipation tests were carried out in the treated “Vertical
Drain Area” as well as in an adjacent untreated “Control Area” for comparison purposes. This study provides support for the
use of piezocone dissipation testing methods for the determination of the coefficient of consolidation due to horizontal flow
and hydraulic conductivity in horizontal direction of marine clays in the region as well as an alternative to piezometer instrumentation
for monitoring of piezometric pressure during consolidation. 相似文献
4.
Myint Win Bo Ming-Fang Chang A. Arulrajah Victor Choa 《Geotechnical and Geological Engineering》2012,30(1):45-62
Geotechnical ground investigation is important in all construction works particularly, land reclamation projects. The Changi
East reclamation project is a mega project that involves creation of land space as large as 3,000 hectares in multiple phases
between 1991 and 2005. Ground investigation plays a critical role in the Changi project which involved substantial amount
of ground improvement works after reclamation by sand filling. One important aspect of the investigation was to evaluate the
geotechnical characteristics of the underlying compressible soils beneath the original seabed for the selection of suitable
methods of ground improvement. The other important aspect of the investigation was to characterize and verify the compactness
of the reclaimed sand fill. Many types of in situ tests were extensively used in the project. The field vane shear test provides
correlations between the undrained shear strength and depth for the upper and the lower marine clay strata in the Northern
part and the Southern Part of the reclaimed site. Combined with laboratory undrained shear strength tests, the field vane
strength profiles allow the derivation of the undrained shear strength over effective stress ratios for the upper and the
lower marine clays. In addition, results from three other in situ tests, the piezocone cone penetration test, the flat dilatometer
test, and the self boring pressuremeter test provided useful verification of these correlations. A field-performance based
method of assessing degree of consolidation in the underlying clay was developed by combining field monitoring, laboratory
testing and conventional as well as specialized in situ testing. An effective use of in situ testing methods for assessment,
the outcome of ground improvement and for fill quality control in the densification of granular soils is illustrated with
field observation data collected at the project site. 相似文献
5.
浙江漩门三期围垦项目中采用爆炸挤淤置换法进行筑堤工程,为了对爆炸置换后海堤的固结沉降预测及稳定性评价提供可靠的试验参数,取爆炸前后地基范围内的海相软黏土,进行一维压缩和各向等压固结试验,并对该地区软土的压缩变形与结构特性进行初步研究。试验结果表明,海相软黏土存在一定的结构特性,表现出与其重塑土不同的性质;通过引入孔隙指数的概念,研究该地区软黏土的结构性,证实土体结构性的存在是其压缩特性不同于重塑样压缩曲线的内在原因,在高压力范围内其压缩曲线趋近于固有压缩曲线。爆炸挤淤作用对海相软黏土产生较强的扰动效应,也对其基本物理性质与压缩特性均产生重要影响;扰动效应造成软黏土的结构屈服应力降低,结构强度下降,采用新定义的结构破坏比来定量评估爆炸挤淤作用对海相软黏土结构性的破坏程度,可为爆炸挤淤置换法处理软基的海堤工程提供一定的理论基础。 相似文献
6.
In ground improvement projects with prefabricated vertical drains, the duration of the preloading period is set in advance
based on the predetermined time rate of consolidation of the compressible layer. If prediction is accurately done, the required
degree of consolidation is met at the pre-determined preloading time. As such, there is a requirement for in-situ tests to be carried out just prior to the removal of surcharge to assess the degree of consolidation of the improved ground.
In-situ tests were carried out after 23 months of surcharge loading at the In-Situ Test Site within the Changi East Reclamation Project in the Republic of Singapore. In-situ testing works in this research study comprises the use of field vane shear, piezocone, flat dilatometer and self-boring pressuremeter.
The in-situ tests were carried out to determine the shear strength and degree of consolidation of the Singapore marine clay at Changi
after 23 months of surcharge loading. The In-Situ Test Site consisted of a Vertical Drain Area as well as an untreated Control Area. Both areas were located adjacent to each
other and were surcharged simultaneously to the same level and surcharge left in place for a period of 23 months. Comparison
was made between the in-situ test results of the Vertical Drain Area and the untreated Control Area. 相似文献
7.
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
8.
The existence of thick compressible varved clayey silt deposits along the Delaware River presents one major obstacle for design and construction of structures or industrial facilities in this region. To understand the characteristics of this thick weak soil layer and then develop reliable soil parameters for future earthwork design and construction, a comprehensive soil testing program was carried out. The program consisted of both in situ tests [e.g., standard penetration test borings, piezocone penetration test (CPT) soundings, Marchetti flat dilatometer test soundings, seismic shear wave test soundings, CPT pore pressure dissipation tests, and field vane shear tests] and laboratory tests (e.g., soil index tests, consolidation tests, triaxial tests, and chemical tests). Additionally, a field surcharge test program with and without installation of wick drains was carried out to investigate the compressibility of the thick clayey silt deposit and the efficiency of wick drains to help accelerate consolidation. The field and laboratory test results showed that the varved clayey silt deposit was normally consolidated to slightly overconsolidated and moderately to highly compressible. Its physical properties were intermediate between those of Savannah muddy clay and Shanghai soft clay, while much closer to that of Shanghai soft clay. Due to its lamination structure in the horizontal direction, the horizontal consolidation coefficient of the varved clayey silts was significantly greater than that in the vertical direction. The measured undrained shear strength of the varved clay silt almost increased linearly with depth. The installation of wick drains in the thick clayey silt deposits accelerated primary consolidation, but showed no effect on the secondary consolidation under constant loading. The findings obtained from this study will be beneficial for future design and construction of earthworks along the Delaware River. 相似文献
9.
软黏土层一维有限应变固结的超静孔压消散研究 总被引：1，自引：0，他引：1
根据土力学固结理论计算分析软黏土层固结过程的超静孔隙水压力值,确定软黏土体固结过程的强度增长,对排水固结法处理软土地基至关重要。软黏土层固结过程中土体变形较大时,有限应变固结理论和小应变固结理论计算分析软黏土固结所得结果差异较大。利用非线性有限元法及程序,通过对软黏土层固结工程算例的计算结果分析,研究了有限应变固结理论和小应变固结理论计算分析软黏土层一维固结超静孔压值消散的差异;探讨了软黏土体一维固结过程中,几何非线性、土体渗透性变化和压缩性变化对超静孔隙水压力消散的影响。研究结果表明,当土体的变形较大时,有限应变固结理论计算出的超静孔压要比小应变固结理论得到的值消散的更快。考虑土体固结过程中渗透性的变化时,超静孔压消散变慢;可用软黏土渗透性变化指数ck 反映渗透性变化对超静孔压消散的影响,渗透性变化指数ck值越小、超静孔压消散越慢。固结过程中软黏土压缩性的大小及变化也影响超静孔压的消散,可用软黏土的压缩指数cc反映固结过程中压缩性的大小及变化对超静孔压消散的影响,软黏土的压缩指数cc越小,固结过程软黏土层中的超静孔压消散越快。 相似文献
10.
海相结构软土的次固结研究 总被引：4，自引：2，他引：2
现有次固结计算方法没有考虑土结构性的影响,但自然沉积土大都具有结构性。海相软土一维次固结试验研究表明,对于结构性土,次固结不仅在超固结状态时与荷载有关,且在土体结构破坏的过程中也与荷载有关。当固结压力小于先期固结压力时,次固结系数随压力增长较快;当固结压力大于先期固结压力且小于结构完全屈服压力时,次固结系数随固结压力增长缓慢;当固结压力大于结构完全屈服压力时,次固结系数不随固结压力变化。次固结系数变化与否的荷载分界点不是先期固结压力,而是结构完全屈服压力。对于海相结构软土,其次固结系数变化在超固结、结构破坏、正常固结3个阶段随荷载变化的规律不同。最后,提出了考虑土结构性的一维次压缩计算方法。 相似文献
11.
围涂工程的海堤直接坐落在软土地基上,致使地基土受到挤淤、排水固结,产生了较大的沉降量。当前计算海堤沉降基本上按照规范规定以分层沉降总和法为主,辅以软土修正系数,对工后沉降要求结合固结计算和类似工程经验等综合分析确定,对不同的设计人员往往会产生较大的计算误差。如何准确判断海积软土在海堤荷载作用下的沉降变形往往是堤防建造和围海造地等重大工程中的关键环节。为研究海积软土的变形特性,在室内试验和实测沉降的基础上,采用plaxis有限元软件对实际的工程项目全过程施工的模拟,认为采用粘性土弹塑性模型对堤坝沉降变形进行平面应变情况的模拟,沉降模拟跟实测比较接近,并能很好地模拟工后沉降,能解决由经验判断产生的较大误差。 相似文献
12.
Towards a general model of quick clay development 总被引：1，自引：0，他引：1
J. KENNETH TORRANCE 《Sedimentology》1983,30(4):547-555
ABSTRACT Within the clear definition of a quick clay as being a soil which has a sensitivity greater than 30 and a remoulded strength less than 0.5 kPa, a general model for quick clay development is presented, based on the influences of various material properties and natural processes on the sensitivity and remoulded strength. The influences are separated according to depositional requirements and post-depositional factors and according to whether the influence is to increase the undisturbed strength or to decrease the remoulded strength. Depositional factors are the requirements for a flocculated structure and the dominance of low activity minerals. Post-depositional factors are cementation and slow load increase, which increase the undisturbed strength, and little consolidation, leaching and dispersants, which decrease the remoulded strength. The application of the model to marine, brackish water and freshwater sediments is discussed. 相似文献
13.
我国江苏北部连云港地区海相软土蒙脱石族矿物含量相对较高,且在海陆交互环境中沉积形成,沉积过程中具有孔隙水盐分较高的特点,但在后沉积过程中由于地表和地下淡水入侵,会使孔隙水盐分发生变化,而相应的次固结行为的变化规律尚不明晰,因此需要深入了解矿物成分、孔隙水盐分在软黏土次固结行为中的作用机制。由于天然软黏土的矿物成分、孔隙水成分差异较大,试验材料采用矿物成分均一的商用高岭土与膨润土组成的人工黏土作为研究对象,配制不同浓度的NaCl溶液作为孔隙水,模拟孔隙水盐分变化。通过常规固结试验,发现对于含蒙脱石矿物的人工黏土,压缩指数Cc随着盐分浓度的增加而减小,主固结完成时间随盐分的增加而提前,且同一应力水平下和孔隙比下,次固结系数随着盐分的增加而减小。在同样的上部荷载下,次固结系数与压缩指数的比值Cα/Cc不再保持为经验常数,而是随着孔隙水盐分的增加而偏离经验值,主要原因为盐分对水膜蠕变的影响。但是,对于主要由高岭石矿物构成的人工黏土,孔隙水盐分浓度则未对其次固结参数产生明显的影响。因此,如果场地的黏性土蒙脱石含量较高且孔隙水含盐量较高,则需要考虑孔隙水盐分的变迁对地基长期变形的影响。 相似文献
14.
15.
为探讨湛江强结构性原状土与相应重塑土在不同应力路径下的强度特性及其与结构性的关联性,开展了在不同固结条件下的主动压缩、被动压缩、主动伸长3种应力路径试验,分析了该强结构性黏土在不同应力条件下的力学性状与强度特性。结果表明,湛江黏土的剪切破坏形态主要是单一型、双交叉剪切带与“腰鼓”型3类,应力-应变特性主要为轻度应变软化、强烈应变软化、轻度应变硬化、强烈应变硬化4类;偏压固结下试样破坏应变小于等压固结相应值,破坏强度及初始弹性模量比后者大;不同应力路径下土的强度差异主要反映在结构屈服前有效黏聚力的不同,结构屈服前,原状土的黏聚力高于重塑土的黏聚力,内摩擦角小于后者;结构屈服后,黏聚力逐渐减小,内摩擦角略有增大。原状土到重塑土的转变过程是黏聚力与内摩擦力在土体内部相互消长的过程,强结构性黏土在结构屈服前的强度指标具有较强应力路径依赖性。 相似文献
16.
《城镇污水处理厂污泥处理处置技术规范》[1]执行前,市政污泥往往直接倾倒于填埋场形成污泥库,导致垃圾设计库容显著降低。为恢复填埋场库容,许多填埋场面临污泥库的原位加固处理。通过2组模型试验,探讨真空预压处理污泥的可行性。试验结果表明,真空预压后污泥含水率显著降低,强度提高至2~4 kPa;污泥排水固结系数随预压过程发展表现出非线性;排水板周围污泥含水率和渗透系数降低明显,阻碍离排水板较远处污泥排水固结,因此减少排水板间距可显著提高污泥处理效果;真空预压过程中污泥中孔压变化规律与常规淤泥质土有明显区别,特别是远离排水板的位置孔压消散幅度小,表明污泥中孔压消散规律不符合传统的太沙基固结理论;污泥真空预压过程中,间歇式通正气压会在处理初期阶段加快排水速率,但整体改善作用不明显;真空预压可作为污泥减量化的一种途径,如要满足后续堆载垃圾的要求,还需配合其他原位处理方法进一步提高强度。 相似文献
17.
This paper presents the analyses of twelve prestressed concrete (PSC) instrumented test piles that were driven in different bridge construction projects of Louisiana in order to develop analytical models to estimate the increase in pile capacity with time or pile setup. The twelve test piles were driven mainly in cohesive soils. Detailed soil characterizations including laboratory and in situ tests were conducted to determine the different soil properties. The test piles were instrumented with vibrating wire strain gauges, piezometers, pressure cells that were monitored during the whole testing period. Several static load tests (SLTs) and dynamic load tests were conducted on each test pile at different times after end of driving (EOD) to quantify the magnitude and rate of setup. Measurements of load tests confirmed that pile capacity increases almost linearly with the logarithm of time elapsed after EOD. Case pile wave analysis program was performed on the restrikes data and was used along with the load distribution plots from the SLTs to evaluate the increase in skin friction capacity of individual soil layers along the length of the piles. The logarithmic linear setup parameter “A” for unit skin friction was calculated of the 70 individual clayey soil layers and was correlated with different soil properties such as undrained shear strength (Su), plasticity index, vertical coefficient of consolidation (cv), over consolidation ratio and sensitivity (St). Nonlinear multivariable regression analyses were performed, and three different empirical models are proposed to predict the pile setup parameter “A” as a function of soil properties. For verification, the subsurface soil conditions and setup information for additional 18 PSC piles collected from local database were used to compare the measured versus predicted “A” parameters from the proposed models, which showed good agreement.
相似文献18.
通过等压固结静、动三轴试验,研究了渤海湾粉质黏土在循环荷载作用下的动力性质和循环荷载后不排水静力性质。试验结果表明,循环应力幅值比越大,平均轴向应变和轴向应变幅值越大;循环应力幅值比达到0.4时,平均轴向应变和轴向应变幅值随着循环周数增加迅速增大;循环应力幅值比相同,固结应力越大,轴向应变幅值越大,而平均轴向应变越小。在较大的循环应力幅值比下,平均孔压比值和孔压幅值比值随着循环周数的增大会达到稳定;循环应力幅值比越大平均孔压比值和孔压幅值比值均越大;相同循环应力幅值,固结应力越大平均孔压比值越小,而固结应力对孔压幅值比值影响较小。循环荷载的作用会导致循环荷载后不排水剪在q-p’平面上有效应力路径和孔压发展表现出超固结土的性质。 相似文献
19.
固结条件与荷载条件对吹填土的力学特性具有明显的影响,且土的微观结构特征是决定其宏观力学性质的本质因素,为了研究吹填软土力学特性在不同固结条件和荷载条件下的变化规律及与微结构参数的关联性,对天津滨海新区重塑吹填软土进行不同初始固结条件与荷载效应综合作用下的蠕变试验和微观结构测试,研究此条件下吹填土力学特性的变化规律,并通过灰色关联度理论建立宏观力学参数与微结构参数之间的关联性。试验结果表明:稳定性蠕变对吹填软土强度的增长起到积极作用,有偏压固结较无偏压固结强度增长更快,且初始固结越充分,强度增长越快;随蠕变时间的增加,颗粒的等效直径、形态比和圆度呈增大的趋势,而颗粒和孔隙的数量与周长、孔隙的等效直径、形态比和圆度则呈减小的趋势;抗剪强度指标C,φ值随颗粒等效直径、形态比和圆度的增大而增大,但随颗粒和孔隙的数量与周长、孔隙的等效直径、形态比和圆度的增大而减小。关联度分析表明,颗粒（孔隙）等效直径和圆度是影响吹填土力学性质演化的重要微结构参数,固结与蠕变越充分,土体微结构参数调整越稳定,强度越高。 相似文献
20.
Guidance is provided for geotechnical engineers designing civil engineering works in silty soils based on a detailed characterisation of a glaciomarine silt from Os in western Norway. It was found that these soils are susceptible to disturbance by good quality fixed piston tube sampling and care needs to be taken when using laboratory derived design parameters, particularly for consolidation and shear strength properties. A technique for assessing sample disturbance using shear wave velocity and suction measurements proved promising. Conventional techniques for determining soil strength from triaxial tests in silt are inappropriate due to the dilational nature of the material and more reliable and logical strength estimates can be made from a limiting strain criterion. Field vane data should be used with caution as measured strength, particularly remoulded values, may be high and it seems more reliable parameters can be derived from CPTU tests. One dimensional consolidation and creep of these silts can be modelled successfully by the well-known Janbu formulation. The behaviour of the Os silts does not fit easily into classical soil mechanics and published frameworks for soft soils. It seems the material is of “transitional” type and this work adds to the database of such soils which includes other natural silts and gap graded soils. For future work it is recommended that larger sample tubes (say 75 mm) with a very sharp cutting edge should be used in parallel with in situ CPTU testing. 相似文献