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1.
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
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.
Characteristics of Singapore Marine Clay at Changi 总被引：2，自引：1，他引：1
Singapore marine clay at Changi is a quartenary deposit that lies within valleys cut in the Old Alluvium. It is locally known
as Kallang formation. The pre-reclamation site characterization and laboratory testing was carried out by conducting marine
sampling boreholes, in situ dissipation tests and field vane test. In situ dissipation tests were conducted with the piezocone,
flat dilatometer, self-boring pressuremeter and BAT permeameter. The purpose of the site characterization was to determine
the consolidation characteristics, strength characteristics, stratigraphy, and mineralogy of Singapore marine clay. The consolidation
properties of marine clay are required prior to land reclamation activities in order to predict the magnitude and rates of
settlement with the expected fill load and future service load as well as for the design of soil improvement works. The shear
strength properties are required for slope stability analyses during reclamation and for the stability analyses of shore protection
works. Clay mineralogy tests and photographic identification of the marine clay was carried out to determine the mineralogical
properties and to visually record the marine clay colour and texture. 相似文献
4.
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
5.
Factors Affecting Consolidation Related Prediction of Singapore Marine Clay by Observational Methods
The use of prefabricated vertical drains with preloading option is the most widely-used ground improvement method for the
improvement of marine clays in land reclamation projects. The assessment of the degree of consolidation of the marine clay
is of paramount importance prior to the removal of preload in such ground improvement projects. This analysis can be carried
out by means of observational methods with the use of field settlement plates and piezometer monitoring. Field settlement
monitoring data can be used to ascertain the settlement of the reclaimed fill from the time of initial installation. The field
settlement data can be analysed by the Asaoka method to predict the ultimate settlement of the reclaimed land under the surcharge
fill. Back-analysis of the field settlement data will enable the coefficient of consolidation due to horizontal flow to be
closely estimated. Piezometer monitoring data can be analysed to obtain the degree of consolidation of the improved marine
clay. Back-analysis of the piezometer data will also enable the coefficient of consolidation due to horizontal flow to be
estimated. The aim of this paper is to highlight the significance and impact of the various factors that affect prediction
by the Asaoka and piezometer assessment methods. The authors findings of the Asaoka method reveal that the magnitude of ultimate
settlement decreases and the degree of consolidation subsequently increases as a longer period of assessment is used in the
prediction. The degree of consolidation predicted by the piezometers is found to be in good agreement with the Asaoka method
for the early period of assessment. However as the assessment period increases, the piezometer indicates lower degree of consolidation
as compared to field settlement predictions. 相似文献
6.
为评估涂抹区土体压缩和渗透系数变化对含竖向排水体地基固结的影响,采用等体积应变假设,考虑涂抹区土体的压缩变形及其水平向渗透系数沿径向分别呈线性和抛物线分布,并考虑井阻作用以及地基附加球应力沿深度任意分布,推导了随时间线性堆载预压条件下固结微分方程的显式解析解答,分析了涂抹区半径、水平向渗透系数的分布模式、以及体积压缩系数对地基整体平均固结度的影响。结果表明,涂抹区土体采用均匀折减的水平向渗透系数明显低估了地基的固结速率,而当涂抹区半径较大时,不考虑涂抹区土体的压缩变形将会高估地基的固结速率。在含竖向排水体地基固结问题的分析中,这些影响不可忽视。 相似文献
7.
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
8.
The coefficient of consolidation is one of the most important parameters that control the rate of consolidation. Conventional consolidation theories assume that the coefficient of consolidation is constant during the whole consolidation process. In the case of sensitive clay, the coefficient of consolidation is strongly dependent on the level of effective stress of clay. With the dissipation of pore water pressure and the increase of effective stress, the soil structure of the upper subsoil is gradually destroyed downwards and its coefficient of consolidation becomes smaller. At the same time, the coefficient of permeability of the vertical drains drops down because of the kinking or bending effect. The destructured upper subsoil and the kinking of the vertical drain hinder the dissipation of the pore pressure in the lower subsoil. This paper presents a model to describe the above important phenomena during the consolidation of sensitive clay with vertical drain. The solution for proposed model can be obtained by extending the closed‐form solution of the consolidation of double‐layered ground with vertical drain by the interactive method introducing the concept of the moving boundary and the reduction of discharge capacity of vertical drain. The numerical results obtained from the finite element method package PLAXIS (Ver. 7.2) are adopted to compare those obtained from the present algorithm. Moreover, the rationality of the moving boundary is explained by the distributions of the excess pore water pressure in natural soil zone along the radial direction. Wenzhou airport project is taken as a case study in this paper. The results for the sensitive soil with decaying sand drain agree very well with the in situ measured data. The calculated results can properly explain two general phenomena observed in the consolidation of soft sensitive soil ground with vertical drains: one is that the time to achieve the same consolidation degree is much longer under heavy loading than that under light loading; the other is that the consolidation speed is much slower in the lower subsoil than in the upper subsoil. Finally, it is indicated that the vertical drains can decrease the hindrance effect of the destructured subsoil. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
9.
Si-jie Liu Xue-yu Geng Hong-lei Sun Yuan-qiang Cai Xiao-dong Pan Li Shi 《国际地质力学数值与分析法杂志》2019,43(4):767-780
The system of vacuum pressure combined with vertical drains to accelerate soil consolidation is one of the most effective ground improvement methods. The consolidation theories of soft soil improved by vertical drains including void ratio–dependent compressibility and permeability have been widely applied in practice to predict the consolidation behavior. In this paper, analytical solutions of the consolidation of vertical drains are derived incorporating the loss and propagating stage of vacuum pressure. In addition, special solutions are obtained for the cases of instantaneous surcharge loading and staged surcharge loading, based on the general solution. The solution is verified by ignoring the propagating stage of vacuum pressure formation and comparing it with an existing solution. The effects of vacuum pressure loss and propagating stage combined with other parameters are investigated through the ratio between excess pore water pressure and surcharge loading. 相似文献
10.
采用Barron轴对称固结及大变形固结问题的某些简化与假定,推导建立了砂井地基大变形固结控制方程,利用建立的双层砂井地基大变形固结方程及编制的计算程序,通过引入软土渗透系数、有效应力与孔隙比之间的幂函数关系k =ced与e=a( )b,对瞬时加载下双层砂井地基固结性状进行算例计算。结果表明：（1）双层软土幂函数渗透关系及压缩关系中诸参数对双层砂井地基固结性状有重要影响：随着两层软土幂函数渗透关系中参数c1、c2的增加（渗透性增加）、或幂函数压缩关系中参数a1、a2的增加,各土层水平径向与竖向孔隙比减小更快,沉降发展速率与超静孔压消散速率也相应增加,且沉降发展速率快于孔压消散速率。（2）两层土在分界面处的孔隙比及平均超静孔压均出现明显的突变,将沿深度分布曲线分成形状不同的两段,表现出不同的固结性状。 相似文献
11.
袋装砂井超载预压法的现场试验研究 总被引：2，自引：0，他引：2
介绍厦门某高速公路软基袋装砂井超载预压大型现场试验结果,讨论了竖向排水井超载预压地基加固效果。通过对测试成果的系统分析,认为厦门某高速公路地基经过加固处理后,其地基工后沉降能满足设计对地基变形的严格要求。结果还表明:安全控制应以沉降速率和水平位移速率为主,其标准可分别采用20mm/d和10mm/d。 相似文献
12.
In this study, some limitations associated with modeling the hydraulic conductivity of soil improved with vertical drains are discussed. In addition, some limitations of conventional methodologies for deducing the hydraulic conductivity from oedometer or Rowe cell tests are investigated. An alternative approach for estimating the hydraulic conductivity in soils improved by vertical drains is discussed. This methodology will allow for simpler finite element modeling of consolidation due to vertical drains. The effectiveness of this technique has been demonstrated using a field study. 相似文献
13.
《Geomechanics and Geoengineering》2013,8(1):63-71
Soil disturbance caused during the installation of vertical drains reduces the in situ hydraulic conductivity of soft deposits in the immediate vicinity of the drains, resulting in a slower rate of consolidation than would be expected in the absence of disturbance. Experimental investigations have revealed the existence of two distinct zones, a smear zone and a transition zone, within the disturbed zone around the vertical drain. The degree of change in the hydraulic conductivity in the smear and transition zones is difficult to assess without performing of laboratory tests. Based on the available literature, four different profiles of hydraulic conductivity versus distance from the vertical drain were identified. Closed-form solutions for the rate of consolidation for each of these four hydraulic conductivity profiles were developed. It is found that different variations of the hydraulic conductivity profiles in the disturbed zone result in different rates of consolidation. 相似文献
14.
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
15.
对于围海造陆工程所开展的超载预压处理方法,地基处理效果通常采用后续变形大小来评价,其大小与超载比和卸载控制时间密切相关。针对天津滨海地区围海造陆工程所形成的典型的上软、下硬的双层软黏土地基,采用改装的固结仪进行了多种超载比和卸载控制时间的试验研究,提出了适宜的超载比和最佳超载作用时间。试验表明：双层软黏土地基超载比大于0.375,超载作用时间超过主固结时间时,超载卸除后地基变形以回弹变形为主,后续的工后沉降将明显减小,减小幅度可高达70%以上;超载卸除后的土体次固结系数明显减小,减小的幅度随超载比的增大、超载作用时间的增加而减小;不同于均质地基和上硬下软的双层地基,上软、下硬双层地基的工后沉降以上部软土层沉降为主,约占总沉降量的73%以上。根据不同超载比和超载作用时间下土体的变形时程曲线,建议适宜天津滨海地区围海造陆工程软黏土地基的超载比控制在0.5以下,超载作用时间控制在1～3倍的主固结时间内。 相似文献
16.
不同平衡堆载条件下桩基承载特性的原位试验研究 总被引：1，自引：0，他引：1
沿海吹填围垦地区土质较差,淤泥软弱土层较厚,在后期填土作用下土体会产生很大的固结沉降。后期不同堆载填土方式对桥梁基础影响较大,可降低基桩承载力,同时平衡堆载主要增加基桩的沉降,而不平衡堆载则对基桩水平位移影响较大。结合台州湾大桥工程建设,选取3根基桩进行了平衡堆载（围载）试验,另外,选取了3根基桩进行了不平衡堆载试验,研究不同堆载条件下对桩基承载特性的影响。现场试验结果表明,平衡堆载条件下主要引起桩侧产生负摩阻力,堆载高度达到4 m,堆载面积为24 m×16 m时,负摩阻力总和达到2 687 kN左右,中性点深度约为29.5 m,约为0.36倍桩长,且负摩阻力的发展是随时间而变化的;不平衡堆载条件下主要产生土拱效应,使桩基产生较大的水平位移,试验中不平衡堆载对吹填区的影响主要在距离地面20 m范围之内,土中最大水平位移出现在距离地面4～5 m左右位置,而桩身最大水平位移出现在桩顶。 相似文献
17.
18.
Hydraulic Conductivity and Coefficient of Consolidation of Two Sulphide Clays in Sweden 总被引：1，自引：0，他引：1
The variation and anisotropy in hydraulic conductivity and the coefficient of consolidation was investigated for two Swedish
sulphide clays. A series of constant rate of strain oedometer tests was performed on samples trimmed in the vertical and horizontal
direction. A methodology to evaluate the horizontal coefficients of consolidation c
h
via the horizontal hydraulic conductivity k
h
and the vertical compression modulus M
v
is proposed. Laboratory evaluations of c
h
are also compared with determinations of c
h
from in situ piezometer measurements in vertically drained sulphide clay. Furthermore, the validity of the empirical correlation
between hydraulic conductivity change index C
k
and initial void ratio e
0, C
k
= 0.5e
0 (Tavenas et al. in Can Geotech J 20(4):645–660, 1983b), was investigated for the sulphide clays. The results from the investigation show large ranges in measured hydraulic conductivities
and coefficients of consolidation. However, the results indicate that the correlation C
k
= 0.5e
0 is valid. The anisotropy in hydraulic conductivity and the coefficient of consolidation of the sulphide clays tested seems
to be small. For design purposes, multiple tests for assessment of hydraulic conductivity and the coefficient of consolidation
should be made, and a partial factor of safety, depending on the requisite level of safety and the spatial variability of
the parameters, should be introduced. For design purposes in this type of clay, k
h
= k
v
and c
h
= c
v
are suggested. 相似文献
19.
废旧轮胎胶粉用于填埋场衬垫材料改性,是提高衬垫系统有效性和扩展废旧轮胎资源化利用途径的一种手段。以高岭土作为黏性土的代表,开展废旧轮胎胶粉-高岭土混合土的力学和水力学性质试验,重点探讨胶粉掺量及尺寸对混合土渗透性、压缩性和收缩性的影响规律。研究表明,废旧轮胎胶粉-高岭土混合土的渗透系数、压缩系数、回弹指数、固结系数和体缩率等均随胶粉掺入比的增加而增大。高岭土及混合土的无侧限抗压强度大于200kPa,50kPa和200kPa压力下渗透系数满足≤1.0×10-7cm·s-1的要求,均属于中压缩性土,且体缩率小于体积应变合格值4%。与30目胶粉相比,12目胶粉-高岭土混合土压缩性和回弹量较小、固结系数较大,胶粉尺寸对无侧限抗压强度、体缩率和渗透系数的影响不显著。在本文试验条件下,为提高黏土衬垫对有机污染物的吸附能力并满足渗透性、强度及变形的要求,12目25%胶粉改性黏土可作为填埋场黏土衬垫材料。 相似文献
20.
The settlement of a structure founded on clay comprises of immediate and consolidation settlements. In the case of clays, consolidation settlement is more than immediate settlement. The parameters influencing consolidation settlement of a normally loaded clay layer are degree of saturation (S%), void ratio (e) of soil prior to excavation, amount of overburden (σo) removed, amount of rebound and intensity of loading (σ) upon building superstructure. This paper presents the effect of the above parameters on compressibility characteristics of a clay. The different steps undertaken for footing construction were simulated in the laboratory. Remoulded clay samples were prepared from oven-dry fraction passing 425 μm sieve. The density of the samples was kept constant at 13 kN/m3. Degree of saturation was varied at 25%, 50%, 75% and 100%. The surcharge on the samples (overburden in the case of field clay layer) was varied as 25 kPa, 50 kPa and 100 kPa. Compressibility characteristics such as initial compression under the applied surcharge (overburden), rebound upon removal of surcharge and recompression were studied through one-dimensional consolidation tests. The rate and amount of initial compression, rebound, e-σ and e-log σ curves, compression index (Cc), coefficient of compressibility (av) and coefficient of volume compressibility (mv) were studied. 相似文献