1、GMSEGEOTECEOSYNONITOLECTED GEGeo-PHNICALGEOTHETICRING, APAPERS O-CHINAShandoChineInstitute oublished bSPECI-CHCIVIL IND ENVFROM THINTERNJuly 2ShanSPONShandong DeparUniversise Nationf the AmeEDSao-JenXinzhuaKwok-Leby the AmerAL PUBINANFRASTIRONMEE PROCEATIONA527, 201dong, ChinSORED BYng Univertment o
2、f Tty of Oklahal Sciencerican SocieITED BY g Chao, Png Cui, Pung Pun, ican SocietyLICATIO20RUCTURNTAL GEDINGS L CONFE6 a sity ransportathoma Foundatioety of Civih.D. h.D. Ph.D. of Civil EnON NO.16 E, DISAEOTECHOF THE FRENCE ion n l Engineergineers 261 STER NICS OURTHs Published by American Society o
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9、an Society of Civil Engineers. All Rights Reserved. ISBN 978-0-7844-8004-5 (PDF) Manufactured in the United States of America. Preface This Geotechnical Special Publication (GSP) contains 20 papers presented at the 4th GeoChina International Conference held in Shandong, China from July 25 to 27, 201
10、6. The conference is endorsed by a number of leading international professional organizations. The technical programs for the 4th GeoChina International Conference came into contact with a balance between the fundamental theories and field applications. The papers in this GSP address a mixture of cu
11、rrent issues in the Advances in Unsaturated Soil, Seepage, and Environmental Geotechnics, Natural Hazard and Disaster Monitoring, and Geosynthetic Reinforced Soil Retaining Structure. Furthermore, this GSP includes investigations and solutions from numerous countries, and it expands ranges of tools
12、that are available to engineers and scientists. Acknowledgments The following individuals have assisted on preparing the GSP and reviewing the papers: Howard Hwang, Hui-Mi Hsu, An Cheng, Wei-Ting Lin, Jiong Zhang, and Yingjie Zheng. *HR and Patrick J. Fox, F.ASCE21Professor, School of Civil Engineer
13、ing and Mechanics, Huazhong Univ. of Science and Technology, Wuhan, Hubei 430074 China. E-mail: 2Shaw Professor and Head, Dept. of Civil and Environmental Engineering, Pennsylvania State Univ., University Park, PA 16802. E-mail: pjfoxengr.psu.edu Abstract: This paper presents a numerical investigat
14、ion of the effects of large strain consolidation on contaminant transport in multi-layer soils. Numerical simulations were conducted using the CST3 model, which accounts for one-dimensional coupled large strain consolidation and contaminant transport in saturated multi-layer porous media. The consol
15、idation algorithm accounts for vertical strain, soil self-weight, general constitutive relationships, relative velocity of fluid and solid phases, changing compressibility and hydraulic conductivity during consolidation, unload/reload, time-dependent loading, time-dependent boundary conditions, exte
16、rnal hydraulic gradient, variable preconsolidation stress profiles, and multiple soil layers with different material properties. The contaminant transport algorithm accounts for advection, diffusion, mechanical dispersion, linear and nonlinear sorption, equilibrium and nonequilibrium sorption, poros
17、ity-dependent effective diffusion coefficient, and first-order decay reactions. Simulation results indicate that layered soil heterogeneity can have significant effects on both consolidation behavior and contaminant transport behavior. Characterization of a multi-layer soil stratum as a homogeneous
18、single layer with average properties may result in significant errors in the analysis of consolidation-induced contaminant transport in multi-layer soils. INTRODUCTION The phenomenon of consolidation-induced contaminant transport is observed in a variety of geoenvironmental engineering applications,
19、 including contaminant transport through landfill bottom liner systems during waste placement operations, confined disposal of dredged contaminated sediments, and subaqueous capping of contaminated sediments (Fox and Shackelford 2010). For these applications, contaminant transport processes involve
20、advection, dispersion, and sorption, which is *HR Li and Cleall 2011), very limited progress has been made in the area of coupled consolidation and contaminant transport in multi-layer soils. Recently, Pu and Fox (2015b) developed a piecewise-linear numerical model, called CST3, to model such proble
21、m. This paper provides an overview of the capabilities of the CST3 model. Then, numerical simulations were performed using CST3 to illustrate the effects of layered soil heterogeneity on the consolidation results and associated contaminant transport results. The errors for modeling multi-layer soils
22、 as a homogeneous single layer were discussed for the analysis of consolidation-induced contaminant transport in multi-layer soils. MODEL DESCRIPTION CST3 was developed on the basis of the CS2, CS3 and CST2 models and follows similar procedures with regard to geometry, effective stress, fluid flow,
23、settlement, and contaminant transport. The CST3 model and its predecessors have undergone extensive validation, including comparisons with experimental data (e.g., Fox and Berles 1997; Fox 2007b; Fox and Lee 2008; Lee and Fox 2009; Pu and Fox 2015b). Only a brief summary is provided below. A saturat
24、ed compressible soil stratum has initial height ToH , contains iR horizontal layers, and is treated as an idealized two-phase material in which the solid particles and pore fluid are incompressible. The initial geometry, prior to application of surcharge load at time t = 0, is shown in Fig. 1. The s
25、tratum is sufficiently wide such that all quantities vary only in the vertical direction and consolidation can be treated as one-dimensional. Vertical coordinate z and layer coordinate i are defined as positive upward from a fixed datum at the bottom of the stratum. Each layer i has initial height ,
26、oiH and the solid phase of layer i is represented as a column of ,j iR vertical solid elements, and thus the total number of solid elements for the stratum is ( ),1iRTs j iiR R=. Layer elevation coordinate iz and layer solid element coordinate j are defined as positive upward from the base of each l
27、ayer. Each solid element j of layer i has unit cross-sectional area (plan view), initial height ,soiL , a central node at initial elevation ,soi jz , and initial void ratio ,oi je . Nodes translate vertically and *HR (b) relative contaminant mass outflow. Fig. 3a compares profiles of excess pore pre
28、ssure exu at t = 0.1, 1, and 5 yr. At t = 0, the initial excess pore pressure is equal to the applied surcharge (= 150 kPa) across the entire stratum. Excess pore pressures then dissipate in response to the distribution of compressibility and hydraulic conductivity properties within the stratum. Pro
29、files of exu for the single-layer case display slight asymmetry due to the effect of soil self-weight, whereas corresponding profiles for the three-layer case show much greater asymmetry due to soil heterogeneity. With elapsed time, the lower hydraulic conductivity for layer 1 delays the dissipation
30、 of excess pore pressures for the three-layer case and causes the location of maximum exu to move toward the bottom boundary. Fig. 3b presents profiles of relative contaminant concentration /occ at t = 1, 10, and 50 yr. Profiles of /occ display smooth transitions between initially contaminated (uppe
31、r) and uncontaminated (lower) layers. Profiles for the single-layer case consistently indicate higher concentrations, which is consistent with Fig. 2b and reflects the higher sorption capacity of the initially contaminated layer for the single-layer case. Fig. 3b also indicates that the effects of s
32、oil heterogeneity on concentration profile increase with elapsed time. *HR (b) relative contaminant concentration. CONCLUSIONS CST3 is a numerical model for large strain consolidation-induced contaminant transport in multi-layer soils. The consolidation algorithm accounts for vertical strain, soil s
33、elf-weight, relative fluid velocity, changing material properties during consolidation, unload/reload, time-dependent loading and boundary conditions, external hydraulic gradient, variable preconsolidation stress profiles, and multiple soil layers with different material properties. The contaminant
34、transport algorithm accounts for advection, diffusion, mechanical dispersion, linear and nonlinear sorption, equilibrium and nonequilibrium sorption, porosity-dependent effective diffusion coefficient, and first-order decay reactions. Layered soil heterogeneity can have a significant influence on se
35、ttlement, excess pore pressure profile, contaminant mass outflow, and distribution of contaminant concentration within the soil stratum. Characterization of a multi-layer soil stratum as a homogeneous single layer with average properties may result in significant errors in both consolidation and con
36、taminant transport results. ACKNOWLEDGMENTS Financial support for this investigation was provided by Grant Nos. CMMI-1001023 and CMMI-1363230 from the U.S. National Science Foundation. This support is gratefully acknowledged. *HR Georgiadis et al., 2002; Vanapalli and Mohamed, 2007; Vanapalli et al.
37、, 2007, Taylan 2012). In this paper, in order to determine bearing capacity of shallow square foundations using unsaturated soil mechanics concepts, a research having two steps was carried out. As the first step of research necessary engineering properties of investigated soils have been computed in
38、 the laboratory. In the second step, obtained soil parameters from laboratory were used so as to find out pressure - displacement (i.e., q ) behavior of investigated foundation system by using of GeoStudio Sigma-W which is a commercial finite element program. The pressure - displacement analysis was
39、 investigated by using three different models. These models are: fully dry soil model, fully saturated soil model and unsaturated models. In the unsaturated models, the soil water characteristic curves belonging to the investigated samples are used. The equations of soil water characteristic curves
40、(SWCC) were obtained by tempe pressure cell and pressure plate tests. In the model analysis, unsaturated case had two different scenarios. The first one refers to ground water level beneath the designed surface as half of foundation width. The second one refers to ground water level beneath the desi
41、gned surface as foundation width. At the last part of the paper, the pressure - displacement relationships are given for different models, and a general result was presented. BACKGROUND Prandtl (1921) was one of the first researchers to propose a comprehensive theory for calculating the ultimate bea
42、ring capacity of shallow foundations. In his study, he determined ultimate bearing capacity of strip footing by laboratory work and he formulated the laboratory work as a mathematical equation (Gulsen, 2014). After Prandtl, many researchers such as Terzaghi (1943), Meyerhof (1963), Hansen (1970) and
43、 Vesic (1973) have proposed different theories for predicting the ultimate bearing capacity. These theories have a notice for the estimation a shallow foundations bearing capacity using the general pattern of a foundation system and possible failure curves in saturated or dry soil profiles. Even tho
44、ugh these studies show basics of conventional bearing capacity understanding, these key studies dont deal with unsaturated case problems. In the unsaturated soil profiles, conventional bearing capacity theories generally consider bearing capacity loss related with the soil saturation. These equation
45、s include different values of unit weight of the soil () that comes due to total or partial submersion. However, other bearing capacity parameters such as the effective cohesion (c) and the effective internal friction angle () are usually assumed too less important role. With this understanding, Ter
46、zaghi and Peck (1948) suggested that the bearing capacity of shallow footings could be nearly reduced *HR Oh et al., 2012; Gulsen and Senol, 2014 ) ()( ) = + uuuaaw(2) where is effective stress of an unsaturated soil, (n- ua) is net normal stress, (ua- uw) is matric suction and Bishops effective str
47、ess parameter. The value of , as suggested by Bishop, is simply the degree of soil saturation, and leads to = 1 (or the change in effective stress is equal to the change in pore-water pressure regarding the prevailing air pressure) for the saturated state and = 0 (or change in effective stress is ze
48、ro) for the dry state (Oh et al., 2012). With the aim of identify behavior of unsaturated soils, Frendlund and Raharjo (1993) made two common scenarios of pore pressure distribution profiles which are illustrated in Figure 1 that includes unsaturated analyses and conventional analyses. Profile 1 dis
49、plays the variation of matric suction above the ground water table, whereas Profile 2 is conventional analyses ignoring the influence of matric suction (Figure 1). For unsaturated soil profile, three different negative pore-water pressures distribution assumptions are possible. These are excessive evaporation condition (I), hydrostatic condition (II) and flooding desiccated soil condition (III). Fredlund and Rahardjo (1993) are given a shear strength equation for unsaturated soils for Profile 1 show
