Overview and Interpretation of Rate-Dependency of the Behaviour of Soft Clays
Z. X. Wu1, Q. Y. Zhu2 and Z. Y. Yin3
1,3Department of Geotechnical Engineering, Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China. LUNAM University, Ecole Centrale de Nantes, Nantes, France
2State Key Laboratory for Geomechanics & Deep Underground Engineering, China University of Mining & Technology, Xuzhou,China
3E-mail: zhenyu.yin@gmail.com
ABSTRACT: Extensive laboratory tests and field observations show that soft clays exhibit significant rate-dependent behavior. The rate-dependency of stress-strain behavior under both 1D and 3D conditions is firstly reviewed. The applicability of five rate-dependency equations in correlating the pre-consolidation pressure and undrained shear strength is also discussed. Furthermore, the rate-dependency of the behaviour of soft clays under complex loading conditions is analysed. Finally, the uniqueness of the rate-dependency under different conditions, i.e. between 1D and 3D, between triaxial compression and extension, between different OCRs is investigated.
KEYWORDS: Pre-consolidation pressure, Shear strength, Rate-dependency, Stress-dilatancy, Over-consolidation ratio
Overview and Interpretation of Stress-Relaxation of Soft Clay
L. Ye1, Q. Y. Zhu2, J. X. Liu3, P. P. Sun4 and Z. Y. Yin5
1Department of Civil Engineering，Zhejiang University of Science and Technology, Hangzhou 310012, China
2State Key Laboratory for Geomechanics & Deep Underground Engineering, China University of Mining & Technology, Xuzhou, China
3,5Department of Geotechnical Engineering, Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China. LUNAM University, Ecole Centrale de Nantes, Nantes, France
4Department of Civil Engineering，Zhejiang University of Water Resources and Electric Power，Hangzhou 310018, China
5E-mail: zhenyu.yin@gmail.com
ABSTRACT: Extensive laboratory tests and field observations show that soft clay exhibits significant stress relaxation characteristics. The evolution of pore pressure and stress of soft clays under both 1D and 3D stress relaxation tests was first studied based on published data from the view of the influence of strain rate and strain level prior to the relaxation phase. The relationship between parameters related to stress relaxation and liquid and plastic limits were discussed. Then, the stress relaxation behavior of soft clays under complex stress conditions was also analyzed. Furthermore, based on stress relaxation curves on double logarithmic plane, the stress relaxation coefficient was originally proposed, and an analytical solution of 1D stress relaxation was derived, which unified three time-dependent characteristics with their key parameters. Finally, the stress relaxation characteristics of soft clay were investigated from the aspect of stress-dilatancy of Hong Kong Marine clay under triaxial extension and stress relaxation conditions with some typical stress-dilatancy equations.
KEYWORDS: Soft clay, Stress relaxation, Rate-dependency, Stress-dilatancy
Modeling Undrained Shear Behavior of Reconstituted Clays considering the Effects of Initial Water Contents
X. Bian1, L. L. Zeng2, J. W. Ding3 And Z. S. Hong4
1Institute of Geotechnical Engineering, College of Civil and Transportation Engineering, Hohai University, Nanjing, China
2Institute of Geotechnical Engineering, College of Civil Engineering, Fuzhou University, Fuzhou, China
3,4Institute of Geotechnical Engineering, School of Transportation, Southeast University, Nanjing, China
1E-mail: bianxia2010@gmail.com
ABSTRACT: This paper presents a new model for describing the undrained shear behavior of reconstituted clays due to the variation of initial water contents based on the concept of critical state soil mechanics. With the decrease of initial water contents, the reconstituted clays behave enhanced strength, stiffness and dilation, which are not involved in the Modified Cam Clay model. These features can be captured by introducing a new hardening parameter (‘quasi-structure’ strength) into the conventional critical state model. The ‘quasi-structure’ strength increases with the decrease of initial water contents. The available test data on the undrained shear behavior of reconstituted clays at different initial water contents are used to verify the proposed model, and the comparisons between computed and measured results show that the proposed model is able to predict the overall pattern of stress-strain curves, pore pressure variations and effective stress paths reasonably well, especially the ultimate undrained strength and pore pressure response at large strain.
KEYWORDS: Reconstituted clay, Initial water content, Constitutive modeling, Critical state.
Statistical Analysis on Physical Properties of Shanghai Soft Clay
Y. M. Lu1, Y. F. Jin2, S. L. Shen3, F. Yu4 and J. Zhang5
1,2,3Department of Civil Engineering and State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai200240, China
2,4Research Institute in Civil and Mechanical Engineering, Ecole Centrale de Nantes, Nantes 44300, France
5Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China
3E-mail:slshen@sjtu.edu.cn
ABSTRACT: This paper studies the statistical properties of the basic physical parameters of the Shanghai soft clay based on data obtained from extensive literature review and tests conducted by the authors. With the database compiled, the statistics of these parameters are assessed, and regression analyses are conducted to obtain the empirical relationships among them. The goodness-of-fits of normal distribution, log-normal distribution, exponential distribution and uniform distribution are assessed for each parameter using the Kolmogorov-Smirnov (K-S) method. The results show that the normal distribution is suitable for initial water content, specific gravity, plasticity index, liquidity index and unit weight, the log-normal distribution is suitable for initial void ratio and plastic limit, the exponential distribution is suitable only for liquid limit, and the uniform distribution is not recommended.
KEYWORDS: Soft clay, Physical properties, Statistical analysis, Distributional function
A Review of the Dynamic Behaviour of Frozen Soils
S. Wang1, J. Qi2 and Z. Y. Yin3
1,2Institute of Geotechnical Engineering, Xi’an University of Technology, Xi’an Shaanxi, 710048, China
2State Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou Gansu 730000, China
3Department of Geotechnical Engineering, Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China. LUNAM University, Ecole Centrale de Nantes, Nantes, France
Email: wangsonghe@126.com
ABSTRACT: The dynamic response of frozen soils is one of the significant factors that should be taken into account when designing and constructing infrastructures in cold regions. This paper firstly reviews the state-of-the-art dynamic testing techniques including dynamic uniaxial/triaxial test, resonant column test, wave velocity test and the SHPB test. Then the correlations of dynamic indexes for frozen soils with test conditions are analyzed i.e., dynamic modulus, dynamic strength, damping ratio as well as dynamic Poisson’s ratio. The typical stress-strain relationships for frozen soils under dynamic loading are summarized such as empirical models, creep modeling and strength criterion for frozen soils. Finally promising prospects of the study in this paper is suggested.
KEYWORDS: Frozen soils, Dynamic modulus, Dynamic strength, Damping ratio, Empirical model
Influence of Mineral Constituents on One-dimensional Compression Behaviour of Clayey Soils
L. Ye1, Y. F. Jin2*, Q. Y. Zhu3 and P. P. Sun4
1Department of Civil Engineering，Zhejiang University of Science and Technology, Hangzhou 310012, China
2Department of Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
3State Key Laboratory for Geomechanics & Deep Underground Engineering, China University of Mining & Technology, Xuzhou,China
4Department of Civil Engineering，Zhejiang University of Water Resources and Electric Power，Hangzhou 310018, China
E-mail: jyf07507108@126.com
ABSTRACT: Only few data are available concerning the effect of the four main clay minerals, kaolinite (K), illite (I), montmorillonite (M) and chlorite (C), on the mechanical properties of clayey soils. This paper discusses the effect of different mineral contents on the compression and swelling indexes of clay mixtures in order to provide correlations between the mineralogical content of a clayey soil and its compressive properties. Four pure clay powders were used to prepare 34 clay mixtures (different proportions of K+I, K+I+M, K+I+C). Conventional oedometer tests were conducted on all the prepared samples. Based on the test results, the evolution of the compressive properties with the proportions of pure clays was estimated and relevant correlations are suggested. All the results demonstrate that the compression and swelling indexes are reasonably well correlated to the proportion of clay minerals. The content in montmorillonite influences significantly the compressive properties of clayey soils, and the contents of illite and chlorite are less influential when added to kaolinite based clayey soils. Moreover, 15 samples with different proportions of K+I+M+C were prepared and tested, and the proposed correlations were validated in light of the results obtained on these materials.
KEYWORDS: Kaolinite, Illite, Montmorillonite, Chlorite, Compression index, Swelling index.
Effects of Addition of Fine-grained Zeolite on the Compressibility and Hydraulic Conductivity of Clayey Soil/Calcium-Bentonite Backfills for Vertical Cutoff Walls
R. D. Fan1, Y. J. Du2, S. Y. Liu3
1,2,3Institute of Geotechnical Engineering, Southeast University, Nanjing, China
2Key Laboratory of Geotechnical and Underground Engineering, Tongji University, Shanghai 200092, China.
E-mail: duyanjun@seu.edu.cn
ABSTRACT: Vertical cutoff walls, using backfill consisting of on-site sandy soil and Na-bentonite are widely used as engineering barriers for the purpose of achieving relatively low hydraulic conductivity and high contaminant sorption capacity. At some sites, locally available clayey soil, Ca-bentonite and natural zeolite may be considered as an alternate backfill. However, studies on the compressibility and hydraulic conductivity of zeolite-amended clayey soil/Ca-bentonite backfills for vertical cutoff walls are very limited. A series of onedimensional consolidation tests is performed to evaluate the compressibility and hydraulic conductivity of fine-grained zeolite-amended clayey soil/Ca-bentonite backfills. Kaolin is used as the control clayey soil, and it is amended with various amounts of Ca-bentonite (5, 10, and 15%) and zeolite (2 – 40%) to prepare zeolite-amended kaolin-bentonite backfills. The results indicate that the addition of fine-grained zeolite has insignificant influence on the compressibility and hydraulic conductivity of clayey soil/Ca-bentonite and sandy soil/Na-bentonite backfills. The hydraulic conductivity of the zeolite-amended clayey soil/Ca-bentonite backfills is generally lower than the typical regulatary limit of 10-9 m/s. Two empirical methods, based on the Nagaraj’s generalized void ratio (e/eL) and Sivapullaiah et al.’s method, are assessed to predict the hydraulic conductivity of the backfills. The proposed method based on the Sivapullaiah et al.’s method is shown to estimate the hydraulic conductivity for the fine-grained zeolite-amended clayey soil/Ca-bentonite backfills with reasonable accuracy.
KEYWORDS: Bentonite, Cutoff wall, Hydraulic conductivity, Soil-bentonite backfill, Zeolite.
Strength of Lime-Treated Fly Ash Using Bentonite
S. Deka1, S. K. Dash2 and S. Sreedeep3
1Department of Civil Engineering, Tezpur University, Tezpur, India
2Department of Civil Engineering, Indian Institute of Technology, Kharagpur, India
3Department of Civil Engineering, Indian Institute of Technology, Guwahati, India
E-mail: shailendeka@yahoo.co.in
ABSTRACT: Fly ash has many bulk applications; but Class ‘F’ fly ash being non-cohesive, has to be strengthened or reinforced when used in structural fills. Portland cement and lime are the usual additives for strengthening fly ash. The strength from such additions comes from pozzolanic reactions. In this study, bentonite was used to augment pozzolanic reactions of fly ash with lime, producing very high unconfined compressive strength exceeding 7000 kPa. The strength increased by 88% because of 20% addition of bentonite at the optimum lime content of 13% by weight. There was no adverse effect in terms of swell after adding bentonite. The addition of bentonite also increased the elastic modulus of fly ash-lime combine.
KEYWORDS: Fly ash, Lime treatment, Bentonite, Unconfined compressive strength, Soil stabilisation
Soil Deformation Induced by Underground Tunnel Construction
L. Wang1, *R. Liu2, and G. G. Wang3
1,2State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 300072, China
3The Third Railway Survey and Design Institute Group Corporation, Tianjin 300142, China
Email: 375217932@qq.com
ABSTRACT: Development and utilization of underground railways can effectively ease the problem of urban traffic congestion. However, surrounding soil disturbance during tunnel excavation is likely to cause serious accidents. Thus, analyzing soil deformation during tunnel excavation is important. Through numerical simulation, this paper analyzes the influence of the step distance of a single-bore tunnel on the disturbance of the surrounding soil. Based on research on a single-bore tunnel, this paper further examines the effects of various spacing, locations, and excavation methods on the deformation of surrounding soils during parallel tunnel excavation. The results show that longer excavation steps lead to more intense disturbance to the surrounding soils. The most intense disturbance occurs at the ends of the tunnel. During new tunnel excavation, the tunnel crossing angle has stronger influence than the tunnel spacing on the original tunnel. Among the four excavation methods, single-bore advanced through is the most secure, whereas simultaneous excavation from opposite directions can cause the most intense disturbance to the surrounding soils. In practical operations, corresponding excavation methods can be employed according to specific conditions. Moreover, in-situ monitoring at key positions should be enhanced to avoid accidents.
KEYWORDS: Parallel tunnels; Numerical simulation; Excavation space; Tunnel spacing; Tunnel crossing angle; Soil deformation
Full-Scale Field Tests on Soil Arching Triggered during Construction of Shallowly Buried HDPE Pipes
M. Zhou1, Y. J. Du2* and F. Wang3
1,2,3Institute of Geotechnical Engineering, School of Transportation, Southeast University, Nanjing, China
E-mail: duyanjun@seu.edu.cn
ABSTRACT: Soil arching significantly affects earth pressures around and above high-density polyethylene (HDPE) pipes in the construction phase. However, few studies have systematically addressed the change of soil arching with respect to soil cover thickness during the installation of HDPE pipes. This paper presents full-scale field investigations on the soil arching above and around three HDPE pipes buried shallowly in trenches. The results demonstrate that the soil arching developed in the backfill above the pipes is getting significant with increasing soil cover thickness. At a given soil cover thickness, more notable soil arching is found at a position closer to the pipe crown. The measured earth pressures acting on the pipe crown are compared with those estimated by the Marston load theory. It is found that the crown earth pressures estimated by the Marston’s trench equation and embankment equation are 8% to 32% and 2% to 14% respectively higher than those obtained from the field tests. The results suggest that a threshold trench width is likely to exist when the Marston load theory is used for calculating the earth pressures on the top of HDPE pipes buried in the trench.
KEYWORDS: HDPE pipe, Field test, Soil arching, The Marston load theory.
A Pollutant Migration Model Considering Solute Decay in Layered Soil
C. Yu1 and X. Q. Cai2
1College of Architecture and Civil Engineering, Wenzhou University, Wenzhou 325035, China
2College of Chemistry and Materials Engineering,, Wenzhou University, Wenzhou 325035, China
E-mail: geoyuchuang@163.com
ABSTRACT: Organic pollutant solute undergoes significant decay during the migration process in clay liner systems and foundation clay. Liner and foundation soil have layered properties. A one-dimensional computational model is established to calculate pollutant migration by considering the decay in layered soil medium. The separation of variable method is used to obtain the analytical solution. To verify the capability of the developed method, a typical example is illustrated by applying this model. The calculated results are compared with the results obtained from the GAEA GAEA Pollute v7. Consistent results demonstrate the reliability and validity of the proposed migration model, which can be a promising tool for landfill liner design when considering the organic pollutant decay.
KEYWORDS: Pollutant migration, Layered soil, Decay, Analytical solution, Numerical validation.
Effect of Cyclic Strain History on Shear Modulus of Dry Sand using Resonant Column Tests
J. Kumar1 and C. C. Achu2
1,2Department of Civil Engineering, Indian Institute of Science, Bangalore-560012, India
1E-mail: jkumar@civil.iisc.ernet.in
2E-mail: achucc@civil.iisc.ernet.in
ABSTRACT: A number of resonant column tests were performed on dry sand specimens to examine the effect of cyclic shear strain history, by including both increasing and decreasing strain paths, on the shear modulus (G) for different relative densities (Dr) and confining pressures (σ3). The specimen was subjected to a series of cycles of increasing and decreasing shear strain paths approximately in a range of 0.001-0.1%. For a particular cycle, with a given strain amplitude, the shear modulus during the increasing strain path becomes always greater than that during the decreasing strain path. For a given cycle, irrespective of relative density of sand, the difference between the values of G associated with the increasing and decreasing strain paths becomes always the maximum corresponding to a certain shear strain level. The maximum reduction in the shear modulus, due to the cyclic variation of the shear strain, was noted to be around one fourth of the maximum shear modulus (G0). This reduction in the shear modulus on account of the cyclic variation of shear strain increases generally with decreases in the values of both relative density and confining pressure. The study will be useful to examine the response of sand media subjected to earthquake excitation.
KEYWORDS: Dynamic properties, earthquakes, resonant column tests, sands, shear modulus, vibrations.
Vertical Uplift Capacity of Circular Anchor Plates
P. Bhattacharya1 and J. Kumar2
1Department of Civil Engineering, Indian Institute of Technology, Kharagpur, India
2Department of Civil Engineering, Indian Institute of Science, Bangalore, India
E-mails: paramita@civil.iitkgp.ernet.in, jkumar@civil.iisc.ernet.in
ABSTRACT: Experimental and numerical investigations have been carried out to determine the vertical uplift resistance of circular anchor plates embedded in cohesionless soil media. Experimental studies are performed on model circular anchor plates placed at different depths in loose to medium dry sand deposit for two different relative densities, namely, 25% and 65%, respectively. The numerical work has been done by using an axisymmetric lower bound limit analysis in conjunction with finite elements and linear programming to compute the uplift resistance offered by circular anchor plates embedded horizontally in sand. In the case of numerical studies, the internal frictional angle of sand was varied from 20o to 45o. Both experimental and numerical studies clearly reveal that the uplift resistance of the circular plate increases considerably with increases in embedment ratio (H/D), and soil frictional angle(ø). The deformation of the anchor plate, corresponding to the failure load, increases with an increase in the values of H/D and relative density of sand. The values of the failure loads obtained from the computational analysis match well with the present experimental results as well with the available data from literature.
KEYWORDS: Circular anchors, failure, load deformation response, limit analysis, sand.
Prediction of Ground Surface Settlements Caused by Deep Excavations in Sands
B. C. B. Hsiung1 and S. D. Dao2
1,2Department of Civil Engineering, National Kaohsiung University of Applied Sciences,
415 Chien-Kung Road, Kaohsiung City, 807, Taiwan
2E-mail: sydandao@gmail.com
ABSTRACT: The objective of this paper is to evaluate the applicability of a simple method for predicting movements, especially the ground surface settlements, caused by deep excavations in sands. A case history of deep excavation in thick layers of sand in Kaohsiung, Taiwan was adopted as a basis for numerical analyses. In order to improve the inconsistence in prediction of ground surface settlements induced by the deep excavation, the analysis using the simple constitutive model but with additional two factors, α and β is applied. The factor α defines the width of primary strain zone behind the retaining wall, and β indicates the difference of soil stiffness in two zones of the primary strain zone and small strain zone. It is concluded that changing α seems not to induce significant change, and values of β from 3 to 5 shall be taken once such approach intends to be adopted for predicting ground surface settlements caused by deep excavations in sands.
KEYWORDS: deep excavation; sand; numerical analysis; ground surface settlement.
SPECIAL FEATURE STORY ON “Soil Mechanics at Emmanuel College – Elegant, Rigorous and Relevant”
J. Burland
Imperial College London
E-mail: j.burland@imperial.ac.uk
ABSTRACT: This paper was first presented by the author as a lecture at Emmanuel College, Cambridge in 2005 and was published in the College Magazine. Intended for non-experts it celebrates the contributions made to Soil Mechanics by Professor Ken Roscoe and many of his students at Emmanuel College. The author had the good fortune to be at Cambridge under Roscoe’s supervision at a very important time when the basic concepts of Critical State Soil Mechanics were being developed. The paper focuses as much on the personalities of the key players as on their technical contributions.
KEYWORDS: Critical State, K.H.Roscoe, Simple Shear Apparatus, True Triaxial Apparatus, Camkometer, Leaning Tower of Pisa
SPECIAL FEATURE STORY ON “Ground Improvement Methods for Port Infrastructure Expansion”
B. Indraratna1, A. Heitor2 and C. Rujikiatkamjorn3
1Prof. and Director, Centre for Geomechanics and Railway Engineering, University of Wollongong, Wollongong, Australia
2Lecturer, Centre for Geomechanics and Railway Engineering, University of Wollongong, Wollongong, Australia
3Assoc. Prof., Centre for Geomechanics and Railway Engineering, University of Wollongong, Wollongong, Australia
1E-mail: indra@uow.edu.au
ABSTRACT: The demand for reliable and efficient transport infrastructure is vital to sustain Australia’s economic growth and quality of life. Due to the forecasted increase in the freight trade demand, existing Ports will need to undergo major expansion, e.g. for accommodating berths suitable for bulk cargoes and container handling. To maximise the use of available land, typically port expansions projects involve land reclamation which includes the use of dredged materials (e.g. Port of Brisbane) or other granular fill materials locally available (e.g. Port Kembla). In both situations, ground improvement methods need to be implemented to ensure the fills and the foundations for the port infrastructure have sufficient shear strength and bearing capacity to comply with serviceability requirements in terms of settlement and lateral displacements. In this paper, typical ground improvement methods employed in Port infrastructure are described and their application in two different Australian Port Infrastructure projects is discussed.
KEYWORDS: Port infrastructure, Port expansion and reclamation, Prefabricated vertical drains, Granular waste materials.
