RESEARCH ON MECHANICAL PROPERTIES OF QUATERNARY SEDIMENTS DISTRIBUTED IN HANOI AREA UNDER DYNAMIC LOADS

MINISTRY OF EDUCATION AND TRAINING UNIVERSITY OF MINING AND GEOLOGY NGUYEN VAN PHONG RESEARCH ON MECHANICAL PROPERTIES OF QUATERNARY SEDIMENTS DISTRIBUTED IN HANOI AREA UNDER DYNAMIC LOADS Specialty: Geological Technology Code: 62.52.05.01 SUMMARY OF DOCTORAL THESIS IN GEOLOGY HANOI - 2016 The research has been accomplished at: Engineering Geology Department, Faculty of Geosciences and Geoengineering, Hanoi University of Mining and Geology Supervisors: Assoc Prof Dr Le Trong Thang Hanoi University of Mining and Geology Reviewer 1: Dr Nguyen Viet Tinh Hanoi University of Mining and Geology Reviewer 2: Assoc Prof Dr Doan The Tuong Vietnam Institute for Building Science and Technology Reviewer 3: Assoc Prof Dr Do Minh Duc University of Sciences, Vietnam National University This thesis is going to be defended at the committee of doctorate thesis examiners of Hanoi University of Mining and Geology, Duc Thang ward, Bac Tu Liem district, Hanoi, Vietnam on 08:30 date … month… year 2016 This thesis can be found at National Library, Ha Noi or Library of Hanoi University of Mining and Geology INTRODUCTION The urgency of the subject Dynamic loads are temporary and generated by two sources: natural sources (earthquakes, collapsed caves, slides, ) and artificial sources (machines, hammers, transportation, ) The research on soil mechanical properties under dynamic load (referred to as "dynamic properties") is very important in the design foundation Hanoi is the Capital of Vietnam with a population of greater focus, along with strong growth in economy, the construction activities are developing and giving rise various types of dynamic loads In addition, Hanoi is located in the 7-8 earthquake zone, some places are As a greater construction, the impact of earthquakes and other seismic are also increasing Other hand, the loads (static and dynamic) decrease with the depth Whereas, the upper ground layers in Hanoi area are mainly sediments of the Holocene, Pleistocene of Hai Hung, Thai Binh and Vinh Phuc formations, these soils are quite sensitive to the effects of dynamic loads However, the information about the dynamical properties of these soils are not sufficient for the research, planning, designing and constructing of building foundation Therefore, “research on mechanical properties of quaternary sediments distributing in the Hanoi area under dynamic loads” is urgent and topical Objectives Determining the soil dynamical properties, including strength and deformation of typical soils in the research area, as well as their variations, in order to serve the research, planning, designing and constructing of building foundation purposes under dynamic loads Object and scope The objects of the study are the dynamical properties of (cohesive and granular) soils belong to Hai Hung, Thai Binh and Vinh Phuc formations Scope areas of the study are the regions of urban districts and Thanh Tri district of Hanoi City Contents - An overview of soil dynamics; - Research on the theoretical basis of soil dynamical properties; - Engineering geological characteristics of Quaternary sediments in Hanoi area and the methods to study dynamical properties of the soil; - Experimental study of dynamical properties of Quaternary sediments in Hanoi area The approach and methodology + The approach: - Systematic approach: The problems are detected from the practice; research in an integrated way to find out the theoretical models and methods; identifying suitable ones; studied by experiment, synthesis and analysis of results to solve the problems - Inherited approach of knowledge and experiences selectively in the dynamics studies - Combining theory and experiment + Methodology: - Synthetic and codified methods of documents on: soil dynamics studies in and outside the country in order to detect the studied problems; geological and engineering geological studies in the area to clarify the objects and scope of the study - Theoretical methods: to find the rules and the factors affecting the dynamic properties; - Geological methods: study of geological characteristics in the area; - Experimental methods: performing experiments to determine the physical and mechanical characteristics of the soil; - Mathematical - informatical methods: data processing Scientific and practical significances Contributions to the science: the research results contribute to clarifying the dynamical properties of the sedimentary formations in the area and the behavior rules of them under the impact of the dynamic force, to serve the planning and construction design; contribute to improving and systematizing the theoretical basis of dynamic properties; providing additional information necessary for following dynamical studies Contributions to practices and research: the research results are as a basis to build the processes, to select input parameters for dynamic triaxial testing; the research results are also as the basis data for solving the ground model with dynamic loads; supplying information for forecasting the risk of the ground under the effect of the earthquake and studying the effects of seismic activities on the geological environment and buildings The scientific arguments - Argument 1: the process of cyclic deformation of the soils was divided into four stages Each stage is characterized by a type of stress - strain loop and dynamical properties which depend on soil type, characteristics of the loads and stress conditions In particular, the linear limit of the deformation equivalents to the limit of volumetric strain - Argument 2: the cohesive soils in the research area are collapsed in the form of plastic slip Whereas, the saturated sands of the Vinh Phuc and Thai Bình formations can be liquefied or not depend on the correlation between particle size, density and the parameters of the dynamic forces The boundaries of cyclic resistance ratio (or liquefaction) of them are described by the expression based on Geniev theory with empirical coefficients of each soil Innovative aspects - The thesis has identified the cyclic deformation characteristics of the research soils based on direct experiments by cyclic triaxial test, and dynamic deformation has been divided into four phases based on evaluation methods of stress - strain graphs and loops; clarifying the difference between static and cyclic deformation - By the experimental data, the thesis has built up the expression that describing the variation of cyclic deformation of the soils in the research area The thesis also points out the similarities between the limit of linear deformation with the volumetric strain limit that is useful for further studies - The cyclic strength of cohesive soils and the liquefaction of fine sand in the research area are determined directly by cyclic triaxial test The concept of liquefaction is clarified on the basis of quantifying specific criteria, thereby the liquefaction possibility of fine sands is evaluated depending on the density - Using Geniev theoretical basis, the thesis has built up the expression combining theory and experiment to describe the rule of cyclic strength, and the experimental coefficients were determined for each soil type Thus, the rule of cyclic strength of each soils is described in a simple and clear way by mathematical expressions, that help the application of research results are more favorable - The thesis has predicted quantitatively the possibility of instability of soils under earthquake effects in the most adverse conditions based on reliable experimental coefficients of each soil Dissertation layout The contents of the thesis consists of chapters and illustrated with 56 tables, 99 figures and graphs, appendices, 14 research publications and items of 76 references 10 Database The thesis was completed on the basis of experimental data that is performed directly by the author, as well as the research results have been published in the Scientific - Technical journal of Mining and Geology (3 articles), Scientific conference Report of the university of Mining and Geology (3 articles) The contents of the thesis are inherited from the projects that were chaired by candidate PhD: T12-32; CTB 2012-02-03; and the project B12-0207 chaired by Assoc Prof Dr Le Trong Thang, the candidate PhD is participation The thesis is also the result of "Project of capacity strengthening of the Geotechnical Laboratory." Chapter OVERVIEW OF SOIL DYNAMICS STUDIES 1.1 The concept and contents of soil dynamics studies Soil dynamics is a part of Soil Mechanics, studies the behavior of soil under the effect of dynamic loads Its contents can be divided into groups: 1) Research on the effect of dynamic loads to changing the physical properties of the soil; 2) Research on soil strength and deformation under the effect of dynamic loads; 3) The research on models of the soil behavior with dynamic loads 1.2 Overview of the research status in the world The research on the change of soil properties under the effect of dynamic loads: the variation of soil cohesion force, friction angle (Porovski, 1934); void ratio and permeability coefficient changing (Barkan, 1962); the variability of microstructure, thixotropy phenomenon (Sukina, 1985) and undrained strength characteristics under dynamic loads (Cadagrander, Seed, Onxon, ) The research on the sand liquefaction: determining the relationship between the deviation of cyclic stress caused liquefaction with the duration of action (Seed and Lee, 1965); studying the variation of sand liquefaction and factors affecting by experiment (Seed and Idriss, 1971; Noorany and Uzdavines, 1989; Shamsher Prakash and Vijay K.puri, 2003; Sitharam, Ravishankar, Jayan Vinod, 2008); research on liquefaction of sand in different density and provided models of dynamic loads to determine the point of liquefaction (Ishihara, 1985); using the method of controlled deformation to study liquefaction (Sitharam, Ravishankar, Jayan Vinod, 2008); building the relationship between the ability of sand liquefaction with field test results (Seed and Alba, 1986; Ronald and Kenneth, 1999; Idriss and Bowlanger, 2004) The research on cyclic strength of cohensive soil: determining the collapsed point at the level of strain equal static collapse (Kokusho et al, 1971); research on cyclic strength of cohesive soil at the level of stress deviation close to damaging static stress (Ishihara, Nagao, and Mano, 1983; Ishihara and Kasuda, 1984); studying the variability of cyclic strength by Kenvin - Voit adjustment model (Geniev, 1997) The research on cyclic deformation of the soil: the theoretical basis based on Kelvin - Voit model (Barkan; Arnold Verruijt; Kenji Ishihara; Shamsher Prakash, ); studying the soil cyclic deformation in the elastic phase (Hardin, Richart, 1963; Stokoe, 1978; Grant and Brown, 1981; Hardin and Black, 1968; ), and in the linear and nonlinear phase (Ishihara, 1984; Vučetić, 1994; ); the variation of cyclic strain characteristics (Ishihara, 1984; Vučetić, 1994; Bratosin, 2002, ); the factors affecting the cyclic strain characteristics (Alarcon, Guzman (1989); Darendeli, 2001; ); the influence of the sample (Kumar and Clayton, 2007); the experimental relationships to determine Gmax according to the results of SPT, CPTU (Seed, Lee, Imai, ) The research on models of the soil behavior with dynamic loads: study modeling and parameter matrix (Miura, Masuda -1995; -1996 Naggar and Novak; ); modeling solution methods for ground – foundation system based on assumptions elastic deformation, equivalent linear deformation (Tamori, Kitagawa - 2001) and nonlinear deformation (Kusakabe, Yasuda -1994; Miura, Masuda – 1995) 1.3 Overview of the research status in Vietnam Studies in Vietnam also includes three groups: 1) Research on the effect of dynamic loads to changing the physical properties of the soil (Nguyen Huy Phuong and Tran Thuong Binh - 2006); 2) Evaluation of sand liquefaction of Thai Binh formation based on the results of SPT (Pham Van Ty et al - 1990); The study on the issue of dynamic consolidation, dynamic strength, sand liquefaction and evaluation of the sensitivity of the soil under the effect of the earthquake in Hanoi (Nguyen Huy Phuong et al - 2011); 3) The research on models of the soil behavior with dynamic loads: seismic zoning studies in Hanoi by Institute of Geophysics (1990); modeling studies the ground – pile system to calculate the transmission of seismic waves when driving pile (Pham Huy Tu - 2003); modeling the ground – pile under horizontal dynamic load (Ngo Quoc Trinh - 2014) 1.4 Comments and Recommendations 1.4.1 Commenting on the research results in the World The study results showed that the influence of the dynamic load to the variation of soil properties The study of sand liquefaction showed: the liquefaction occurs in saturated sandy soil; the rule of liquefaction is represented by the boundary of liquefaction resistance ratio There are two methods commonly used to study the cyclic strength of cohesive soils: surveying the relations of stress and strain at the strain threshold close to static collapse, and using dynamic loading in the stress deviation close to collapsed static stress; the variation of soil dynamic strength can be expressed in terms of Geniev theory The cyclic strain characteristics vary with the soil deformation and can be determined by many different experimental methods The studies of soil behavior model under dynamic loads are used to study transmission stress in the ground and the behavior of the ground - foundation system under dynamic loads 1.4.1 Commenting on the research results in Vietnam 1) Achieved results: These studies have adequately addressed the deserve attention issues in soil dynamics 2) Some restrictions: the theoretical basis of soil dynamics has not been systematized adequately; the dynamical characteristics of the soil have not been determined directly; The factor affecting the dynamic properties of the soil has not been studied; The study of soil behavior model has not used directly dynamical characteristics of the soil; 3) The issues should be studied in Vietnam: the theoretical basis of soil dynamical properties should be systematized sufficiently; the characteristics of soil dynamical deformation and strength (or liquefaction) should be experimented directly; and simultaneous identification of the rules of their variation (build up the boundary of dynamical resistance ratio), in service for the evaluation of work stability under dynamic loads and earthquake; build up behavior models of ground - foundation system under dynamic loads for each type of background structure (in an area), which uses the dynamic characteristic of the soil Based on the research objectives and domestic equipment conditions, this thesis focused on the first three issues based mainly on the results of cyclic triaxial test Chapter THE THEORETICAL BASIS OF SOIL DYNAMICAL PROPERTIES 2.1 Concepts, classification and calculation of dynamic loads The load that its eigenvalues change over time F = F (t) is known as dynamic load This load is temporary and is divided into types: circulatory, non-circulatory, harmonic, harmonic damping Harmonic load is described by a sinusoidal, while the circulatory load is described by a chain of harmonic oscillator Dynamic loads (or stresses) are calculated based on ground earthquake acceleration or other seismic forces For machine foundation, the load is determined by the eccentricity and the angular frequency of the machine 2.2 Soil dynamical properties and research models Soil dynamical properties are the ability of the soil to behave mechanically under the effect of dynamic load, including: cyclic deformation is the ability to change the shape and volume of the soil; cyclic strength is the ability of the soil bearing maximum stress in a certain period without being collapsed Cyclic deformation is studies based on Kelvin - Voigt model, along with oscillation theory of a degree of freedom system Cyclic strength can be studies based on Kelvin - Voigt adjustment models (elastic element is replaced with plastic elements) and Geniev theory 2.3 Theoretical basis of soil cyclic deformation Cyclic deformation theory based on the analysis of a degree of freedom system under harmonic oscillator force Accordingly, cyclic deformation of the soil is completely determined if known the dynamical characteristics, that are dynamic module (Gd) and damping ratio (D) The phases of cyclic deformation Based on the relationship between stress - strain, N M Ghexevanov divided soil deformation into three phases [9]: compaction phase; plastic deformation phase; sliding deformation phase In the cyclic deformation research, soil strain is divided into phase based on the degree of strain [75]: very small strain, the strain ( is smaller than the threshold of elastic strain (tl); small strain, when  is larger than tl and smaller than the threshold of volumetric strain (tv); medium to large strain: the strain  is larger than 10-2% to a few percent Based on the characteristics of each phase and mechanical models can be used, the thesis divided the soil deformation into four phases: elastic, assuming elastic (linear), elastic - plastic (non-linear) and slide (summarized in table 2.2) Table 2.2 The phrases of soil cyclic deformation The Deformation The model of Deformation Volume degree of characteristics the phases phrases change strain Change Type of loads Elastic (≤ tl) - very small No Assuming elastic tl ≤ ≤ tv linear (compaction) small Yes Yes Transportation, machine foundations, weak earthquakes medium Yes Yes Strong earthquake large No No (Gmin, Dmax) Strong earthquake Elastic - plastic non-linear tv (Ctb) > (Stb) > (Shh) > (Ytb) > (Yhh) The modulus of soils in linear phase (Gd-tt or Ed-tt) is decreasing order: (Svp) > (Cvp) > (Ctb) > (Shh) > (Stb) > (Ytb) ≈ (Yhh) Interpretation of the research results: - Dynamic load is temporary and changes over time, so that pore water does not have enough time to escape, and the process of compaction could not complete leads to dynamic deformation is small (large deformation module) In compaction phase, the soil is compacting with static deformation Covertly, dynamic deformation increases leading to Ed decreased - Stiff sandy clay belong to Thai Binh formation in natural state (Stb2) has low saturated degree, so that its capability of volumetric immediate reduction is greater than completely saturated soil (Stb1), that why Ed of (Stb2) 0.5% for Stb1) The ratio Ru begins to rise to a few percent for clayey soils and Ru > 10% for sandy soil In this phase, residual deformation is large; the lower saturation is the greater residual deformation - Sliding phase of (large deformation): graphs of strain and loop are form 3; the slope of stress - strain curve is very high; Specimen strain rises continuously to a few percent and make specimen collapsed Therefore, it is necessary to study cyclic strength in this phase Analysis of the variation of damping ratio D in different phases: Theoretically, D = in elastic phase and D = 0.637 at the stage of plastic deformation In assuming elastic phase and elastic – plastic phase, D increasing in line with cyclic strain The study results showed: - In linear phase, damping ratio D is common in the range (0.089 ÷ 0.115) for all research soils; - Nonlinear phase: damping ratio D is in the range (0.141 ÷ 0.223) for clayey soils and lower by (0.120 ÷ 0.128) for sands Overall, D depends mainly on cyclic strain The greater ability of soil instantaneous compaction (depends on the void ratio, saturation and composition) is the larger D: the void ratio of soils Cvp, Ctb, Svp is low then D is small; the ratio D of Yhh3 is high (D = 0.200), due to the organic matter content of this soil is greater than other soils The significance of research results: The results identify the parameters characterizing dynamic deformation for assuming elastic phase allow solve the model of soil behavior with dynamic loads under the assumption "equivalent linear deformation " The input parameters (Ed, D) are a constant corresponding to the degree of deformation Construction results of relationship between Ed and D with dynamic deformation (equations from 4.1 to 4.6) allow solve the model of soil behavior on the assumption of nonlinear deformation (input parameters are functions) Meanwhile, the research results will be more accurate 18 Chapter RESEARCH ON SOIL CYCLIC STRENGTH BY CYCLIC TRIAXIAL TEST 5.1 The study results of clayey soil strength The soil samples were tested with different amplitude of cyclic loads From the experimental results, building up graphs of stress, strain and the ratio of pore water pressure versus number of cycles (or time) Based on these graphs, the stress - strain curves by cycles were built and then determined the stress amplitude, as well as the cyclic stress ratio at the strain threshold of 0, 5%; 1%; 2% and 5% From these results, building the boundary of cyclic resistance ratio and empirical coefficients (a and b) corresponding to the different strain threshold for each soil After analyzing experimental data, determining the initial collapsed strain is a = 2%, collapsed strain a = 5% Determination results of empirical coefficients describing the boundary of cyclic resistance ratio for soils are as follows: * Yellowish grey, stiff sandy clay – Thai Binh formation (Stb2) - Initial collapsed threshold (2%): a = 0,231; b= 3,8 (s) - Collapsed threshold (5%): a = 0,258; b= 10,5 (s) * Blackish grey, soft sandy clay – Thai Binh formation (Ytb) - Initial collapsed threshold (2%): a = 0,194; b= 1,4 (s) - Collapsed threshold (5%): a = 0,249; b= 1,9 (s) * Bluish grey, firm clay – Hai Hung formation (Shh) - Initial collapsed threshold (2%): a = 0,243; b= 1,6 (s) * Blackish grey, soft sandy clay – Hai Hung formation (Yhh) - Initial collapsed threshold (2%): a = 0,167; b= 1,5 (s) - Collapsed threshold (5%): a = 0,212; b= 2,0 (s) * Reddish brown, very stiff sandy clay – Vinh Phuc formation (Svp) - At strain threshold 0,5%: a = 0,636; b= (s); (Tested with stress amplitude is greater than 1.5 times the dynamic stress due to the biggest earthquake in the area, the soil specimen has not been collapsed and the largest strain is 0,704 %) The significance of the empirical coefficients a and b: the coefficient a equal to the minimum CSR (cyclic stress ratio) that can cause cyclic collapse (reaching the threshold of collapsed strain as time progresses to infinity); the coefficient b is inversely proportional to the chamber pressure (coefficient ) and proportional to the viscous resistance of the soil (inversely proportional to o) When td = b, then CSR = 1,74a Thus, b is considered to the period of time necessary to cyclic deformation reaching the collapsed deformation in stress ratio CSR = 1,74a  19 5.2 Research results on the possibility of sand liquefaction There are a variety of sands belong to different formations in study area In particular, fine sand of Thai Binh (Ctb) and Vinh Phuc (Cvp1) formations has an wide distribution and sensitive to the effects of dynamic loads These sands are likely to be liquefied under the effects of dynamic loads Therefore, the content of this section focused on the liquefied possibility of two sands Saturated sand is liquefied when Ru = 100% and there are dramatically change appearances of stresses and strains Sand specimens were prepared by dry vibration method in a membranelined split mold attached to the bottom platen of the triaxial cell Then, specimens were saturated by back pressure and consolidated by the chamber pressure The specimens were tested with different amplitude of cyclic loads Based on experimental results, building the graphs of stress, strain and the pore pressure ratio versus cycles The liquefied point is determined based on the analysis of these graphs 5.2.1 Research results of soil liquefaction for fine sand of Thai Binh formation (Ctb) Sand specimens were tested at the density Dr = 0.53 ± 0.2 (medium dense) Experimental results showed that the specimens be liquefied at a relatively strain = (5 ÷ 8)% and the strain amplitude = (1.5 ÷ 3)% The empirical coefficients of the liquefied boundary for Ctb is; a = 0.315; b = 10s 5.2.2 Research results of soil liquefaction for sands of Vinh Phuc formation (Cvp) Fine sand (Cvp1): The density of specimens were prepared in two categories: specimens Cvp1-1, Cvp1-3, Cvp1-5 in loose density (Dr = 0.26 ± 0.1) and specimens Cvp1-2, Cvp1-4 in medium dense (Dr = 0.35) The results showed that: at the time of liquefaction, relatively strain = (4 ÷ 6)% and the strain amplitude = (3 ÷ 4)% The empirical coefficients of the liquefied boundary for Cvp1: a = 0.185, b = 3,5s for loose density and a = 0.221; b = 5s for medium dense (Dr = 0.35) Medium grained sand (Cvp2): Specimen was tested in a simulated stress conditions for the actual conditions The density of the specimen is Dr = 0.802 Experimental results showed that the greatest ratio of pore pressure (Rumax) reached 95% at cycle of 340 The strain of the specimen is extension strain (a a (Stb)> a (Shh)> a (Y) Because the “a” is essentially a function of shear angle, so “a” dependent primarily on soil internal friction angle:  (Svp) = 21o >  (Stb) = 14o20’ >  (Shh)= 10o02’ >  (Y) = (8 ÷ 9)o The coefficient a does not depend directly on the initial stress conditions Coefficients b reflects the ability of viscous resistance of the soil and expressed in the latency of strain, so b increases with strain threshold At the same strain threshold, the soil with greater strength has greater b and opposite (creep resistant of stiff soil is better than soft soil): b (Svp) > b (Stb) > b (Shh) > b (Y) This rule is explained as follows: + The soil has higher cohesion, synonymous with higher viscous resistance and b is higher, too; + The void ratio of soils: eo (Svp) = 0.661 < eo (Stb) = 0.776 < eo (Shh) = 0.945 < eo (Y) = (1,270 ÷ 1,456) If void ratio of soil is high, then immediately strain is large and cyclic strain reaches strain threshold faster (b is smaller); Coefficients b is inversely related to chamber pressure 5.3.2 Variations of empirical coefficient of sand liquefaction by density The meaning and change rules of the coefficients a and b are the same as the clayey soil If two sands Ctb and Cvp are considered similar in composition particles (fine sand) and ignore the formation, it can determine the change rules of a, b by the density (Dr) as shown in Figure 5.29 Accordingly, a and b increase by density The directly proportional relations between a and b with Dr are almost straight line Based on the graph in Figure 5.29, the coefficients a and b can be determined easily for fine sand in the different density (in the range of Dr = 0.26 ÷ 0.53) 12 b (s) a 0.35 Hệ số b Hệ số a 10 0.30 0.25 0.20 0.15 0.10 0.05 0.2 0.25 0.3 0.35 0.4 Độ chặt Dr 0.45 0.5 0.00 0.55 Hình 5.29 Biến đổi hệ số a, b theo Dr 5.3.3 Characteristics of cyclic collapsed sand in the different density According to the test results of fine sands (Ctb, Cvp1) and medium-grained sand (Cvp2) in different density (loose, medium dense and dense), the characteristics of cyclic collapsed sands in the different density are as follows: 21 - Loose fine sand (Dr = 0.26): initially, Ru increases slowly and the amplitude of stress and strain did not change significantly when Ru increased by 60%, the stress amplitude began declining and strain amplitude began increasing quickly At the time of Ru =100%, strain amplitude reach the maximum value by (3 ÷ 4)% The modulus Ed has increased in the first few cycles due to sand is compacted, then pore water pressure increased as Ed decreased quickly to zero when Ru = 100% Thus, loose fine sand is completely liquefied when Ru = 100%; - Medium dense fine sand (Dr = 0,53 ± 0,2): experimental results showed that the increase of Ru and strain amplitude, and the attenuation of stress amplitude occurred as soon as loading; At the time of Ru =100%, strain amplitude reach the maximum value by (1.5 ÷ 3)% At this density, modulus Ed reduced as soon as loading and down to a minimum value of approximately 100kPa when Ru = 100% Thus, this sand is considered to be liquefied when Ru = 100% (this time, the soil is equivalent only as mud) Liquefied state of the specimens retained after the test ending; - Dense fine sand (Ctb-4, Dr = 0,70) and dense medium-grained sand (Cvp2, Dr =0,802) were not collapsed in the form of liquefaction In particular, cyclic strain of Cvp2 is extension strain 5.3.4 Practical significance of research results in the stable calculation of the ground under the effect of the dynamic loads Practical significance of dynamical resistance boundary (or liquefaction boundary) is especially important in the stable evaluation of ground under the effect of the dynamic loads Stability conditional of a point in the ground under the effect of dynamic stresses are evaluated based on this curve Accordingly, points are considered unstable (or liquefaction) if CSR> CSRgh, meaning the point of stress state is above the dynamic resistance curve Using the research results, the thesis has forecasted on the risk of losing stability of typical soils in the Hanoi area under the effect of earthquake based on the most unfavorable conditions (5.18) Calculation results in Table 5.18 shows: - At what point in the ground with only strata stress, the earthquake caused only CSR = (0.06 ÷ 0.07) In about this CSR and smaller, deformation of all soils in the study area is the elastic and linear deformation (small deformation); - In the given conditions (with building load), the fine sand in density Dr ≤ 0,35 (layer – Thai Binh formation and layer - Vinh Phuc formation) were liquefied Whereas the clayey soils and fine sand with Dr = 0.53 remained stable 22 Table 5:18 Calculation results and stable evaluation of the soils around the pile when earthquake has agr = 0.1097 Shear stress Dynamic resistance CSR (kPa) ratio (CSRgh) Soil Depth EvaluaInitial Extreme layer (m) Static Dynamic tion Dynamic Total threshold theshold d  CSRgh1 CSRgh2 4 0.07 0.14 0,28 0,46 stable 10 0.06 0.13 0,21 0,27 stable 0,56 (Dr=0,53) stable Lique0,28 (Dr=0,35) 10 34 0.06 0.36 fied Lique0,22 (Dr=0,26) fied 10 0.07 0.20 0,25 stable 5 0.07 0.15 0,17 0,23 stable 35 0.07 0.70 0,8 stable 0,56 (Dr=0,53) stable Lique0,28 (Dr=0,35) 12 34 0.06 0.32 fied Lique0,22 (Dr=0,26) fied - The stable evaluation results in Table 5.18 is appreciation for stability at a depth and in the given conditions When the input conditions change, stable evaluation results will be different, for example: fine sand with Dr = 0,53 will be liquefied if its depth is 5m (CSR = 0,56 = CSRgh); at a depth of 15m, fine sand with Dr = 0,35 is not liquefied (CSR = 0,27 0,42 have CSRgh> CSR = 0,36 then it will not be liquefied In fact, the piles are often designed through many different soil layers and at different depths, so the assessment of the overall stability of the pile is only done with the behavior model of groundpile system 23 CONCLUSIONS AND RECOMMENDATIONS Conclusions 1) Cyclic deformation of the research soils were divided into four phases: elastic, assuming elastic (linear), elastic - plastic (non-linear) and plastic (slide) Of these, the first three phases were studied under deformation problem The research results of theory and experiment showed: - Elastic phase: dynamic deformation is smaller than 10-4%; dynamic modulus is at the greatest value (Gmax); stress - strain loops are as a line and, damping ratio D is zero; - Assuming elastic phase (linear): graphs of strain and loop are the form 1; strain amplitudes threshold (a)gh varies from 0.018% to 0.030% for clayey soils, from 0.025% to 0.040% for soft soil, and equal 0.030% for sands, common is (a)gh = (0.020  0.030)%; damping ratio D of soils varies between 0.089 ÷ 0.115; - Elastic - plastic phase: graphs of strain and loop are form and Strain amplitudes threshold (a)gh at this phase varies from 0.4% to 1%; damping ratio D varies between 0,141 ÷ 0,223 for clayey soils and D = 0,120 ÷ 0,128 for sands; 2) The correlations between specific modules for soils are as follows: Gd-tt = (0,17 ÷ 0,22)Gmax, Gd-pt = (0,06 ÷ 0,07)Gmax, and Ed-tt = 5,6 ÷ 8,1 Eo for soft soils (Thai Bình and Hai Hung formation); Gd-tt = 0,10 Gmax; Gd-pt = 0,03Gmax; and Ed-tt = 2,1Eo for stiff sandy clay of Thai Binh formation; Gd-tt = 0,12Gmax, Gd-pt = 0,03Gmax, and Ed-tt = 2,5Eo for firm clay of Hai Hung formation; Gd-tt = 0,35Gmax; Gd-pt = 0,10Gmax, Ed-tt = 2,2Eo for very stiff sandy clay of Vinh Phuc formation; Gd-tt = (0,33 ÷ 0,43)Gmax, Gd-pt = 0,22Gmax, and Ed-tt = (3,9 ÷ 4,6)Eo for fine sand of Vinh Phuc formation; At the same level of deformation, the modulus of soil Svp > Stb > Shh > Ytb > Yhh; 3) Deformation characteristics of research soils vary by strain with a clear law: at the strain amplitude threshold of 0.01%, clay – sandy clay soil has Ed-tt(0,01) = 40±10 Mpa (the lower is soft soil and the upper is stiff soil), D(0,01) = 0,1 ± 0,02; at the strain amplitude threshold of linear (a ≈ 0,03%), Ed-tt(0,03) = 0,62Ed-tt(0,01); D(0,03) = 1,45D(0,01); at the strain amplitude threshold of sliding, Ed-tr = 0,06Ed-tt(0,01); Dtr = 2D(0,01) These results allow solving the behavior model of the ground under the assumption of equivalent linear deformation (input parameters are constant) The variation law of soil deformation characteristic is described by the correlation functions (3.3 to 3.8), and helps solving behavior model of the ground under the assumption of nonlinear deformation (input parameters are function) 4) Pore pressure ratio Ru of clayey soils is less than 1% in assuming elastic phase and increase to few percent in elastic – plastic phase; with sandy soil, Ru = (1-2)% in assuming elastic phase and increase to more than 10% in 24 elastic – plastic phase The study results also showed that linear strain threshold (agh is equal to volumetric strain threshold tv 5) The increase Ed by chamber pressure depends on the composition and consistence of the soil: sandy clay has greater ability to increase Ed than clay; the lower soil saturation is the greater increment of Ed Damping ratio D tends to decrease when the chamber pressure increases, but this is not obvious In the range of frequency smaller 10Hz, the influence of frequency to characteristics of cyclic deformation is negligible 6) Collapsed characteristics of research soils are as follows: - Clay, sandy clay were collapsed in the form of plastic slide with maximum Ru = (10 ÷ 20)% Saturated fine sand in loose and medium dense was collapsed in the form of liquefaction when Ru = 100% Fine sand was liquefied with strain amplitude = (1.5 ÷ 3)% for medium dense and equal (3 ÷ 4)% for loose dense Fine sand (Thai Binh formation) and medium-grained sand (Vinh Phuc formation) in dense consistence were not collapsed in the form of liquefaction - The collapsed point of clayey soil is determined based on the curve stress strain over time In particular, the initial collapsed point is determined corresponding to 2% of strain and 5% for determining the extreme collapsed point The collapsed point of saturated sands was determined by Rumax 7) Geniev theory can be used in conjunction with empirical research to determine the variation of soil dynamic strength (or dynamic resistance) By this method, dynamic strength of research soils is represented by the boundary of dynamic resistance ratio under the expression (2.43) with the empirical coefficients a and b (in tables 5.8 and 5.9) For clayey soil: coefficient a is directly proportional to the friction angle of the soil; coefficient b is directly proportional to the cohesive force of the soil For sands, the coefficients a and b increase with density 8) When an earthquake occurs with greatest ground acceleration: loose – medium dense, saturated fine sand of Thai Binh, Vinh Phuc formations which distributed in depths of less than 10 ÷ 12m has a high risk of liquefaction; Fine sand and medium-grained sand in dense consistence (Thai Binh and Vinh Phuc formation) would be not liquefied in real conditions Recommendations for further studies 1) For improving and increasing the reliability of soil dynamic information in study area, further studies should be on the issues: determining the soil deformation characteristics in different strain phases by a combination of directly experimental methods such as seismic refraction tests, cyclic torsional shear tests, cyclic simple shear tests, resonant column tests; research on the effect of the component (particle, organic content), state (saturation, density) to the dynamical properties of soils in this area; research on the 25 liquefaction of sands with different grained composition and density, determining the density limits of sands that has no liquefaction 2) The further studies can inherit the results of the research in the following areas: research on deformation characteristics by the strain control method (method B) with strain amplitude a = 0.01% for assuming elastic phase, a = 0.05; 0.1; 0.5 and 1% for the elastic – plastic phase (the assumption nonlinear background); research on cyclic strength of clayey soils by method B with strain amplitudes a = 0.5; 1; 2; and 10%; research on soil cyclic strength by method A with stress ratios: the smallest CSRmin = a, the maximum of stress ratio CSRmax = 1,74a, in which the coefficient a is estimated by static strength test 3) Based on the information about the dynamical properties of the soils in Hanoi area, it can be carry out the studies of behavior model with dynamic loads for each ground structure, including: determination of reflectance spectra serves building construction against earthquakes; research on the behavior of ground – pile system; assessing ground stability; determining the affected area of shocking construction LIST OF BUBLISHED REASEARCHES Nguyen Van Phong (2004), Application of a combination of research methods to determine the undrained shear strength of soft soil belong to Hai Hung formation distributed in Hanoi area, Scientific Proceeding 16th of University of Mining and Geology, Hanoi, p 37-43 Ta Duc Thinh, Nguyen Huy Phuong, Nguyen Hong, Nguyen Van Phong (2004), Research on the distribution and geological properties of soft soil belong to Hai Hung formation distributed in Hanoi area, Scientific Proceeding 16th of University of Mining and Geology, Hanoi, p 61-66 Nguyen Huy Phuong, Ta Duc Thinh, Pham Van Ty, Nguyen Hong, Nguyen Van Phong (2004), Zoning of the soft soil ground in Hanoi area, workshops environmental Geotechnical Vietnam - Japan VJSGE, Hanoi, p 49-52 Nguyen Huy Phuong, Nguyen Van Phong (2006), The law of the distribution and the variation of geological characteristics of soft soil belong to Hai Hung formation distributed in Hanoi area, Scientific – technical journal of Mining and Geology, Hanoi, No 14, p 46-50 Nguyen Van Phong, Ta Duc Thinh (2008), Determining the mechanical properties of soft soil by piezocone penetration test (CPTu), Scientific Proceeding 18th of University of Mining and Geology, Hanoi, p 75-82 To Xuan Vu, Nguyen Van Phong (2010), Overview of geological characteristics of soft soil distributed in Bac Bo Delta, Scientific – technical journal of Mining and Geology, Hanoi, No 31/7, p 69 – 74 26 Nguyen Van Phong, Ta Duc Thinh (2010), The initial results for determining coefficient of horizontal consolidation by dissipation test and some experimental coefficient of soft soil in Bac Bo Delta, Scientific Technical Journal of Mining and geology, Hanoi, No 31/7 p 44-48 Nguyen Van Phong (2012), Determination of physical and dynamical properties of clayey soil distributed in Bac Bo Delta by piezocone penetration test, Scientific - Technical Journal of Mining and geology, Hanoi, No 40/10, p 37-43 Pham Thi Viet Nga, Nguyen Van Phong (2012), Initial study on thixotropic properties of the soft soils of Hai Hung formation in Ha Noi area, Scientific Proceeding 20th of University of Mining and Geology, Hanoi, p 11-15 10 Nguyen Van Phong, Le Trong Thang (2013), Study of dynamic properties of clayed soil of Thai Binh formations distributed in the Hanoi area by Cyclic triaxial tests, Scientific - Technical Journal of Mining and geology, Hanoi, No 44/10, pp 5-11 11 Le Trong Thang, Nguyen Van Phong (2013), Preliminary studies of the Soil dynamics parameters in Hanoi area by Cyclic triaxial tests, Scientific Proceedings 2013 of Vietnam Institute for Building Science and Technology 12 Nguyen Van Phong (2014), Types and characteristtics of soft soil in coastal areas of Bac Bo Delta, Scientific - Technical Journal of Mining and geology, Hanoi, No 46 / p 24-29 13 Nguyen Van Phong, Le Trong Thang (2014), Study of dynamic strength of soft soil distributed in Northern coastal area by Cyclic triaxial tests, Scientific Proceeding 21th of University of Mining and Geology, Hanoi 14 Le Trong Thang, Nguyen Van Phong (2014), Some correlation between dynamic and static properties of soil in Hanoi area, Scientific - Technical Journal of Mining and geology, Hanoi, No 45/01 pp 32-37 [...]... CHARACTERISTICS OF ENGINEERING GEOLOGY OF QUATERNARY SEDIMENTS IN HANOI AREA AND RESEARCH METHODOLOGY OF THEIR DYNAMICAL PROPERTIES 3.1 Characteristics of stratigraphy and groundwater in Hanoi area 3.1.1 Summary of Quaternary sediments in research area The structure of Quaternary sediments in this area are present of formations in order from the bottom up is Le Chi, Hanoi, Vinh Phuc, Hai Hung and Thai Binh: -... in Hanoi area, Scientific Proceeding 16th of University of Mining and Geology, Hanoi, p 37-43 2 Ta Duc Thinh, Nguyen Huy Phuong, Nguyen Hong, Nguyen Van Phong (2004), Research on the distribution and geological properties of soft soil belong to Hai Hung formation distributed in Hanoi area, Scientific Proceeding 16th of University of Mining and Geology, Hanoi, p 61-66 3 Nguyen Huy Phuong, Ta Duc Thinh,... determination of reflectance spectra serves building construction against earthquakes; research on the behavior of ground – pile system; assessing ground stability; determining the affected area of shocking construction LIST OF BUBLISHED REASEARCHES 1 Nguyen Van Phong (2004), Application of a combination of research methods to determine the undrained shear strength of soft soil belong to Hai Hung formation distributed. .. dense Fine sand (Thai Binh formation) and medium-grained sand (Vinh Phuc formation) in dense consistence were not collapsed in the form of liquefaction - The collapsed point of clayey soil is determined based on the curve stress strain over time In particular, the initial collapsed point is determined corresponding to 2% of strain and 5% for determining the extreme collapsed point The collapsed point of. .. Nguyen Hong, Nguyen Van Phong (2004), Zoning of the soft soil ground in Hanoi area, workshops environmental Geotechnical Vietnam - Japan VJSGE, Hanoi, p 49-52 4 Nguyen Huy Phuong, Nguyen Van Phong (2006), The law of the distribution and the variation of geological characteristics of soft soil belong to Hai Hung formation distributed in Hanoi area, Scientific – technical journal of Mining and Geology, Hanoi, ... sand and medium-grained sand in dense consistence (Thai Binh and Vinh Phuc formation) would be not liquefied in real conditions Recommendations for further studies 1) For improving and increasing the reliability of soil dynamic information in study area, further studies should be on the issues: determining the soil deformation characteristics in different strain phases by a combination of directly experimental... deformation for assuming elastic phase allow solve the model of soil behavior with dynamic loads under the assumption "equivalent linear deformation " The input parameters (Ed, D) are a constant corresponding to the degree of deformation Construction results of relationship between Ed and D with dynamic deformation (equations from 4.1 to 4.6) allow solve the model of soil behavior on the assumption of nonlinear... penetration test, Scientific - Technical Journal of Mining and geology, Hanoi, No 40/10, p 37-43 9 Pham Thi Viet Nga, Nguyen Van Phong (2012), Initial study on thixotropic properties of the soft soils of Hai Hung formation in Ha Noi area, Scientific Proceeding 20th of University of Mining and Geology, Hanoi, p 11-15 10 Nguyen Van Phong, Le Trong Thang (2013), Study of dynamic properties of clayed soil of. .. 5.2 Research results on the possibility of sand liquefaction There are a variety of sands belong to different formations in study area In particular, fine sand of Thai Binh (Ctb) and Vinh Phuc (Cvp1) formations has an wide distribution and sensitive to the effects of dynamic loads These sands are likely to be liquefied under the effects of dynamic loads Therefore, the content of this section focused on. .. Van Phong, Ta Duc Thinh (2010), The initial results for determining coefficient of horizontal consolidation by dissipation test and some experimental coefficient of soft soil in Bac Bo Delta, Scientific Technical Journal of Mining and geology, Hanoi, No 31/7 p 44-48 8 Nguyen Van Phong (2012), Determination of physical and dynamical properties of clayey soil distributed in Bac Bo Delta by piezocone penetration