BEHAVIOUR OF SOILS UNDER THE IMPACT OF EARTHQUAKES: A STUDY CASE FROM THE CENTER OF HANOI

Transcription

1 VOL. 13, NO. 13, JULY 218 ISSN Asian Research Publishing Network (ARPN). All rights reserved. BEHAVIOUR OF SOILS UNDER THE IMPACT OF EARTHQUAKES: A STUDY CASE FROM THE CENTER OF HANOI Gospodarikov Alexandr 1 and Thanh Nguyen Chi 1, 2 1 Saint Petersburg Mining University, Saint Petersburg, Russia Federation 2 Hanoi University Mining and Geology, Vietnam nguyenthanh.xdctn47@gmail.com ABSTRACT Hanoi located in the North of Vietnam; it is the capitol and second largest city in Vietnam. Hanoi has contains many important and large buildings. Hanoi is affected by two major fault systems; there are Red River fault and Lai Chau - Dien Bien - Son La fault. According to studies and assessments, the center Hanoi s could be impacted by earthquakes of magnitude up to 6.5 richter, the maximum ground acceleration under the impact the largest earthquake that occurs in Hanoi a max =.2g, so the study for effects of earthquakes to layers of soil in the center Hanoi s is needed to serve the research, design and construction of works that are safe under the impact of earthquakes. This paper presents the results of research and experiments about changes parameters of soil layers under the impact of earthquakes-dynamic load, which are G- dynamic shear modulus and D-damping ratio these are two main parameters for describing the dynamic performance of soil layers in the center of Hanoi under the impact of dynamic load corresponding to the impact earthquakes. Keywords: dynamic, dynamic shear modulus, damping ratio, triaxial test. 1. INTRODUCTION The impact of earthquakes in analysis methods and experimental be able to expressed by dynamic loads. Under the impact dynamic loads caused by the earthquakes, parameters of soil layers in the earthquakeaffected area will be altered and will directly affect works in the area. At present, some important parameters of soil layers for evaluation, calculation and design of structures in earthquake-affected areas are G-dynamic shear modulus and D-damping ratio. The change in the values two main parameters of soil, G and D will to change results of assessment about the impact of earthquakes to works. Based on the experimental results on the geological and hydrogeological conditions soil layers in the central of Hanoi, perform experiments on soil s, that were collected in the center of Hanoi under the influence of dynamic loading to have received results about the variation of important parameters of soil layers in central Hanoi. There are many experimental methods to determine the two important parameters G and D of soil under the influence of dynamic loading along with many authors such as: Seed et al., 1986 [1]; Vucetic and Good, 1991 [2], Seed and Idriss, 197 [3], Hardin and Drenvich, (1972) [4]. In this paper, has used experimental cyclic triaxial test. This method gives high precision results because that could simulate the condition of s almost actual condition. 2. PARAMETERS OF LAYERS SOIL IN HANOI CENTRE The central of Hanoi is located in the catchment area Red River [5]. According to results of experiments about geological and hydro-geological, the central of Hanoi is considered to have a fairly high level of groundwater, with a groundwater level of 3m and the center of Hanoi has got 6 soil layers that were distributed according to the Figure-1 [6]. According to the study authors [5, 7], Hanoi is located in an area affected by two faults: Red River and Lai Chau - Dien Bien - Son La. In 1983 the earthquake occurred in Hanoi with the magnitude of 6.3 Richter. According to the assessment, the magnitude largest earthquake that can occur in Hanoi can reach the value of M w = 6.5 Richter, a distance from the epicenter to center of Hanoi of about 2 to 5 km, the peak acceleration of a max =.2g. 4126

2 Number of soil layers VOL. 13, NO. 13, JULY 218 ISSN Asian Research Publishing Network (ARPN). All rights reserved. Elastic module, E, MPa Table-1. Parameters of layers soil in Hanoi Centre [5, 7, 8, 9]. Poisson s ratio, Shear modulus, G, MPa Thickness of layer (h), m Measured SPT blow count, N Shear stress reduction coefficien t, r d, m deviator stress amplitude,, kp Density soil, ρ, g/cm m 6.3 m Soil Layer 1 - Backfill - thickness 4.6 m Soil Layer 2 - Soft clay - thickness 1.1 m Soil Layer 3 - Stiff lean clay-thickness 11.8 m Tunnel Soil Layer 4 - Dense clay sand - thickness 12.5 m Soil Layer 5 - Very dense clay sand - thickness 11. m Soil Layer 6 - Coarse sand with Gravel - thickness 7. m Bed rock Figure-1. Layers soil in centre of Hanoi [7]. 3. TRIAXIAL TESTING METHODOLOGY AND SAMPLING Changes in parameters of soil under the influence of dynamic loads have been investigated by many authors. Some investigations also focused on the degradation of dynamic shear modulus G and on the damping ratio D due to cyclic loading. In this paper, cyclic triaxial test method has used to study the impact of dynamic loads on the change of soil's parameters in central of Hanoi. cyclic triaxial test, s of soil were taken into the laboratory equipment and conducted under conditions such as changing the deformation along the test axis with radial stresses (confining pressure) are constant [6-9]. The size of s of soil usually has values: the dimension of 1 mm diameter, the height is 2 mm-this condition will depend on machine testing. Depending on the type soil and on the requirements and purpose experiment, s have built often prepared directly from saturated compacted s either undisturbed or remolded. The specimen in vertically enclosed in a thin rubber membrane and placed between two rigid ends inside a pressure chamber, with soils of type is cohesion-less soils, s will be prepared with molds to create the shape and size required by the experiment. The upper plate could transfer vertically and make vertical stresses to the specimen. The axial strain/stress effect to the is controlled through the movement of this vertical axis. The confining pressure in this test is controlled by the pressure of water, that surrounding the in the pressure chamber. The volume change during the test is controlled by measuring the exact volume of moving water. The water pressure is controlled by external devices through the valve control system as shown in Figure-2. In this study, using triaxial test apparatus Tritech 1 (TAS), this instrument has the following features: The maximum test frequency is 1 Hz; The maximum axial load is 13 kpa; The maximum chamber pressure is 1 kpa; The maximum deformations 15 mm. The device is able to control the loop according to stress and deformation in all three axes 4127

3 VOL. 13, NO. 13, JULY 218 ISSN Asian Research Publishing Network (ARPN). All rights reserved. Change in secant shear modulus with shear strain amplitude [15]: G 1 (2) G 1 / a r Ratio damping D has been change with strain amplitude [15]: 4 1 G/ G G 2 D 1 ln( ) (1 G / G ) 1 G / G G (3) Where a new parameter, strain is defined as [15]: r called reference Figure-2. Triaxial test apparatus [1]. f r (4) G Based on experimental results, the damping ratio and consequently of soils are strain-dependent because the cyclic behaviour of soils is nonlinear and hysteretic. Where G is the maximum shear modulus, G is the secant shear modulus corresponding to a and a and W is the area enclosed by the loop, V S is the velocity S wave in the soil layer, is the mass density of soil and D is the damping ratio. Figure-3. GDS Triaxial Automated System (TAS) components Tritech 1 [5, 11, 12] Shear modulus ratio, G/G Damping ratio, D Figure-4. Shear modulus ratio and damping ratio for hyperbolic model [13-21]. Ishihara in 23 [15-21] introduced theories for calculating the variation of dynamic shear modulus G and D-damping ratio of sandy soils. In this theory, the initial dynamic shear modulus value is determined by the formula: G = ρv (1) 2 s Figure-5. Definition of elastic stored energy and dissipation of energy [15-21]. 4. TEST RESULTS AND DISCUSSIONS From drilling s of different soil layers in the central of Hanoi, prepare s soil to perform the dynamic cyclic triaxial test for these soil s in order to obtain the results. Base on these results, evaluate of soils parameters in the central of Hanoi under the influence of earthquakes and dynamic loads. The following are conditions for conducting experiments for 4128

4 VOL. 13, NO. 13, JULY 218 ISSN Asian Research Publishing Network (ARPN). All rights reserved. soil s in different layers central of Hanoi and the results obtained. In order to research the influence of the dynamic loading, in the dynamic cyclic triaxial test, including confining pressure σ 3, limit cyclic deviator stress amplitude for soils first layer in the center of Hanoi, that has got value is less than the limit value in Table-1, vibration frequency f = 2 Hz. With 5 soil specimens first soil layer and all soil specimens are saturated soil specimens, have been received results in Table-2. Table-2. Results of dynamic Triaxial Test for the first layer soil. Confining Deformation Maximum deviator stress Shear Damping pressure amplitude, deformation, amplitude modulus of ratio of soil, σ 3, kp, % max, % soil, G, kp D, % L L L L L Shear modulus(kpa) Damping ratio(%) Figure-6. Cyclic shear modulus degradation for first layer soil. Figure-7. Damping ratio versus shear strain for first layer soil. In second layer soil, proceed with 5 s in the dynamic cyclic triaxial test, including confining pressure σ 3 =5 kp, limit cyclic deviator stress amplitude for soils second layer in the center of Hanoi, that has got value is less than the limit value in Table-1, vibration frequency f = 2Hz. With 5 soil specimens-saturated soil specimens second soil layer, have been received results in Table

5 VOL. 13, NO. 13, JULY 218 ISSN Asian Research Publishing Network (ARPN). All rights reserved. Table-3. Results of Dynamic Triaxial Test for the second layer soil. Confining deviator Deformation Maximum Shear Damping pressure stress amplitude, deformation, modulus of ratio of σ 3, kp amplitude, % max, % soil, G, kp soil, D, % L L L L L Figure-8. Cyclic shear modulus degradation for of the second layer soil. Figure-9. Damping ratio versus shear strain for of the second layer soil. In third layer soil, proceed with 5 s in the dynamic cyclic triaxial test, including confining pressure σ 3 = 5 kp, limit cyclic deviator stress amplitude for soils third layer in the center of Hanoi, vibration frequency f = 2Hz. With 5 soil specimens - saturated soil specimens third soil layer, have been received results in Table-4. Table-4. Results of dynamic Triaxial Test for the third layer soil. Confining pressure σ 3, kp deviator stress amplitude Deformation amplitude,, % Maximum deformation, max, % Shear modulus of soil, G, kp Damping ratio of soil, D, % L L L L L

6 VOL. 13, NO. 13, JULY 218 ISSN Asian Research Publishing Network (ARPN). All rights reserved. Figure- 1. Cyclic shear modulus degradation for third layer soil. Figure-11. Damping ratio versus shear strain for third layer soil. In fourth layer soil, proceed with 5 s in the dynamic cyclic triaxial test, including confining pressure σ 3 = 8 kp, limit cyclic deviator stress amplitude is soils of fourth layer in center of Hanoi, vibration frequency f = 2 Hz. With 5 soil specimens - saturated soil specimens forth soil layer, have been received results in Table-5. Table-5. Results of dynamic Triaxial Test for the fourth layer soil. Confining pressure σ 3, kp deviator stress amplitude Deformation amplitude,, % Maximum deformation, max, % Shear modulus of soil, G, kp Damping ratio of soil, D, % L L L L L Figure-12. Cyclic shear modulus degradation for fourth layer soil. Figure-13. Damping ratio versus shear strain for fourth layer soil. 4131

7 VOL. 13, NO. 13, JULY 218 ISSN Asian Research Publishing Network (ARPN). All rights reserved. In the fifth layer soil, proceed with 5 s in the dynamic cyclic triaxial test, including confining pressure σ 3 = 8 kp, limit cyclic deviator stress amplitude for soils of fifth layer in the center of Hanoi, vibration frequency f = 2Hz. With the fifth soil specimens fifth soil layer-saturated soil specimens, have been received results in Table-6. Table-6. Results of Dynamic Triaxial Test for the Firth Layer Soil. Confining Deformation Maximum Shear deviator stress Damping pressure σ 3, amplitude, deformation, modulus amplitude ratio of of soil, G, kp, % max, % soil, D, % kp L L L L L Shear modulus(kpa) Figure-14. Cyclic shear modulus degradation for fifth layer soil. Figure-15. Damping ratio versus shear strain for fifth layer soil. In the sixth layer soil, proceed with 5 s in the dynamic cyclic triaxial test, including confining pressure σ 3 = 8 kp, limit cyclic deviator stress amplitude for soils sixth layer in the center of Hanoi, that has got value is less than the limit value in Table-1, vibration frequency f = 2Hz. With 5 soil specimens-saturated soil specimens fifth soil layer, have been received results in Table

8 VOL. 13, NO. 13, JULY 218 ISSN Asian Research Publishing Network (ARPN). All rights reserved. Table-7. Results of dynamic Triaxial Test for the sixth layer soil. Confining Deformation Maximum deviator stress Shear Damping pressure amplitude, deformation, amplitude modulus of ratio of σ 3, kp, % max, % soil, G, kp soil, D, % L L L L L Shear modulus(kpa) Shear modulus(kpa) Layer 1 Layer 2 Layer 3 Layer 4 Layer 5 Layer Figure-16. Cyclic shear modulus degradation for sixth layer soil. Damping ratio(%) Figure-17. Damping ratio versus shear strain for of sixth layer soil Figure-18. Cyclic shear modulus degradation for of layers soil. Damping ratio(%) Layer 1 Layer 2 Layer 3 Layer 4 Layer 5 Layer Figure-19. Damping ratio versus shear strain for of layers soil. From the results obtained in the above experiments, it was found that the relationship between the shear modulus G and the dynamic shear strain of soil in each layer of soil in the central of Hanoi. In the first layer.479 of soil: G= * ; the second layer of soil: G= 4133

9 VOL. 13, NO. 13, JULY 218 ISSN Asian Research Publishing Network (ARPN). All rights reserved *.724 ; the third layer soil: G=888.1* ; the fourth layer soil: G=468.6* ; the fifth layer soil:.615 G=1272.5* ; the sixth layer soil: G= *.496. Similarly, the relationship between damping ratio D of soil and shear strain of soil can be determined through experimental results of cyclic triaxial test: The first layer of soil: D=8.8194ln( ) ; the second layer of soil: D=13.72ln( ) ; the third layer soil: D=9.628ln( ) ; the fourth layer soil: D=9.628ln( ) ; the firth layer soil: D= ln( ) ; the sixth layer soil: D= ln( ) Based on the experimental results of cyclic triaxial test obtained above, the relationship between dynamic shear modulus and ratio damping with the shear strain of soils under the influence dynamic load can be explained as follows: - In the first stage-the elastic deformation stage, soil s will respond elastically without any significant degradation in its stress-strain and shear strength response. The relationship between the shear modulus G and the shear strain is linear and in this stage, cyclic shear 2 strain is small ( 4.1 % ). The change of ratio damping D in this stage were negligible. - In the second stage in the cyclic of soil under effect of dynamic loading, once the elastic threshold is exceeded, the soil will respond in an elastic-plastic manner. In this stage, the induced cyclic shear strains did to strain plastic for soil, particle structure breakdown, making values of pore pressure are increased and a rapid decrease of stress-strainshear strength characteristics of soil up to the limit of plastic. When the limit of plastic has exceeded, the soil will has experienced large shear strain because accumulated degradation dynamic shear modulus 2 ( 4.1 % 1% ). The corresponding change of ratio damping D second stage is linear. - The third stage, this stage is plastic flow stage in the cyclic behaviour of soils. At the third stage, when the shear strain variable is exceeded limit, the soil s in a plastic phase with breakdown the particle structure of soil as well as the accumulated pore pressures increase significantly, all problems above have lead to the cyclic shear strain reduction rate increases drastically ( 1% ). In this state, soil s have been destroyed along with very high soil deformation and the shear modulus of s soil is very small. In third stage, ratio damping D were nonlinear and have got great values (D.32). Depending on the type of soil in layers, there will be varying degrees of deformation and limit of states are different (depending on the porosity soil, the pore water pressure in the soil, etc.). 5. CONCLUSIONS In this paper the survey of geological conditions and hydrogeological conditions central area of Hanoi, conducted drilling and collecting s at different soil layers in the central region of Hanoi and presents features of cyclic triaxial test for soil s and given theories for change to parameters of soil s under the influence of dynamic loading. Next, conducted triaxial test experiments for soil s; these have been collected at the soil layers in the central of Hanoi. Based on the results obtained from the experiments of triaxial test could give rules of variation for the two most important parameters of soil under the influence of dynamic loading, these are dynamic shear modulus G and ratio damping D and comment, explain these transformational rules. As be able to see, with the six soil layers in the central of Hanoi, under the influence of dynamic loading, there are 3 stages of change in soil parameters including: elasticity stage, plastic stage and sliding stage-soil have been destroyed. Stages of each type of soil have limits values depending on the type of soil and parameters of soils. Detail parameters of layer soils in centre of Hanoi have been given in this paper, special as dynamic shear modulus G and ratio damping D (have been represented by equations showing the relationship between the dynamic shear modulus G and ratio damping D with the shear strain of soil). It be able to see at the stage of elastic deformation, the frame structure soil has not been destroyed so the shear modulus G soil is greatest and the strain of the soil when the soil must be subjected to the static load or dynamic load is no significant difference in this stage. When the load is large enough to break the frame structure of soil, soil has got phenomenon that will be rearrange the soil particles to become tighter. The strain soil under the effect of dynamic loading now includes elastic strain and residual strain. Because the dynamic loads that have variable values over time, the pore water in the soil could not escape in time, causing strain soil is small and causing the dynamic shear modulus G soil under the influence of dynamic load during this period is value large. Also during this stage, ratio damping D has small change value. In the nonlinear strain stage of soil, the strain increases rapidly and has got value large during this stage. The strain soil is residual strain (this can be seen by the difference between the maximum strain and the amplitude strain that has got a large deviation) and the soil will be destroyed. The ratio damping D is directly proportional to the strain soil during this stage. Dynamic shear modulus G and ratio damping D, these are parameters of soils very important for design, construction works when works are affected by earthquake, dynamic loading. Based on the results obtained, that could be used to design and construction works in the central of Hanoi, has got considering the influence of earthquakes or dynamic loads in the area. 4134

10 VOL. 13, NO. 13, JULY 218 ISSN Asian Research Publishing Network (ARPN). All rights reserved. ACKNOWLEDGEMENTS This study was supported by the Saint Petersburg Mining University, Russia Federation and Hanoi University Mining and Geology, Vietnam. The authors wish to thank Saint Petersburg Mining University, Russia Federation and Hanoi University Mining and Geology, Vietnam for facilities and resources provided and we thank two anonymous reviewers for their comments that were very valuable for revising the manuscript. REFERENCES [1] Seed HB, Wong RT, Idriss IM, Tokimatsu K Moduli and damping factors for dynamic analyses of cohesionless soils. J Geotech Eng ASCE 112(11): [2] Vucetic M, Dobry R Effect of soil plasticity on cyclic response. J. Geotech Eng ASCE. 117(1): [3] Seed HB, Idriss IM Soil moduli and damping factors for dynamic response analyses. Rep. No. EERC-7/1, Earthquake Engineering Research Center, Univ. of California at Berkeley, Berkeley, CA. [4] Hardin B O, Drnevich V P Shear modulus and damping in soils: measurement and parameter effects. (Terzaghi lecture) [J]. Journal soil mechanics and foundations division. 98(6): [5] Gospodarikov Alexandr and Thanh Nguyen Chi Liquefaction possibility of soil layers during earthquake in Hanoi. International Journal of GEOMATE. 13: [6] Gospodarikov Alexandr and Thanh Nguyen Chi The impact of earthquakes of tunnel linings: a case study from the Hanoi metro system. International Journal of GEOMATE, Jan. 14(41): [7] Nguyen L.M., Lin T.L., Wu Y.M., Huang B.S., Chang C.H., Huang W.G., Le T.S., Nguyen Q.C. & Toan Dinh V The First Peak Ground Motion Attenuation Relationships for North of Vietnam. Journal of Asian Earth Sciences. 43: [8] Systra Hanoi Pilot Light Metro Line 3, Section Nhon - Hanoi Railway Station, Package number: HPLMLP/CP-3 (Ver. 2). [9] Phong N.V Nghien cuu tinh chat co hoc cua tram tich de tu phan bo o khu vuc Hanoi duoi tac dung cua tai trong dong. Hanoi, Luan an Tien sy. pp [1] The EO-MINERS project. [11] Seed H.B., Idriss I.M. and Arango I Evaluation of Liquefaction Potential Using Field Performance Data. Journal of Geotechnical Engineering. 19(3): [12] Weiguo Liang et al Experiments on mechanical properties of salt rocks under cyclic loading. Journal of Rock Mechanics and Geotechnical Engineering. 4(1): [13] Shajarati Amir; Sørensen, Kris Wessel; Nielsen, Søren Dam; Ibsen, Lars Bo Manual for Cyclic Triaxial Test. Aalborg University, Denmark. pp [14] Sean Rees. What is Triaxial Testing? GDS website [15] Kenji Ishihara. 23. Soil Behaviour in Earthquake Geotechnic. Oxford University Press, ISBN , pp , 23. [16] Andr es Nieto Leal, Victor N. Kaliakin Behavior of Cohesive Soils Subjected to Cyclic Loading: An Extensive Review of Pertinent Literature. Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, U.S.A. September 213. [17] Marshall L. Silver, Load Deformation and Strength Behavior of Soils under Dynamic Loadings. University of Illinois, Chicago, Illinois, pp [18] A.J. Brennan1, N.I. Thusyanthan &S.P.G. Madabhushi. 24. Evaluation of Shear Modulus and Damping in Dynamic Centrifuge Tests. Wolfson College, University of Cambridge. pp [19] R. Bahar, L. Saci & S. Louadj, E. Vincens Numerical evaluation of shear modulus degradation and damping curves of Algerian soils using geophysical tests. WCEE 15 Lisbon. pp [2] Sas W, Szymański A., Gabryś K The behaviour of natural cohesive soils under dynamic excitations. Proceedings 18 th International Conference on Soil Mechanics and Geotechnical Engineering, Paris. pp [21] B. D Elia, G. Lanzo & A. Pagliaroli. 23. Small- Strain Stiffness and Damping of Soils in a Direct Simple Shear Device. Pacific Conference on Earthquake Engineering. pp