scholarly journals Site Response Analysis of S2 Soil Deposits Focusing on the Effects of Liquefaction and Pore-Pressure Dissipation on the Ground Surface Response Spectrum

2021 ◽  
Author(s):  
Maria Anthi ◽  
NIKOS GEROLYMOS
Keyword(s):  
Wave Propagation ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Response Spectrum ◽  
Water Pressure ◽  
Ground Surface ◽  
Response Analysis ◽  
Soil Profiles ◽  
Ground Response ◽  
Ground Response Analysis

Abstract A numerical algorithm for executing non-linear ground response analysis of layered sites is developed, capable of reproducing liquefaction phenomena, considering the simultaneous dissipation of the excess pore water pressure through soil grains. Τhe wave propagation algorithm is based on the plasticity constitutive model for sand Ta-Ger expressed in a one dimensional p-q space form, which exhibits remarkable versatility in representing complex patterns of sand cyclic behavior, such as stiffness decay and decrease in strength due to build-up of pore-water pressure. Its calibration is based on shear modulus reduction and damping curves for drained loading conditions and liquefaction resistance curves for undrained conditions. A detailed presentation of the numerical model formulation is provided, indicating the numerical approach of the wave propagation and consolidation differential equations. The recorded seismic ground response of the Port Island array from Kobe 1995 earthquake is used as a benchmark for testing the validity of model predictions. The model is finally applied to estimate the elastic response spectra at the surface of soil profiles with liquefiable layers (ground type S2) as per EC8:2004. The investigation study involves the ground response analysis of diverse soil profiles, all including a liquefiable zone, excited with a suite of earthquake motions at their base. The acceleration time histories were extracted from the PEER Ground Motion Database having characteristics compatible with the NGA-estimated response spectrum at the bedrock and with key seismological parameters such as the earthquake magnitude Mw and horizontal distance from the fault RJB. Two different methods are applied regarding the selection of base excitations: Amplitude scaled records (to match a target response spectrum) and spectral matched records. From the results an idealized response spectrum is deduced in terms of the design spectrum parameters S, η, ΤΒ and TC. It is shown that the idealized ground surface response spectrum is marginally sensitive to method of base excitation selection.

ENGINEERING CHARACTERISTICS AND EARTHQUAKE RESPONSE ANALYSIS OF GROUND

2018 ◽  
Vol 5 (2) ◽  
Author(s):  
Haruyuki Yamamoto ◽  
Munkhunur Togtokhbuyan
Keyword(s):  
Shear Modulus ◽  
Ground Surface ◽  
Response Analysis ◽  
Soil Profiles ◽  
Lumped Mass ◽  
Ground Response ◽  
Ground Response Analysis ◽  
Natural Period ◽  
Soil Deposits ◽  
Computational Procedures

One-dimensional layered soil lumped mass ground response analysis was conducted for the representative site in Ulaanbaatar, Mongolia. The surficial geology of the site is predominantly composed of the gravely and sandy soil typical of this region in the central part of Ulaanbaatar. The natural period of soil profiles needs to be investigated under several circumstances. For example, these parameters-based study has indicated that damage due to earthquakes occurs when the natural periods, T1 and T2, of the ground are closer to that of a superstructure. Various computational procedures or methods have been proposed for this kind of the ground response analysis. In this paper, the numerical analysis method such as the lumped mass method within eigenvalue analysis is used to determine the natural periods of the ground. The ground surface, soil deposits, and bedrock are assumed to be horizontal. The soil deposits are subjected to shear deformation such as shear modulus, G, on the other hand, excitation of vibration could be a shear modulus on each layer. As well as to determine an engineering bedrock depth in the site, the methodology that is utilized in this paper is focused on the use of the correlation between SPT-N value and soil elastic Young's modulus, E, in the soil profiles, and used over 100 boreholes data with SPT-N values in the vicinity of Ulaanbaatar.

One-Dimensional Effective Stress Non-Masing Nonlinear Ground Response Analysis of IIT Guwahati

2017 ◽  
Vol 8 (1) ◽  
pp. 1-27 ◽  
Author(s):  
Devdeep Basu ◽  
Arindam Dey ◽  
Shiv Shankar Kumar
Keyword(s):  
Pore Water Pressure ◽  
Water Pressure ◽  
Response Analysis ◽  
Eastern Region ◽  
Seismic Zone ◽  
Ground Response ◽  
Accurate Identification ◽  
Ground Response Analysis ◽  
Soil Medium ◽  
One Dimensional

Ground response analysis (GRA) helps to assess the influence of the soil medium on the propagating shear waves and indicates about the characteristics of the waves reaching the ground surface from the bedrock level. Such a study becomes imperative for the urbanized alluvial banks of North-Eastern region of India, which is located in the highest seismic zone of the country. Conventionally, GRA is carried out based equivalent linear approach, which being a simplistic approach is unable to capture the nonlinear characteristics of saturated silty sands subjected to seismic shaking. This article presents the outcome of seismic one-dimensional nonlinear GRA of IIT Guwahati (located on a varying geology in the saturated alluvial banks of River Brahmaputra) considering pore-water pressure dissipation characteristics and non-Masing unload-reload criteria. Various ground response parameters obtained from the study helps in the accurate identification of the earthquake intensity based site amplification of the region expressed through a 2-D mapping.

Downslope movements at shallow depths related to cyclic pore-pressure changes

1993 ◽  
Vol 30 (3) ◽  
pp. 464-475 ◽  
Author(s):  
K.D. Eigenbrod
Keyword(s):  
Pore Water ◽  
Slip Surface ◽  
Pore Water Pressure ◽  
Limit Equilibrium ◽  
Water Pressure ◽  
Ground Surface ◽  
Soil Mass ◽  
Passive Resistance ◽  
Pressure Changes ◽  
Timber Piles

Slow, shallow ground movements in a slope near Yellowknife caused excessive tilting of timber piles that supported an engineering structure. To avoid damage to the structure, the pile foundations had to be replaced by rigid concrete piers that were designed to resist the forces of the moving soil mass. Downhill movements were rather slow and, during an initial inspection, were indicated only by soil that was pushed up against a series of piles on their uphill sides, while gaps had formed on their downhill sides. No open cracks or bulging was observed on the slope. A stability analysis indicated that the slope was not in a state of limit equilibrium. To obtain a better understanding of the creep movements in the slope and their effect on the rigid concrete piers, extensive instrumentation was carried out after the construction of the piers. This included slope indicators, piezometers, thermistors, and total-pressure cells against one of the concrete piers. In addition, a triaxial testing program was undertaken in which the effect of cyclic pore-water pressure changes on the long-term deformations of the shallow clay layer was investigated. From the data collected in the field and laboratory, it could be concluded that (i) tilting of the original timber piles was caused by downslope movements related to cyclic pore-water increases; (ii) the lateral soil movements increased almost linearly with depth from 2 m below the ground surface, with no indication of a slip surface; and (iii) the pressures exerted by the moving soil mass against the rigid concrete piers within the soil mass were equal to the passive resistance activated within the moving soil mass. Key words : soil creep, slope movements, soil pressures, pore-water pressures, freezing pressures, permafrost, cyclic loading.

scholarly journals Numerical Evaluation of The Nonlinear Behavior of Soil-Pile Interaction Under The Effect of Coupled Static-Dynamic Loads

2021 ◽  
Author(s):  
Duaa Al-Jeznawi ◽  
ISMACAHYADI Mohamed Jais ◽  
Bushra S. Albusoda
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Three Dimensional ◽  
Ground Surface ◽  
Frictional Resistance ◽  
Saturated Soil ◽  
Shaking Table ◽  
Physical Models ◽  
Soil Layers

Abstract Liquefaction of saturated soil layers is one of the most common causes of structural failure during earthquakes. Liquefaction occurs as a result of increasing pore water pressure, whereby the rise in water pressure occurs due to unexpected change in stress state under short-term loading, i.e., shaking during an earthquake. Thus, general failure occurs when the soil softens and eliminates its stiffness against the uplift pressure from the stability of the subsurface structure. In this case, the condition of soil strata is considered undrained because there is not enough time for the excess pore water pressure to dissipate when a sudden load is applied. To represent the non-linear characteristics of saturated sand under seismic motions in Kobe and Ali Algharbi earthquakes, the computational model was simulated using the UBCSAND model. The current study was carried out by adopting three-dimensional-based finite element models that were evaluated by shaking table tests of a single pile model erected in the saturated soil layers. The experimental data were utilized to estimate the liquefaction and seismicity of soil deposits. According to the results obtained from the physical models and simulations, this proposed model accurately simulates the liquefaction phenomenon and soil-pile response. However, there are some differences between the experiment and the computational analyses. Nonetheless, the results showed good agreement with the general trend in terms of deformation, acceleration, and liquefaction ratio. Moreover, the displacement of liquefied soil around the pile was captured by the directions of vectors generated by numerical analysis, which resembled a worldwide circular flow pattern. The results revealed that during the dynamic excitation, increased pore water pressure and subsequent liquefaction caused a significant reduction in pile frictional resistance. Despite this, positive frictional resistance was noticed through the loose sand layer (near the ground surface) until the soil softened completely. It is worth mentioning that the pile exhibited excessive settlement which may attribute to the considerable reduction, in the end, bearing forces which in turn mobilizing extra end resistance.

Seismic Ground Response Analysis of Some Typical Sites of Guwahati City

2013 ◽  
Vol 4 (1) ◽  
pp. 83-101 ◽  
Author(s):  
Shiv Shankar Kumar ◽  
A. Murali Krishna
Keyword(s):  
Ground Motion ◽  
Amplitude Ratio ◽  
Response Spectrum ◽  
Strong Motion ◽  
Response Analysis ◽  
Ground Response ◽  
Ground Response Analysis ◽  
Ground Acceleration ◽  
Surface Level ◽  
Guwahati City

In this study, one dimensional equivalent–linear ground response analyses were performed for some typical sites in the Guwahati city, India. Six bore locations covering about 250 km2 area of the city were considered for the analyses. As the strong motion significantly influences the ground response, seven different recorded ground motions, varying in magnitude (6.1 to 8.1) and other ground motion parameters, were adopted. Seismic site analyses were carried out for all layers of borelogs using all the seven earthquakes. Results are presented in terms of surface acceleration histories, strain and shear stress ratio variation, response spectrum, Fourier amplitude ratio versus frequency. The results indicate that accelerations were amplified the most at the surface level. The range of peak ground acceleration (PGA) values obtained at the ground surface is about 0.2 g to 0.79 for a range of PGA considered at bedrock level (rigid half space at bottom of borelog) of 0.1 g to 0.34 g. The Fourier amplifications of ground motion at surface are in the range of 4.14 – 8.99 for a frequency band of 1.75 Hz to 3.13 Hz. The maximum spectral acceleration at six locations varies in the range of 1.0 g – 4.71 g for all the seven earthquakes. The study clearly demonstrated the role for site effect and the type of ground motion on the ground response. For a given earthquake motion, amplification factors at surface level change by almost about 20% to 70% depending on local site conditions.

scholarly journals An Analytical Continuous Upper Bound Limit Analysis of Pore Water Effect on the Tail Stability of Underwater Shield Tunnels during Construction

2020 ◽  
Vol 143 ◽  
pp. 01015
Author(s):  
Wenjie Song ◽  
Yanyong Xiang
Keyword(s):  
Pore Water ◽  
Upper Bound ◽  
Limit Analysis ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Ground Surface ◽  
Support Pressure ◽  
Tunnel Support ◽  
Transverse Stability ◽  
Upper Bound Limit Analysis

An analytical continuous upper bound limit analysis is developed to analyse the effects of seepage on the transverse stability of underwater shield tunnels. The approach is based on an analytical continuous upper bound limit analysis method for cohesive-frictional soils. It employs the complex variables solution of the displacement field due to tunnel deformation and movement, and the analytical solution of the pore water pressure field for steady state seepage due to pore water influx at the tunnel perimeter. The most critical slip line position and the minimum required tunnel support pressure are determined by using a particle swarm optimization scheme for various generic situations. The method is verified via finite element simulation and comparison with the solution from using rigid block upper bound limit analysis. The parametric analysis revealed among other things that both the infimum of the necessary tunnel support pressure and the most critical plastic zone increase when the hydraulic head at the ground surface increases, but decrease when the tunnel influx increases due to the fact that pore water pressure at the tunnel perimeter decreases with the tunnel influx.

Investigation of field-installation effects of horizontal twin-jet grouting in Shanghai soft soil deposits

2013 ◽  
Vol 50 (3) ◽  
pp. 288-297 ◽  
Author(s):  
Zhi-Feng Wang ◽  
Shui-Long Shen ◽  
Chu-Eu Ho ◽  
Yong-Hyun Kim
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Ground Surface ◽  
Prediction Methods ◽  
Jet Grouting ◽  
Soil Deposits ◽  
Lateral Displacements ◽  
Surface Heave

This paper presents a case study of an investigation into the responses of the surrounding ground to the horizontal twin-jet grouting method (HTJGM) in soft soil deposits of Shanghai. During the field test, the variation of pore-water pressure, lateral earth pressure, lateral displacements of the subsurface soils, and ground surface heave induced by the installation of five horizontal jet-grouted columns were monitored. The monitoring results indicate that the excess pore-water pressure reached 4 to 6 times the undrained shear strength of the soils, while maximum lateral displacements and ground surface heave were up to 80 and 17 mm, respectively. The influence range due to the installation of jet-grouted columns was between 15 and 20 times the nominal column radius. The development of prediction methods for lateral displacements and ground surface heave induced by the HTJGM installation process are presented and discussed. Results from the investigation suggest that the proposed prediction methods can be used to provide reasonable estimates of ground response and influence range of horizontal jet grouting.

scholarly journals A Numerical Investigation of the Deformation Mechanism of a Large Metro Station Foundation Pit under the Influence of Hydromechanical Processes

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Yan Wang ◽  
Yongjun Zhang ◽  
Mingfei Li ◽  
Yi Qi ◽  
Tianhui Ma
Keyword(s):  
Pore Water ◽  
Heavy Rainfall ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Ground Surface ◽  
Horizontal Displacement ◽  
Horizontal Distance ◽  
Foundation Pit ◽  
Metro Station ◽  
Ground Conditions

Considering the unique conditions of deep and large subway foundation pit excavation affected by heavy rainfall in soil-rock composite strata, this paper employs finite element numerical simulation methods to study foundation pit instability under the influence of heavy rainfall. According to the hydraulic coupling conditions caused by rainfall, a fluid-solid coupling numerical model for a deep and large subway foundation pit in soil-rock composite strata is established in this paper. By selecting the Anshan road station of Qingdao subway line 4 as the engineering background, various parameters related to foundation pit excavation affected by heavy rainfall at different excavation depths were analyzed. The study found that after the foundation pit was excavated, the surrounding pore water pressure decreased and the pore water pressure near the ground surface increased rapidly due to rainfall. As the horizontal distance from the foundation pit increased, the pore water pressure at the same depth also increased. The excavation of the foundation pit caused uplift of the bottom of the pit. After rainfall, the uplift value decreased compared with that before rainfall. With increasing excavation depth, the decreased value of the bottom uplift decreased and then increased. The rainfall caused the horizontal displacement of the pit walls on both sides of the pit to increase. When the excavation depth was 10 m, the horizontal displacements on both sides of the pit were equivalent. When the excavation depth was 20 m, the horizontal displacement was concentrated in the first 10 m; when the excavation depths were 30 m and 40 m, the horizontal displacement was concentrated in the first 13 m. This finding shows that when the foundation pit was affected by rainfall, the sidewall collapsed at a distance of 13 meters from the ground. As the excavation depth increased, the depth of excavation instability was closer to the bottom of the pit. The research in this paper can provide a reference for the construction of deep and large foundation pits in similar composite ground conditions that are affected by rainfall.

Three-dimensional numerical investigations of groundwater responses in an unsaturated slope subjected to various rainfall patterns

2001 ◽  
Vol 38 (5) ◽  
pp. 1049-1062 ◽  
Author(s):  
C WW Ng ◽  
B Wang ◽  
Y K Tung
Keyword(s):  
Pore Water ◽  
Short Duration ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Three Dimensional ◽  
Ground Surface ◽  
Rainfall Pattern ◽  
Initial Water ◽  
Pore Water Pressures ◽  
Rainfall Patterns

Three-dimensional (3D) numerical analyses were conducted to investigate groundwater responses in an initially unsaturated cut slope at Lai Ping Road in Hong Kong subjected to rainfalls with various patterns, durations, and return periods. Initial and boundary conditions were established from field monitoring data. The computed results show that rainfall pattern has a significant influence on pore-water pressures in soil layers near the ground surface but its influence gradually diminishes with depth. Rainfall with an advanced storm pattern of 24 h duration was found to be the most critical because it results in the highest pore-water pressure in the slope. At a given depth, the influence of rainfall pattern on pore-water pressures depends on the initial groundwater conditions: the higher the initial water table, the smaller the influence of rainfall pattern on pore-water pressures. Under a given rainfall duration, the rise of pore-water pressure at the study site is significant only when the return period increases from 10 years to 100 years, but not from 100 years to 1000 years. Short-duration, intense rainfall causes larger variations in pore-water pressure at shallow depths, whereas long-duration rainfall has a greater influence on groundwater in deep soils because of the generally greater amount of rainfall. For prolonged rainfalls, the difference in pore-water pressure distribution resulting from different rainfall patterns is less significant than that from short-duration, intense rainfalls.Key words: Lai Ping Road, rainfall patterns, pore-water pressure distributions, suction, unsaturated slope.

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