Dynamic Characteristics Of Soil Research Articles

Research on Key Problems of Seismic Design of Soft Foundation of Large Pumping Station

Based on the large-scale pumping station project of Suining Second Station, the seismic design theory of large-scale pumping stations on soft foundation is studied in this paper. A 3D fluid-structure interaction simulation model of pumping station- foundation- water is established. It can simulate the soil dynamic characteristics of the foundation and the contact nonlinearity of the opening and closing between different structures during strong earthquakes. A semi - underground structure integrated design scheme is finally proposed in this paper: the steel plates pressed together are used to connect the pumping station body, the maintenance room and the control room. The scheme with a combination of the underground continuous wall, bolts and bored piles for foundation reinforcement is proposed. And then a similar semi - underground structure is constituted. It turns out the design scheme has greatly improved the seismic performance of the Suining Pumping Station and solved the key technical problems of the seismic design of large pumping stations on soft foundation.

An investigation on the evaluation of dynamic soil characteristics of the Elazig City through the 1-D equivalent linear site-response analysis

Consideration of the effects of the site response in the design of civil structures systems is of important to mitigate the damages to a certain extent on structures and the environment. Hence, it is relatively crucial to reliably attain the dynamic soil parameters of an earthquake-prone city/state. In the current study, a comprehensive investigation on the dynamic soil properties of the city of Elazig with very close proximity to the East Anatolian Fault Zone (EAFZ) having a high potential of producing destructive earthquakes is carried out. Performing probabilistic seismic hazard analysis (PSHA), the moment magnitude of the city is determined as Mw = 7.7 according to 10% probability of exceedance in 50 years. Bedrock-level acceleration spectra is developed utilizing different attenuation relationships for the city, and 1-D equivalent linear site response analysis is conducted on an example soil profile of the city through the SHAKE2000 software considering 16 earthquake motions recorded at the bedrock level. Local surface acceleration spectra obtained from the analysis are then compared to the design spectra of the Turkish Seismic Code for Buildings (TSCB) and Eurocode-8 (EC8) in an attempt to identify the difference between the code spectra and local surface spectra. In addition, in situ geotechnical tests of standard penetration and seismic refraction are conducted at different locations of the study area. Incorporating the results from the field tests into the site response analysis, the soil amplification factor, predominant soil period, peak ground acceleration and spectral maps for the period of T = 0.2 and T = 1.0 s are obtained for the study area. The outcomes from the analysis reveals that structures with higher vibration period than T = 1.0 s are subjected to lower spectral acceleration (Sa), whereas higher Sa values can be used for those with a vibration period lower than T = 0.2 s.

Experimental Investigation of the Deformation Characteristics of Tianjin Clays under Coupled Dynamic Stress and Seepage Fields

The causes, prevention, and control of clay disasters are of great concern in practical engineering applications. Recently, due to unprecedented economic development, increasing numbers of tunnels and subgrades of tidal flat areas have been built in Tianjin, China. Soft soil ground not only bears the vibration load during operation and construction but also receives seepage effects caused by the bursting of pipelines and variations in groundwater levels. Under the coupling action of dynamic and seepage loads, large settlement can occur in soft soil since the deformation is related to both cyclic stress and seepage. Therefore, it is significant to understand the dynamic deformation characteristics of soil to ensure the safety of engineering applications. In this study, a series of laboratory cyclic triaxial tests were conducted to study the deformation behaviours of Tianjin clays under coupled cyclic stress and seepage fields. To simulate the seepage field, water pressure is applied at the bottom of the specimen, and the water can be drained from the top of the specimen to form a head difference in the specimen during the tests. The effects of the seepage pressure, cyclic stress ratio (CSR), and a number of cycles (N) on the hydraulic conductivity, axial deformation, hysteresis curve and dynamic modulus of Tianjin clays were systematically investigated. The laboratory results show that the hydraulic conductivity (k) decreases with the increasing seepage pressure, CSR, and N, and its range is from 4.6 × 10−8 cm/s to 7.4 × 10−8 cm/s. The axial deformation of the soil increases with increasing CSR and seepage pressure. With an applied water pressure of 150 kPa at the bottom of the specimen and a CSR of 0.3, the maximum cumulative plastic strain reaches 4.78%, increasing by 53.2% compared with a CSR of 0.1. The hysteresis curve gradually becomes denser or thinner with increasing CSR and N; the hysteretic curve tends to a straight line for N of 5,000. The dynamic modulus increases with increasing N and depends on the CSR and seepage pressure. Empirical equations are suggested for calculating the dynamic modulus with different CSR values and seepage pressures. The results of this study can provide reference parameters for the construction and design of tunnels and subgrades of tidal flat areas in clay strata under the influence of water environments.

Experimental Study on Dynamic Elastic Modulus and Critical Dynamic Stress of Cinder-Improved Soil Subgrade

The dynamic elasticity modulus and critical dynamic stress of improved soil under different confining pressures and frequencies are investigated by using GDS dynamic triaxial test system to examine the dynamic characteristics of cinder-improved soil as subgrade under medium and low confining pressure. The attenuation model of the dynamic elastic modulus was established to analyze the influence of different confining pressures and loading frequencies on the dynamic modulus. A fuzzy linear regression model based on structural element method was used according to the uncertainty of critical dynamic stress. Results show that the dynamic elastic modulus of soil decreases exponentially with the increase of loading times. The attenuation model can reflect the influence of frequency and confining pressure on the dynamic modulus of elasticity. The critical dynamic stress of soil is negatively correlated with the frequency of loading and is positively correlated with the confining pressure. The fuzzy linear regression model based on the structural element method can reflect the relationship between the critical dynamic stress and the frequency and confining pressure.

The coupling loss of a building subject to railway induced vibrations: Numerical modelling and experimental measurements

Railway induced vibrations can be amplified or attenuated as they propagate through the foundations, floors and spans of nearby buildings. This change in vibration level, known as the building's coupling loss, is often accounted for in vibration predictions using generic, frequency independent adjustment factors. In this paper, a detailed investigation is conducted to identify methods for determining the coupling loss in new build scenarios and to investigate its dependence on various system parameters. Using the approach of separate source, propagation and receiver terms, the coupling loss is characterised as the difference between vibration velocity levels measured inside and outside the building. Three different configurations of the railway-soil-building are explored: the case where both track and building are present; the case of a new building; and the case of a new railway. In situ experiments of a building subject to excitation from nearby train passages and hammer impacts on the track are used to quantify the building response. The influence of the location of the sensors in the free field and in the building (both within a single floor and across multiple storeys) is investigated. The findings from the experimental study supports separate characterisation of the source and receiver terms, thus demonstrating that the railway can be represented by a series of on-track impacts when determining the building's coupling loss. Using this representation, a 3D building model is used to investigate the effect of dynamic soil characteristics, surface foundation type, and building geometry on the building's response to railway induced vibrations.

Study on dynamic undrained mechanical behavior of saturated soft clay considering temperature effect

In order to study the influence of temperature on soil dynamic characteristics, a temperature-controlled triaxial test apparatus was developed, in which a curved heating plate was designed as heating cell. The heating system can achieve the accurate control of the sample temperature within the scope of 10–100 °C. The dynamic undrained characteristics of saturated soft silty clay in Ningbo were studied under different temperatures, dynamic stress amplitude, confining pressure and initial static deviation stress by using the newly developed temperature-controlled triaxial test system. The test results showed that the temperature has great influence on the accumulative plastic strain, pore water pressure, damping ratio and dynamic elastic modulus of soft clay. As temperature increases, the cumulative plastic strain, the dynamic damping ratio and the dynamic pore pressure decrease, while the dynamic elastic modulus increases. Furthermore, the saturated soft clay exhibited a tendency of thermal hardening. Finally, a unified empirical strain model, which can consider the effect of temperature, dynamic stress amplitude, confining pressure and initial static deviator stress on accumulative plastic strain, was proposed. By using the test results, it is confirmed that the proposed empirical model is capable of predicting the undrain cumulative plastic strain of soft clay under different conditions.

Correlations between Shear Wave Velocity and Geotechnical Parameters for Jiangsu Clays of China

The shear wave velocity ( $$V_{\text{s}}$$ ) is an important factor reflecting the dynamic characteristics of soil. Measured $$V_{\text{s}}$$ values are always used in combination with laboratory parameters (e.g., effective confining pressure, $$\sigma_{\text{m}}^{{\prime }}$$ , and void ratio, e) and in situ penetration parameters from the standard penetration test (SPT) and piezocone penetration testing (CPTU). This study aims not only to estimate Vs based on correlations with other parameters in the absence of site-specific data, but also to outline relationships for estimation of soil properties. A database of seismic CPTU (SCPTU) and soil properties information for Jiangsu clays in East China was used to develop correlations between $$V_{\text{s}}$$ and geotechnical parameters (vertical effective stress, unit weight, preconsolidation stress, site-specific parameters, undrained shear strength, and CPTU net cone resistance). Laboratory tests were carried out on thin-walled tube samples and high-quality block samples to measure soil properties. The results showed that the predicted values of $$V_{\text{s}}$$ were in good accordance with measured values from field tests, especially the Vs values predicted from the CPTU net cone resistance. The relationship between $$V_{\text{s}}$$ and the undrained shear strength showed better performance than the others. The good relationships between $$V_{\text{s}}$$ and geotechnical parameters could be used to interpret engineering properties of Jiangsu clays for site investigation.

Sensitivities of the Rayleigh and Love Phase Velocities and Attenuation Coefficients

AbstractIn situ characterization of dynamic soil characteristics by means of surface wave tests frequently involves the determination and inversion of dispersion and attenuation curves. The inverse...

Effect of excavation blasting vibration on adjacent buried gas pipeline in a metro tunnel

To ensure the safety of gas pipeline during tunnel blasting excavation, it is crucial to investigate the dynamic response of gas pipeline to blast vibration under tunnel excavation. In this paper, the blasting excavation of Beijing metro line 16 was selected as a case, and the blasting vibrations in the field were monitored. Based on the field monitoring data, a mathematical model was established and proposed to describe the attenuation of peak particle velocity (PPV) of ground surface soils with respect to the depth of tunnel blasting. Next, a 3D numerical model was established to analyze the response characteristics of burial gas pipeline subjected to blasting vibration and its reliability was verified using the field monitoring data. The effects of metro tunnel blasting vibration on gas pipeline under different tunnel blasting conditions were further calculated, and the dynamic response characteristics of soil, pipe and pipe surrounding soil were discussed. At last, to better and more conveniently assess and predict the influence of blasting vibration, a PPV prediction model of gas pipeline under metro tunnel excavation blasting for this project was proposed.

Wind erosion enhanced by land use changes significantly reduces ecosystem carbon storage and carbon sequestration potentials in semiarid grasslands

AbstractWind erosion exerts a fundamental influence on the biotic and abiotic processes associated with ecosystem carbon (C) cycle. However, how wind erosion under different land use scenarios will affect ecosystem C balance and its capacity for future C sequestration is poorly quantified. Here, we simulated different intensities of land uses in Inner Mongolia: control, 50% of vegetation mowed (50 M), 100% vegetation mowed (100 M), and tillage (TI). We monitored abiotic C flux caused by wind erosion, net ecosystem exchange (NEE), and soil characteristics from 2013 to 2016. We found that the frequency of heavy wind exerts a fundamental control over the severity of soil erosion, and its interaction with precipitation and vegetation characteristics explained 69% of the variation in erosion intensity. With increases in land use intensity, the abiotic C flux induced by wind erosion increased rapidly, equivalent to 33%, 86%, 111%, and 183% of the NEE of natural steppe in the control, 50 M, 100 M, and TI sites, respectively. The erosion‐induced decrease in fine fraction soils led to 31%, 43%, and 85% permanent losses of C sequestration potential in the surface soil for 50 M, 100 M, and TI sites. Overall, our study demonstrates that the abiotic C flux associated with wind erosion is too large to be ignored. The loss of C‐enriched fine particles not only reduces the current ecosystem C content but also results in an irreversible loss of future soil C sequestration potential. These dynamic soil characteristics need to be considered when projecting future ecosystem C balance in aeolian landscapes.

The Determination of Damping Ratio Based on Cross-correlation Function Method

For a long time, the regular, even sinusoidal dynamic load is used to study the development of pore pressure and strain in soil dynamic tests. But in fact, the dynamic loads in the study of soil dynamic characteristics are mostly irregular and even random. At present, the equivalent linear model method is used to calculate the dynamic characteristics of soil under random loads. However, this method does not take into account the plastic deformation of soil which is contrary to the actual deformation of soil. In this paper, the stochastic process theory is introduced into the measurement and analysis of soil dynamic characteristics. The dynamic stress time history, dynamic strain time history and dynamic pore pressure time history are all regarded as random processes. So a cross-correlation function method based on stochastic theory is proposed, and the feasibility of determining the damping ratio of soil by this method is verified by means of experiments and numerical analysis. The results show that the cross-correlation function method can not only solve the damping ratio of soil under periodic load, but also determine the damping ratio of soil under random load.

Back analysis of ground vibrations which cause cracks in buildings in residential areas Karakuyu (Dinar, Afyonkarahisar, Turkey)

The Karakuyu village (Dinar) is located in the south-western Turkey. Karakuyu settlement area suffered from ground vibration. There are two reasons for ground vibration in that area. One of them is earthquake and other is rock blasting. Geological structure and tectonics have great influence on vibrations in the area. An earthquake of magnitude Ms = 6.1 occurred on 1 October 1995, causing causalities and damage to buildings in Dinar and its vicinity. The earthquake forces during the main shock were amplified by poor dynamic characteristics of alluvial soils, thus resulting in damage to buildings. Limestone quarries are other source of ground vibration because of blasting. In this study, the source of vibration causing cracks in buildings in the Karakuyu residential area was investigated. Blasting at limestone quarries and past earthquake activities are analysed of ground vibrations which cause cracks in buildings. In the scope of this study, the source of the vibrations which cause the observed cracks in buildings were investigated using back analysis. As a result of the study, earthquake-induced vibrations on structural behaviour of buildings were found critical.

Numerical simulation for underground explosion problem and dynamic characteristics of Okinawa's unique soil

Numerical simulation for underground explosion problem and dynamic characteristics of Okinawa's unique soil

Dynamic equivalent soil characteristics identification using earthquake records

Dynamic equivalent soil characteristics identification using earthquake records

Linear and nonlinear site response analyses to determine dynamic soil properties of Kirikkale

In order to make reliable earthquake-resistant design of civil engineering structures, one of the most important considerations in a region with high seismicity is to pay attention to the local soil condition of regions. It is aimed in the current study at specifying dynamic soil characteristics of Kirikkale city center conducting the 1-D equivalent linear and non-linear site response analyses. Due to high vulnerability and seismicity of the city center of Kirikkale surrounded by active many faults, such as the North Anatolian Fault (NAF), the city of Kirikkale is classified as highly earthquake-prone city. The first effort to determine critical site response parameter is to perform the seismic hazard analyses of the region through the earthquake record catalogues. The moment magnitude of the city center is obtained as Mw=7.0 according to the recorded probability of exceedance of 10% in the last 50 years. Using the data from site tests, the 1-D equivalent linear (EL) and nonlinear site response analyses (NL) are performed with respect to the shear modulus reduction and damping ratio models proposed in literature. The important engineering parameters of the amplification ratio, predominant site period, peak ground acceleration (PGA) and spectral acceleration values are predicted. Except for the periods between the period of T=0.2-1.0 s, the results from the NL are obtained to be similar to the EL results. Lower spectral acceleration values are estimated in the locations of the city where the higher amplification ratio is attained or vice-versa. Construction of high-rise buildings with modal periods higher than T=1.0 s are obtained to be suitable for the city of Kirikkale. The buildings at the city center are recommended to be assessed with street survey rapid structural evaluation methods so as to mitigate seismic damages. The obtained contour maps in this study are estimated to be effective for visually characterizing the city in terms of the considered parameters.

Joint deconvolution of building and downhole seismic recordings: an application to three test cases

In this study, the joint deconvolution is applied to recordings of three test cases located in the cities of Bishkek, Kyrgyzstan, Istanbul, Turkey, and Mexico City, Mexico. Each test case consists of a building equipped with sensors and a nearby borehole installation in order to investigate different cases of coupling (impedance contrasts) between the building and the soil by analyzing the wave propagation through the building-soil-layers, and hence resolving the soil–structure-interactions. The three installations considering different dynamic characteristics of buildings and soil, and thus, different building-soil couplings, are investigated. The seismic input (i.e., the part of the wave field containing only the up-going waves after removing all down-going waves) and the part of the wave field that is associated with the waves radiated back from the building are separated by using the constrained deconvolution. The energy being radiated back from the building to the soil has been estimated for the three test cases. The values obtained show that even at great depths (and therefore distances), the amount of wave field radiated back by the building to the soil is significant (e.g., for the Bishkek case, at 145 m depth, 10% of the estimated real input energy is expected to be emitted back from the building; for Istanbul at 50 m depth, the value is also 10–15% of the estimated real input energy while for Mexico City at 45 m depth, it is 25–65% of the estimated real input energy). Such results confirm the active role of buildings in shaping the wave field.

Application of the microtremor measurements to a site effect study

Earthquake has left much life and property damages. The occurrence of such events necessitates the execution of plans for combating the earthquakes. One of the most important methods for combating earthquakes includes assessing dynamic characteristics of soil and site effect. One of the methods by which one can state dynamic characteristics of the soil of an area is the measurement of microtremors. Microtremors are small-scale vibrations that occur in the ground and have an amplitude range of about 0.1–1 microns. Microtremor measurement is fast, applicable, cost-effective. Microtremor measurements were taken at 15 stations in the Babol, north of Iran. Regarding H/V spectral ratio method, peak frequency and amplification factor were calculated for all microtremor stations. According to the analysis, the peak frequency varies from 0.67 to 8.10 Hz within the study area. Also, the authors investigated the validity of the results by comparing them with SESAME guidelines and geotechnical conditions of study area. The microtremor analysis results are consistent with SESAME guidelines and geotechnical condition of study area. The results show that the microtremor observations are acceptable methods for assessing dynamic characteristics of soil and site effect in the Babol City.

Effect of the Time-Varying Soil Resistivity on the Performance of the Protective Devices under the Electromagnetic Fields from Lightning

Background/Objectives: Transients in the overhead power lines due to lightning events can be caused by both direct and indirect strokes. Both direct and indirect events can cause severe issues in the power system. Methods/Statistical Analysis: The frequency of the indirect lightning return strokes is more when we consider the lightning studies on the overhead lines considering the height of the present distribution and transmission lines. Lightning-induced voltages on the overhead transmission lines have been computed using the finite-difference time-domain method. A source of lightning surge wave on power transmission lines is modelled as a double exponential wave using Modified Transmission Line with Exponential current decay (MTLE) model. Computation of overvoltage caused by lightning waves is calculated for single conductor lines with and without considering the soil reflections taking into account the dynamic characteristics of soil under lightning conditions. Findings: Computations are carried out for the various configurations of multi-conductor transmission lines. The effectiveness of the protective devices such as shield wires is also studied here. The surge arrester modelling is carried out and the design parameters for these protective devices are finalised after optimization. MATLAB and PSCAD software are used for simulation. Triangular configuration gave a better response to lightning than the horizontal and vertical configuration. Applications/Improvements: A 3D approach on the problem with use of COMSOL will give a better insight on the field pattern.

Experimental Study on Geosynthetic Reinforced Soil Dynamic Characteristics under Cyclic Loading

The technology of geosynthetic reinforced soil has been widely used in the structural strengthening of highway subgrade. Under the action of long-term vehicle cyclic loading, geosynthetic reinforced soil can effectively improve the bearing and deformation resistance capacity of the subgrade, improve the long-term stability of the highway structure and prolong the service period of the road. At present, the quasi-static method to design the geosynthetic reinforced subgrade under the action of traffic load is not perfect enough, the research on dynamic property, design theory and parameters still lags far behind engineering practice and technology development. In this paper, we investigated the dynamic triaxial tests in laboratory with different kinds of soils (clay and silt), different confining pressures (50 Kpa, 100 Kpa and 150 Kpa), and different reinforcement layers (0 layer, 1 layer and 2 layers) to show the changes and influencing factors of dynamic elastic modulus and damping ratio. The experimental results will provide the basis for the parameter choice of geosynthetic reinforced subgrade with the influence of traffic load.

RETRACTED ARTICLE: Virtual reality research of the dynamic characteristics of soft soil under metro vibration loads based on BP neural networks

In this paper, in order to research the dynamic characteristics of soft soil under metro vibration loads, the mathematical expression of metro vibration loads is obtained. According to the loading form, drainage requirement and vibration frequencies of the actual situation, the corresponding experiment is conducted through indoor dynamic triaxial equipment. Then, the dynamic characteristics of experimental results are analyzed. An empirical formula is proposed to compute the dynamic characteristics of soft soil. Then, the computational results obtained by empirical formula are compared with those of the experimental. They are consistent with each other, and the results show that empirical formula is reliable to compute the dynamic characteristics of soft soil. Then, based on the verified empirical formula, the dynamic characteristics such as the vertical strain and pore water pressure with different CSR are also computed and compared. With the increase in CSR, the dynamic characteristics will be larger when the other parameters are consistent. However, empirical formula can only predict the dynamic characteristics of the simple model. In order to realize virtual reality of the dynamic characteristics of the complex model more accurately, the BP neural network and finite element are adopted, respectively. Then, the computational results are also compared with those of the experimental to verify their reliabilities. In the future, the BP neural network and finite element method can be also used to realize virtual reality of the dynamic characteristics of the more complex model.