Dynamic Response of Foundations during Startup of High-Frequency Tunnel Equipment

The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is supported by the foundation of the units,and the magnitude of vibration and the operating frequency fluctuate in different engineering contexts,leading to variations in the dynamic response of the foundation.The high-frequency units yield significantly diverse outcomes under different startup conditions and times,resulting in failure to meet operational requirements,influencing the normal function of the tunnel,and causing harm to the foundation structure,personnel,and property in severe cases.This article formulates a finite element numerical computation model for solid elements using three-dimensional elastic body theory and integrates field measurements to substantiate and ascertain the crucial parameter configurations of the finite element model.By proposing a comprehensive startup timing function for high-frequency dynamic machines under different startup conditions,simulating the frequency andmagnitude variations during the startup process,and suggesting functions for changes in frequency and magnitude,a simulated startup schedule function for high-frequency machines is created through coupling.Taking into account the selection of the transient dynamic analysis step length,the dynamic response results for the lower dynamic foundation during its fundamental frequency crossing process are obtained.The validation checks if the structural magnitude surpasses the safety threshold during the critical phase of unit startup traversing the structural resonance region.The design recommendations for high-frequency units’dynamic foundations are provided,taking into account the startup process of the machine and ensuring the safe operation of the tunnel.

Dynamic analysis of bio-inspired helicoid laminated composite plates resting on Pasternak foundation excited by explosive loading

This paper uses isogeometric analysis(IGA)based on higher-order shear deformation theory(HSDT)to study the dynamic response of bio-inspired helicoid laminated composite(B-iHLC)plates resting on Pasternak foundation(PF)excited by explosive loading.IGA takes advantage of non-uniform rational Bspline(NURBS)basic functions to exactly represent the structure geometry models and the attainment of higher-order approximation conditions.This method also ensures a C1 continuous function in the analysis of transverse shear deformation via HSDT.Furthermore,IGA eliminates the requirement for correction factors and delivers accurate results.Pasternak foundation with two stiffness parameters:springer stiffness(k_(1))and shear stiffness(k_(2)).The derivation of the governing equations is based on Hamilton's principle.The proposed method is validated through numerical examples.A comprehensive analysis of the impact of geometrical parameters,material properties,boundary conditions(BCs),and foundation stiffness on dynamic response of B-i HLC plates is carried out.

Energy-based dynamic parameter identification for Pasternak foundation model

Parameter identification of Pasternak foundation models(PFM)is never satisfactory,which discourages the application and popularization of PFM.In the present study,an energy-based model to predict the dynamic foundation coefficients was proposed using the vibration kinetic energy and potential energy of a Pasternak foundation-rigid plate system.On the basis of the Pasternak foundation,the relationship among the natural frequency,dynamic foundation coefficients,rigid plate configuration,and vibrating soil equivalent mass per unit area was considered.To obtain the natural frequencies of the Pasternak foundation-rigid plate system,dynamic tests were performed.Using two or more dynamic test results of various rigid plates on a foundation,a set of equations of dynamic foundation coefficients was set up to directly identify the foundation coefficients and equivalent mass per unit area of vibrating soil.The feasibility of the proposed method was verified by comparing it with the outdoor and indoor test results and finite element analysis results.When the proposed method is used to obtain the dynamic parameters,PFM can be generalized and applied more widely in engineering practice.

Application of artificial neural networks for predicting the impact of rolling dynamic compaction using dynamic cone penetrometer test results

Rolling dynamic compaction(RDC),which involves the towing of a noncircular module,is now widespread and accepted among many other soil compaction methods.However,to date,there is no accurate method for reliable prediction of the densification of soil and the extent of ground improvement by means of RDC.This study presents the application of artificial neural networks(ANNs) for a priori prediction of the effectiveness of RDC.The models are trained with in situ dynamic cone penetration(DCP) test data obtained from previous civil projects associated with the 4-sided impact roller.The predictions from the ANN models are in good agreement with the measured field data,as indicated by the model correlation coefficient of approximately 0.8.It is concluded that the ANN models developed in this study can be successfully employed to provide more accurate prediction of the performance of the RDC on a range of soil types.

Application of strength reduction method to dynamic anti-sliding stability analysis of high gravity dam with complex dam foundation

Considering that there are some limitations in analyzing the anti-sliding seismic stability of dam-foundation systems with the traditional pseudo-static method and response spectrum method, the dynamic strength reduction method was used to study the deep anti-sliding stability of a high gravity dam with a complex dam foundation in response to strong earthquake-induced ground action. Based on static anti-sliding stability analysis of the dam foundation undertaken by decreasing the shear strength parameters of the rock mass in equal proportion, the seismic time history analysis was carried out. The proposed instability criterion for the dynamic strength reduction method was that the peak values of dynamic displacements and plastic strain energy change suddenly with the increase of the strength reduction factor. The elasto-plastic behavior of the dam foundation was idealized using the Drucker-Prager yield criterion based on the associated flow rule assumption. The result of elasto-plastic time history analysis of an overflow dam monolith based on the dynamic strength reduction method was compared with that of the dynamic linear elastic analysis, and the reliability of elasto-plastic time history analysis was confirmed. The results also show that the safety factors of the dam-foundation system in the static and dynamic cases are 3.25 and 3.0, respectively, and that the F2 fault has a significant influence on the anti-sliding stability of the high gravity dam. It is also concluded that the proposed instability criterion for the dynamic strength reduction method is feasible.

Liquefaction mitigation in silty soils using composite stone columns and dynamic compaction

The objective of this study is to develop an analytical methodology to evaluate the effectiveness of vibro stone column (S.C.) and dynamic compaction (D.C.) techniques supplemented with wick drains to densify and mitigate liquefaction in saturated sands and non-plastic silty soils. It includes the following: (i) develop numerical models to simulate and analyze soil densitication during S.C. installation and D.C. process, and (ii) identify parameters controlling post-improvement soil density in both cases, and (iii) develop design guidelines for densification of silty soils using the above techniques. An analytical procedure was developed and used to simulate soil response during S.C. and D.C. installations, and the results were compared with available case history data. Important construction design parameters and soil properties that affect the effectiveness of these techniques, and construction design choices suitable for sands and non-plastic silty soils were identified. The methodology is expected to advance the use of S.C. and D.C. in silty soils reducing the reliance on expensive field trials as a design tool. The ultimate outcome of this research will be design charts and design guidelines for using composite stone columns and composite dynamic compaction techniques in liquefaction mitigation of saturated silty soils.

Experiment Study of Dynamics Response for Wind Turbine System of Floating Foundation

The floating foundation is designed to support a 1.5 MW wind turbine in 30 m water depth. With consideration of the viscous damping of foundation and heave plates, the amplitude-frequency response characteristics of the foundation are studied. By taking into account the elastic effect of blades and tower, the classic quasi-steady blade-element/momentum（BEM） theory is used to calculate the aerodynamic elastic loads. A coupled dynamic model of the turbine-foundationmooring lines is established to calculate the motion response of floating foundation under Kaimal wind spectrum and regular wave by using the FAST codes. The model experiment is carried out to test damping characteristics and natural motion behaviors of the wind turbine system. The dynamics response is tested by considering only waves and the joint action of wind and waves. It is shown that the wind turbine system can avoid resonances under the action of wind and waves. In addition, the heave motion of the floating foundation is induced by waves and the surge motion is induced by wind. The action of wind and waves is of significance for pitch.

Improvement parameters in dynamic compaction adjacent to the slopes

Dynamic compaction is a cost-effective method commonly used for improvement of sandy soils. Anumber of researchers have investigated experimentally and numerically the improvement parametersof soils using dynamic compaction, such as crater depth, improvement depth, and radial improvement,however, these parameters are not studied for improvement adjacent to the slopes or trenches. In thisresearch, four different slopes with different inclinations are modeled numerically using the finiteelement code ABAQUS, and impact loads of dynamic compaction are applied. The static factors of safetyare kept similar for all trenches and determined numerically by application of gravity loads to the slopeusing strength reduction method （SRM）. The analysis focuses on crater depth and improvement regionwhich are compared to the state of flat ground. It can be observed that compacted area adjacent to theslopes is narrower and slightly away from the slope compared to the flat state. Moreover, crater depthincreases with increase in slope inclination.2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Reinforcement effects of ground treatment with dynamic compaction replacement in cold and saline soil regions

The mechanical property of saline soils varies with moisture and climate in the cold and salt lake region of Qinghai-Tibet Plateau, which influences project construction. In order to improve foundation reinforcement effect of the QarharvaTrolmud Highway, Qinghai Province, China, dynamic compaction replacement （DCR） composite foundation was applied in saline soils. A field experiment was conducted in this area, where strength and working mechanism of pier-soil and deformation modulus of the composite foundation was analyzed after reinforcement. This paper presents methods for determining the coefficient on the bearing capacity evaluation and deformation modulus of composite foundation with DC1L Reinforcement case of DCR is highly effective in saline soils of the salt lake regions, which helps the mi-tion of water and salt in saline soils.

Dynamic earth pressure on rigid retaining walls induced by a neighboring machine foundation,by the meshless local Petrov-Galerkin method

Dynamic earth pressure induced by machine foundations on a neighboring retaining wall is analyzed with emphasis on factors which control the intensity and location of the design forces. The meshless local Petrov-Galerkin (MLPG) method is used to analyze the problem for a variety of retaining wall and machine foundation geometries. The soil medium is assumed to be homogeneous and visco-elastic. The machine foundation is idealized as a harmonic sinusoidal dynamic force often encountered in practice. A number of analyses have been made to reveal the effect of the loading frequency, the location and size of the foundation and the soil shear wave velocity on the distribution and magnitude of the dynamic earth pressure. Results indicate that there is a critical frequency and a critical location for which the passive pressure takes the maxima in the entire duration of the dynamic load.

SEMI-ANALYTICAL AND SEMI-NUMERICAL METHOD FOR DYNAMIC ANALYSIS OF FOUNDATION

A semi-analytical and semi-numerical method is proposed for the dynamic analysis of foundations. The Lamb＇s solution and the approximate formulae were used to establish the relation of the contact force and deflection between the foundation and soil. Therefore, the foundation can be separated from soil and analyzed by FEM as for the static cases. The plate can be treated as that the known forces are acting on the upper surface, and the contact pressure from soil can be represented as the deflection. So that only the plate needs to be divided into elements in the analysis. By this method, a series of vibration problems, including various shapes and rigidities of foundations, different excitation frequencies, were analyzed. Furthermore, it can be used for the embedded foundation. The numerical examples show that this method has simplicity, highly accurate and versatile. It is an effective method for the dynamic analysis of foundations.

Application of dynamic compaction and rolling compaction in the subgrade improvement of Qarhan-Golmud Highway

Melt shrinkage, salt bulge, and corrosiveness are common problems with saline soils, which damage highway foundations and cause huge financial losses. In order to improve the saline soil subgrade, dynamic compaction （DC） and rolling compaction （RC） technology were applied on the Qarhan-Golmud Highway in Qinghai Province, China. A field experi- ment was conducted in which shear strength, deformation modulus, and the working mechanism of the composite foun- dation were analyzed after reinforcement. Both the DC and RC methods were found to be effective and helped to improve the foundation strength of saline soils, although the ultimate bearing capacity and deformation modulus of the RC method were lower than that of the DC method.

Analysis of Dynamic Stability of Ocean Gravity Structure Foundations

Based on unified equivalent harmonic loading on seabed foundation and energy approach suggested by the authors, the development of dynamic pore water pressure and stability of soil foundation for the vibration of ocean gravity structures excited by random wave loading are analysed. It may be seen that the present method for the study of dynamic problems of ocean gravity structure soil foundations is more reasonable and convenient.

GENERAL SOLUTION FOR DYNAMICAL PROBLEM OF INFINITE BEAM ON AN ELASTIC FOUNDATION

Based on the theory of Eider-Bernoulli beam and Winkler assumption for elastic foundation, a mathematical model is presented. By using Fourier transformation for space variable, Laplace transformation for time variable and convolution theorem for their inverse transformations, a general solution for dynamical problem of infinite beam on an elastic foundation is obtained. Finally, the cases of free vibration,impulsive response and moving load are also discussed.

DYNAMIC RESPONSE ANALYSIS OF PLATFORM-CYLINDERGROUP FOUNDATION DUE TO IMPACT BY WATER WAVE FLOW

This paper deals. with the problem of dynamic response of platform-cylinder group foumdation. Dynamic interaction of cylinder group foudation-water-soil is taken into account and the analysis of dynamic response to excitation of water wave force is given by analytic method ..The numerical examples are presented and the influence of systent’s parameters on the dynamic behaviour is discussed.

Analytical evaluation and experimental validation on dynamic rocking behavior for shallow foundation considering structural response

The challenge in the practical application of rocking foundations is the estimation of its performance,particularly the rotation angle,during a strong earthquake.In this study,the dynamic rocking behavior for a shallow foundation considering structural response was evaluated through two analytical approaches:the conventional soil-foundation-structure interaction(SFSI)governing equation of a single-degree-of-freedom(SDOF)structure on a rocking shallow foundation,and the Housner rocking model(i.e.,a rocking rigid block on a rigid base).Both approaches were validated with dynamic centrifuge tests.The test models consisted of a soft soil deposit,a shallow rectangular foundation,and an SDOF structure dominated by a bending behavior.A total of 11 foundation-structure systems and six seismic waves,including recorded earthquake signals and sinusoidal waves,were utilized.The results showed that the conventional SFSI equation well predicted the maximum rotation during strong earthquakes.However,this method was less accurate regarding the rotational phase information and maximum rotation of the foundation during weak earthquakes.On the other hand,although the modified Housner′s rocking model required five parameters relevant to a soil-foundation-structure system,it overestimated the maximum rotation of the foundation when compared with the results from dynamic centrifuge tests.

Numerical Study of the Mechanical Behavior of a Foundation Raft under the Hydrodynamic Influence of the Mechanical Characteristics of Clay Soils

The clay soils of the city of Douala are constantly saturated with water, which permanently favors the hydrodynamic behavior of the soils (swelling or consolidation). This phenomenon can cause serious disturbances in the structure of buildings resulting in the appearance of cracks in structures (buildings, road bridge, viaduct, etc.). The foundation raft is a very important structure in the dimensioning of structures. Given the soil-structure interactions, its mechanical characteristics must be the subject of a special study linked to the building environment. In this article, we present a study of the mechanical behavior of a foundation raft anchored in a laminate floor. The aim is to highlight the influence of the mechanical properties of the foundation soil on the evolution of the mechanical behavior of the raft. The method used is a numerical simulation. A physical model taking into account a 5-storey building based in Douala in the Denver district is studied. The foundation on the raft foundation of this building follows an elastic constitutive law with Mazars damage, and rests on a laminated soil of plastic elastic model with Camclay plasticity criterion. The ground-raft and ground-ground interfaces are carried out with the finite elements joined to three nodes (JOI3), and obey the Coulomb model;it is an expansion joint model with Mohr-Coulomb type criterion and associated flow. The numerical resolution is carried out by the finite element method, and the numerical simulations via the Cast3M calculation code. The results from the simulations show that the mechanical characteristics of foundation soils, in this case the water content, the compactness, the state of consolidation, greatly influence the mechanical behavior of the foundation slab. There is indeed a significant settlement and a great deformation of the raft foundation when the water content of the soil layers increases, and when the states of consolidation and compactness are low. This article allows us to predict and control the evolution of the behavior of the ground-structure interface of a raft foundation and to adopt a new model appropriate for the sizing of civil engineering structures.

Numerical Analysis and Study of the Dynamic Response of Structural Systems for Machinery Foundations

This work aims the deterministic dynamic analysis,in the time and frequency domain,of a reinforced concrete floor supported by a pre-cast pile foundation system,when subjected to the excitation produced by a large compressor installed in an industry for the production of air gases.The concrete slab presents a dimension of 12 m×15 m,required to support a compressor-motor assembly weighting 1,900 kN and positioned at a height of 4m of the investigated concrete floor.In this investigation,two numerical models were developed and the difference between these models is characterized by the discretization of the support points(pre-cast concrete piles).The developed numerical model adopted the usual mesh refinement techniques present in finite element method simulations implemented in the CSi SAP2000 V.17.2.0 software.Based on the developed analysis methodology,the dynamic structural response of the foundation system is evaluated in terms of natural frequencies,vibration modes,displacements,velocities,and accelerations.The maximum values of the dynamic response of the system are compared with the limit values recommended by standards and project recommendations,aiming a careful evaluation,regarding the performance of the structure in terms of excessive vibrations and the economic aspects involved in the design of the foundation system.Finally,the obtained results of the two developed numerical models are compared,as to evaluate if there are benefits in refining the support points modelling.

Dynamic Characteristics Analysis on Wind-Blown Sand Ground under Dynamic Compaction Vibration

In the 6000 kN·m energy level dynamic compaction on Inner Mongolia wind-blown sand foundation treatment process, the dynamic characteristics and dynamic response are measured. Vibration action time, vibration main frequency, peak acceleration and peak velocity are analyzed. The vibration acting time is very short, the vertical average vibration acting time increases obviously with distance increasing, and the horizontal average vibration time does hardly change. The main frequency of vibration is at 4.60 - 24.90 Hz, which depends on the soil properties and soil layer distribution. The peak acceleration and peak velocity space distribution are similar. The maximum of horizontal acceleration peak is close to vertical velocity peak, and is near to 51 g under rammer. The maximum of horizontal velocity peak is close to vertical velocity peak, and is near to 54 m/s under rammer. The peak acceleration and velocity are rapidly attenuated, but the vertical peak acceleration and peak velocity are slowly attenuated than horizontal direction. The effective treating depth arrives 13 m for wind-blown wind, peak acceleration is 1.8 g or so, and peak velocity is 2.1 m/s or so. Horizontal treating range is 2.6 times of rammer diameter, and vertical treating range is 5.65 times of rammer diameter.

Genetic programming for predictions of effectiveness of rolling dynamic compaction with dynamic cone penetrometer test results

Rolling dynamic compaction (RDC),which employs non-circular module towed behind a tractor,is an innovative soil compaction method that has proven to be successful in many ground improvement applications.RDC involves repeatedly delivering high-energy impact blows onto the ground surface,which improves soil density and thus soil strength and stiffness.However,there exists a lack of methods to predict the effectiveness of RDC in different ground conditions,which has become a major obstacle to its adoption.For this,in this context,a prediction model is developed based on linear genetic programming (LGP),which is one of the common approaches in application of artificial intelligence for nonlinear forecasting.The model is based on in situ density-related data in terms of dynamic cone penetrometer (DCP) results obtained from several projects that have employed the 4-sided,8-t impact roller (BH-1300).It is shown that the model is accurate and reliable over a range of soil types.Furthermore,a series of parametric studies confirms its robustness in generalizing data.In addition,the results of the comparative study indicate that the optimal LGP model has a better predictive performance than the existing artificial neural network (ANN) model developed earlier by the authors.