Abstract:

With the advantages of large carrying capacity， continuous transportation， and economic ef? ficiency， buried pipelines， which are known as the "lifeline" for energy transmission， are widely used in many fields， such as water conservancy engineering， municipal engineering， and marine engineer? ing. However， due to the complex and changeable working loads and geological environments， the buried pipelines are prone to vertical uplift buckling failure. There are complex pipe-soil interactions in the uplift process of pipelines， and it is of great significance to master their deformation and failure mechanism to predict the uplift resistance and optimize pipeline design. Based on the study of soil de? formation and failure modes during vertical uplift buckling of pipelines， domestic and overseas schol? ars have discussed the influence factors of soil resistance， including soil type， soil compactness， drain? age conditions， pipeline diameter， uplift rate， burial rate， etc.， and have proposed corresponding pre? diction models. The state-of-the-art in the deformation mechanism of the soil around the vertical buck? ling pipeline is summarized into three aspects， i.e.， the failure modes of the soil， the influence factors of the soil resistance and the prediction model of the soil resistance， and the future development direc? tion of this field is also pointed out.

Abstract:

Earthquakes are one of the main causes of damage to the integrated pipe gallery. Once the integrated pipe gallery is damaged， the consequences will be much more complex than the traditional buried pipeline. In this paper， several common joint forms of integrated pipe gallery are introduced， fi? nite element models are established for different joint forms， the standard section of the integrated pipe gallery is selected， the concrete plastic damage model and soil constitutive model are considered， and the seismic response analysis of the pipe gallery with different joint forms and the internal pipelines is analyzed by applying viscoelastic artificial boundary and equivalent nodal force by the self-programmed program. The results show that the response of the monolithic cast-in-situ structure is higher than that of the prefabricated assembled structure for the maximum longitudinal displacement difference under different ground motion intensities， and the response difference will further increase with the increase of ground motion intensity. Under the two joint forms， the damage of the standard section of the pipe gallery under the seismic action is very small， and only minor damage will occur when the peak accel? eration of ground motion reaches 0.4g and above， which will not affect its serviceability states. Under the same seismic action， the pipe stress level of the small diameter pipe will be smaller than that of the large diameter pipe. The joint form of combining a rubber water stop belt with a prestressed steel bar at the same time will be more conducive to reducing the stress level of the pipeline in the corridor than the joint form of only a rubber water stop belt. Considering that the prefabricated assembled structure connected by prestressed steel bars will further improve the safety level of the pipelines in the corri? dor， therefore， when the cost permits， not only the waterproofing of the joints should be considered， but also the adjacent sections should be connected with prestressed ribs to further improve the seismic performance of the integrated pipe gallery.

Abstract:

Seismic dynamic reliability of urban lifeline networks is an important index for evaluating the seismic risk and resilience of lifeline engineering. The calculation methods include the simulation method represented by the Monte Carlo method and the non-simulation method represented by the ex- tended recursive decomposition algorithm. The latter is more advanced because it can give the main failure mode of the lifeline networks. However， due to the problem that high-dimensional Gumbel Copula parameters cannot be estimated， the current extended recursive decomposition algorithm can- not calculate the seismic dynamic reliability of large lifeline networks (the number of structures or equipment constituting the lifeline network is more than 60). To solve this problem， a fitting formula for high-dimensional Gumbel Copula parameters estimation is proposed and embedded into the extend-ed recursive decomposition algorithm to form a calculation method for seismic dynamic reliability of large lifeline networks. The calculation and analysis of seismic dynamic reliability of a practical 220 kV substation equipment network show the application process， suitability and effectiveness of this meth- od.

Abstract:

Based on the finite element analysis method， a three-dimensional finite element model for utility tunnel-soil structure interaction simulation was established， and the dynamic response character- istics of the stepped double-layer multi-warehouse integrated utility tunnel under non-uniform seismic stimulation were investigated. Through modal analysis， the natural vibration frequency and deforma- tion characteristics of the stepped double-layer multi-warehouse integrated utility tunnel with three joint forms of cast-in-place， flat and tongue-and-groove were obtained. The dynamic response of the utility tunnel was calculated for the entire tunnel， tunnel body and joints under the non-uniform excitation of the small earthquake (0.05g)， medium earthquake (0.1g) and large earthquake (0.2g). The result shows that： for the three kinds of joint types， the torsional shear failure occurred first at the joint， and the stress level at the joint of the utility tunnel was obviously higher than that of the utility tunnel body，of which the tongue-and-groove joint was particularly obvious； Under the non-uniform seismic excita- tion， the response time history curves of the points on both sides of the utility tunnel joints showed very obvious inconsistency in response. The dynamic responses of the three types of joints were mainly transverse (X) and vertical (Y) vibrations， and supplemented by axial (Z) vibrations. The displace- ment along the roof axis of the utility tunnel increased gradually with the increase of the seismic force， and there was an obvious mutation of displacement at the joints of the flat and cast-in-place utility tun- nel. The mutation was mainly in the transverse direction. The displacement distribution curve was con- tinuous and has nearly no mutation for the tongue-and-groove joint because of its good integrity. There was obvious stress concentration at the joints of the utility tunnel. The stress concentration phenome- non of cast-in-place and mouth joints mainly appeared at the corner， and that of the tongue-and-groove joints mainly appeared at the mortise， tenon and corner. Cast-in-place and flat-mouth joints showed "re- verse bell mouth" deformation and up-and-down displacement. The tongue-and-groove joints illustrat- ed nearly no up-and-down dislocation except a higher stress level because of its good integrity.

Abstract:

The pipeline joint is a key and weak segment affecting the daily operation safety of the mu- nicipal water supply network. However， most of the current investigations were devoted to the me- chanical performance of pipeline joints under seismic and axial loading， while there were few studies on the flexural mechanical behaviors of ductile iron water supply pipeline joints under vertical loading， resulting in a lack of comprehensive evaluation on this type of pipeline joints. In this study， the ductile iron water supply pipeline joint is taken as the main research object to study its damage behavior under vertical loading by experiment and numerical simulation. The results indicate that：(1) the contact fail- ure of the rubber sealing ring in joint is the main cause of the pipeline leakage；(2) the relative rotation angle of the pipeline joint and the vertical load have a good positive correlation；(3) The relative rota-tion angle when the pipeline exhibits water leakage is around 12°. Therefore， there is a need to per- form a refined design for water supply pipeline joint and rubber sealing ring in order to avoid the failure of pipeline joint under different loading circumstances such as contact sliding， rotation and drawing， so as to increase the maximum allowable relative angle of the pipeline joint， and to develop the excellent compression and deformation ability of the rubber sealing ring.

Abstract:

As a new type of structural wall pipe， the axial-hollow-wall pipe is widely used in municipal engineering in recent years because of its simple geometry， high space utilization， and good energy dis- sipation. To study the mechanical response and energy dissipation characteristics of the axial hollow-wall pipe under the action of low-velocity impact， twenty experimental conditions were designed， and the drop weight impact experiment was used to simulate the rockfall impact and mechanical impact in the construction process. A calculation method for peak impact force based on dimensional analysis was proposed， and the finite element software ABAQUS was used to verify the experimental results and analyze the pipeline deformation properties and damage mechanism. The research shows that the numerical analysis results are in good agreement with the experimental results， the trend of the impact force curve is basically the same， and the error of the peak impact force is within 5%. The pipeline has good shock resistance， and its double-wall hollow structure has good energy dissipation. A large im- pact force can occur at the moment when the drop hammer hits the pipe. An impact force of 15.28kN can be produced by a 12.9kg hammer falling freely from a height of 2m. The calculated impact force is compared with the tested one for the 20 test conditions， indicating that the error is small， with a maxi- mum error of 5.8%， which proves the calculation method of the impact force has high accuracy. As the height and weight of the falling hammer increase， the impact force， damage area and dent depth al- so increase. The maximum plastic strain is transferred from the inner side of the outer wall to the con- nection between the outer wall and the stiffener， showing two damage modes of the outer wall damage and the stiffener damage. The calculation method for the impact force and the plastic damage laws of pipes provide a theoretical basis for the safety evaluation of axial hollow-wall pipelines under the action of rockfall impact and mechanical impact during the construction process.

Abstract:

In view of the simulation problem caused by large displacement problems such as soil slid- ing， the influence of landslide disaster on the operation of aviation fuel pipeline laid across the slope is analyzed. Using the SPH-FEM coupling algorithm and adopting different contact models to establish the full-size coupling models of pipe-soil interaction and pile-soil interaction， the nonlinear analysis is carried out to obtain the law of mechanical response of pipeline-soil， and the anti-slide performance of slide-resistant piles is analyzed to ensure the safety of the pipeline body in the landslide area. The re- sults show that， under the working condition of this paper， when the landslide tends to be stable， the maximum values of displacement and stress developed in the pipeline under the action of soil thrust ap- pear in the landslide body. However， due to the “soil arching effect” between the pile and the soil， the sliding soil behind the pile is more likely to stabilize， and the pipeline does not twist along the tube ax- is. With the increase of the number of slide-resistant piles， the anti-slide performance increases. How- ever， for the working condition in this paper， the anti-slide scheme comprising two anti-slide piles with concrete strength of C30 can ensure the safe operation of the pipeline. The conclusions can pro- vide theoretical support for the safe operation of aviation fuel pipeline， and present a feasible simula- tion method for the study of the mechanical behavior of pipelines under landslide and the anti-slide per- formance of slide-resistant piles.

Abstract:

Seismic analysis of long transport oil and gas pipelines is an important factor affecting the seismic design of the pipeline. The study of the seismic response of oil and gas pipelines under spatial? ly correlated multi-point action will provide a theoretical basis for it. In this paper， a scaled-down mod? el of a buried oil and gas pipeline is designed and fabricated. Shaking table tests were conducted to ana? lyze the trends of seismic response of buried oil and gas pipelines and soil with increasing loading lev? els during longitudinal multi-point excitation. The final results show that： the displacement of each measurement point along the height in the soil box is different， and the shear effect between the soil bodies is especially obvious during multi-point excitation； The comparison of the peak accelerations of the soil and the pipe shows that the peak accelerations of both increases with the increase of the load? ing level， and the difference between the peak accelerations peaks increases continuously； Multi-point excitation will cause hysteresis for the peak acceleration of the pipe； The axial strain at the top of the pipe is smaller on both sides and larger in the middle along the pipe axis， and the strain of the pipe grows faster and generates a larger strain during multi-point excitation.

Abstract:

Geological disasters and pipeline defects are two major risks to safe operation of oil and gas pipelines. Mountain landslides are a common geological disaster in long-distance oil and gas pipelines. Cracks are one of the pipe defects that are difficult to be found but often occur in pipeline operation. When a pipeline pass-ing through the landslide area encounters pipe cracks， the effect of multiple loads may lead to the aggrava-tion of pipe cracks and even fracture failure. Based on the limit analysis design criterion， the influence of relevant factors on the axial crack of pipelines in the landslide area is studied. The influence of landslide width， landslide displacement， crack location， crack depth ratio， crack shape ratio and pipeline internal pres-sure on crack J integral is analyzed by the finite element method. Results showed： The greater the landslide width， the smaller the J integral， and the greater the land- slide displacement， the greater the J integral. When the crack is located at the 12 o’clock position， the J integral value is the largest， that is， the axial crack is the most dangerous when it is perpendicular to the landslide surface. The increase of crack depth ratio and pipe-line internal pressure will lead to an exponential increase in the maximum value of the J integral， while the increase of crack shape ratio will lead to a linear decrease in the maximum value of the J integral， and the maximum value of J inte- gral is obtained at the deepest part of the crack. A larger crack depth ratio will lead to crack propaga- tion velocity along the depth direction being much larger than that along the length direc-tion， and a larger crack shape ratio will lead to crack propagation velocity along the length direction being higher than that along the depth direction.

Abstract:

In recent years， with the frequent occurrence of geological disasters and extreme weather phenomena caused by human activities， pipeline failure accidents and secondary disasters caused by de? bris flow are constantly occurring. In order to grasp the dynamic response law of oil and gas pipelines impacted by viscous debris flow in mountainous areas， a multi-physics field coupling model compris? ing debris flow and pipelines in a mountainous area was established based on finite element method and smooth particle hydrodynamics (FEM-SPH). By simplifying the mud-rock flow slurry to a nonNewtonian fluid—Bingham fluid， the impact response process of the steel pipe X70 under the action of debris flow was studied， and the displacement and stress time history characteristics at different po? sitions of the steel pipe were obtained. The results show the following three points： Firstly， simplify?ing debris flow slurry into Bingham fluid and discretizing it into SPH particles can not only truly show the process of debris flow， but also clearly reflect the dynamic response law of the pipeline to the de? bris flow. Secondly， the impact process of viscous debris flow was simulated by a multi-physical field coupling model， it is found that the acceleration of the rock blocks embedded in the mud is limited by the slurry resistance. And the third point is that the destructive force of the debris flow acting on the pipeline mainly comes from the instantaneous impact force generated by the “fore-end” and the local impact force caused by the rock blocks. Under the action of mud， the stress developed in the pipeline distributes mainly in the central section of the impact face and the interface between the pipeline and rock mass opposite to the impact face. The impact force caused by the rock blocks mainly concentrates on the impact points and has little effect on the back surface of the pipeline. The impact displacement of the pipeline due to the debris flow generally distributes in a symmetrical “saddle shape”. The nonNewtonian fluid model adopted in this study provides a new way to simulate the impact of debris flow on buildings (structures)， and the relevant research conclusions can provide a theoretical reference for the disaster prevention and control of pipeline in debris flow areas.

Abstract:

The seismic reliability of a water supply network is the service level of the network underpossible seismic intensities， which is mostly estimated using Monte Carlo simulations to generate alarge number of seismic damage samples， and this method will bring great workload and ultra-hightime cost for seismic reliability assessment of large and complex networks. In order to overcome theseproblems， not only a multi-burst pipe pressure drop calculation model is proposed， but also a scenarioreduction method is introduced to improve the calculation efficiency. Firstly， the multi-burst pipe pres‐sure drop model is used to calculate the nodal water pressure under the seismic damage scenario. Sec‐ondly， the scenario merging and classification of nodal water pressure in seismic damage is performedusing the cluster averaging method in system clustering. Then， k-medoids clustering is used to selectthe center point of each cluster as a typical scenario. Finally， the node reliability index and system reli‐ability index are determined by the typical scenarios. The proposed algorithm is applied to a practical pipe network and compared with the results of traditional Monte Carlo simulation. The results showthat the multi-burst pipe pressure drop model based on linear estimation is reasonable； the reliabilityassessment based on the scenario reduction method is feasible； and increasing the number of typicalscenarios can reduce the assessment error. Therefore， the proposed algorithm can ensure the accuracyof the results while improving the computational efficiency.

Abstract:

In the 21st century， with the rapid development of urban underground engineering con- struction and operation at home and abroad， sudden explosions occur frequently， causing huge casu- alties and serious property losses. This paper studies the typical explosion hazards of urban under- ground engineering， sorts out the existing classification methods of explosion hazards， and puts for- ward a classification method for typical explosion hazards of urban underground engineering. This pa- per analyzes the spatial distribution characteristics of explosive sources， and describes the possible lo- cations of sudden explosions in urban underground engineering. At the same time， this paper gives the causes of all kinds of explosions in urban underground engineering， analyzes the triggering mech- anisms and conditions of typical sudden explosions in urban underground engineering， and summariz-es the corresponding preventive measures. In this paper， the typical explosion hazards of urban under- ground engineering are identified， which expects to help enterprises and the government to take pre- ventive measures and emergency plans to reduce the incidence of explosion accidents in urban under- ground engineering.

Abstract:

The forecast of landslide occurrence time is very important in disaster prevention and mitiga? tion. Accurate forecasting can effectively prevent the catastrophic consequences of disasters. In order to solve the problem that only the landslide displacement and other related parameters instead of the landslide occurrence time are predicted and estimated in the current landslide forecast method， a mixed Gaussian hidden Markov model (MOG-HMM) is proposed to establish the landslide occur? rence time calculation model. The macro-information prediction criterion is calculated by the mixed Gaussian algorithm based on the full-cycle data of the landslide hazard evolution process and matched with the state in the hidden Markov model to establish the landslide evolution state model， which can reflect multiple states of the full-cycle data. When the displacement data collected in real time is need?ed for time forecasting， the current data is first decoded using the decoding algorithm， that is， to calcu? late which state the landslide belongs to， then the time from the current state to the occurrence of the landslide is predicted using Dijkstra optimal path planning algorithm， achieving the prediction of the occurrence time of the landslide. The simulation results of the Xintan landslide and the Wolongsi land? slide show that the presented method can accurately calculate the landslide occurrence time. At the same time， the validation of the prediction results by using prediction indicators indicates that the re? sults meet the accuracy requirement of the forecast indicators.

Abstract:

The instability and destruction of slope caused by seismic activity is one of the main earth? quake damages in the loess area. It is of great significance for urban seismic planning and post-earth? quake rescue to determine the seismic hazard of slopes quickly and accurately. The field survey data including 620 groups of landslides and 380 groups of stable slopes during the 1920 Haiyuan earth? quake were used to verify the influence of the longitudinal profile shape on the seismic hazard of loess slopes using the single-factor wald test. The single-factor wald test results indicated that the longitudi? nal profile of the slope had positive significance for the rapid identification of the seismic hazard of landslides. Using the easy-to-obtain factors such as slope height， slope angle， longitudinal profile shape and seismic intensity in the field survey， a Logistic regression model for determining the seis? mic hazard of slopes in the Loess Plateau region was established， and a fast determining formula for the seismic hazard of loess slopes was given. This formula was used to verify the regression of the landslide induced by the Haiyuan earthquake in 1920 and the loess landslide induced by the Tongwei earthquake in 1718. At the same time， the results of the logistic regression model without considering the shape of the longitudinal section were compared. The calculations show that：1. The seismic haz? ard of loess slopes can be quickly distinguished using the Logistic regression model by reasonably de? termining the influencing factors and adjusting the parameters of each influencing factor in the Logistic regression. The calculated slope instability characteristic is more consistent with the actual landslide evolution；2. The slope longitudinal profile shape is an important factor that affects the seismic risk of slopes. The prediction formula obtained by considering this factor in the Logistics regression model can produce about 3% more accuracy in identifying the slope instability than that without considering this factor.

Abstract:

To ensure the safety of the superstructure rising from the slope rock wall， extensive studies on the stability of a high and steep slope in a karst area with complex geological conditions were car? ried out， with reference to the Changsha Xiangjiang happy city rose from a deep abandoned mining pit. In this study， considering the inherent spatial variability of rock and soil and the influence of karst cav? erns， slope stability is evaluated through both deterministic and reliability analysis. Firstly， the safety factor of the multi-step high slope with a non-circular sliding surface is calculated using the Morgen?stern-Price method. Then the probability analysis of the high steep stepped slope subjected to structur? al load is carried out considering spatial variability of the shear strength indices based on the random field theory. Additionally， the effect of the karst carven condition on the reliability of the high and steep slope is discussed. The results indicate that in the soil-rock dual structural slope without the ef? fect of the karst cavern， the sliding failure generally develops only in the upper soil mass with poor me? chanical properties. And the spatial variability has a significant impact on the failure probability of slopes， ignoring the variation leads to an overestimation of the failure probability. As for the karst cav? erns， the location and shape of the cave both significantly affect the slope stability. The closer the cave is to the steep free face， the greater the influence of the slope is. Generally speaking， circular caverns are more likely to cause slope instability and damage than square caverns.

Abstract:

Obtaining detailed information on soil parameters is a significant precondition for slope rein- forcement and risk assessment. At present， the Markov chain Monte Carlo (MCMC) simulation is frequently used to update the statistical information of uncertain parameters based on in-situ and/or lab- oratory test data， but it is difficult to solve the problem of high-dimensional slopes due to a large amount of calculation consumption and poor convergence. In this paper， a slope displacement surro- gate model based on particle swarm optimization back propagation neural network is constructed to ac- celerate the calculation process. An improved Bayesian updating with subset simulation (BUS) is pro- posed for updating the statistics of soil parameters and slope reliability based on the monitoring data of slope displacement. The proposed method is then applied to a practical slope project (Changchun West Railway Station's Deep Foundation Pit Slope Project). The results indicate that the proposed method can effectively update the statistics of soil parameters， infer their posterior probability distribu- tion， and further update the probability of slope failure. Then， the slope displacement evaluated using the updated soil parameters agree well with the measured data， which confirms the applicability and ef- fectiveness of the proposed method. Additionally， after the Bayesian updating with the monitoring da- ta， the uncertainties of soil shear strength parameters are significantly reduced， but the probability of slope failure can be increased due to the influences of the ambient temperature， monitoring positions and values of monitoring data.

Abstract:

With rapid developments in computer visualization and numerical analysis，3D geological modeling and finite element analysis have been widely applied to geotechnical engineering. The logical connection between 3D geological modeling and finite element modeling， however， hasn’t been ex- ploited efficiently， leading to a high workload and low modeling efficiency. Towards the problem， a fast finite element modeling method based on 3D geological survey data platform was developed. Based on limited boreholes and non-uniform data of boreholes， a visualization platform for strata mod- eling was established using Python programming language. In more detail， the inverse distance weighted (IDW) interpolation method and the Kriging method were employed to identify the interfac- es of soil layers， and then the topological relations between these interfaces were analyzed and opti- mized. With the aid of the concept of virtual boreholes， a data extraction method was proposed to con-vert the regional data of the 3D stratigraphic model into executable files of different commercial finite element software. Taking Plaxis-3D as an example， rapid finite element modeling and analysis for dif- ferent partitions of the same large-scale site were accomplished， illustrating that the presented finite el- ement modeling technique is promising and shall be a future trend in disaster prevention and mitigation of geotechnical engineering.

Abstract:

Based on the laboratory direct shear tests， the strength parameters of granite residual soil at different water contents were obtained， and the finite difference software was used to study the dis- placement field， acceleration field and axial force of anchor bolt of granite residual soil slope at differ- ent water contents (13%、17%、21%、25%) and peak seismic acceleration (0.05g、0.1g、0.2g、0.4g). The results show that the horizontal displacement of the slope is mainly concentrated in the residual soil layer under the action of EL wave. The higher the water content and the greater the seismic peak acceleration， the greater the horizontal displacement of the slope at the same location. The amplifica- tion coefficient of PGA increases with the increase of slope height and shows a superficial amplification effect. The higher the water content and the smaller the seismic peak acceleration， the larger the PGA amplification coefficient at the same position. The maximum axial force of the prestressed bolt is locat- ed at the anchor head， and the axial force changes little along the free section， while that of the inner anchor section decreases gradually from the beginning to the end. The higher the water content and the greater the seismic peak acceleration， the greater the axial force of bolt at the same position. When the peak seismic acceleration is small (PGA=0.05g)， the bolt axial force is the largest at the foot of slope. When the peak seismic acceleration is large (PGA=0.4g)， the bolt axial force is the largest at the top of slope.

Abstract:

Microbial-induced calcite precipitation (MICP) technique has promising application pros? pects in soil improvement field for its ability to take into account the ecological environmental benefits. In order to study the cementation process of MICP-treated sand， a method combining the electrical re? sistivity tomography (ERT) technique and MICP technique is proposed. An indoor experiment was carried out to verify the feasibility of the method. Quartz sands were filled into a cylindrical mold with a height of 60 mm and a diameter of 176 mm， and 16 electrodes were inserted around it. Three rounds of MICP treatments were performed on the specified area of the sand sample surface with the spraying method. The self-developed ERT system was used to test the resistivity distribution of the sample at different treatment stages， and then the variation of internal electrical parameters of the samples was analyzed during the MICP process. The results show that：(1) In the process of MICP treatment， the treated sand area presents low resistivity. The range and resistivity value of the low-resistivity area mainly depend on the infiltration and diffusion process of bacterial solution and cementation solution in the sand sample.(2) After washing off the salt from the MICP-treated sand， the resistivity value of the MICP-treated sand increased， resulting in an increase of density.(3) ERT technique can effective? ly track the formation and expansion of the sand area with abnormal resistivity during the MICP pro? cess and establish a connection between the MICP curing process and the cementation effect， which shows that the ERT technique is feasible for monitoring the MICP process. This study provides new technical ideas for studying the mechanism of MICP-treated sand and evaluating the cementation effect.

Abstract:

China is accelerating the industrialization of natural gas hydrate exploitation. However， large-scale commercial exploitation of marine hydrate may affect the bearing capacity of deep-water foundations and in turn induce engineering accidents and environmental risks. Adopting the indepen- dent improved physical model test system， a physical simulation experiment was conducted to simu- late the exploitation and dissociation process of hydrate， and the pullout performance of an anchor foundation under different degrees of dissociation was studied. The results show that with the expan- sion of the dissociation front， the degree of dissociation increases， and pull-out bearing capacity of the foundation reduces sharply. After complete dissociation of hydrate， the bearing capacity of the plate anchor decreases to 2.89‰ of that before dissociation. A positive correlation was found between the degree of the pullout capacity reduction and the relative distance of the dissociation fronts， while the pullout failure changes from brittle to plastic.

Abstract:

In order to study the mechanical characteristics of calcium silicate hydrate (C-S-H)， the main component of cement materials， a molecular model with a calcium-to-silicon ratio of 1.67 and a density of 2.4 g/cm3 was constructed based on the Tobermorite model. Then， mechanical properties of C-S-H under compression and tension at varied temperatures were studied by molecular dynamics simulation. Stress-strain relationships， peak stress and Young's modulus of C-S-H at varied tempera- tures were obtained. Results of molecular dynamics simulation show that： peak stress and Young's modulus of C-S-H in both tensile and compressive tests decrease significantly with the increase of tem- perature； peak stress of C-S-H in compression is significantly greater than that in tension； tensile frac- ture pattern of C-S-H in Z-direction changes from plastic failure to brittle failure with the increase of temperature.

Abstract:

The interaction characteristics of cement paste with surrounding rock and lining segment in a subsea shield tunnel were studied by taking the subsea shield section of Xiamen Metro Line 2 as the engineering background. Numerical simulation and field measurement were carried out to analyze the solidification process of grouting slurry， focusing on the influence characteristics of compressive strength， stiffness， shrinkage and creep of cement paste on mechanical behavior and deformation of the tunnel， and the stress characteristics of the lining segment with different strata distribution and dif- ferent tunnel depths. Also， the influence of sea water level change on the stress of the lining segment was studied by the fluid-structure coupling technique. The calculation results show that the stiffness ra- tio E1/E28 of grouting material has less influence on the final axial force of the lining segment and the pressure of surrounding rock， producing a variation range of no more than 0.885%， while has a large influence on formation deformation. The setting time can be adjusted by additives to make the grout solidify and harden as early as possible； It is suggested that the grout with a low bleeding rate should be used， and its shrinkage value should be controlled in a small range； The creep parameters have lit- tle effect on the axial force，with a maximum variation range of less than 1.35； The shrinkage parame- ter mainly considers the solidification shrinkage of grouting material in the later stage， while creep pa- rameter mainly considers the creep shrinkage of grouting material in the earlier stage； If the soft soil is thick， the effective pressure arch is not easy to form， which leads to a large surrounding rock pres- sure； The semidiurnal tide has little effect on stratum deformation and segment stress， and the general development trend is similar to that under the static water level. Finally， the monitoring results show that the numerical simulated time history variation law of soil and water pressure in the segment is ba- sically consistent with the measured one.

Abstract:

Wave load is one of the main environmental loads on the foundation of sea-crossing bridges. In order to investigate the difference between various wave load calculation methods on large-scale bridge foundations， the Morison equation， the code， the three-dimensional diffraction theory based on the boundary element method and the CFD method based on the Navier Stokes equation are used to calculate the wave load on a large-scale round ended caisson foundation of a sea-crossing bridge， re? spectively. The influence of the relative scale of the structure on the results of each method is studied. The distribution of three-dimensional flow field and pressure field of the latter two numerical methods is compared in detail and the influence of the nonlinear second-order force effect is focused on. It is found that when the relative scale of the structure is about 0.2， the results of the above method are sim? ilar. With the increase of the relative scale， the boundary element method is still in good agreement with the CFD method， while the code gives a more conservative wave load， and the Morison equation may overestimate the contribution of the wave drag force. The results of flow the field and pressure field obtained by the boundary element method and CFD method are consistent in trend， but there are obvious differences in local areas such as free surface and object surface at the front of the open caisson and wave trough at the side of the open caisson， which may be due to the difference between the two theories that consider the diffraction effect and the viscosity effect， respectively. The second-order force effect will increase the wave load slightly and add the difference frequency and sum frequency components into the frequency spectrum. After considering the nonlinear second-order force effect， the frequency spectrum curve of the boundary element method is more consistent with that of the CFD meth? od， and the boundary element method can calculate the wave load more accurately. Both the boundary el? ement method and CFD method can reasonably give the wave load results of large-scale structures. The results provide a basis for the accurate calculation of wave load on sea-crossing bridge engineering.

Abstract:

To investigate the damage characteristics and change laws of ground fissures sites under earthquakes， the shaking table model test on soil was designed and completed， based on the ground fissures site of f4 in Xi'an. The damage process of the ground fissures site was analyzed by the mea- sured data in soil， based on the Hilbert margin spectrum. The results showed that：(1)The inconsis- tent deformation of the hanging-wall and footwall of the ground fissures site leads to tensile stress on both sides of the main fissure. Thus， the main fissure gradually cracked and expanded， and the crack surface was in a sawtooth shape. The number of secondary fissures was more than that on the foot- wall.(2)The development law of damage index was consistent with the experimental phenomenon， indicating that the damage quantification method was suitable for detecting the damage development of ground fissures sites under earthquakes.(3)Distribution laws of damage index and peak acceleration on the surface were highly consistent. All parameters reached the maximal value at the fissure， and the peak value gradually decreased from the main fissure to the two sides， showing “hanging-wall/foot- wall effect”. The damage state of soil was related to the input peak acceleration， soil type and other factors.

Abstract:

Soil arching effect is an important basis for theoretical research of pile-soil interaction. But due to less research on the soil arching effect mechanism of anti-slide piles with different cross-sec- tions， the traditional cross-section is mostly used in the design of anti-slide piles. Considering the shortcomings of traditional rectangular anti-slide piles in forming soil arching effect， the trapezoidal cross-section was proposed to optimize the design of the anti-slide piles. Based on the theory of materi- al mechanics， the stress state in the compression zone at the foot of the soil arch on the side of the trap- ezoidal piles was deduced by using the oblique section stress calculation model of the axial compres- sion bar， and the ultimate bearing capacity of the trapezoidal piles was obtained by combining the Mohr-Coulomb strength criterion. The ultimate bearing capacity of the soil arch on the side of the trap- ezoidal and rectangular piles was analyzed by a numerical example， and the theory and calculation re- sults were verified by a numerical simulation analysis. The results show that the ultimate bearing ca-pacity of the trapezoidal piles is significantly improved compared with that of the rectangular piles， and the maximum bearing capacity is about 2.5 times that of the rectangular piles； Under the same condi- tions， the increment of soil displacement and shear strain between trapezoidal piles is smaller， while the stress concentration is more obvious. The trapezoidal sectional pile is more favorable to the forma- tion and development of soil arching effect.

Abstract:

Among other factors,artificial slope cutting is one of the most common triggering factors oflandslide. In this paper,a series of model tests and numerical simulation have been conducted to inves?tigate the failure mechanism and evolution process of the slope under slope cutting. As the coupling be?tween sensing cables and soil directly affects the accuracy of monitoring results. Firstly,a new pullout apparatus is designed and the coupling deformation relationship between sensing cables and soil isacquired through pull-out tests under different confining pressures. According to the pull-out tests,asurcharge loading test model was designed. Strain-sensing cables that can capture the strains at differ?ent positions of the model slope were embedded in the soil mass. The measurement data of the cutslope were analyzed. It can be found that an abnormal strain-field area obtained by horizontal and verti?cal sensors coordinated with the location of the potential slip surface. This is verified by a comparisonbetween the measurements of the cables and numerical simulation results. Based on the BOTDA da?ta,an empirical relationship is explored between the horizontal characteristic maximum strain and thesafety factor to estimate the slope stability condition and perform early-warning of landslide under theaction of slope cutting. The conclusions drawn in this study are of great significance to stability evalua?tion of artificial cut slopes.

Abstract:

In order to improve the seismic performance of conventional infilled masonry wall，an inno? vative configuration named damped infilled wall/wallboard(DIW)was proposed by introducing the principle of viscoelastic damper. DIW has a simple construction，explicit working mechanism and inde? pendent intellectual property right. In this paper，the configuration and working mechanism of DIW was introduced. The material suitable for damping layer construction and its corresponding hysteretic performance were given. Seismic performance tests were carried out on DIW unit as well as plane frame structures with DIW. The in-plane working mechanism that the shear hysteretic deformation which is casued by relative movement between adjacent subpanel of DIW dissipates the input seismic energy was revealed. The double bracing macro-modelling method was proposed. The proposed mod? el was used in the time-history analysis of a 3D frame structure with DIW. Results show that DIW is able to significantly reduce the influence on the dynamic characteristic and seismic performance of the main structures，and to protect the wall from suffering damages through decreasing the stiffness effect of wall/wallboard on structure. Out-of-plane performance of DIW was also studied by tests. The re? sults reveal that the out-of-plane mechanism is the arching mechanism and the failure mode is fourhinge arching.The problems and directions that need to be further studied were given.

Abstract:

Due to the strong surface disturbance caused by the "5.12" Wenchuan earthquake，mountain torrent disasters have occurred frequently in Wenchuan County in recent years，causing serious dam? age to local houses. In Wenchuan County，two mountain torrent disasters，"8.20" and "8.17"，occurred in 2019 and 2020. Taking some of the damaged village buildings in the two disasters as research ob? jects，this paper summarized the damage characteristics of different structural types of buildings，the spatial variability of the damage degree of buildings along the river and the building masking effect，as well as the damage modes of impact，scouring，siltation and immersion through disaster data mining and typical case analysis. Based on the research and analysis，this paper improved the existing building damage grading criteria by combining the characteristics of mountain torrent damage，and then pro? posed the classification of mountain torrent damage to rural buildings. Applying random forest algo? rithm and statistical analysis methods，the main influencing factors of building flood damage and their relationships were comprehensively analyzed in terms of water depth exposure，site exposure，and physical vulnerability. Finally，based on the analysis of building damage，some suggestions were pro? posed to improve the flood mitigation capacity of buildings in mountainous villages. The research re? sults lay the foundation for further research on the physical mechanism of building flood damage，and also provide references for flood prevention planning and disaster mitigation design of buildings in mountainous villages and towns.

Abstract:

The southeast region of Tibet is the largest marine glacier area in China. For investigating the physical and mechanical characteristics of glacial tills along the Sichuan-Tibet railway， and evaluating their stability as a geological hazard source and engineering foundation， 32 points of glacial tills in the Parlung Zangbo basin were taken as cases. A series of in-site and indoor tests on natural density， grain size analysis， large direct shear， triaxial shear， compressive strength， permeability coefficient and so on were carried out. Combining with field investigation methods such as sectional surveying and mapping， the distribution， morphological characteristics， physical and mechanical properties of glacial till and their correlation were analyzed. The result shows that physical and mechanical properties are closely related to moisture content， void ratio and clay content. The natural density and compression modulus are negatively linear related to the void ratio. The vertical permeability coefficient and the free expansion ratio show a quadratic relationship with clay content. The shear strength and compressive strength are binary relationship with void ratio and moisture content. Start-up patterns in three different deposit sites (modern glacier tongue， middle reaches of the valley， and the main river bank) were summarized， and the stability of the glacial tills was preliminarily discussed. The countermeasures for dealing with the glacial tills in Sichuan-Tibet railway and highway projects were suggested， such as passing by bridges or tunnels， engineering slope， and cutting or foundation， etc.

Abstract:

Superstructures of seismically isolated structure keep in elastic or slightly elastic-plastic range subjected to rare earthquakes, thereby protecting superstructure effectively. However, very-rare earthquakes may happen in design reference period due to uncertainty of earthquake intensity and cha?racter. On basis of “survive rare earthquakes by sustaining significant damage but without globally collapsing” design, horizontal deformation of isolation bearings and overturning resistance under very-rare earthquakes, performance and cost of seismically isolated structure based on “survive very-rare earthquakes” are worth researching. Dynamic responses of three seismically isolated structures with different heights are obtained from elastic-plastic time history analysis. Main failure modes of seismically isolated structures subjected to very-rare earthquakes are presented by comparing the responses such as inter-story drift ratios, horizontal displacements of isolation bearings and overturning moments. The results show that under very-rare earthquakes, horizontal displacements of isolation bearing in all three classic seismically isolated structures are excessive, while other two responses both meet the requirements. With isolation bearings increasing suitably, new structures can avoid destruction by deformation of isolation layer increasing and survive very-rare earthquakes, while isolation effectiveness reduce slightly. Reducing the aspect ratio of superstructure appropriately can control the overturning of whole structure especially high-rise structure subjected to very- rare earthquakes. Therefore, considering both safety and economy, it is an effective and economical way to increase the ultimate displacement of isolation bearing, appropriately reduce the aspect ratio of high-rise seismically isolated structures, and realize resistance ability of isolated buildings subjected to very-rare earthquake.

Abstract:

To improve the seismic performances of bridges with very tall piers in high seismicity area, design concept of the bridge with very tall piers, which is composed mainly of concrete-filled steel tubular (CFST) columns and energy dissipating mild steel plates (EDMSP), is proposed based on the principle of earthquake restorable structures. Trial design of a bridge with the proposed innovative composite box section tall piers is carried out based on a typical continuous rigid frame highway bridge with tall RC box section piers. The static and seismic performances of the bridge according to fundamental loading combination and E2 level seismic action are analyzed respectively. The seismic performance of the designed bridge under E2 level seismic action is compared with the bridge with conventional RC box section piers. The results show that: (a) under fundamental loading combination, the bridge with innovative composite box section piers can well meet the requirements of structural strength and stability; (b) under E2 level seismic action, the conventional designed bridge experiences medium damage in the piers, while only the replaceable EDMSP elements of the innovative designed bridge undergo plastic deformation, indicating the innovative designed bridge is earthquake restorable; (c) the seismic displacement responses of the innovative designed bridge is significantly smaller than that of the conventional designed bridge under E2 level seismic action.

Abstract:

On September 14，2019，a large loess landslide occurred in Tongwei County，Dingxi City， Gansu Province. Through on-site investigation of the loess landslide and drone aerial survey，the to? pography，geomorphology，hydrogeology and other conditions that gave birth to the landslide were as? certained，and the morphological characteristics，structural characteristics and movement patterns of the landslide body were studied in-depth，revealing the Tongwei landslide Disaster mechanism. The high-density electrical method is used to detect the stratum structure，thickness of the sliding body， groundwater distribution and spatial distribution of the landslide area. Combining the finite element method and Morgenstem-Price method to calculate the stability of the slope，the distribution of the maximum shear strain and the variation of slope stability with rainfall duration are obtained. The re?sults show that：(1)the shape of the Tongwei landslide is a chair-like shape，which is divided into three typical failure areas，forming a large number of vertical ridges，and the thickness of the loess slid? ing is approximately 8~50 m；(2)the Tongwei landslide belongs to the "traction-push" type of bedding landslide，and the movement mode is "pull toe instability traction-hindered sliding in the middle partinstability shift in the rear part"；(3)the groundwater is mostly fissure karst water，and the geological structure is not obvious. The geological structure activities such as early earthquakes have a great influ? ence on the stratum；(4)the stability of loess slope decreases continuously with rainfall duration，and the maximum shear strain region is mainly distributed in the middle and upper part of the slope，and develops from mudstone contact to slope surface；(5)rainfall is the most direct factor triggering the Tongwei landslide，and the development of gullies，river erosion and agricultural production activities are important disaster-generating conditions

Abstract:

A three-dimensional discontinuous deformation analysis(3D DDA)method was used tooutput the kinetic energy and motion trajectory of rolling blocks. Compared with the results of the ex?isting laboratory experiment and numerical simulation method,the accuracy of the 3D DDA methodwas verified. By analyzing the influence of the rockfall platform on the kinetic energy,motion trajecto?ry and movement law of blocks along rock slopes with different slope heights,slope angles and foldingpoint positions,the influence law of the rockfall platform on the block movement was studied. Final?ly,the rockfall slope with a complex slope shape at Lang village in Tibet was simulated,and the pro?tective effect of the rockfall platform on rockfall disaster was analyzed. The results show that the rock?fall platform can decrease the kinetic energy of the rolling block,change the block motion trajectory,and reduce the impact of the rolling block on the protection structure or the traffic line at the slope bot?tom. Meanwhile,the general laws including the block movement and the corresponding platform de?sign width under different slope characteristics are given,and they provide a basis for the design ofrockfall platform.

Abstract:

The finite element inversion analysis method, allowing for describing the creep behavior of soft soil, is presented for simulating the subgrade settlement. The finite element analysis software, ABAQUS, was embedded into the improved whale algorithm by MATLAB, thus the calculation parameters of soft soil can be obtained quickly and accurately. The modified Drucker-Prager and time hardening creep model were used to simulate the subgrade settlement and deformation. In order to test the reliability of the proposed method, the finite element inversion model was built for a highway subgrade crossing soft soil and the deformation of the subgrade was simulated during the whole construction period. The simulation results indicate that the subgrade deformation obtained by the inversion analysis agreed well with the measured data. In addition, the post-construction settlement was also predicted and the settlement was within 10 cm in ten years after construction, which provides good theoretical guidance for the operation and management of the highway.

Abstract:

In order to explore the characteristics of dynamic shear modulus G and damping ratio λ for various marine soils in the Jintang Strait, a series of resonant column tests were carried out on various undisturbed marine soils with different depth from four sampling boreholes in the Jintang Strait. The test results show that: (1) various marine soils exhibit strong nonlinearity and hysteresis characterized by “low shear modulus and high damping ratio”; the maximum dynamic shear modulus G_max for various marine soils increases with increasing depth, and the increasing rate of G_max with soil depth decreases follwing the sequence of silty clay, silt, silty clay mixed silty sand and silty sand. (2) with increasing depth, the G/G_max — γ curves of various marine soils shift towards the upper right characterized by low nonlinearity, while the λ — γ curves move downward and rightward characterized by decreasing hysteresis. (3) parameters of G/G_max — γ and λ — γ curves of various marine soils with depth in the Jintang Strait are presented.

Abstract:

During the Kobe earthquake in Japan, different degrees of earthquake damage occurred on the subway underground structures. Only one zone of the standard section of Daikai station totally collapsed, while the other zones of Daikai station, its running tunnels and other subway underground structures did not have serious earthquake damage. In this paper, the earthquake damage responses of the standard section, central hall and running tunnel structure of Daikai station were analyzed based on nonlinear finite element analyses which can reasonably simulate the damage of underground structures. Numerical results indicate that different width of structural cross section and burial depth lead to different overlying earth pressure on the structures at the standard section, central hall section and running tunnel section. The different overlying earth pressure generated different axial compression ratio of the three structural columns. In addition, the three structures with different lateral racking stiffness had different degree of damage and stiffness degradation, and further led to different lateral racking deformation. Eventually, the columns of Daikai station standard section destroyed due to the excessive relative deformation under the high axial compression ratio, which caused the total collapse damage to the entire frame structure. On the contrary, the columns of central hall and running tunnel section have not destroyed because there were not excessive relative deformation under the lower axial compression ratio, which kept the bearing capacity of the entire frame structure.

Abstract:

Soil liquefaction is a common natural disaster during earthquakes. In recent years, the evaluation of soil liquefaction potential based on shear wave velocity has received increasing attention. In this paper, the maximum likelihood method is used to calibrate the worldwide used deterministic liquefaction evaluation model based on shear wave velocity proposed by Andrus and Stokoe. On this basis, a probabilistic evaluation model of soil liquefaction potential based on shear wave velocity is proposed. The results show that the liquefaction evaluation curves obtained from lognormal distribution, normal distribution, minimum Gumbel distribution and maximum Gumbel distribution have some differences when the liquefaction probability is 5% and 15%, and little difference when the liquefaction probability is 35%. The model correction coefficient calibrated by the minimum Gumbel model is mostly supported by the liquefaction case database according to the Bayesian information criterion. The mean value of the model correction coefficient is 0.879, indicating that the factor of safety obtained by the model proposed by Andrus and Stokoe is smaller than the true factor of safety in the average sense. The coefficient of variation is 0.387, indicating that the model error involves some uncertainties. The liquefaction evaluation curve of the probability model established in this paper is consistent with that obtained by Bayesian mapping function in the literature, and is quite different from that obtained based on logistic regression method in the high cyclic stress ratio range in the literature.

Abstract:

A large number of soil slope collapses-slides disaster have developed after the“8.8”earth?quake in Jiuzhaigou,which is more fragmented and has a smaller thickness. When the traditional trans?fer coefficient calculation model is applied to stability calculation of such slopes,there is a problemthat the overall slope calculation cannot reflect the stability of a slider. In this paper,the fragmenteddegree of collapse-slide slope is divided into:extreme fragmentation,high fragmentation,moderatefragmentation,slight fragmentation,and no fragmentation. Based on the transfer coefficient methodand considering the five degrees of fragmentation of the slope,this paper improves landslide stabilitycoefficient and thrust calculation model. Taking the collapses and slides of old Rexi stockade PowerPlant in Jiuzhaigou County as an example,the results of two calculation methods are compared. Theresults indicate:Compared with the traditional calculation method,the block differential stability cal?culation model more consistent with the actual situation,so there is a difference in the stability of eachslider calculated by this method. Some are not stable under extreme conditions and some are unstable.Based on the difference calculation results of the block method,a block control model for the collapseslide slope was obtained.

Abstract:

The nonlinearity of soil has a great influence on the spectral characteristics and intensity of ground motions. The modified Matasovic model is accepted to well characterize the nonlinear behavior of soil. The profile soil models of 50 boreholes for the quaternary deep sediment layers are established for site seismic response based on software DeepSoil. The predominant period T_p, average spectral period Tavg of the acceleration response spectrum and the mean period T_m of the Fourier amplitude spectrum of an acceleration time history are employed as the proxy to characterize the spectral characteristics of surface ground motions. The ground motion intensity is characterized by the Arias strength Ia and the peak ground acceleration (PGA). The results show that: (1) T_p doesn't characterize the changes of seismic motions spectral characteristics during the seismic wave propagating from bedrock to surface ground. Tavg and Tm have a good similarity in characterizing the spectral characteristics of seismic motions. (2) When the seismic bedrock motions are rich for high frequency components, Tavg and Tm show a linear growth trend with increasing peak bedrock acceleration. However, there are inflection points in the growth trend lines of Tavg and T_m if the seismic bedrock motions are rich in low frequency components. (3) The nonlinear generation rates of PGAs and Ia with increasing peak bedrock acceleration are essentially consistent, and the values of PGAs and Ia show much greater dispersion with increasing peak bedrock accelerations.

Abstract:

This paper aims to analyze the behavior of the isolated containment vessel for the nuclear power plant under earthquake considering soil-structure interaction (SSI) and to optimize the number of isolation bearings. Therefore, a three-dimensional finite element model is established for CPR1000, and ABAQUS is used to simulate the seismic acceleration and displacement response under the LBNS seismic wave. The simulation conditions are: analysis with and without SSI, isolated and non-isolated structure, and different number of lead rubber bearings. For non-isolated containment, after considering the SSI effect, the maximum acceleration response decreases by 44.39%, and the maximum displacement response increases by 27.03%. For the isolated structure, the influence of SSI effect is relatively small, and the changes in maximum acceleration and displacement response are 3.17% and 10.73%, respectively. However, the SSI effect cannot be ignored when considering the displacement response. With the increase in the number of isolation bearings, the stiffness and damping of the isolation layer increases. As a result, the maximum acceleration response of the containment increases linearly. The maximum displacement response declines rapidly when the number of bearings decreases from 100 to 300. Then it slows down when the number rises above 300. That means the decrease of displacement response is not obvious at this stage, while the acceleration response will increase. Therefore, 300 is relatively the optimal number for isolation bearings.

Abstract:

In order to calculate the limit bearing capacity of subgrade in the karst areas, combining the theorem of the limit analysis with finite element method, the computation procedure was provided based on MATLAB. The modified Hoek-Brown criterion was adopted to describe the non-liner characteristic of the rock mass, which was also embedded into the computation procedure. On this basis, dimensional parameters N_σ and η were defined to estimate the effect of voids on the bearing capacity of subgrade, and the effect of different parameters was also analyzed in detail. The results reveal that N_σ non-linely increases with increasing the values of D/L (the ration of thickness to span) and GSI (the geological strength index), and decreases with increasing the value of H/L (the ratio of height to span), and the linear relation between N_σ and m_i. The value of η first increases, then decrease with an increase in the value of α, when D/L has smaller values. The value of α (rotation angle) has a little influence on η, when D/L has larger values. The physical mechanics parameters (GSI, m_i and γ) of rock mass has a negligible effect on η. The failure mechanics could be classified punch failure of roof, combined roof punch and side wall failure, combined roof falling and side wall failure. The results of bearing capacity for strip footing on a rock mass are compared with previous study, and the difference within 3%. This indicates that the method proposed in this paper is correct. Meanwhile, for the convenience of design in engineering practice, design tables are provided, which could be meet most requirements in engineering practice.

Abstract:

In order to study the seismic response characteristics of the buried pipeline in soil with soft interlayer，the software ADINA and nonlinear constitutive model was adopted in this paper. The interaction model was also utilized to simulate the contact of pipeline and soil. The influence of different factors including the buried depth, the soft interlayer thickness and the dip angle on seismic response of pipeline was obtained. Results show that the influence of the soft interlayer indexes on the seismic dynamic response of buried pipeline is different. The soft interlayer has an effect of isolation with a proper thickness and a suitable buried depth. When enhancing the inhomogeneity of the ground，soft interlayer will have unfavorable impact on the seismic response of the buried pipeline. The effective stress and deformation of the pipeline decrease with the increase of the soft interlayer thickness. The soft interlayer plays a certain buffering role when its thickness reaches a certain value. The effective stress and deformation of the pipeline decrease with the increase of the buried depth of the soft interlayer，but the influence degree is less than that of the interlayer thickness. The effective stress and deformation of the pipeline increase with the increase of the dip angle of the soft interlayer which increases the inhomogeneity of the ground.

Abstract:

In order to study the local stability of slurry trench of diaphragm wall in cohesive soil sandwiched sand, mechanical model was established to analyze the stress state of the sand layer. Based on Rankine limit equilibrium principle, calculating method for local stability coefficient of slurry trench was proposed. The main conclusions through the analysis of example are as follows: (1) excavation will lead to negative pore water pressure in the soil element with sand layer, and the local stability coefficient will gradually decrease with the dissipation of negative pore water pressure. (2) the variation of local stability coefficient with relevant factors was obtained: the stability coefficient decreases about 7% for each 10 kPa increase of ground overload and increases about 13% for each 0.5 kN/m³ increase of mud gravity. It increases about 11.5% for every 3 degree increase of effective internal friction angle. Local stability coefficient increases with the depth of the groundwater level at a decelerated growth rate, while decreases with the increase of slurry liquid level depth at an accelerated growth rate.

Abstract:

Safe and efficient demolition of reinforced concrete support beam in deep foundation pit under complex environment is a key point in the process of urban construction. On the basis of theoretical analysis on lateral restraint mechanism of stirrups, the evolution law for the stress state of the concrete element and the blasting effect of the supporting beam is revealed before and after the remove of the lateral restraint effect of the stirrup. The methods for stirrup cutting, shothole arrangement and millisecond delay initiation network are developed. A comparatively systematic technology on blasting demolition of support beams is formed. The result of engineering application shows that, the blasting demolition effect can be significantly enhanced by the linear cutting pretreatment method. The coupling state of explosion energy can be improved and the hazard of blasting flying rocks can be reduced by the method of multi-directional synergy arrangement of shotholes. The vibration intensity can be effectively controlled and the network reliability can be improved by the millisecond delay detonating network based on the blasting network connection unit.

Abstract:

Based on slip line field to give a simple and convenient graphic method it have great theoretical and engineering significance aiming at the problems of complex calculation method and large amount of calculation in tunnel stability analysis. Firstly, the method of the whole section slip line field at unsupported in loess tunnel was developed and improved. Secondly, the visual analysis program of the slip line network method is realized by MATLAB. Combined with the test results of the experimental loess tunnel collapse, the analysis program of the method of the whole section slip line field at unsupported in loess tunnel was verified. Finally, the influence of the internal friction angle and cohesion of the shear strength of loess on the collapse range of surrounding rock and the ultimate bearing capacity of soil arch in loess tunnel are evaluated.The results show that the ultimate bearing capacity of loess arch increases with the increase of cohesion also the sensitivity. The ultimate bearing capacity of loess arch decreases with the increase of friction angle then the sensitivity decreases, and the sliding range decreases with the increase of friction angle.