Abstract:The geotechnical parameters of slope have great variability which makes it difficult to determine the load of the support structure accurately. The partial coefficient method,which considers design uncertainty and is simple to calculate, is capable of solving this problem effectively. Based on the limit state equation, this study takes the shear strength parameter as normal distribution,derived the calculation formulas of the partial coefficients and the loading of the slope support structure via the general separation method.Then it analyzed two typical slope cases:single sliding surface and polyline sliding surface, by using this proposed method. The results show that the loading values corresponding to the target reliability index of different slopes can be easily obtained;and there is a deviation between the reliability index obtained by the Monte Carlo method and the target reliability value by the presented method; for single slide slope, the deviation is mainly negative about 6%, while for polyline sliding type, when the target reliability index is 1.65, the negative deviation is about 7%, but when the target reliability index is greater than 1.65, the deviation became positive. Therefore, the load value of the retaining structure calculated by the partial coefficient method is generally unconservative.

Abstract:Compared with the common deep foundation pit engineering, the asymmetric construction of subway deep foundation pit is more difficult and risky. To conduct risk evaluation of the asymmetric construction reasonably and effectively, a risk evaluation index system was established based on enclosure structure, asymmetric soil pressure of existing stations, foundation pit environment, surrounding environment and site safety management, which rely on a subway deep foundation pit project in Guangzhou. Fuzzy analytic hierarchy process and multi-level fuzzy comprehensive evaluation method were used to set up an evaluation model for asymmetric construction of subway deep foundation pit. According to the quantitative calculation results, the risk ranking of asymmetric construction risk of deep foundation pit could be obtained, which match well with the evaluation set and the practical engineering.According to the weight of each index obtained from the evaluation results, relevant measures can be taken to reduce the risk.

Abstract:The calculation of the non-linear correlation between the landslide inventories and their environmental factors is an important factor that affects the uncertainty of the landslide susceptibility prediction (LSP) modeling. In order to study the changing patterns of LSP under the influence of the uncertain factors, taking Yanchang County of China as example, 82 landslides and 14 environmental factors are obtained, and the frequency ratio (FR) and weight of evidence (WOE) connection methods are coupled with the chi-squared automatic interaction detector (CHAID) decision tree model to carry out LSP. Then the original environmental factors data (hereinafter referred to as "original data") is used as the input variable to compare the individual CHAID decision tree model to realize the analysis of LSP modeling pattern. ROC accuracy, mean, standard deviation, and average rank are adopted to analyze the uncertainty characteristics in the LSP modeling process. Results show that:1) LSP uncertainty of the WOE-CHAID model is lower than that of the FR-CHAID model, and WOE has relatively excellent nonlinear correlation performance. 2) The prediction accuracy of individual CHAID decision tree model is slightly lower than that of the WOE-CHAID and FR-CHAID models, but it has higher modeling efficiency. 3) In terms of reflecting the spatial correlation between landslides and its environmental factors, the CHAID decision tree model coupled with FR and WOE connection methods have significant advantages. Generally, WOE is a better connection method and CHAID decision tree model has good prediction performance and high prediction efficiency. Susceptibility prediction by the WOE-CHAID decision tree model is less uncertain and more in line with the actual landslide probability distribution characteristics.

Abstract:When the shield passes through the composite stratum, the content of water rich gravelly sand layer is high, which is prone to "gushing", tunnel face instability, and the content of argillaceous siltstone stratum is high, which is more prone to mud cake, tool locking, eccentric wear and slag discharge. In view of these construction problems above, the shield section of Qili station-Minyuan Road West Station of Nanchang Metro Line 4 as an example, which passes through the water rich gravel sand-argillaceous siltstone composite stratum, this paper conducts the soil conditioning tests for five tunnel faces with different composite degrees and examines the reasonable proportion of soil conditioning mixture ratio in these varying composite of earth pressure balance shield. The results show that:with the ratio increase of argillaceous siltstone from 10% to 90%, the foam injection ratio increases from 20% to 50%, and the injection ratio of bentonite slurry decreases from 20% to 0. The field application results show that the soil conditioning scheme above can ensure the good fluidity and low permeability of the muck, and solve the problems of gushing and mud cake during shield tunneling in different degrees of composite stratum.

Abstract:Based on the similar principle of model tests and characteristics of soft rock in-situ, a new kind of similar material of soft rock which consists of clay, barite powder and gypsum is developed to simulate dynamic characteristics of prototype soft rock. Orthogonal test is carried out, and influential patterns of ingredients content on density, initial shear modulus G_max and reference strain γ_r are achieved via variance and range analysis method. Based on the results, an ultimate proportioning test is conducted. The test results indicate that the proportion of blanc fixe imposes primary effect of density of similar material. Reference strain γ_r increases as the content of gypsum increases and decreases as the content of clay increases. Initial shear modulus G_max of similar material decreases as the proportion of clay increases, while increases as the proportion of barite powder or gypsum increases. The relationship between dynamic stress and dynamic strain and shear wave velocity of the similar material shows great consistence with that of prototype.

Abstract:Collapse always frequently occurs during the construction of tunnels due to the unfavorable geological conditions or other factors such as the excavation method, causing casualties, equipment damage, time delay or other adverse consequences. However, the current qualitative assessment method cannot satisfy the needs of project risk management.Hence, a novel quantitative assessment model of collapse risk is developed. Considering the variability of physical and mechanical parameters of surrounding rock, the probability of collapse is obtained by the Monte-Carlo method combined with the numerical method.The relevant zone of collapse is predicted by Protodyakonov's theory.With the predicted probability and zone of collapse, the risk of casualties, time delay and economic loss is analyzed quantitatively via introduction of spatiotemporal distribution index and vulnerability index.The quantitative assessment of collapse risk is realized by quantifiable risk acceptance criterion based on the way of ALARP principle and F-N curve.Finally, validated by engineering case history, the operability and applicability of the developed risk quantitative assessment model is illustrated.

Abstract:This paper presents a vector-valued fragility analysis of shallow tunnel in soft soil deposits. Firstly, numerous nonlinear dynamic analyses were performed for soil-tunnel system, and based on the calculated results, a series of 15 intensity measures (IMs) were all tested based on their efficiency, practicality and proficiency, according to the regression analyses between the IMs and the damage index (DI) for the examined tunnel.The peak ground acceleration (PGA) at the ground surface was demonstrated to be optimal IM, followed by peak ground velocity (PGV) and acceleration spectrum intensity (ASI). Then, the scalar-valued fragility curve was developed in terms of optimal IM (PGA) for shallow tunnel. Finally, the fragility surfaces based on vector-valued IMs were developed to obtain the exceeding probability of various damage states as a function of two IMs (PGA, ASI). This study reveals that the scalar-valued fragility curves cannot represent the effect of a second IM on the seismic behavior of the tunnel, and the development of vector-valued fragility surfaces lead to more reasonable evaluations of seismic performance of tunnels.

Abstract:In railway construction, operation and maintenance, due to the influence of engineering geological factors, natural and construction activities and other factors, the safety of high cutting slope is one of the main key concerns of railway engineering. For the long-term stability of railway roadbed slope,based on the slope safety factor and deformation relationship, long-term strength of rock and soil, and tempo relationship, this paper established the safety factor of slope, shear deformation and time relation model, proposed three cut high slope stability evaluation index, including the long-term stability safety coefficient, the exponential value of deformation rate and the index of limit,and four-level and eight-level early warning schemes for high slope safety and stability,specified the emergency treatment measures which should be taken under different early warning levels.Through the actual engineering monitoring data, the instantaneous stability safety factor, long-term stability safety factor and long-term cumulative deformation state of high railway cut slope were systematically analyzed, and the risk warning classification of the high cut slope was determined.

Abstract:The soil properties of embankment slope filled with cement solidified dredged sludge commonly feature high variability. Meanwhile, in construction process of cement-mixed embankment, horizontal drainage plate is generally used to accelerate the consolidation of cement-mixed soil, which makes the soil strength show a spatial distribution trend at the vertical direction (perpendicular to the drainage plate) after the primary consolidation finished. The traditional stationary or quasi-stationary random field model cannot well characterize this trend. This paper proposes a non-stationary model to characterize the attenuation trend of soil strength along the normal direction of drainage plate. The strength reduction method and Monte Carlo simulation are combined to evaluate the reliability of slope, and the proposed model is compared with two existing models (i.e., traditional stationary random field model and depth trend non-stationary random model). The influence of different random filed models on safety factor and slip surface are investigated, and the impact of trend parameters in the proposed model on slope reliability are discussed. The results show that the stationary random field model and depth trend non-stationary random field model may overestimate the reliability of embankment slope, and the proposed non-stationary random field model can consider both the trend term and random fluctuation term in vertical direction and the attenuation trend in normal direction of drainage plate, which is in good agreement with the existing research.

Abstract:Reasonable liquefaction assessment of construction sites is the basis of mitigating liquefaction hazards. The current Chinese seismic design code evaluates the liquefaction potential by comparing the critical value of standard penetration test blow count with the measured value. However, due to the significant uncertainties associated with the process of establishing empirical liquefaction criteria, the deterministic method is not an accurate measurement for evaluating the liquefaction potential. To solve this problem, the maximum likehood method is used to calibrate the parameters of four generalized linear models based on the liquefaction case base of Chinese standard penetration test, and four probabilistic evaluation models applied to China are established. The results show that the four generalized linear models differ significantly when the liquefaction probability is small, and the prediction results of the four models are similar when the liquefaction probability is between 30% and 70%. Comparison of the models shows that the Log-log model fits the database best. The formulas for calculating the liquefaction probability and the critical value of standard penetration test blow count under specified liquefaction probability based on the Log-log model are provided. The results of verification analysis show that the overall judgment success ratio of the proposed probabilistic evaluation model of liquefaction is higher than the current Chinese seismic design code.

Abstract:Cone penetration test (CPT) is commonly used to determine the stratification of underground soil and the mechanical parameters of soils in stratification. Due to time, resources and/or technical constraints, the number of CPT soundings along with a horizontal direction is generally limited. In such cases, spatial interpolation or stochastic simulation methods is a necessary choice to estimate CPT data at un-sampled locations. This paper proposes an efficient method for simulating CPT data at un-sampled locations directly from a limited number of CPT records. The approach couples the framework of 2D Bayesian compressive sensing with Gibbs sampling, where Kronecker product is introduced for facilitating its simulation efficiency. Both numerical simulations and case histories are used to illustrate the presented method.Results show that the proposed method is reasonable, which can not only reflect the non-stationary characteristics of the data, but also significantly reduce the time cost and have reasonable adaptability after using the sequential updating technique. In addition, the accuracy and reliability of interpolation are negatively and positively proportional to the distance from existing CPT soundings and the number of existing CPT soundings, which demonstrates the data-driven nature of the proposed method.

Abstract:After loess is contaminated, the composition and internal structure of the soil will change, so that the tensile strength of the soil will also change. Based on this, in this paper, four kinds of polluted liquids with different molar concentrations of hydrochloric acid, sulfuric acid and nitric acid were manually configured, and the direct tensile failure test was carried out by comparing distilled water and contaminated soil samples, and discussed the tensile stress-tensile strain characteristics and process of acid contaminated loess. The effects of different acid solution types and concentrations on the evolution of soil tensile strength were further analyzed. The results show that the tensile strength of loess is lower than that of the unpolluted state with the invasion of the acid polluted liquid. With the increase of the concentration of the contaminated solution, the tensile strength of the loess polluted by hydrochloric acid and nitric acid were decreased, while that of sulfuric acid gradually recovered.The fitted concentration of the contaminated solution showed a good power function relationship with the tensile strength. Finally, based on the tensile strength and shear strength of the polluted loess, the fitting relationship of the combined shear strength of contaminated loess was discussed.

Abstract:In order to explore the strength characteristics of ecologically reinforced soil with plant shells, the authors conducted a series shear test study on the loess reinforced with different petal-shaped buckwheat husks. First, we carried out the tests on the basic properties of buckwheat husks and loess, and then divided the buckwheat husks, added the divided the buckwheat husks to the soil according to a certain mass ratio of buckwheat husks to dry soil, compacted them into specimens, and carried out direct shear tests. The research results showed that the change law of shear stress-shear displacement curve of buckwheat husk reinforced loess is basically the similar to that of plain soil. The strength of the soil reinforced with buckwheat husks has been significantly improved, with a maximum increase of 23%. In terms of strength indicators, the main manifestation is that after reinforcement, the angle of internal friction of the soil has been greatly improved, with the maximum increase of 6.13°, while the cohesion has decreased to varying degrees, but the decrease is not much, within 8 kPa. It was also found that when the addition rate of buckwheat husk is greater than a certain percentage, the strength of buckwheat husk reinforced soil is greater than that of plain soil, and the percentage was related to the splitting of buckwheat husk. When the buckwheat husk is used as a reinforced material, there is a limit reinforcement rate. When the reinforcement rate is less than the limit reinforcement rate, the shear displacement required for the buckwheat husk to function generally increases with the increase of the vertical pressure.When the reinforcement ratio is greater than the limit reinforcement ratio, the shear displacement required for the buckwheat husk to function roughly decreases with the increase of the vertical pressure, the limit value is also related to the splitting of the buckwheat husk.In comparison, natural buckwheat husks and two-petal buckwheat husks are more suitable as reinforcing materials.

Abstract:In order to explore the microbial mineralization reaction process and influencing factors in the seawater environment, the Microbially Induced Carbonate Precipitation (MICP) aqueous solution experiment was carried out by changing the concentration of nutrient salts, the volume ratio of bacterial solution to nutrient salts and environmental temperaturein seawater and deionized water. Then, SEM, XRD and EDS tests were used to detect the aqueous solution products, and the mechanism of MICP reaction in seawater environment was speculated. The results showed that:(1) under different water environment conditions, when the nutrient concentration was 1 mol/L and the volume ratio of bacterial liquid to nutrient was 30:120, the reaction rate was the fastest and the sediment produced was the largest; (2) The effect of temperature on the precipitation reaction of calcium carbonate is obvious. The reaction rate at room temperature (25℃) is higher than that at low temperature (4℃), and the reaction is fully carried out. (3) In seawater aqueous solution test, high pH value can accelerate the reaction, and the presence of Mg²⁺, Ba²⁺ plasma in seawater makes the precipitate contain a small amount of basic magnesium carbonate (Mg₅(CO₃)₄(OH)₂·4H₂O), BaCO₃ and other mineral components in addition to CaCO₃.

Abstract:Grouting method has been widely used as a measure to compensate the ground settlement. Current research mainly focuses on the principle of grouting and the recovery of the settlement. However, the influence of soil parameters and injection parameters on the horizontal displacement of tunnel has not been systematically studied. Therefore, based on a field grouting test of a project in Tianjin, this paper used strain method to simulate the grouting process, and studied the influence of soil conditions, grouting amount, grouting distance, grouting length and grouting depth range on the horizontal deformation of soil. The results show that the maximum horizontal displacement of soil caused by grouting is located near the top of the grouted zone. Soil strength and stiffness have little influence on grouting effect, which indicates that the applicability of grouting to control horizontal displacement is wide. The horizontal displacement of soil near the grouting point increases rapidly with the increase of grouting amount and slowly when it is far from the grouting point, and the horizontal displacement of soil decreases rapidly with the increase of grouting distance. Therefore, the distance between the grouting point and the correcting object should be shortened. When the grouting length is small, the influence range of grouting is concentrated and the maximum displacement of soil is large. On the contrary, the influence of grouting is relatively dispersed and uniform. The grouting length should be selected according to the distance of grouting and the range of depth of correcting object to maximize the effect of grouting correction.

Abstract:Resistance-reducing with slurry is a key technique in the construction of long-distance pipe jacking. The thickness of the slurry is closely related to the engineering quality.Based on the basic principle of impact image method, a rapid detection method for accurately grasping the distribution condition of slurry outside the pipe jacking is proposed in this article, and the validity of the detection method is explored through model test and field test.According to the results of model test, the normalized impact response intensity is taken as the evaluation index to reflect the distribution condition of slurry. Finally, it has been successfully applied to a large-scale water diversion project in Suzhou. The research shows that the impact image method has obvious advantages over the traditional pressure observation method in detecting the thickness of slurry, which effectively improves the efficiency of detection and the identification ability of high resistance zone. At the same time, the construction cost can be greatly saved by replenishing the weak area of slurry precisely. This method can be popularized for similar projects.

Abstract:The uncertainty of the consolidation coefficient is the fundamental reason for the limitation of the traditional consolidation theoretical calculation, which ignores the variation of permeability coefficient k and porosity ratio e with the consolidation state and time during the consolidation.In this paper, the porosity time-history is derived on the basis of five commonly used prediction models of permeability coefficient in engineering, having the relationship between consolidation degree and confined compression.Thus,the calculation formula of permeability coefficient related to both time and consolidation stress is constructed. Here the one-dimensional consolidation theory is modified by substituting the permeability coefficient formula into the consolidation coefficient C_v and considering the consolidation state as well as consolidation stress and time variation. The comparations with the literatures and engineering cases confirm the necessity of the time effect on the porosity. The change of consolidation coefficient C_v cannot be ignored when suffering a larger overlying load. At the same time, it is proved that it is necessary to consider the process of porosity ratio e and seepage coefficient k changing with time by comparing with other modified consolidation theories.

Abstract:Four groups of concrete-filled steel tube specimens with different internal structure forms such as setting stiffening ribs and reinforcing lattice angles were tested. The test results show that the inserted reinforcing lattice angle can delay concrete cracking in tensile zone and steel tube yielding in compression zone of specimens, and improve its bending behavior effectively. The finite element software ABAQUS is used to simulate the test specimens, and the finite element results are in good agreement with the test results. On this basis, the influence of the steel tube diameter to thickness ratio, steel-reinforced limb spacing, steel-reinforced size and steel-reinforced strength, concrete strength on the bending behavior of the concrete-filled steel tubular members with internal reinforcing lattice angle were analyzed. The results show that the main parameters that affect the bending behavior of members are the steel tube diameter to thickness ratio, steel-reinforced size and steel-reinforced strength. Concrete strength and steel-reinforced limb spacing have little influence on its bending bearing capacity. of specimens is calculated by using Chinese code. The bending bearing capacity and flexural rigidity of specimens is calculated by using Chinese, US and Europe codes, and the calculated results are compared with the test results. The results show that the calculation of bending bearing capacity is conservative by using Chinese code, the calculation of flexural rigidity is conservative by using US and Europe codes, while it is great error by using Chinese code.

Abstract:In order to systematically evaluate the seismic collapse resistance of RC frame structures in China, 66 typical RC frame structures were designed in accordance with the current codes. Based on OpenSEES platform, the lumped plastic hinge model of typical RC frame structures considering shear deformation of joints was established. IDA curves and collapse points of typical structures were obtained by IDA analysis method. Furthermore, effects of building seismic fortification levels, storeys and span on the collapse margin ratio (CMR) were analyzed, and the seismic collapse resistance of the RC frame structure under major earthquakes and severe earthquakes was evaluated. The results show that, the CMR of the RC frame structure designed according to China's current codes has a negative correlation with the seismic fortification levels and stories, but has a weak correlation with the span; the RC frame structure designed in accordance with the current code can meet the fortification requirements of major earthquake, but its ability to withstand the effects of severe earthquakes is obviously insufficient. Among them, the 7.5 degree fortified RC frame structure has the weakest ability to resist collapse.

Abstract:Based on the rigid body rule, an improved plastic hinge model is adopted to produce a spatial elasto-plastic beam element for the stability analysis of the steel dome structure of LNG storage tank by the consideration of the nonlinearity of geometry and materials.Two different methods of considering initial imperfections between local load disturbance and global modal disturbance and whether to consider the influence of material nonlinearity on the stability of the structure are studied. The results show that the initial defects, material nonlinearity and reduction of restraint stiffness will all reduce the stable bearing capacity of the grid dome structure. The stable bearing capacity of the structure under load interference is sensitive to the magnitude of the interference but not to the position; the modal interference is an overall geometric defect, the overall initial deformation of the structure is large, and the load-displacement curve is smooth.Compared with ABAQUS, the elasto-plastic rigid body criterion spatial beam element and its corresponding nonlinear analysis method are more efficient and accurate. It is suitable for nonlinear analysis of large and complex engineering structures, and has advantages in dealing with the effects of local defects on the structural stability.

Abstract:To study the influence of fiber distribution on the mechanical properties of Reactive Power Concrete(RPC) members under quasi-static loading, the four-point bending test was carried out on aligned steel fiber RPC and steel fiber RPC specimens at the same fiber content (2%) and different fiber lengths (13~20 mm).By selecting the initial crack point, peak point and other characteristic points on the bending load-deflection curves, the bending properties of aligned steel fiber RPC(ASFRPC) and steel fiber RPC(SFRPC) were analyzed quantitatively. The experimental results show that orientation coefficient of steel fibers in the direction of main tensile stress has a strong impact on the deflection hardening behavior in bending. First of all, the bending tensile peak stress and bending ductility of ASFRPC is greater than that of SFRPC.In particular, when the mid-span deflection reaches L/150, the residual strength of ASFRPC specimen is still 4.35~6.9 MPa higher than that of the initial crack strength.Secondly, when the fiber length increases from 13 mm to 20 mm, the flexural property of ASFRPC specimen improves more significantly than that of SFRPC specimen, and the advantage of fiber length diameter ratio is more significant with the increasing load of ASFRPC specimen. Thirdly, the fiber distribution of ASFRPC is uniform at the fracture, most of which are perpendicular to the main crack direction.Besides, the anchorage length is also long, and the bridging effect is significant at the fracture. In conclusion, considering the equivalent bending stress and energy absorption capacity of ASFRPC specimens, the mechanical properties of aligned steel fiber specimens perform best when the fiber content is 2% and the fiber length is 20 mm.

Abstract:The detection and evaluation of the corrosion characteristic parameters of steel bars is the basis for the performance evaluation of corroded reinforced concrete structures. The corroded steel bars with different target corrosion degrees were obtained by electrochemical accelerated corrosion test. Three-dimensional laser scanning technology was adapted to establish 3D geometric models of corroded steel bars, and the relevant corrosion characteristic parameters were extracted. Then the relationship between the average and maximum cross-sectional area loss ratio, as well as the corrosion non-uniformity coefficient were analyzed based on the probability theory. The probability distribution model of corrosion non-uniformity coefficient was also established. The results show that with the increase of average cross-sectional area loss ratio, both the maximum cross-sectional area loss ratio and the corrosion non-uniform coefficient increase as power function, and the parameters of power function are dependent on the diameter of the corroded steel bar. The corrosion non-uniform coefficient could be characterized by the generalized extreme value distribution. The shape, scale, and location parameters of the probability distribution increase linearly with the increase of corrosion degree, which are also dependent on the element length and the diameter of the corroded steel bar.