Jun-Jie Zheng

Experimental Study and Numerical Simulation on Concrete Box Culverts in Trenches

Concrete culverts in trenches have been widely used in expressways. Problems frequently take place because of improperly estimated vertical earth pressures on culverts. Different codes have been used in China to estimate the design load on culverts. In this study, a full-scale experiment and FEM simulation were conducted to evaluate the variation of vertical earth pressures and soil arching in backfill and to examine the accuracy of the methods recommended by different design codes including the prevailing Chinese General Code for Design of Highway Bridges and Culverts based on the linear earth pressure theory. The measured vertical earth pressures from the experiment were compared with those from the current theoretical methods. The variations of foundation pressure and settlement were also analyzed. The FEM simulation investigated the key influencing factors on the vertical earth pressures including the height of the embankment fill, the width of the trench, the slope angle of the trench, the dimensions of the culvert, the properties of the backfill, and the elastic modulus of the foundation soil. This research reveals that soil arch formed when the backfill on the culvert reached a certain height, but it was unstable. The coefficient of the vertical earth pressure on the top of the culvert was significantly different from that recommended by the Chinese General Code for Design of Highway Bridges and Culverts.

Statistical Evaluation for Strength of Pile by Deep Mixing Method

This paper presents a statistical method to evaluate the strength of heterogeneous stabilized pile by deep mixing method using cement as an additive reagent. The cross-section of stabilized shaft is conceptually divided into small elements in order to examine the characteristics of its heterogeneity due to imperfect mixing. The properties of each element are treated as independently identical. Typically, the unconfmed compressive strength of cemented clay is regarded as a random variable of which the probability density distribution is assumed as log-normal. Based on probabilistic and statistic theory, another random variable, denoted as the factor of mixing uniformity, is proposed to quantitatively assess the influences of mixing quality on the strength of pile shaft. The probability density function of this factor is studied, and its applications in conventional design and Reliability-Based Design (RBD) method are analyzed as well.

Reliability-based Design Applied to Multi-column Composite Foundations

This paper presents an approach based on Reliability-Based Design (RBD) to evaluate area replacement ratios (percent coverage) of columns in a multi- column composite foundation. A geostatistical technique is implemented to estimate the autocorrelation distance of foundation soil along the vertical direction. Instead of using differential and simulation processes to estimated reliability indices from the nonlinear and complex limit state equations, the Immune Algorithm method is introduced as a new and effective technique to provide a more accurate solution to optimization problems. Reliability analyses of both bearing capacity and settlement of multi-column composite foundations are performed to obtain relationships between reliability indices and area replacement ratios of columns. Based on previous studies, a target reliability index of 3.0 is selected as a criterion to estimate area replacement ratios of composite foundations.

Evaluation of the New Technique of Geogrid-Reinforced and Pile-Supported Embankment at Bridge Approach

Differential settlement between the bridge approach embankment and bridge abutment is a major issue in bridge engineering. To mitigate the differential settlement, a new ground-improvement technique, a fixed-geogrid-reinforced and pile-supported embankment (referred to as a FGT embankment) was proposed. To investigate the performance of the FGT embankment, a numerical analysis was performed for a trial bridge approach embankment in Changzhi, China. The numerical model was carefully calibrated to ensure good representation of the realistic conditions. The comparison analyses and parametric study were conducted to evaluate the effects of the traffic load, long-term tensile stiffness of the geogrid, and long-term elastic modulus of the soil. The results show that the FGT embankment can reduce the settlement, enhance the stability, and offer a better performance measure for the construction of a high embankment at the bridge approach.

Notice of Retraction Risk analysis of shield tunnel segment failure based on Fuzzy Fault Tree method

Through analyzing and summarizing the types of shield tunnel segment failure and the relevant causes of the accident, Fuzzy Fault Tree Analysis (FTA) was employed to study the failure risk of segment and the Fuzzy Fault Tree system model of segment and segment-related systems were established. The potential failure modes of risk accidents and their influencing factors were discussed through qualitative and quantitative analysis. With its application on practical project, some effective control measures were proposed. This research could be valuable reference for the design, construction and control of shield tunnel segments.

Notice of Retraction Reliability analysis of vertical bearing capacity of pile using random-fuzzy entropy principle

The fuzziness of the failure process of piles should be given full consideration when analyzing the reliability of vertical capacity of piles. The density function of performance function is calculated by using the non-dimensional calculation module and the maximum entropy principle, which assures the convergence of iteration and makes the calculation results closer to the fact. To overcome the deficiencies of the membership functions which were usually used in practice, a Beta distribution function is proposed in this paper to solve the fuzziness of the failure process of piles. The Beta distribution function not only retains the merits of the membership functions, such as simple form and convenient calculation, but also has its own advantages. Therefore, it is more rational to use the Beta distribution function as the membership function of the failure events of piles. Finally, the entropy density function and the Beta distribution function are employed to calculate the fuzzy failure probability of piles. It is a more rational and effective method to judge the safety of the pile foundation engineering.

Effect of Liner Consolidation on Contaminant Transport Through a Landfill Bottom Liner System

In municipal solid waste landfills, a triple-layer composite liner consisting of a geomembrane liner (GML), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) is commonly used at the landfill bottom to isolate the leachates from surrounding environment. This paper presents a numerical investigation of the effect of liner consolidation on the transport of a volatile organic compound (VOC), benzene, through the GML/GCL/CCL composite liner system. The numerical simulations were performed using the model CST3. The performed numerical simulations considered the impact of consolidation on contaminant transport for a GML/GCL/CCL liner system. The simulation results indicate that, depending on conditions, consolidation of the GCL and CCL can have significant impact on the transport results of benzene, both during the consolidation process and long after the completion of consolidation. The traditional approach for the assessment of liner performance neglects consolidation of the liners and fails to consider the consolidation-induced transient advection and concurrent changes in material properties and, therefore, can lead to significantly different results.

Numerical Analysis of Ground Displacement and Pile Response Due to Tunneling in Soft Soil Considering the Creep Behavior

The additional pile response due to the creep behavior of the soil is disadvantageous to the safety of pile. However, in the current studies for considering the creep behavior of the soft soil, the pile response induced by the long-term settlement of soil is seldom investigated. This paper mainly discusses the pile response during the excavation and operation periods considering the creep behavior of soft soil. The finite difference software FLAC3D is utilized to simulate the excavation of tunnel and the creep behavior of soil based on the two-stage analysis method. In the first stage, the displacement controlled method (DCM) is applied to simulate the instantaneous settlement of soil during excavation period. In the second stage, the creep behavior of soft soil is considered to estimate the long-term settlement of soil during operation period. While the creep behavior of soil is not considered, the simulation results such as the shape of trough, pile response are compared with the results of existing studies, and the numerical model is verified to be acceptable. While the creep behavior of soil is considered during the operation period, the influence of the creep behavior on the pile response such as its deflection, settlement, axial force and bending moment of the long-term soil settlement are discussed. The effects of the four typical mechanical parameters in the creep model on soil deformation and pile response are investigated.

3D Parametric Study of Geosynthetic-Reinforced Column-Supported Embankments

Column-supported geosynthetic-reinforced embankments have been increasingly designed and constructed. Since settlement analysis has not been well considered in current design methods, numerical modeling has been often adopted to predict the long-term serviceability of the embankment by coupling hydraulic and mechanical models. To assess the influence of various factors on the settlement of column-supported embankments, coupled 3D numerical analyses were performed using FLAC3D in this study. Once calibrated by a well-documented case history in Finland, the coupled 3D numerical modeling scenario was implemented in a parametric study to fulfill the objective of this study. In the parametric study, a prototype case with a typical configuration served as the baseline case. One parameter was changed at one time to investigate the influence of a certain factor on the settlement. In the analyses, the foundation soils including soft and firm soils, the embankment fill, and the columns were modeled as linearly elastic-perfectly plastic materials with Mohr-Coulomb failure criteria. The geosynthetic reinforcement was simulated by geogrid elements in the FLAC3D, which in realty are plane-triangular elements, sustaining in-plane forces only. The staged construction was approximated by building the embankment in lifts with duration equal to the construction time plus the lapse time between two consecutive stages. The computed settlements were presented, compared, and discussed in this paper.

Theoretical and Numerical Analysis on Geosynthetic-Reinforced and Pile Wall-Supported Embankment

The vertical reinforcement (pile walls) is combined with the horizontal reinforcement (geosynthetics) to provide an economical and effective solution for ground treatment of high embankments constructed on soft soil. Theoretical and numerical analyses were conducted to investigate the interaction among geosynthetics, pile walls and soft soil. The differential settlement between pile wall and soft soil will generate soil arching in embankment fill. Soil arching and tensioned membrane of geosynthetics are combined to transfer embankment loads from soft soil to competent substratum (such as bedrock) through pile walls, which minimize the yielding of the soft soil and potentially reduce the total and differential settlements. The soil arching efficiency, the pile wall efficiency, the differential settlement of the embankment, and the distribution of tension force in the geosynthetics have been analyzed with the consideration of four major influencing factors: the elastic modulus of the pile wall, the tensile stiffness of the geosynthetics, the height of the embankment fill, and the area ratio of the pile wall. Some conclusions are drawn as a reference for the design and construction of geosynthetic-reinforced and pile wall-supported embankment over soft ground.