Analytical Elasto-plastic Solution for Frost Force of Cold-Region Tunnels considering Anisotropic Frost Heave in the Surrounding Rock Abstract There is an increasing trend of tunnel infrastructure construction in cold regions due to the advance of a western development strategy. To reduce the frost damage sustained by a tunnel, it is important to consider the mechanical properties of frost heave in the surrounding rock by analyzing the anisotropic frost heave of a cold-region tunnel. This paper elaborates on the behavior of anisotropic frost heave in the rock surrounding a cold-region tunnel, and the coefficient of displacement relief is adopted to indirectly quantify the influence of the tunnel construction process. The analytical elasto-plastic solutions of the stress and deformation in the surrounding rock are derived with Drucker-Prager criteria (hereinafter referred to as the D-P criteria) by modifying the constitutive equation for the frozen surrounding rock. Finally, an example is given to obtain the influence law of the distribution of stress and deformation in the surrounding rock. The results indicate that the plastic radius and frost force calculated by considering isotropic frost heave are greater than those obtained by considering anisotropic frost heave. The influence of the related parameters also analyzed. Some useful insights are provided for future numerical simulations and the design and construction of cold-region tunnels.

Mechanical Properties of Alkali Activated Fly Ash Geopolymer Stabilized Expansive Clay Abstract It has always been a challenge for civil engineers to lay roads in the areas covered by expansive soil. The expansive soil undergoes extreme phase changes from being hard in hot summer to being slushy and without strength in monsoon season. Thus, the engineering properties of the expansive soil must be improved before laying the roads. This paper presents the results of experimental work carried out to improve the engineering properties of an expansive clay i.e. black cotton soil (BCS) by using fly ash geopolymer. Sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solutions were mixed in different ratios (0.5, 1, 1.5, and 2) and used for synthesizing the geopolymer. The stabilized BCS samples were characterized in the laboratory for various properties viz., Atterberg’s limits, free swell ratio, and unconfined compressive strength. The untreated and treated BCS samples were also analyzed for their microstructural and morphological properties by using the SEM (scanning electron microscope) images and the XRD (X-ray fiffractometer) and FTIR (Fourier-transform infrared spectroscopy) spectra. An increase in the unconfined compressive strength and reduction in free swell ratio as well as shrinkage limit was observed after stabilization with geopolymer. Results also indicate binding of soil particles and formation of dense microstructure resulting in higher strength and less swelling and shrinkage characteristics. Furthermore, the bender element test was used to indicate the improvement in stiffness of the geopolymer stabilized expansive soil in terms of shear wave velocity.

Water Inflow Prediction and Grouting Design for Tunnel considering Nonlinear Hydraulic Conductivity Abstract Grouting prevents groundwater leakage into tunnels, based on the exponent model that expresses the nonlinear variation of the hydraulic conductivity of the surrounding rock, the formulas for predicting the magnitude of water inflow and outer water pressure of the lining after grouting are deduced. The parameter analysis shows how the water inflow decreases as the hydraulic conductivity of the grouting circle diminishes and the thickness of the grouting circle increases. When the parameter α (attenuation coefficient), which expresses the decreasing amplitude of the permeability coefficient of the surrounding rock with depth, is greater than 0, the water inflow increases until it reaches a maximum at a certain depth, and then the inflow decreases to 0 if deep enough. After considering the variation in the hydraulic conductivity of the surrounding rock, the thickness and hydraulic conductivity of the grouting circle may be designed to be too large to reduce the magnitude of the water inflow. Meanwhile, to reach the limited drainage criterion of the tunnel groundwater, the grouting circle thickness decreases gradually as α increases after the nonlinear variation of the hydraulic conductivity of the surrounding rock, which can reduce the cost for plugging the groundwater. Thus, it is critical to consider hydraulic conductivity variation during water inflow predicting and grouting when designing tunnels.

Hydrological Performances on the Modified Permeable Pavement with Precast Hollow Cylinder Micro detention Pond Structure Abstract In this study, a permeable pavement with an on-site subsurface micro-detention pond was developed. Common permeable pavements are typically composed of fine layered particles attributed with low porosity. The permeable pavement with micro-scale detention storage (PPDS) developed in this study is a modified type of interlocking block permeable pavement consisting of a hollow cylinder with a hexagonal cover at the top and bottom of the PPDS. The PPDS was designed with a void volume of 70% and a water storage capacity of 0.19 m3/m2. A rainfall simulator was used to perform the tests on the profile of the hydrological pavement such as the storage capacity, detention period, permeability rates and infiltration performance over various storm events. The PPDS showed its ability to detain first flushes of rainfall within a 15-minutes period for a 100 year return period. Meanwhile, the permeability rate of the PPDS was subjected to the infiltration capacity of the subgrade soil following a linear relationship between the flow depths over time. The testing performances indicated that the PPDS has met the basic hydrological design considerations, as those in the typical permeable pavement, from the perspective of permeability rates, infiltration capacity, storage and detention capability.

An Optimal Model based on Multifactors for Container Throughput Forecasting Abstract Containerization plays an important role in international trade. Container throughput is a key indicator to measure the development level of a port. In this paper, Lianyungang Port and Shanghai Port are chosen to study the method for container throughput forecasting. Gray model, triple exponential smoothing model, multiple linear regression model, and backpropagation neural network model are established. Five factors are selected as influential factors. They are total retail sales of consumer goods, gross domestic product of the local city, import and export trade volume, total output value of the second industry and total fixed assets investment. The growth and the raw datasets are used in the prediction, respectively. The datasets from 1990 to 2011 are chosen to build models and the ones from 2012 to 2017 are used to assess the performance of the models. By comparison, the backpropagation neural network model is applicable to both Shanghai Port and Lianyungang Port for container throughput forecasting. The volume of container throughput at both ports from 2018 to 2020 is predicted.

Effects of Clogging on Settlement Predictions of Ground Improved with Stone Columns Abstract Clogging of stone column (i.e., the mixture of column material and surrounding soil) is widely reported as well as its hindrance effect on the consolidation rate of soft ground improved with stone columns, however, its influence may be more complicated in settlement estimations. In this study, a modified consolidation model is proposed for making predictions of settlement with consideration of clogging. Its influence on permeability and compressibility is included while both radial and vertical flow in stone column are taken into account. Parametric studies reveal that the consolidation rate will be largely impeded if the permeability of clogged column drops below that of surrounding clay. The short-term settlement is lower mainly because of the reduction of permeability. On the contrary, the long-term settlement becomes larger due to an increase in compressibility. This finding implies that the final settlement may be underestimated if the clogging effects are not incorporated even when early field observations are available, as supported by a design example.

Dynamic Response of High Speed Train Moving on Consecutive Bridges Abstract This research demonstrates how to analyse the dynamic response of a high-speed train moving over consecutive bridges. The authors explain in detail how to apply the uncoupled iterative method to consecutive bridges, by deriving the complete motion history for one bridge segment at a time, using the solution of the train as an initial condition for the next bridge. This algorithm is a highly cost-effective approach to analysing the train-bridge interaction for a high speed railway (HSR). The authors perform this analysis on two existing bridges: a simply supported Taiwan HSR bridge, and a three-span continuous Korea HSR bridge. The results show that both types of bridges are capable of supporting HSR trains at speeds up to 400 km/h with negligible carbody displacements and accelerations. This speed is greater than the current service speed of 300 km/h.

Compressive Behavior of Damaged Tubular T-joints Retrofitted with Collar Plate Abstract The static bearing capacity and failure modes of damaged tubular T-joints retrofitted with collar plates under axial compression were investigated. Two-step loading was applied: First, the chord deformation was loaded to the pre-designed degree, followed by unloading and collar plate installation. Subsequently, the specimens were reloaded. The maximum capacity and corresponding displacement (Δ1,m) were determined, and the ratio of the chord deformation of the other joints to Δ1,m was utilized to define the damage degree. The maximum capacity of retrofitted tubular T-joints could be up to 13–77% in second step loading, compared with that of unreinforced T-joints; however, the capacity decreased by 2–10% compared to that of directly reinforced T-joints. Sixty-nine finite element models were generated. The effects of chord wall thickness, chord diameters and collar plate lengths on the bearing capacity under different damage degrees were analyzed. A satisfactory effect could be obtained by using a suitable size of expanded collar plates under a constant damage degree. Retrofitting with collar plates could mitigate the development of equivalent plastic strain in the joint intersection, even for considerably damaged tubular T-joints. A modified formula considering the damage degree was proposed for bearing capacity prediction of retrofitted tubular T-joints.

Stability Analysis for Cofferdams of Pile Wall Frame Structures Abstract Pile wall frame structures (PWFSs) are double-wall sheet-pile structures with an integrally precast framework of reinforced concrete to connect double rows of closely placed piles. An engineering test on a cofferdam of PWFSs was conducted in Binzhou, where lateral displacement along pile shaft was carefully monitored during the hydraulic filling process. A 3D finite element model (FEM) of the test was established to study the stability failure mechanism of PWFSs. Then, a design method for PWFSs was proposed through a structural stability analysis based on the limit equilibrium method, with special consideration of the cutting pile force influenced by row spacing. According to FE results, lateral pile displacements drawn from the FEM correspond well with field observations, and earth pressures applied on closely spaced piles are in line with Rankine’s theory. Results of the theoretical analysis indicate that the control slip surface lies on the bottom of a soil layer with a poorer shear strength index. The effects of framework width, pile spacing, pile length and diameter on structural stability are also evaluated. The feasibility of PWFSs has been verified by an engineering test, and the simplified design method established here is reasonable and effective for structural stability prediction.

The Estimation of Reliability Probability of Structures based on Improved Iterative Response Surface Methods Abstract Response surface method (RSM) provides an efficient way to performance reliability analysis for structures. However, the locations of samples are very important due to its great influence on computational accuracy and efficiency of RSM for reliability analysis. To further improve computational accuracy and efficiency of RSM, new methods of selecting samples are proposed based on a new starting center point, 2n + 1 directions and a linear interpolation. The objective of the new methods is to find samples which are close to limit state function (LSF) around design point, thus the fitting precision of response surface function (RSF) to LSF can be improved, and a quadratic polynomial without cross terms is employed as the RSF in each iteration. Then improved iterative RSMs are formed. Two mathematical examples and a truss structure are employed to demonstrate the accuracy and efficiency of the proposed RSMs. Results show that the proposed RSMs can improve the fitting precision of RSF to LSF and achieve more accurate results with relatively high efficiency.