ALBERT

Description: In the past decades, horizontal directional drilling (HDD) has been successfully used to install various pipelines in different strata. However, construction accidents such as drill-burying and drill-sticking occur occasionally when pipelines installed by HDD method in an unstable stratum such as sand cobble stratum. Recently, HDD with dual drill pipes was used to install pipelines in unstable stratum, and the effect is significant. The law of cuttings migration for HDD with dual drill pipes is still unclear. Therefore, it is necessary to study the law of cuttings migration in reverse circulation with dual drill pipes. This study performs numerical simulations and experimental research on the cuttings-carrying process in reverse circulation directional drilling with dual drill pipes. Based on the assumption of dual concentric pipes, simulations of fluid-solid two-phase flows are conducted in different flow channels between the inner and outer drill pipes. An experimental cuttings-carrying model is then established. By combining the results of the numerical simulations and experimental investigation, the hydraulic parameters of the dual drill pipe system are optimized, and the rationalities of the drill tool design and the grading selection are validated. The results of this study provide a reference cuttings-carrying model during reverse circulation HDD with dual drill pipes.

Description: In urban environment, it is often unavoidable for shallow tunnels to be constructed adjacent to existing pile foundations. To obtain the ground displacements and stresses induced by shallow tunneling and existing pile foundation loads, the key procedure involves superimposing the analytical solution for shallow tunneling in green-field with the analytical solution for existing structure loads. In green-field, the complex variable method provides exact analytical solutions of ground displacements and stresses caused by shallow tunneling. However, the exact analytical solutions are not directly expressed as explicit functions of the coordinates (x, y) in the physical plane (called implicit form of exact analytical solutions), whereas the displacements and stresses induced by existing structure loads are explicit functions of the coordinates (x, y) in the physical plane, which makes it difficult to superpose the displacements and stresses induced by existing structure loads. In this paper, explicit form of exact analytical solutions of displacements and stresses induced by shallow tunneling in green-field is obtained by using the inverse conformal transformation and the Cauchy–Riemann equations. Comparison with implicit form of exact analytical solutions shows that the explicit form of exact analytical solutions is intuitional and easily used by engineers, and moreover, the calculation amount is much smaller than that for the implicit form of exact analytical solutions. Then, an application involving superimposing the explicit form of exact analytical solutions with Mindlin’s solution is implemented to analyze the secondary stress field and the related potential plastic zone caused by shallow tunneling adjacent to pile foundations. Moreover, the influences of pile foundation parameters on the ranges and shapes of the potential plastic zones induced by nearby tunneling are analyzed.

Description: The digital image correlation method (DICM) has been applied to similar material simulation experiments for rock-like materials, to overcome the weakness of traditional measurements, for example, data discontinuous. In this paper, the movement and fracturing process of the overlying strata during excavation are observed and studied, and the distributions of stress, strain, and deformation in the overlying strata are obtained based on similar material simulation. The DICM is applied to improve the testing method and to optimize the discontinuity of testing points; of course, the difference of rock deformation in the overlying strata during excavation is considered. Full-field deformation and strain are analyzed by the DICM. To verify the accuracy of the DICM, results obtained from the DICM, numerical simulation and similar material simulation, are compared. The DICM can reflect the characteristics of locality and randomness of rock-like materials more real than numerical simulation, and comparing with similar material simulation, it can directly reproduce the movement and fracturing process of the overlying strata during full-field excavation. It shows that, the DICM is entirely feasible to using in the large scale full-field deformation measurement on complex rock structure, and it is of theoretical importance for testing for rock-like materials.

Description: The expansion of urban underpass has become the mainstream of development to cope with urban congestion, and the effect on adjacent existing structures during enlarging construction is also an important issue in the construction process. In order to better understand the influence of tunneling on adjacent structures, the pedestrian underpass expanding project above-crossing Xi’an Metro Line 1 was investigated. The aim was to analyze the deformation curves characteristics of adjacent structures by field observation of ground settlement, heave of existing tunnels, and settlement of piles. The results show that the ground settlement curve in the vertical direction of the underpass is similar to the shape of V, and the maximum settlement appearing in the center line of underpass is 18.7 mm. Due to the effect of existing tunnels on the ground deformation, the settlement curve in the parallel direction of the underpass is similar to the shape of M. Above-crossing tunneling would cause the existing tunnels to heave, and the heave mainly occurs in the range of −6 m to 12 m between the pedestrian tunnel face and the center line of each tunnel. The heave curve is similar to the shape of inverted U. The settlement of piles is linear with its axial stress and significantly affected by its location. The settlement curve of piles is similar to the shape of S in two dimensions. On the basis of deformation curves, this paper presents some equations to describe the shape of V, M, inverted U, and S, respectively, by the inverted Gaussian distribution curve, superimposed Gaussian distribution curve, Gaussian distribution curve, and arctangent function.

Description: Cold recycled asphalt mixture (CRAM) has been reported to be able to provide a cleaner method to rehabilitate damaged asphalt pavement. This work used the CRAM containing emulsified asphalt (AE) and cement to investigate the methods of improving its early-age strength by considering mixture composition, including the types of AE and cement and the contents of AE, cement, and moisture. The curing conditions, such as temperature and humidity, were also involved. The results show that the mixture should be carefully designed to determine optimum AE and moisture content. Also, high cement content was helpful to increase the early-age strength. By changing the curing environment, it was found that raising curing temperature and applying a relatively low humidity contributed to the early-age strength improvement. The interaction of cement hydration and AE demulsification was investigated using microimage and laboratory experiments. The results show that AE particles were easy to cluster because of the negative ions released by cement hydration. AE delayed the early cement hydration but improved the later intensity of cement hydration. The coupling effect of AE and cement resulted in higher early-age strength than those of the mixtures only with cement or only with AE. The results presented in this work are expected to give guidance for preparing a CRAM with high early-age strength.

Description: For the last ten years, the number of cases of large-scale fires which occur on bridges, tunnels, and underpasses has increased. Such fires cause primary and secondary damage, including loss of human life, traffic congestion, and extensive financial damage. Therefore, a risk grade model and effective response plan need to be established for such cases in order to minimize the social and economic costs of bridge fires. In this study, the hazard factors contributing to bridge fires were selected to apply a risk grade model. A total of 144 bridge fire simulations were performed to calculate a surface temperature based on time by using Fire Dynamics Simulation (FDS). A risk grade in accordance with the degree of surface damage state caused by temperature of bridges was presented, and the mobilization time criteria for fire suppression were proposed. The surface temperatures based on time can be classified according to the vertical clearance and mobilization time criteria for fire suppression. Through the classified maximum surface temperatures based on time for bridges, the risk grade can be estimated according to the degree of surface damage state caused by temperature. In order to evaluate the applicability of the established risk grade model to the actual bridge, the arrival time taken from the bridge to the fire station was calculated through a Geographic Information System (GIS) network analysis, and the grades for actual bridge cases were assessed. The purpose of this bridge fire risk grade model is to establish a disaster prevention strategy based on risk grades and to minimize the subsequent social damage by determining a priori the disaster scale.

Description: In this paper, the pile-soil interaction of a low-rise pile cap foundation of an inclined straight alternating pile on two or three layers of a soil liquefaction site under seismic load is studied. By inputting the 0.5 g El Centro seismic wave in FLAC3D, the pile-soil interaction rule of the pile foundation of the inclined and straight pile groups of the low-pile cap under seismic action is simulated. By analyzing the soil acceleration, the pore pressure ratio, the horizontal displacement of the pile body, the vertical displacement, and the pile body bending moment, the law of pile-soil interaction between the pile and soil when the lower part of the pile is embedded in the clay layer is studied, and the low-rise pile cap inclined straight alternating group pile foundation on the two-layer soil and the three-layer soil free field is compared and analyzed. The results show that, under seismic load, the maximum acceleration of soil mass in the two-layer soil and three-layer soil model is discrete, and the pore pressure ratio of sand soil increases from bottom to top. By analyzing the displacement and bending moment of pile body, the bending moment at the joint between the pile cap and the top of pile body is the largest and the most vulnerable to damage. The maximum value of pile displacement and bending moment in the three-layer soil is less than the maximum value of the two-layer soil, indicating that the pile group foundation in the three-layer soil free site model is safer.

Description: Disposal of plastic wastes causes negative impacts including degradation of land and ocean and climate change. Reusing plastic wastes in concrete is one of the effective methods of reducing plastic disposal. Polyethylene terephthalate (PET) is one of the most abundantly available plastic wastes as it is commonly used for plastic bottles and food containers. This paper investigates the effects of treating PET wastes using hydrogen peroxide solution (H2O2) and calcium hypochlorite solution (Ca(ClO)2) before incorporating in concrete as coarse aggregate replacements. The physical and mechanical properties of concrete were analyzed for three different percentages, namely, 10%, 20%, and 30%, replacement of natural aggregates with plastic aggregates. For all percentage of replacements, it was found that chemically treated plastic aggregates have no effects on the fresh density, but the slump decreased due to roughened surface of treated plastic aggregates. Chemical treatment improved the bond strength between cementitious matrix and plastic aggregates and reduced the gap at the interfacial transition zone (ITZ). These phenomena contributed to the improvement the compressive strength and lower the permeability and porosity.

Description: To study the settlement and deformation characteristics of a long-short pile composite foundation and its influencing factors, the indoor centrifuge model test and numerical simulations were performed under the actual working conditions to treat the saline soft soil foundation in the Soltan salt lake area of Iran. Firstly, the settlement of a long-short pile composite foundation and the law of pile-soil stress ratio development with time were studied using a centrifuge model test. In addition, FLAC3D was used to simulate the test conditions, and it has been observed that the numerical and experimental results were in good agreement. Based on the numerical model, the effects of the replacement rate of long and short piles, cushion modulus, and pile length on the settlement of the composite foundation and the stress ratio of long and short piles were analyzed. The results show that the long-short pile composite foundation can effectively control settlement. Compared to the untreated foundation, the total settlement of a long-short pile composite foundation was reduced by 67%, and the postconstruction settlement was reduced by 47.7%. Compared to the final settlement of the composite foundation obtained using the centrifuge model test, the error range of the numerical simulation results was between 2.4% and 8%. The influence of pile spacing on the settlement and stress characteristics of a long-short pile composite foundation is greater than that attributable to the arrangement of the piles. Under this geological condition, it is reasonable to choose a pile spacing of 4d∼5d. When the long pile reaches the bearing stratum, the length of the short pile should not exceed 0.6 times the length of the long pile. The setting cushion not only reduces uneven settlement of the composite foundation but also improves the joint bearing capacity of the pile and the soil between the piles.

Description: The settlement calculation of postgrouting piles is complex and depends on the calculation method and parameters. Static load tests were conducted to compare the settlement characteristics of nongrouting and postgrouting piles, and three vital parameters in the layer-wise summation method were revised to predict the settlement of postgrouting piles. The elastic compression coefficient was deduced based on the Mindlin–Geddes method by considering the influence of the change in the pile side resistance distribution and end resistance ratio on the elastic compression after grouting. The relationship between the compression modulus and soil gravity stress and cone penetration resistance were established, respectively, using experimental data. The optimum value of the settlement empirical coefficient was determined using regional data. Finally, we used the postgrouting pile of the Wuqi–Dingbian expressway as a practical example. The results obtained from the layer-wise summation method after parametric optimization were close to the measured values. The results of this study provide reference data and guidance for the settlement calculation of postgrouting piles in this area.