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Laboratory and field test data on the lateral pile response with caps due to adjacent excavation are rather limited. The current practice for design of capped piles is to consider the cap resistance and the pile capacity independent of each other. This paper presents some results from three-dimensional finite-difference analyses that couple the constrain effect of pile cap on the lateral pile performance adjacent to an excavation. The analyses were performed in saturated homogeneous clays, and 38 cases of various pile head conditions restrained by caps including embedded depths of the pile into the cap, relative pile cap–pile modulus and pile cap–pile interface stiffness were carried out. The results have shown that the pile–pile cap connections can significantly affect the distribution of lateral pile deflections and bending moments and change the lateral pile performance, especially with a deep-buried and completely fixed cap. To combine the effects of the pile head embedded depths and the cap material properties, a convenient design method based on statistical analysis for estimating the pile–pile cap connections was presented. The proposed constraint coefficient method can be used to assess the lateral performance of the capped pile and simplify the design procedure of the pile cap due to excavations.

Excavation types of foundation pits for large-scale or special-purpose urban construction have been more and more complex, and the environmental safety issues caused by pit excavations are unprecedentedly significant. This paper presents an interpretation of the lateral response of group piles to a peculiar pit-in-pit excavation where the inner foundation pit located in the center of the outer pit is continued to excavate after the completion of the outer pit excavation. The support system of the pit-in-pit excavation is provided by diaphragm walls and multiple levels of rigid bracing. The numerically horizontal displacement of the diaphragm wall and the surface settlement of the outer pit caused by inner pit excavation were examined and compared with theoretical models. The cumulative influence of the pit-in-pit excavation system on the lateral bearing mechanism of existing piles in the transition zone and the additional impact characteristics of the piles induced by inner pit excavation were analyzed. A parametric study was subsequently conducted to investigate the effects of the inner pit geometry (plane area and excavation depth) on the lateral pile performance. Results revealed that the mechanism of lateral piles in the transition zone is attributed to the coupling effect of the inner and outer pit excavations. Moreover, the excavation area of the inner pit plays the significant influence compared to inner pit excavation depth. Finally, a loss ratio (δ) method to practically evaluate the degree of loss of lateral bearing capacity of the piles at different locations of the transition zone due to pit-in-pit excavation was proposed.

Classical theoretical approaches to evaluate CPTU-based hydraulic conductivity gave the expression of a bilinear relation defined by KD-BqQt, for undrained and drained soils. In fact, a dividing line may be selected with a certain degree of subjectivity, and several undrained/drained points occur in opposite sites, which may make us doubt the necessity of two intersecting lines to distinguish the undrained and drained soils. And a uniform and relatively simple curve including an arc, parabola, or ellipse correlation may be more suitable and accessible from a practical point of view. A database in the Yangtze Delta region has been collated to assess the three curves compared with the bilinear line. With the graphical and statistical analyses, the results indicate that the arc, parabola, and ellipse simplified curves could give better performance than the bilinear line. Through the statistical analyses and the number of variables, the overall best curve was the ellipse with only two variables, which is expected to improve the application scope and simplicity of hydraulic conductivity.

The lateral response of combined pile-raft foundations (CPRFs) adjacent to tunnel excavation is a challenging problem owing to the complexity of the pile-raft connections. In current engineering practices, the impact of these connections on the lateral performance of CPRFs is frequently overlooked, despite their importance. To address this issue, this study conducted three-dimensional finite element analyses to evaluate the contribution of pile-raft connections to the tunnelling-induced lateral performance of CPRFs in saturated clay. In the analysis, both passive and active loading at the pile head could be considered by varying the tunnel depth. Several parameter studies, such as relative pile-raft modulus, pile embedded modulus, pile embedded depths, and pile shaft skin friction, were conducted to determine the optimal design parameters for CPRFs. The results indicate that pile-raft connections significantly affect the tunnelling-induced deflections and bending moments of pile groups. Inspired by the results, a simplified design method, the pile-raft connection coefficient Kc was proposed. Additionally, the pile-head restraint percentage was established to make a relationship with the pile-raft connection coefficient in order to assess the pile-raft connection and guide the pile-raft design. In this paper, the recommended range value of Kc is 10–200 and the range value of pile-head restraint percentage is 24%–42%.

[Display omitted] •Accelerated strength degradation under different environmental conditions (5 WD cycles + 4 FT cycles) was quantified.•Optimal water-binder ratio (0.4) maximized strength in NXI/NXII-stabilized clay, outperforming conventional agents.•Rod-like hydration products with macropores conversion to needle-like ettringite(AFt) with micropores were revealed under DWFT cycles.•NXII and NXI agents enhanced durability via hydration-induced bridging and pore-filling mechanisms, validated by SEM/XRD.•Life-cycle assessment confirmed NXII’s superiority that 35% lower cost and 42% carbon emissions were reduced. The freezing and grouting methods are among the main construction techniques for the lateral connection passages of shield tunnels in soft soil areas. Therefore, the surrounding rock undergoes freeze–thaw (FT) and dry–wet (DW) cycles caused by water level changes during operation, leading to the deterioration of mechanical properties and instability. However, this research achievement is very limited. In this study, the macro and micro damage mechanisms of the surrounding rock in lateral connection tunnels under FT and DW cycles were systematically investigated. Initially, clay was sampled from a cross-tunnel of Hangzhou Metro Line 4 in Zhejiang Province. Cement (NXI), ground granulated blast furnace slag (GGBS), and fly ash (FA) (NXII) were used to solidify the clay subjected to DW and FT cycles. Finally, the uniaxial compressive strength and microstructure were examined using scanning electron microscopy and X-ray diffraction (XRD) to obtain 15 DW cycles (0, 5, 10, 15) and 12 FT cycles (0, 4, 8, 12) after 7 and 28 d curing periods. The results indicated that the compressive strength decreased after the DW-FT cycles, with rod-like hydration products (macropores) transitioning to needle-like ettringite (AFt) in the micropore-dominated structures. Simultaneously, the GGBS-FA mixture (NXII) promoted tight microstructures via hydration-induced bridging and pore filling, enhancing the water stability by 23% and DW-FT resistance by 18% compared with cement-only formulations. The NXII composite demonstrated superior long-term strength retention (89% at 180 d) and formed distinctive hydration phases, including calcium silicate hydrate and hydrotalcite-like compounds. Subsequently, the increasing pressure on the surrounding rock was calculated to degrade its mechanical properties (20% and 24.4%, respectively). Finally, a life-cycle assessment confirmed that the GGBS-FA system reduced material costs by 35% and carbon emissions by 42% compared with conventional cement-lime stabilization. These findings elucidated the microscale hydration damage mechanisms of GGBS-FA systems for soft soil solidification to advance sustainable tunnel engineering.

This paper aims to study the deflection of high-density polyethylene (HDPE) corrugated pipeline subjected to differential settlements of the ground using the finite difference method-discrete element method (FDM-DEM) coupling simulation method in 3D. Various physical characteristics of the pipeline, including diameters, corrugations, and elastic modulus have been investigated. Soil particles with different shapes are considered. The variation of soil settlement of soil particles with three different shapes under the uneven settlement condition is studied. The soil arching effects, including positive soil arch and negative soil arch, have been respectively analyzed. The results reveal that the change in pipe corrugation influences the stiffness of the pipe and the friction between the pipe and soil to some extent, which also causes the change of vertical deflection of the pipe. The soil composed of four particles is easier to form soil arch, which makes the soil more self-stabilized, thus alleviating the circumferential deformation of the pipeline.

The excavation of deep foundation pits can cause variations in the displacement and stress fields of surrounding soils, which hence induces adverse effects on adjacent structures. This study presents a two-stage method to quantify the impact of the excavation of a deep foundation pit on the adjacent double-curved arch bridge in the historical city of Nanjing, Southeastern China. The entire process of the foundation pit excavation was simulated and the induced deformation of the arch foot was obtained in the first stage by hardening soil model with small-strain stiffness. Then, the obtained deformation of the arch foot was applied to the bridge structure as a displacement boundary in the second stage to calculate the internal forces and deformations of the double-curved arch bridge structure. The tensile strength of concrete is taken as the limit value of the tensile stress of the double-curved arch bridge. The limit values of arch foot displacement under four evaluation conditions are obtained by step loading calculation. The present results provide construction guidance and safety warning for the process of foundation pit excavation adjacent to double-curved arch bridges for historical preservation.

The confined aquifer dewatering for long-deep excavations usually encounters challenges due to complicated geotechnical conditions, large excavation sizes, and high hydraulic pressures. To propose the most efficient scheme of confined aquifer dewatering for long-deep excavations, dewatering optimizations were performed using the simulation–optimization method. An open cut tunnel of the Jiangyin-Jingjiang Yangtze River Tunnel Project was taken as an example. The methods of finite element and linear programming (LP) were combined to optimize the dewatering process. A three-dimensional finite element model was developed. After simulating the pumping tests, hydraulic conductivity was inverted. Then, necessary parameters in the LP method were determined by simulating dewatering with each pumping well, and various LP models were developed based on some important influence factors such as dewatering sequence, considered pumping wells, and pumping rate limitation. Finally, the optimal pumping rates were solved and applied to the numerical model, with induced drawdown and ground settlement computed for comparison. The results indicate that the optimization can significantly reduce the required wells in the original design. Dewatering in the deepest zone exhibits the highest efficiency for long-deep excavations with gradually varying depths. For the dewatering sequence from the shallowest to the deepest zone, more pumping wells are required but less energy is consumed. Higher quantity and more advantageous locations of pumping wells in the LP model usually result in lower total pumping rate, drawdown, and ground settlement. If more pumping wells are considered in the deepest zone, pumping rate limitation of single well will only slightly increase the total pumping rate, number of required pumping wells, drawdown, and ground settlement.

In order to improve the understanding of such floodplain sediments and determining the validity of the tests, an extensive series of multifunctional seismic piezocone tests with pore pressure dissipation phase have been performed and supplemented with conventional borings, standard penetration, laboratory testing, and so forth. Sounding results from SCPTU were used to determine the stratigraphic profiles and the soil characteristics of two anchorage sites. A comparison of the boring and laboratory results with the CPTU profiles showed that the CPTU provided excellent information on soil stratigraphy and good guidance for determination of behavior and engineering implications of recent Yangtze River floodplain. At an area where local correlations based on modern SCPTU do not exist, methods for estimating coefficient of earth pressure at rest (K0), hydraulic permeability (kh), and equivalent stiffness (G0) associated with bridge foundation design are presented, compared, and verified. Results also illustrate the complexity and variability of the floodplain stratigraphy and soil properties, which means that the suggestions in this study should be updated when more local experience is obtained. This case study suggests that such enhanced seismic piezocone test should be considered as a potential tool and the instrument of first choice in site characterization programs for design of bridges founded on complicated soils in China.

Based on the complex deep foundation pit group process of the Huimin Avenue Comprehensive Reconstruction Project in Nanjing, the finite element numerical simulation method is used to analyze the deformation characteristics of the retaining structure and the coupling effect between foundation pits during the whole process of excavation and support construction of the complex foundation pit group. Meanwhile, the differences in the deformation characteristics and coupling effects of the retaining structure under different construction time sequence schemes of the foundation pit group are studied. Finally, some suggestions are put forward for the monitoring and construction in this project, which provides a reference case for the design and construction of similar foundation pit groups.