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Deformations in deep excavations can be controlled by providing adjustable support using servo struts; however, the design of strut positions and applied forces remains to be optimized. In this study, the influences of varied forces applied by servo struts on excavation-induced wall deflection and ground settlement were analyzed through numerical simulations and a field investigation. A reference numerical model and input parameters were validated using a well-documented excavation case study. Using the validated model, three servo struts were installed on a diaphragm wall at the top, middle, and bottom levels of an excavation model, and a constant force was applied on the beam elements. Comprehensive numerical simulations were carried out with various forces applied at the upper-, middle-, and lower-level struts. Both wall deflection and ground settlement were analyzed in relation to the applied force. Additionally, a field investigation was carried out at an excavation site in Hangzhou, China, where comparative analyses of applied forces and servo strut locations were performed. Both the numerical and field results confirm the effectiveness of servo struts in controlling excavation-induced wall deflection and ground surface settlement. Their effectiveness is closely related to their applied force and installation position. Wall deformation and ground settlement decrease with increases in applied force. Middle-level servo struts showed the greatest efficiency in controlling maximum wall displacement and maximum ground surface settlement.

When a foundation pit is hydraulically connected with surroundings, the dewatering inside the excavation would both induce water-level decline and enclosure wall deflection, which together cause ground settlement outside the excavation. However, the current studies have not fully revealed the settlement behaviour under the combined actions of the above two factors; meanwhile, the individual effect of the two factors on the ground settlement is still indistinguishable. In this study, in situ pumping test and numerical simulations were both conducted to ascertain the above issues. Specifically, a fluid–solid coupling numerical model was developed to simulate a practical foundation pit dewatering test; measured ground settlement and groundwater drawdown were adopted to validate the numerical model; then, a series of numerical simulations were performed to revel the characteristics of ground settlement due to the combined actions of groundwater drawdown and wall movement; on this basis, the individual impacts of the two factors on the ground settlement were separated. Results show that the settlement ratio caused only by enclosure wall movement (ηb) varies in the range of 2.5–43%, depending on the pumping location, pumping time and hydraulic connectivity in strata; ηb is overall greater during the pumping of phreatic aquifer compared to the pumping of confined aquifer, while with the pumping time elapsed, ηb would both decrease apparently regardless of the pumping location.

The growing demand for fuel efficiency and emission reduction in the aviation industry has significantly driven the adoption of weight-reduction strategies, notably through the use of thin-walled parts (TWPs). These parts are fabricated from structurally efficient materials such as light alloys (e.g., aluminum) and hard-to-machine alloys (e.g., titanium and nickel). However, the machining of thin-walled parts presents significant challenges, including high material removal rates, reduced rigidity, elevated vibration levels, residual stresses, and dimensional deformations, all of which complicate the processing of these components. To address these challenges, recent research has led to the development of several innovative machining solutions. In order to implement the findings of these researches in the industry, there is a need for guideline development that can be helpful for both practitioners and researchers by comparing these solutions in terms of the extent of changes required in the current machining setup, level of controls achieved for different dimensional and material categories of workpieces. Hence, the current work reviews causes of machining deflection of thin-walled parts by systematically reviewing all major seven countermeasures proposed by researchers. Based on this, a decision support table has been developed to aid in deciding a deflection mitigation strategy based on the categorization of workpiece thickness, machinability, and level of changes required in the existing machining setup to implement the mitigation strategy and reported extent of control achieved on different machining quality parameters. The novelty of current research is the development of a decision support table and comprehensive review of thin-wall machining based on a mitigation strategy. The findings of this research will be useful for machining technologists to identify thin-wall machining-related challenges and will assist in deciding available solutions for implementation to enable accurate and efficient machining practices.

Retaining wall movements are often estimated from a datum at the start of soil excavation. However, recent studies indicate that significant wall movements may occur during pre-excavation dewatering. In this study, the effectiveness of a buttress wall (that is, a short length of wall at 90° to the main wall) in limiting wall movement during pre-excavation dewatering is investigated numerically, focusing in particular on the buttress wall length (LB). Results indicate that wall movement decreases as LB increases. However, a smaller LB (less than 50% of the excavation width) may be sufficient if the drawdown or pumped depth is small (less than 30% of the total depth of retaining wall). With drawdowns greater than 60% of the total wall depth, a larger LB (greater than 75% of the excavation width) is needed to effectively control the deformation.

Purpose Deep excavation in soft clay often causes additional deformations to surroundings. Then, if deformations cannot be predicted reasonably, the adjacent buildings may be threatened by the deep excavation. Based on the good field observations from ten deep excavations in Hangzhou, this paper aims to thoroughly investigate the characteristics of wall deflections and ground settlements induced by deep excavations. Design/methodology/approach On the basis of good field observation of ten deep excavations, the performances of excavations, supported by contiguous pile in Hangzhou, were studied, and also compared with other case histories. Findings The maximum wall deflections (dhm) rang mostly from 0.7 to 1.2 per cent He, where He is the final excavation depth, larger than those in Taipei and Shanghai. The observed maximum ground settlement in the Hangzhou cases generally ranges from 0.2 to 0.8 per cent He. Then, the settlement influence zone extends to a distance of 2.0-4.0 He from the excavation. The relatively large movements and influence zones in Hangzhou may be attributed to low stability numbers, large excavation widths and the creep effect. The excavation width is justified to have a significant influence on the wall deflection. Therefore, to establish a semi-empirical formula for predicting the maximum wall deflection, it is necessary to include the factor of excavation width. Originality/value The relevant literature concentrated on the characteristics of deep excavations supported by the contiguous pile wall in Hangzhou soft clay can rarely be found. Based on the ten deep excavations with good field observation in Hangzhou, the characteristics of wall deflection and ground settlements were comprehensively studied for the first time, which can provide some theoretical support for similar projects.

This study aims to identify the relationship among the maximum wall deflection, system stiffness, and factor of safety ( FS ) against push-in failure for deep excavations in loose to medium-dense sand. It is concluded that when the FS against push-in failure is greater than or approximately equal to 1.2, the excavation remains stable, and the abovementioned relationship can be used to determine the maximum wall deflection. Empirical approaches for determining the maximum wall deflection are classified by the FS against push-in into two categories: 1.2 ≤  FS  < 1.5 and 1.5 ≤  FS  ≤ 2. Furthermore, the impacts from the strutting systems, such as the strut sizes and horizontal strut spacing, are further scrutinized by using non-linear multiple regression analysis to improve the reliable prediction of the wall deflection for deep excavation in loose to medium-dense sand. The outcome is also validated by excavation cases that have similar ground and retaining systems in this study.

A series of three-dimensional finite element analyses of deep excavations with the integrated system between buttress walls and diaphragm walls was conducted to investigate the effect of the buttress wall intervals, treatments, locations, height, and thickness on limiting deformations induced by deep excavation. The integrated retaining system was formed by maintaining buttress walls when soil was excavated. The wall deflection control mechanism of the integrated retaining system mainly came from the combined stiffness between the buttress wall and the diaphragm wall. In addition, the ground settlement control mechanism came from the combined stiffness between the buttress wall and the diaphragm wall, and the frictional resistance between the buttress wall and the surrounding soil. For achieving 50% reduction in the wall deflection and the ground surface settlement, the length and intervals of buttress walls that were applied to the integrated retaining system were at least 4 and 8 m, respectively. When the deflection at the diaphragm wall head was well restrained, for example, by the floor slab, the position of the buttress wall head could be located at a depth the diaphragm wall starts to bulge out. In such a case, the performance between the full height and limited height of buttress walls was quite close. Furthermore, a new well-documented excavation project was analyzed to verify the performance of the integrated retaining system. Results showed that the integrated retaining system worked excellently if the joints between buttress walls and diaphragm walls were constructed properly.

•The potential for dewatering-induced movements of a diaphragm wall is identified.•Pre-excavation groundwater drawdown effects on adjacent in-situ walls were assessed via lab-scale wellpoint test.•Wall movements and changes in lateral stress associated with the dewatering are assessed.•The mechanisms of dewatering-induced wall movement prior to bulk excavation are identified. Significant movement of in-situ retaining walls is usually assumed to begin with bulk excavation. However, an increasing number of case studies show that lowering the pore water pressures inside a diaphragm wall-type basement enclosure prior to bulk excavation can cause wall movements in the order of some centimeters. This paper describes the results of a laboratory-scale experiment carried out to explore mechanisms of in situ retaining wall movement associated with dewatering inside the enclosure prior to bulk excavation. Dewatering reduces the pore water pressures inside the enclosure more than outside, resulting in the wall moving as an unpropped cantilever supported only by the soil. Lateral effective stresses in the shallow soil behind the wall are reduced, while lateral effective stresses in front of the wall increase. Although the associated lateral movement was small in the laboratory experiment, the movement could be proportionately larger in the field with a less stiff soil and a potentially greater dewatered depth. The implementation of a staged dewatering system, coupled with the potential for phased excavation and propping strategies, can effectively mitigate dewatering-induced wall and soil movements. This approach allows for enhanced stiffness of the wall support system, which can be dynamically adjusted based on real-time displacement monitoring data when necessary.

In order to exploit the deep underground space, the construction of ultra-deep excavation in Shanghai is growing rapidly. In multi-aquifer strata, deep excavations typically require dewatering of confined aquifers to ensure engineering safety. However, existing studies have seldom conducted in-depth analysis on the influence of the soil parameters and construction measures on the deformation of retaining structures. In this study, a three-dimensional hydro-mechanical numerical model was developed to evaluate the performances of excavation and dewatering of the foundation pit. The model was validated by comparing the calculated and measured wall deflections and groundwater drawdowns of a 45 m ultra-deep double-wall excavation in Shanghai. According to the characteristics of soil stratification and construction activities, three parameters were selected for subsequent analysis, including the hydraulic conductivity of aquitard below the bottom of the pit, the pumping rate in the second confined aquifer and the construction of TRD wall. The stress distributions on both sides of the diaphragm wall were examined to elucidate the deformation mechanism. The results indicate that the aquitard hydraulic conductivity directly affects the effective stress of the overlying aquifer, which plays a crucial role in resisting wall deflection. An increase in the hydraulic conductivity leads to smaller effective stress, greater wall deflection and larger ground settlement. While an appropriately increased pumping rate enhances effective stress, over-pumping may induce excessive wall deflection at depth and disproportionate ground settlement. The TRD wall is quite useful in terms of waterproofing but the effect on deformation control is limited. The findings of this study provide valuable insights for engineering practices and the optimization of deep excavation construction measures in multi-aquifer strata.

Mechanically Stabilized Earth Segmental Wall (MSESW) is a composite retaining structure consisting of cruciform panel facing, geosynthetic strips, and granular backfill which is extensively utilized in various infrastructure projects. MSESW's typical vertical spacing between primary reinforcement is 0.75 m, which is a notably significant distance that may result in the wall bulging. The implementation of the secondary reinforcement, GeoGrid, is positioned in the gaps between such spacings. This research focuses on how secondary reinforcement affects the behavior of the MSESW. MSESW behavior can be observed through the back analysis of the field monitoring data collected with a total station. 2D and 3D Finite Element Method, which generates the most realistic models, is used to perform the back analysis. The most practically ideal model is the gap between panels that are installed with bearing pads. Parametric studies are also conducted by varying the secondary and primary reinforcement properties, i.e., type, length, and ultimate tensile strength. Secondary reinforcement improves the MSESW’s behavior significantly, in terms of wall deflections, tensile loads, and reinforcement deformations. The optimum length for applying secondary reinforcement is 0.5 of the primary reinforcement’s length. Secondary reinforcement primarily enhances internal stability, i.e., rupture, pull-out, and connection failure, but not compound failure. For MSESW, Biaxial GeoGrid use is not advantageous. Applying tensile loads at the connection of facing and reinforcement is mandatory, as per many international standards, i.e., American Association of State Highway and Transportation Officials (AASHTO), Canadian Standards Association (CSA), Association Française de Normalisation (AFNOR), and British Standards Institution (BSI).