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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 fou...
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To investigate the three-dimensional earth pressure distribution and deformation characteristics of piled embankments with retaining wall， ten groups of model tests considering the embankment height， the clear distance between piles as well as even and uneven settlements of soil between piles were carried out using a multiple trapdoor test setup. T...
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... It involves various methods such as mechanical interventions, chemical treatments, and other techniques aiming to maintain soil stability, improve engineering characteristics, limit water absorption capacity, and reduce compressibility (Zada et al., 2023;Sharma et al., 2018;Suresh and Murugaiyan, 2021). In the past several decades, precast concrete with high strength and fast installation has been extensively used for soft-ground improvement (Chen et al., 2019;Ding et al., 2020;Li et al., 2018;Pengjiao et al., 2020;Tong et al., 2022;Wang et al., 2018a;Wang et al., 2018b;Zhuang et al., 2020). ...
This study examines possibility of improving clayey soils in the Handere Formation exposed in the vicinity of Adana (S. Turkey), one of the largest cities in southern Turkey. The Handere Formation, from where the samples for this study are taken, is stratigraphically at the upper most part of the marine sediments of the Adana Basin. The unit is located at the northern part of Adana city. The samples were examined in the geotechnical laboratory to determine the effect of plaster mortar (Master Cast) on the geotechnical properties of the soil and its ability to improve the soil. shear box, consolidation, unconfined compressive strength tests were applied on the samples. It has been shown that the master cast used can improve soil properties geometrically and can be used as a soil stabilizer. The plasticity values of the soils were reduced by master cast addition. Besides, it was determined that the highest maximum dry unit weight and the lowest optimum moisture content were obtained by 15% master cast addition. The soil strength properties were reached to the top values in case of 15% master cast added into the mixtures. Besides, it is determined that the coefficient of volume compressibility (Mv) and the pre-consolidation pressure values are ideal when the master cast ratio in the mixtures are 10% and 5% respectively.
... Stiffened composite piles have been widely used in ocean engineering as a new form of composite piles for soft ground improvement [1][2][3][4][5][6][7][8]. Composite material piles, such as fiber-reinforced plastic (FRP) and structure-reinforced plastic (SRP), are unique solutions to problems including wooden pile deterioration and steel corrosion in tradition [9]. ...
A new stiffened composite pipe pile was developed for improving the foundation of reclaimed ground in ocean engineering. To study the bearing capacity of the stiffened composite pipe pile group, a combination of field test and finite element method was used. Firstly, field tests were performed on the proposed single stiffened composite pipe pile. The single stiffened composite pipe pile model was verified by comparing the numerical simulation results with the field test results. The load transfer mechanism from the stiffened core to the cemented soil and the surrounding soil was clarified. Further, a 3D finite element model of the stiffened composite pipe pile group was established based on the single stiffened composite pipe pile model. Finally, the bearing capacity of the pile group and the stress distribution of each pile were analysed and the influence of the pile spacing on the pile bearing capacity was discussed. The results showed that the axial stress of both the side and corner piles decreased rapidly with an increase in the pile spacing, and the stress-bearing ratio decreased. The stress-bearing ratio of the central pile increases with an increase in pile spacing. The smaller the pile spacing, the larger the load proportion of the composite pile group and the larger the foundation settlement. The optimal design scheme was a composite pile with a 500 mm stiffened core diameter, 700 mm outer cemented soil diameter, and a spacing between piles of four times the cemented soil diameter (2.8 m) considering the group pile bearing capacity and the economic benefits of the project. These results provide a reference for the design and construction of stiffened composite piles for ground improvement projects.
... A variety of pile techniques have been developed to meet various engineering needs, such as stone columns, deep mixing (DM) columns, T-shaped DM columns, jet grouted columns, and precast cement (PC) piles [8][9][10][11]. To give full play to merits of different pile techniques, the combined use of multiple pile techniques for soft soil ground improvement was developed [12][13][14][15]. Because the combined composite foundation (CCF) can take advantage of multiple performances of every pile technique, it is becoming more well-liked everywhere, but notably in China. ...
As the composite pile, the precast concrete piles reinforced with cement-treated soil (PCCS) is formed by driving the precast cement (PC) pile into the deep mixing (DM) column, which has been successfully and widely utilized to support buildings and embankments over soft soil. To increase the pile spacing and give full play to the economic merits of the PCCS, a reinforcement scheme, which involves the combined use of rigid piles and flexible columns, employing penetrated PCCSs and floating DM columns is proposed and utilized for soft soil ground treatment. However, there is a lack of feasible method for consolidation behaviors of this combined composite foundation (CCF) reinforced with penetrated PCCSs and floating DM columns under flexible loads. This paper developed an analytical solution to predict the average consolidation degree of this CCF based on a cylinder consolidation model and double-layer ground consolidation theory. The excess pore pressure and average consolidation degree were calculated by considering the composite pile penetration into the cushion. The analytical method agrees well with results obtained by numerical analysis. Additionally, a parametric study was conducted systematically to analyze the effect of key influence factors on the average consolidation degree of this CCF. The results indicate that the consolidation rate of this CCF can be much faster than that of the natural ground. The consolidation rate strongly depends on the compressive modulus and area replacement ratio of PCCSs. The increasing inner core-outer core modulus ratio and the inner core-subsoil modulus ratio increase the consolidation rate of this CCF. In addition, the consolidation rate increases with the gravel cushion-subsoil modulus ratio, while it decreases with the loading period.
... In order to consider the influence of the surrounding soil layer on foundation pit structure, the length and width of the soil layer are taken as four times that of the foundation pit size, and the thickness of the soil layer is taken as twice that of the foundation pit depth. The total size of the ABAQUS finite element model is set as 576 m × 860 m × 30 m [22]. An eight-node C3D8R volumetric element is adopted for the soil layer and the number of elements is about 334,000. ...
... The material parameters of each component of the foundation pit supporting structure are shown in Table 2, and the finite element model is shown in Figure 4. The outer soil and diaphragm wall have face-to-face contact, and the normal contact is set as hard contact which means that the normal pressure can be transmitted between the two contact surfaces only when they are not separated [22,23]. The penalty function is adopted in the tangential direction, and the friction coefficient is taken as 0.2. ...
In this paper, a real-time monitoring system—including vibration acceleration sensors, temperature sensors, and static and dynamic strain sensors—is used to monitor the safety status of a steel assembly bracing in a practical project. It uses 5G wireless networking technology to transmit monitoring data to a cloud server for early warning of abnormal changes and development trends. Real-time monitoring data obtained in a construction site are used as the inputs of the finite element model and the corresponding results of numerical simulation are compared with the results from the real-time monitoring. It can be concluded that: (1) the stress caused by environmental temperature is very significant which can be higher than the initial prestress of the steel assembly bracing; (2) the stress caused by the vertical vibration mainly from construction vehicles is not remarkable, however, the vertical frequency-weighted acceleration of support vibration is relatively large which can affect the sense of safety of engineering technicians on site; (3) the combination of the environmental temperature and vertical vibration does not affect the safety of the steel assembly bracing.
... The enclosure deflection of DW induced by excavation, a key factor in the safety of deep foundation pits, has been investigated through field tests (Cheng et al., 2018;Li et al., 2017;Tan and Wang, 2015b;Zeng et al., 2018;Zhao et al., 2021), laboratory tests (Chen et al., 2021a,b;Azzam and Elwakil, 2017), and numerical simulations (Guo et al., 2019;Lim et al., 2020;Tong et al., 2022). Additionally, Ou et al. (2019) predicted the lateral displacement of DW using the Ritz method. ...
... Meanwhile, the effect of the jacking force on the launch shaft exhibits an apparent 3D effect (Sun et al., 2014;Sun et al., 2015). Furthermore, FEM is widely used to analyze braced exvacation (Cattoni and Tamagnini, 2020;Guo et al., 2019;Lim et al., 2020;Tong et al., 2022). Thus, the 3D FEM of the pipe jacking launch shaft was established by ABAQUS to deepen the visualization of the 3D effect. ...
The stability of braced structures for the launch pit in pipe jacking plays a vital role in structural safety during excavation and jacking drive. Through a deep launch pit in Foshan, the real-time deformation and mechanical response of the diaphragm walls, internal struts, and the soil behind the wall induced by braced excavation and pipe jacking operation are obtained from in-situ monitoring and three-dimensional finite element model. The internal struts restrict the further wall deflection and earth pressure in the braced excavation, displaying the apparent time-space effect or corner effect of the limited-scale & deep launch pit. Moreover, pipe jacking operation influences the reaction wall within a certain zone, contributing to the apparent spatial effect. The outward deformation and the increase in the soil pressure occurred in the disturbed zone. Although part of the mucky soil reaches the ultimate equilibrium during the deep excavation and jacking drive, the diaphragm walls still indicate superior strength and stiffness.
... To protect the surrounding environment during excavation, an effective and efficient retaining technique is necessary to limit wall deflection and ground settlement [8,16,18,29]. Various retaining structures have been developed to control ground displacement and to protect surrounding facilities [4,15,17,19,22,26,27,31,36,39,42]. ...
A new excavation retaining structure, referred to as an outward inclined-vertical framed retaining wall (OIVFRW), has been developed and adopted in practice. This retaining structure can limit excavation-induced ground movement and protect adjacent infrastructures. A case history shows that it performs well in controlling wall deflection, but its retaining mechanism and the factors influencing its performance are not fully understood. Therefore, this paper aims to investigate the behaviour of an OIVFRW to provide a better understanding of the retaining mechanism of this newly developed retaining structure. A case history of an OIVFRW in soft soil is first introduced, and a finite element model is then established. Parametric studies are carried out to investigate the relationship between influencing factors and the performance of an OIVFRW. Subsequently, the location of the neutral plane, the mobilization of the skin friction and the distribution of the axial force are analysed. Moreover, the retaining mechanism of this structure is discussed on the basis of the parametric investigation, and the contribution of pile length to the retaining mechanism is investigated. The results show that an OIVFRW structure performs well in limiting deformation, and the length of the vertical pile and the inclination angle show significant contributions to limit the structure movement. Moreover, the axial force of the vertical pile, which stems from the relative displacement between the soil and vertical pile, acting on the head of the inclined pile is beneficial to resist the deformation of the OIVFRW.
In soft soil layers, piles are frequently loaded laterally by horizontal soil movements. In many cases, the lateral pressure acting on piles due to horizontal soil movements is calculated with empirically or analytically based approaches, respectively. However, most of these design approaches do not consider possible influences on the resulting pile loads. This paper presents the results of model tests and numerical simulations on single piles and pile groups in cohesive soil subjected to lateral loads which were carried out to overcome limitations of available design approaches. Based on extensive small-scale 1 × g-model tests and numerical investigations with the finite element method, influencing factors on the lateral pressure, such as the roughness of the pile–soil interface, the pile size, the pile shape and the pile spacing were identified. A parametric study with the numerical model quantified the most relevant factors influencing the development of lateral pressure on piles due to adjacent surface loads and lead to the development of a simplified analysis approach.
To effectively mobilize concrete strength, a newly developed composite pile, the so-called “Precast Concrete Piles Reinforced with Cement-treated soil (PCCS)”, has been used to improve the bearing capacity of soft ground. However, there are limited studies on the consolidation behavior of the PCCS in soft ground. This paper proposes an analytical solution for the consolidation of the composite ground reinforced by PCCSs based on a modified equal strain assumption. This composite ground is simplified as a double-layered consolidation ground according to the geometrical configuration of the PCCS. Subsequently, the analytical expression of the average consolidation degree is derived by considering the pile pierced into the gravel cushion and the additional stress that varies with time and depth. The accuracy of the proposed solution for consolidation is compared and validated by numerical analysis and current calculation methods. Furthermore, a parametric analysis is conducted to systematically investigate the influence factors of replacement ratio, core length ratio, modulus ratio of inner core-soil, modulus ratio of inner-outer core, modulus ratio of cushion-soil, permeability coefficient ratio and loading period on the consolidation behaviors of PCCSs reinforced ground. The proposed solution provides a theoretical guideline available for calculating the long-term settlements of such composite piled foundation.
