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Open caissons are an increasingly common means of constructing underground storage and attenuation tanks as well as launch and reception shafts for tunnel-boring machines. The caisson walls typically feature a tapered base, referred to as the ‘cutting face’, to aid the sinking process by reducing the vertical soil reaction. The primary aim of this...
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Citations
... In recent years, many studies have investigated open caissons using both experimental tests and numerical simulations to monitor and capture the importance of the effects of these mechanisms on the mechanical behavior of open caissons [8]. Several researchers have focused on two effective factors concerning resistance to side friction [9] and the sloping angle of the cutting edge on caissons [10]. In addition, laboratory tests on external skin friction in sandy soil were conducted by Wang et al. [11] and Zhou et al. [12], and field and model tests on the bearing capacity of such problems in clay were conducted by Houlsby et al. [13], Guo et al. [14], and Chavda et al. [15]. ...
Open caissons are increasingly utilized for underground construction due to the increasing demand for aboveground structures, which employ the principle of submersion using the self-weight of the edge cutting face and the applied bearing pressure to mitigate the vertical soil reaction. This paper examines the bearing capacity factor of the edge cutting face in anisotropic clays, approximated using the finite element limit analysis (FELA) method and considering the average results between the upper and lower bounds. The influence of the adhesion factor at the interface of the cutting edge (α), the ratio between the depth of the internal embedment and the embedded width (H/B), the ratio between the radius and the embedded width (R/B), the anisotropic shear strength (re), and the cutting face angle (β) is investigated. The results indicate a significant influence of the anisotropic shear strength on the adhesion factor at the interface of the cutting edge. An increase in re denotes a decrease in the undrained shear strength obtained from the triaxial compression test, resulting in an increase in the value of N. An increase in α influences β, such that when β <90°, the value of N remains constant when β = 90°. In addition, a highly efficient hybrid model called DNN-PBT was established utilizing a deep neural network (DNN) and a population based training (PBT) approach, specifically for the purpose of accurately predicting the bearing capacity factor of circular open caissons positioned in undrained clay. Both computational and comparative outcomes demonstrate that the proposed DNN-PBT can precisely forecast the bearing capacity, achieving an R2 value higher than 0.999 and a mean squared error (MSE) less than 0.007. These findings highlight the accuracy and efficiency of the suggested approach. Furthermore, the sensitivity analysis results demonstrated that the anisotropic shear strength (re) is the most important input variable for estimating the bearing capacity factor of the edge cutting face.
... Based on the identical framework, the impact of different penetration types and the sinking depth of the caisson on the ultimate load of the open caisson were also investigated (Chavda and Dodagoudar 2022a). Later on, a novel numerical method namely the finite element method (Sheil and Templeman 2023;Chavda and Dodagoudar 2022b) and finite element limit analysis (Templeman et al. 2021;Royston et al. 2022;Sheil and Templeman 2023) were used to compute the bearing capacity factors of cutting edge. Recently, the undrained stability solution of the circular open caisson was evaluated by Chavda et al. (2023) by employing the finite element limit analysis (FELA) techniques under different sinking conditions. ...
... Based on the identical framework, the impact of different penetration types and the sinking depth of the caisson on the ultimate load of the open caisson were also investigated (Chavda and Dodagoudar 2022a). Later on, a novel numerical method namely the finite element method (Sheil and Templeman 2023;Chavda and Dodagoudar 2022b) and finite element limit analysis (Templeman et al. 2021;Royston et al. 2022;Sheil and Templeman 2023) were used to compute the bearing capacity factors of cutting edge. Recently, the undrained stability solution of the circular open caisson was evaluated by Chavda et al. (2023) by employing the finite element limit analysis (FELA) techniques under different sinking conditions. ...
In the study, a thorough analysis of the drained bearing capacity factors of cutting edges of open caissons with and without interference has been carried out which helps in planning the controlled sinking of caissons. Five different conditions are analysed in this study: single circular, single planar, V-shape planar, interfering planar, and interfering V-shape planar cutting edges. Implementing upper and lower bound finite element limit analysis (FELA) in accordance with Terzaghi's conventional bearing capacity equation, the bearing capacity factors of the cutting edge of open caissons are evaluated. The design charts for the bearing capacity of cutting edges are determined by accounting for the effects of the radii ratio of the circular caisson, distance ratio of planar cutting edges, cutting angle of cutting edge, soil internal friction angle, and spacing between the cutting edges. The soil failure planes corresponding to the aforementioned aspects of the cutting edges are also evaluated. ARTICLE HISTORY
... During the sinking process, the cutting face of the cutting edge plays a crucial role by diminishing the vertical bearing capacity and promoting the progression of the soil failure mechanism toward the central area of the caisson (Nonveiller 1987;Sheil et al. 2018). Several investigations in the literature have focused on specifying the cutting face angle, denoted as "β", within ranges such as 30°-90° (Sheil and Templeman 2021) or 30°-45° (Chavda and Dodagoudar 2022b), illustrating various approaches. ...
Open caissons are commonly used in the construction of various underground structures, such as launch and reception shafts for tunnel-boring machines, storage or attenuation tanks, and cofferdams. During the sinking phase, the cutting edge of a caisson wall with a cutting face encounters soil and is subjected to loading to facilitate and control the sinking process. In this regard, the bearing capacity factor (N) of the cutting face of a circular open caisson in heterogeneous clay is evaluated via finite element limit analysis, which accounts for the increase in the undrained shear strength with depth. The parameters considered in this study cover practical aspects, including the excavation geometry, soil strength profile, and caisson geometry. This investigation also explored the impacts of the cutting face angle (β), roughness (α), ratio of the internal embedment depth to the embedment width (H/B), ratio of the internal radius to the embedment width (R/B), and strength gradient ratio (ρB/su0). In particular, when the H/B > R/B ratio, the N value tends to stabilize. Crucially, when H/B > 4, an increasing trend in R/B leads to a rise in N until R/B exceeds 10, i.e., large diameter caissons, stabilizing the N value. Furthermore, the results reveal the significant dependency of the cutting face roughness and strength gradient ratio of clay on N. The artificial neural network model, which is a soft computing-based model, is also developed to present the undrained bearing capacity forecasting equation. Compared with conventional regression, including the multiple linear regression model and the multiple nonlinear regression model, it has excellent performance, as measured by eight indices. In addition, ANOVA and Z-tests can support the research hypothesis and reject the null hypothesis.
... The evaluation of bearing capacity of the cutting edge will help in planning the controlled sinking. The bearing capacity of cutting edge has been investigated using experiments (Chavda et al. 2020;Chavda and Dodagoudar 2022a), slip line method (Berezantsev 1952;Solov'ev 2008;Yan et al. 2011), finite element method (Sheil and Templeman 2022;Chavda and Dodagoudar 2022b) and finite element limit analysis (Templeman et al. 2021;Sheil and Templeman 2022;Royston et al. 2022a). There are several practical possible cases of caisson sinking in clayey soil starting from only cutting edge embedded in soil, cutting edge and steining complete embedded in soil, embedded caisson with soil removed within caisson, with different roughness conditions (α = 0 to 1) of steining (Chavda and Dodagoudar 2022a). ...
... The evaluation of bearing capacity of the cutting edge will help in planning the controlled sinking. The bearing capacity of cutting edge has been investigated using experiments (Chavda et al. 2020;Chavda and Dodagoudar 2022a), slip line method (Berezantsev 1952;Solov'ev 2008;Yan et al. 2011), finite element method (Sheil and Templeman 2022;Chavda and Dodagoudar 2022b) and finite element limit analysis (Templeman et al. 2021;Sheil and Templeman 2022;Royston et al. 2022a). There are several practical possible cases of caisson sinking in clayey soil starting from only cutting edge embedded in soil, cutting edge and steining complete embedded in soil, embedded caisson with soil removed within caisson, with different roughness conditions (α = 0 to 1) of steining (Chavda and Dodagoudar 2022a). ...
Circular open caissons are deep foundations sunk into the ground utilising the self-weight of cutting edge and steining as driving force along with the subsequent failure of soil in bearing. During the sinking of the caisson, the clay in contact with the cutting edge is subjected to undrained loading and the controlled sinking of the caisson can be achieved by evaluating the undrained bearing capacity of the cutting edge. In the study, the undrained bearing capacity factor (N) of the cutting edge for varying cutting angle (b), radius ratio of the caisson (r i /r o), full embedment of the caisson (d), removal of soil within the caisson (d'), and different roughness (α) conditions of the steining are evaluated using finite element limit analysis (FELA). The factors affecting the undrained stability of caisson considering all practical scenarios are addressed and presented as charts to be used in practice.
... For this reason, a key design concern for these structures in the permanent state is flotation when the tanks are emptied due to the significant reduction in downward force. For monolithic caissons, the use of lubricating fluids to minimise external caisson-soil friction during the sinking process (Sheil & Templeman, 2022) means that long-term antiflotation frictional resistance is typically neglected in design. ...
Deep, large-diameter caisson shafts are a popular means of constructing underground storage and attenuation tanks and pumping stations for the water and wastewater industry. One of the key design concerns for these structures is resistance to flotation during periods when the tanks are only partially filled or empty. In this paper, two-dimensional numerical analysis is used to explore the undrained uplift resistance provided by under-reaming the walls of the caisson shaft to create an enlarged base. The primary aim of the study is to assess the influence of the taper angle of the anchor (i.e. the protruded base) on the resulting uplift resistance. The effects of the anchor–soil interface roughness factor, soil weight, surcharge pressure and caisson radius are also investigated. The results indicate that the effect of the taper angle on both the uplift bearing capacity and the developed horizontal reaction can be very significant. The numerical output informs the development of a closed-form approach for application in routine design. The new design method is shown to provide an excellent agreement with both finite-element and additional finite-element limit analysis calculations. By way of example, the proposed design method is applied to a hypothetical design scenario.
... The clayey backfill under drained conditions was simulated using an elastic, perfectly plastic Mohr-Coulomb (MC) model. The roughness of the wall-soil interface is characterised by a roughness factor μ such that the interface friction angle δ is given by tan δ = μ tan ϕ (Sheil & Templeman, 2021). From the MC failure criterion, the shear strength of the interface satisfies ...
Active earth pressure on retaining structures supporting a narrow column of soil cannot be properly analysed using Coulomb's theory. Finite-element limit analysis (FELA) shows that the soil forms multiple failure surfaces if the soil column is sufficiently narrow. This paper proposes a framework for active earth pressure estimation for narrow soils by combining an arched differential element method and a sliding wedge method. The analytical framework considers both soil friction and cohesion, soil arching effects and shear stress between adjacent differential elements. The solution obtained is validated against experimental data and FELA results. Through parametric studies, the effects on the active earth pressure of the aspect ratio, soil friction, soil cohesion and wall–soil interface roughness are examined. To facilitate the use of the proposed framework in design, a modified active earth pressure coefficient and an application height of active thrust are provided.
... The constitutive model of ground soil, disturbance soil, and cement-soil reinforcement area adopts the Mohr-Coulomb criterion. The Mohr-Coulomb model has the advantages of having fewer input parameters and being easy to obtain in laboratory testing, and it has been widely used in deep foundation analysis [20,21]. The input parameters of the ground soil in this paper are determined from geological reports and laboratory testing results. ...
The bearing capacity of an open caisson under lateral loads is a key factor affecting the normal operation of an open caisson. It will inevitably have a disturbing effect on the surrounding soil layers during the sinking process of the caisson; that is, a disturbance ring will develop around the caisson. Based on the Jurong Yangtze River water supply project, the lateral bearing characteristics of the open caisson are analyzed by the numerical method with due consideration to soil disturbance, and the reinforcement scheme is optimized. The numerical results show that when the thickness of the disturbance ring is less than 0.5 m the disturbance ring has little effect on the lateral bearing capacity of the open caisson. An arc-shaped cement–soil reinforcement at the loading area can effectively improve the lateral bearing performance of the caisson. The optimized reinforcement thickness is 2 times that of the disturbance ring, and the reinforcement angle is approximately 60°.
The development of underground spaces inevitably poses significant risks to nearby infrastructure due to construction-induced ground displacements. While our understanding of tunnel-induced ground movements is now relatively mature, there is a distinct lack of literature on large-diameter open caisson shafts. This paper fills this gap by describing results from a small-scale laboratory study exploring soil deformation mechanisms during caisson construction in dry sand. Results from seven tests are analyzed to identify the influence of key caisson geometric properties as well as the effectiveness of external cofferdams in minimizing soil displacement. The results show that the primary mechanisms driving ground movements are a compressive ‘bearing’ front beneath the cutting face and a ‘frictional’ contribution above the cutting face. The normalized radial settlement profile is also shown to be insensitive to the normalized caisson embedment depth, and the settlement zone of influence extends up to 0.25 diameters below the caisson cutting edge. Furthermore, the presence of an external cofferdam is shown to be highly effective in reducing soil settlements. Quantitative analysis reveals a significant decrease in soil settlement with an increase in cofferdam depth from 0.25 to 0.5 of caisson depth, with good consistency between results for different soil elevations. In addition, larger cofferdam diameters provide maximum benefits in minimizing ground displacements.
The use of supporting fluids to stabilise excavations is a common technique adopted in the construction industry. Rapid detection of incipient collapse for deep excavations and timely decision making are crucial to ensure safety during construction. This paper explores a hybrid framework for forecasting the collapse of fluid−supported circular excavations by combining physics-based and data-driven modelling. Finite element limit analysis is first used to develop a numerical database of stability numbers for both unsupported and fluid−supported circular excavations. The parameters considered in the modelling include excavation geometry, soil strength profile and support fluid properties. A data-driven algorithm is used to ‘learn’ the numerical results to develop a fast ‘surrogate’ amenable for integration within real−time monitoring systems. By way of example, the proposed forecasting strategy is retrospectively applied to a recent field monitoring case history where the observational method is used to update the input parameters of the data-driven surrogate.
