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Properties of Leighton Buzzard DA30 sand

Properties of Leighton Buzzard DA30 sand

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Conference Paper
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An open-dug caisson shaft is a form of top-down construction in which a concrete shaft is sunk into the ground using the weight of the shaft and additional kentledge, if required. Excavation at the base of the caisson shaft wall allows the structure to descend through the ground. A thorough understanding of the interaction between the caisson shaft...

Contexts in source publication

Context 1
... experiments were conducted using a dry, yellow Leighton Buzzard DA30 silica sand, the properties of which are summarised in Table 1. Loose sand samples were prepared using a sand raining procedure in conjunction with a low drop height. ...
Context 2
... order to validate the test results and sample preparation, a 90° piece (flat piece) was used to compare present measurements to published literature. The relative density of each test sample was calculated using the data presented in Table 1 which, in turn, was used to determine the value of 'max. Bearing failure was assumed to occur at 0.1B, neglecting soil cohesion and influence of overburden, the bearing capacity, qrd, can therefore be defined as follows: ...

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... It is evidenced that the construction scales of bridge foundations, tunnels, excavations and open caissons continue to enlarge, highlighting the sustained importance of large and deep excavation works. Recently, large diameter deeply-buried (LDDB) open caissons (inner diameter D in ≥ 15 m and buried depth H ≥ 30 m) are widely used to provide a temporary access to the subsurface for piping and tunnelling, or as permanent works, are utilized for deep foundations, elevators, underground storage, ventilations, pumping stations and sewerage purposes (Dachowski and Kostrzewa, 2017;Fischer et al., 2004;Khasawneh et al., 2017;Lai et al., 2020, Lai et al., 2021Li et al., 2022;Royston, 2018;Royston et al., 2016;Schwamb, 2014;Tomlinson and Boorman, 2001). The cross section of caisson shafts can be rectangular or circular. ...
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... However, the different configuration of the cutting edge, i.e., variation in the tapered angles of the cutting edge is not explicitly accounted in their study. It is noted that only one study reports the experimental evaluation of the influence zone in sand for varying tapered angles of the cutting edge considering plane strain idealization [22]. The bearing capacity of ring footing is evaluated by experimental investigations [6,10,12,20,23,24], the limit equilibrium method, the upper-and lower-bound plastic limit analyses [16], the method of characteristics [11,15], the finite difference method [3,4,13,21,35], and the finite element method [7,9,17,18,30]. ...
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... The same is observed from the image analysis in this study (Section 4.2). Due to the inward inclined face of the cutting edge, the soil flow is observed only within the caisson for the steeper cutting angles (Chavda and Dodagoudar, 2018;Royston et al., 2016). The experimental and numerical studies performed by Royston et al. (2016) and Chavda and Dodagoudar (2018) on the effect of cutting angles on the zone of influence have clearly shown that the extent of the influence zone in the horizontal and vertical directions is 4B and 2.5B within the caisson, respectively, where B is the width of the cutting edge. ...
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Large-diameter 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. A ‘cutting face’ at the base of the caisson wall, resembling an inclined ring footing, is typically used to aid the sinking phase. This paper describes a suite of over 15,000 finite element limit analyses exploring the bearing capacity of a caisson cutting face, partially- or wholly-embedded in undrained soil. The primary aim of the study is to assess the influence of the cutting face inclination angle on the vertical bearing capacity. The effects of cutting face roughness, internal overburden and surcharge, and caisson radius are also investigated. In particular, the results indicate that a steepening of the inclination angle may not always reduce the bearing capacity, if the cutting face is rough. 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 representation of the numerical output.
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... The detailed site investigation, engineering judgment, instrumentation, skilled labor, informed decisions, etc. are necessary to avoid such problems. The experimental investigations have been carried out and reported to evaluate the contact pressure distribution at the base and sides of the caisson, load settlement and deflection behaviour, earth pressure mobilization in caissons embedded in soft clay, and the formation of failure zone in sand during penetration of the cutting edge of the caisson (Katti and Dewaikar 1977;Alampalli and Peddibotla 1997;Kumar and Rao 2010;Royston et al. 2016). It is observed from the above literature that many difficulties have been faced during the execution of the open caisson. ...
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... The bearing failure at the cutting edge is important to permit the controlled sinking of the open caisson. Recently, Royston et al. (2016) conducted the experiments to identify the influence zone at the cutting edges in the sand under plane strain condition. Using Particle Image Velocimetry technique, soil displacement contours are plotted for varying cutting edge angles of 30°, 45°, 60°, 75° and 90°. ...
Chapter
Full-text available
Open caissons are sunk into the ground by removal of soil within the caisson shaft. During sinking of caisson, the stresses in the soil at the cutting edge increase and result in the bearing failure of soil. The extent of soil failure in the excavation side of the open caisson is termed as influence zone. In this paper, the finite element analysis is carried out to study the effect of geometric configuration (radius ratio and tapered angle of the cutting edge), strength parameters (c’ and φ'), unit weight of soil and surcharge on the extent of the influence zone. The caisson considered in the study is having a radius ratio of 0.8, steinning thickness of 1 m and cutting edge with a tapered angle of 45°. The reaction offered by the soil at the cutting edge is also evaluated. The identification of the extent of failure zone at the cut-ting edge of the caisson helps in devising proper excavation strategy in the field for the controlled sinking of the caisson.
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Thesis
Full-text available
Open caissons are deep foundations sunk in the ground by the removal of the soil within the caisson shaft. A cutting edge with a tapered inner face is used at the bottom of the caisson to allow the bearing failure of the soil and hence the continued sinking. In the present study, the bearing capacity factors of the cutting edge for the wide range of radii ratio (ri/ro = 0.35 to 0.95), varying friction angles of the soil ( = 5 to 35) and different tapered angles of the cutting edge ( = 30 and 45) are evaluated using finite element (FE) analysis. Before evaluating the bearing capacity of the cutting edge, the preliminary investigations are carried out considering the strip and ring footing problems to frame the guidelines for the FE evaluation of the open caisson problem. A series of 1g model tests have also been performed to investigate the load penetration response of the cutting edge at different stages of the sinking and the soil flow mechanism in the soil beneath the cutting edge. Using strip footing problem, the sensitivity analysis is carried out to examine the ultimate capacity of the strip footing considering the strength parameters, width of the footing, unit weight of the soil, surcharge at the base level of the footing, and deformation parameters as the variables. Then the effect of different material models on the ultimate capacity of the strip footing is examined. A few suggestions are given in regard to the FE analysis of the ring footing and open caisson problems to assess their bearing capacities. The bearing capacity factors N'c, N'q and N' of the smooth and rough base ring footing are evaluated using the finite element method (FEM). In the analyses, the radius ratio is varied from 0 to 0.75 with an increment of 0.25 and friction angle of the soil is varied from 5 to 35. The Mohr-Coulomb yield criterion and non-associative flow rule are used in the analyses. Then the superposition of the three components of the bearing capacity equation is assessed, i.e., cohesion, surcharge and unit weight of the soil. The methodology adopted for the ring footing is used for the open caisson problem. A series of 1g model tests are performed to investigate the load-penetration response and soil flow mechanism in the soil during different stages of the sinking of the caisson. The effect of smooth and rough base conditions, varying tapered angles, different types of penetration of the cutting edge, and varying depths of sinking on the load-penetration response of the cutting edge is investigated. The soil flow mechanism corresponding to the varying tapered angles of the cutting edge, varying magnitudes of the penetration, and varying depths of sinking is examined using the image processing technique. The values of bearing capacity factor, N' of the cutting edge of the circular open caisson are also evaluated using the results of the experimental studies. The experimental studies have been performed for the embedded and rough base conditions of the cutting edge and the same are simulated in the FE analysis of the circular open caisson. The formation of influence zone in the soil beneath the cutting edge of the caisson is termed as failure zone. The extent of the failure zone in the vertical and radial directions is evaluated using the FE analysis. The effects of variation in the tapered angles and radii ratio of the cutting edge, unit weight, friction angle and cohesion of the soil, and magnitude of the surcharge on the extent of the failure zone are studied. Using the results of FE analysis, multivariate linear regression analysis is performed and easy to use predictive equations are developed to estimate the extent of the failure zone in the soil beneath the cutting edge. The predictive equations are assessed for their practical applicability using the results of the 1g model tests. The vertical bearing capacity factors, N'c, N'q and N' of the cutting edge of the open caisson are evaluated using the FEM. Two tapered angles of the cutting edge,  = 30 and 45, varying radii ratio = 0.35 to 0.95, and  = 5 to 35 are considered in the analyses. The applicability of the methodology used for the ring footing problem is examined by evaluating the bearing capacity factors for the varying values of cohesion, surcharge and unit weight of the soil. The bearing capacity factors evaluated using the FE analyses are compared with those available in the literature. The FE results are presented in the form of design charts and tables for the practical use. A complete understanding of the different aspects of the open caisson, such as load penetration response, soil flow mechanism beneath the cutting edge, and bearing capacity of the cutting edge will help in planning and controlled sinking operation of the open caisson.
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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.