Open Caisson Research Articles

FELA evaluated bearing capacity factors for circular, planar, and interfering cutting edges of open caisson

ABSTRACT 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.

Soft Computing-Based Models for Estimating Undrained Bearing Capacity Factor of Open Caisson in Heterogeneous Clay

Soft Computing-Based Models for Estimating Undrained Bearing Capacity Factor of Open Caisson in Heterogeneous Clay

Research and application of sinking-aided methods for circular open caisson under complex formation conditions: case study

Open caissons have been widely used owing to their good structural integrity and waterproofing performance, convenient construction, and low cost. However, sinking construction is affected by many factors, such as geological conditions, groundwater, designed depth, and self-weight. Improper measures may lead to severe subsidence of the surface and adjacent structures of an open caisson and even adversely affect its structure. This study using a large-diameter circular open caisson in the Jinshan Lake, Zhenjiang, first examines the causes of its substantial sinking and stagnation during construction. Owing to the different leading causes, sinking-aided methods differ. Therefore, these methods and their subsequent optimization schemes are established, and their effects are analyzed to provide a reliable reference for future related projects.

Data‐Driven Decision Algorithm for Open Caisson Foundation Construction

The accuracy of instructions for the extraction of large open caissons directly affects the construction quality and safety. This study is focused on developing a smart construction methodology for predicting open caisson excavation instructions. The proposed approach aims to reduce the errors in excavation instructions attributable to the subjective and varying experiences of decision‐makers. The multilabel classification task of predicting the instructions of large open caisson excavation is accomplished through the problem analysis. The study conducted a comparative analysis of a multilayer perceptron model, a classifier chain model, and a multilabel K‐nearest neighbor model (MLKNN) based on Hamming loss and accuracy. The results revealed that MLKNN exhibits significant differences from the other models and is most suitable for predicting open caisson excavation instructions. Furthermore, the traditional MLKNN model was improved by refining the normalization and distance measurement methods for the open caisson scenario. The prediction accuracy of the improved MLKNN model is 89.04% for the excavation instructions and 98.63% for the nonexcavation decisions. The successful prediction of excavation instructions for a large open caisson can compensate for the lack of data mining capability of the existing monitoring system. This can reduce construction risks. Finally, this study discussed the robustness of the improved MLKNN in a real project, highlighting the model’s high accuracy during the midstage of open caisson construction.

基于深度神经网络的微扰动压入式沉井顶压力智能预测方法

基于深度神经网络的微扰动压入式沉井顶压力智能预测方法

Ground settlement prediction for open caisson shafts in sand using a neural network constrained by empiricism

Accurate prediction of soil settlements induced by open caisson construction in sand is essential for safe and reliable delivery of critical underground urban infrastructure. This paper presents a novel prescriptive design approach using a neural network (NN) constrained by empirical relationships, referred to as an ’empiricism-constrained neural network’. The proposed approach is benchmarked using a traditional closed-form empirical expression. Both methods are calibrated using experimental data from reduced-scale laboratory testing for the prediction of surface and subsurface settlement trough shape and magnitude. The outcomes demonstrate that while both methods accurately capture the primary effect of caisson depth on surface and subsurface soil settlements, the NN approach exhibits superior prediction accuracy. These methods are developed in a form amenable for routine design use in industry and have the potential for broader applicability in other design scenarios, such as building damage assessment and risk-assessment exercises.

GBDT-based multivariate structural stress data analysis for predicting the sinking speed of an open caisson foundation

ABSTRACT Open caisson foundations are often used in large-span bridge construction because of their advantageous, and an open caisson foundation gradually sinks to a predetermined position via earth excavation. Excessive sinking speed may result in various construction risks (e.g. inclination and structural damage of the open caisson). To prevent these risks, it is important to analyse the sinking situation of the foundation and predict the sinking speed during the sinking process. A sinking speed prediction model is proposed based on the gradient boosting decision tree (GBDT) algorithm, and the model can extract the data features of the structural stress monitoring data to predict the sinking speed of open caissons. Taking the supersized open caisson foundation in the Changtai Yangtze River Bridge Project as a case study, the proposed model was validated by using the monitoring data of this foundation. The validation results of this project indicate that the proposed model has high prediction accuracy, short time consumption, a good prediction effect and high practicability. Based on the model’s prediction, an earth excavation scheme can be flexibly adjusted to prevent the potential construction risks of open caissons caused by excessive sinking speed.

Laboratory Testing of Construction-Induced Ground Displacements for Open Caisson Shafts in Sand

Laboratory Testing of Construction-Induced Ground Displacements for Open Caisson Shafts in Sand

Wave Amplification inside an Open Circular Caisson for Wave Energy Conversion in Waters with Medium Energy Density

Wave energy is one of important marine renewable energy resources. Many studies have been devoted to harnessing the energy for human use. Though they are almost everywhere in the sea, waves can be much more significant in some sea areas than others. For example, the wave energy density in Asian waters is usually much less than that in European west coasts.
 To make the wave energy harvesting more viable in Asian waters with medium wave energy density, we propose to employ an open caisson to amplify the wave locally and to combine it with a wave energy converter to tap the amplified wave energy. In this study, we focus on the effect of incident wave height on the amplification factor which is defined as the ratio of the wave height inside the caisson to that of the incident wave. Shown in Figure 1, the caisson is mounted vertically on the horizontal seabed in the open sea. At the edge of the opening, it has two guides on the two sides of the opening. They are identical in geometry and part of a solid cylinder. The purpose of the two guides is to enhance the wave amplification inside the caisson.
 The study was conducted primarily by CFD computations and partially verified by experiments. In computations, the finite volume method was employed to discretize the Navier-Stokes equations. A multi-block grid was generated for computational purposes. The volume-of-fluid (VOF) method was used to capture the free surface. The nonlinear iterations were conducted with the PISO method. And the implicit time marching scheme was adopted in the time direction. It is interesting to find that the amplified wave height in the caisson is not linearly related to the incident wave height. Furthermore, the amplification factor is also a function of the incident wave period. The wave period at which the peak value of the amplification factor appears is insensitive to the wave height. The amplification factor is usually greater than unity for a wide range of incident wave period.

An information-entropy-inspired optimal layout method for structural stress sensors of supersized open caissons

The layout of sensors directly influences the effectiveness of structural stress monitoring of open caissons during the sinking process. In this study, an optimal layout method for structural stress sensors is proposed inspired by information entropy. The information gains of different sinking states from different layout locations of structural stress sensors are calculated, and the important layout locations are identified through the calculation of information gains. According to these important layout locations, the optimal sensor layout scheme is obtained. The proposed method was validated via an engineering case study of the Changtai Yangtze River Bridge Project. The results show that the proposed method successfully determined the optimal sensor layout scheme and that the number of required structural stress sensors decreases by 51.5% compared with the number of structural stress sensors deployed in the engineering case. With all R2 values greater than 0.96, the optimal scheme has high prediction accuracy for three sinking states: sinking speed, transverse height difference and longitudinal height difference. In addition, the spatial distribution of the important layout locations was identified. This study is meaningful for obtaining high-quality monitoring data of structural stress to both ensure the steady sinking of open caissons and reduce monitoring costs.

Study on distribution of sidewall earth pressure on open caissons considering soil arching effect

Based on the soil arching effect theory, the magnitude and distribution of sidewall earth pressure on open caissons when the embedded depth is large was analyzed by using theory of non-limit state earth pressure theory and horizontal differential element method. The theoretical formula was deduced. The theoretical calculation results are compared with the field test results and centrifugal model test results respectively. The results show that when the embedded depth of the open caisson is large, the distribution of earth pressure on the side wall of the open caisson first increases with the increase of embedded depth, reaches a peak value, and then sharply decreases. The peak point is located at 2/3 ~ 4/5 of the embedded depth. In engineering practice, when the embedded depth of the open caisson is 40 m, the relative error between the field test value and the theoretical calculation value is − 55.8% ~ 1.2%, with an average error of 13.8%. When the equivalent embedded depth of the open caisson in the centrifugal model test is 36 m, the relative error between the centrifugal model test value and the theoretical calculation value is − 20.1% ~ 68.0%, with an average error of 10.6%, The results are consistent well. The results of this article provides reference for the design and construction of open caisson.

Foundation design of single-span arch bridges in China

Arch bridges have been constructed in China more than 1400 years ago. This study collated the details of 120 single-span arch bridges with spans of more than 100 m that have been constructed or undergoing construction in China over the recent three decades. The type proportion, span to rise ratio, spatial distribution, and span length of the 120 arch bridges were reported in this paper. An examination of the foundation of the 120 single-span arch bridges was further conducted. Based on the analysis of the arch bridge foundations, it was found that the foundation types can be grouped into enlarged footing, pile foundation, composite foundation, and “others”. Thus, the application rate of various foundation types, characteristics of each foundation type, and development trend of arch bridge foundations were investigated and discussed. Finally, case studies of single-span arch bridge with composite foundations consisting of open caisson and shaft, and foundation with barrette piles were reviewed. The construction techniques, applicable conditions and resistance characteristics of various foundations were analyzed and evaluated. The case studies highlighted in this paper illustrated the advancement, innovation and development in foundation engineering of single-span arch bridges in China.

FELA evaluation of undrained bearing capacity of cutting edge of circular open caisson

ABSTRACT 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.

Undrained uplift resistance of under-reamed open caisson shafts

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.

Investigation on the Stratigraphic Response and Plugging Effect Induced by Press-In Open Caisson in Mucky Soil

Press-in open caisson method, which sinks into soil with the aid of mechanical pressure without excavation, is becoming an important method of construction in extremely soft foundations. However, many engineering problems are prone to occur in the construction of caissons, such as sinking and large deformation. In this study, the stratigraphic response model, such as soil migration during the press-in process of open caisson, is focused on. Through model tests of soil and caissons, the migration patterns of each part of the soil were carried out, and the mechanism underlying the stratigraphic response pattern was investigated. The three primary conclusions are as follows: 1) The bottom edge foot of caisson produces lateral extrusion on surrounding soil in the range of 10 cm (20%H) below, resulting in lateral movement of soil. 2) two kinds of plug, i.e., “wedged” and “unwedged” plugs exist, and the driven forces for the soil migration can be divided into three stages, i.e., caused by soil plug with active arch, by soil plug with passive arch and caused by soil squeezing effect. 3) there is a significant linear correlation between the soil plug changes, the horizontal movement of the deep soil body, and the displacement of the surface uplift. The soil plugging effect and squeezing effect are interacted and enhanced with each other. This study provides a new understanding of the stratigraphic response in the construction of press-in open caissons, and guides safety control of open caissons construction.

Research on Prefabricated Open Caisson Construction Technology

With the continuous improvement of urban residents’ lives, the demand for of urban infrastructure construction increases, requiring more and more advanced engineering technology. We should not only speed up the progress of the project, but also reduce the impact of the construction on the surrounding environment. Our company has had several achievements in this regard, and prefabricated open caisson construction process is one of them. In this paper, the application of prefabricated caisson construction method is analyzed in depth according to the actual situation of the rain sewage reconstruction treatment project of Minghe ecological water system in Dancheng County. Through practice, it is concluded that this construction method greatly improves the construction efficiency, shortens the overall construction process, reduces the construction cost, and effectively improves environmental quality of the construction site, which has good reference value.

Settlement analysis of the giant open caisson during the construction of the Changtai Yangtze River Bridge

With the increasing size of open caissons in large-span bridge projects, the overall settlement of giant open caissons is vital to the safe construction of bridge superstructures. Taking the engineering case of the Changtai Yangtze River Bridge, the overall deformation of an open caisson was studied during the construction stage of the bridge’s superstructures. First, the theoretical layer-wise summation method was utilized to analyze the settlement of the open caisson. Then, a 3-D finite element model was established to simulate the installation stage of the bridge superstructure. Finally, a large centrifuge model test was performed to obtain the deformation of the open caisson at each step of bridge’s construction. The results of these approaches demonstrated that final settlements were quite consistent—approximately 225 mm when the bridge superstructure was completely installed—and the settlement deformation curve could be divided into three stages: slowly increasing, rapid, and stabilizing. This study can provide significant guidance for the construction of the Changtai Yangtze River Bridge and be a reference for similar open caisson engineering projects.

Inclination prediction of a giant open caisson during the sinking process using various machine learning algorithms

Machine learning (ML) models based on 12 ML algorithms were established to predict the open caisson inclination. The prediction performance of these models was evaluated in the main pier open caisson monitoring of the Changtai Yangtze River Bridge Project, and the prediction performance was compared based on prediction results, corresponding residuals, prediction accuracy, calculation time and training sample dependence to determine the suitable prediction models. Then, the influence of 3 key parameters was analysed, and the models with the best prediction performance were optimized. The results showed that 7 ML algorithms were suitable for inclination prediction of this project. The best performance was obtained using models based on extra trees (XT) and k-nearest neighbour (KNN). The influence of the 3 key parameters on the prediction accuracy was determined, which is beneficial to further optimize the prediction models. After optimization, the root mean square error and the calculation time of the KNN model were decreased by 45% and 33%, and the best prediction accuracy was obtained using the default parameter settings of the XT model.

Analysis of Mechanism of Sand Gushing and Sudden Sinking of Ultra-large Deep-water Open Caisson in sand via Field and Model Tests

In view of the sinking of the largest and deepest open caisson in sand, detailed statistical analyses of sand gushing (29 times) and sudden sinking (18 times) are conducted for the first time. Through on-site monitoring tests and sinking simulation tests of sand gushing and sudden sinking, the relevant laws are investigated. Statistics show that an ultra-large deep-water open caisson is prone to sand gushing and sudden sinking when the burial depth is more than 50m. Sand gushing is the inducement of sudden sinking, and there is a progressive failure mode. Field and model tests indicated that the probability of sand gushing and sudden sinking is positively correlated with the penetration near the blade foot and negatively correlated with the blade foot resistance and lateral pressure. In addition, the development laws of sand gushing, sudden sinking and inclination after changing the force balance of caisson are put forward and verified. Spatial effects of stress distribution and inclination result in local stress concentration, which accumulates potential energy for sudden sinking. Thus, based on the assumption of limit equilibrium in elastic semi-infinite space and instantaneous failure of core soil column, a judgment model for sand gushing is proposed and a calculation method for engineering application is established, which is used to validate the sand gushing case in Section 3.2.

Experimental study on the distribution law of the blade foot resistance of a large deep-water open caisson in sand

Research on the sinking of large deep-water open caissons in sand via field monitoring, centrifugal model testing and 1 g simulation testing shows that the distribution law of the blade foot resistance is related to the caisson burial depth, mud surface height inside the blade foot and sinking state, and stress concentrates near rectangular caisson corners. When the height of the mud surface inside the blade foot does not exceed the top of the slope, the stress of the tread in the noncorner area increases linearly with the mud surface height and with the burial depth of the caisson. The slope stress exhibits a cubic distribution, and the ratio of the average slope stress to tread stress is a constant 0.28. When the height of the mud surface inside the blade foot exceeds the top of the slope, the slope stress maintains a cubic distribution, and the slope stress near the foot surface of the blade increases more obviously. Based on the cross-validation of different tests, a method for calculating the blade foot resistance of a large deep-water caisson is proposed, and the application scope is explored by centrifugal model tests and deep soil load tests.