This paper explores a new method for rapid structural damage inspection of steel tube slab (STS) structures along randomly measured paths based on a combination of compressive sampling (CS) and ...ultrasonic computerized tomography (UCT). In the measurement stage, using fewer randomly selected paths rather than the whole measurement net is proposed to detect the underlying damage of a concrete-filled steel tube. In the imaging stage, the ℓ1-minimization algorithm is employed to recover the information of the microstructures based on the measurement data related to the internal situation of the STS structure. A numerical concrete tube model, with the various level of damage, was studied to demonstrate the performance of the rapid UCT technique. Real-world concrete-filled steel tubes in the Shenyang Metro stations were detected using the proposed UCT technique in a CS framework. Both the numerical and experimental results show the rapid UCT technique has the capability of damage detection in an STS structure with a high level of accuracy and with fewer required measurements, which is more convenient and efficient than the traditional UCT technique.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Ground surface settlement is one of the critical parameters that needs to be controlled strictly during pipe jacking. The calculation model for estimating the ground deformation induced by pipe ...jacking is scarce in the literature, especially for pipes with irregular cross-section (e.g., circular pipes with flanges). In this study, considering the pipe-soil interaction, the distribution characteristics of frictions between pipe and soil, and the support force at the tunnel face, a settlement formula is proposed for a single jacked pipe using the Mindlin’s solution and the Stochastic medium theory. Based on the cavity expansion theory, a relationship for calculating the circumferential plastic zone is developed considering the effect of flanges. The distribution of the plastic zone around the pipe and the superimposition effect due to multiple pipes are discussed. Finally, a correlation is established to estimate the ground surface settlement for three types of multiple jacked pipes with different spacing. A case study of a subway station project using the Steel Tube Slab (STS) method is presented. Comparisons of ground settlement from field measurements and theoretical calculations show that the proposed approach can reasonably predict the ground surface settlement for multiple jacked pipes.
Recently, increasing numbers of box tunnels have been built in urban areas due to their high space utilization. Rectangular boring machines are commonly used in box tunneling, and tunnels are driven ...by thrusting prefabricated linings. Sometimes, when a tunnel machine encounters obstructions, such as boulders or steel plates, the excavation efficiency decreases. The tunnel drive has to be suspended to remove obstructions in the working chamber. Mostly, for ordinary machines, obstruction removal is carried out under open air, and the working face is no longer fully supported. This paper investigates the working face stability of box tunnels redundant on the situation in which the working face is not fully supported. According to practical experiences, the support pressure provided by the remains in the chamber is explored, and unsupported and supported areas at the face are identified. To analyze the ground stability, an analytical model is proposed by modifying the traditional silo-wedge model. In the proposed model, the wedge and prim blocks are divided into sub-blocks, and the interactions between the blocks are taken into account. Based on the proposed model, the solution of the pressure for stability is derived through limit equilibrium analysis. Parametric analysis is carried out to determine the effects of the factors on stability. A comparison of the proposed model and the traditional model is performed, and the rationality of the current model is discussed. This paper ends with the validation of the current model by investigating a case of a box tunnel in Suzhou, China.
Pipe jacking is a commonly used trenchless technology to install pipelines especially in congested urban areas or river crossings. However, the estimation of the jacking force is often heavily ...dependent on empirical calculations. The jacking force needs to be greater than the combined frictional resistance and face resistance. This investigation proposes to use a modified Protodyakonov’s arch model to compute the face resistance. A series of direct shear tests is performed to provide data of interface friction coefficient between different types of soil and pipe. The influence of slurry lubricant is also considered. A two-dimensional plane strain numerical model is conducted, where the surrounding soil is simulated as discrete particles and the lining is simplified as a single big particle. The novel modeling technique enables the evaluation of the normal force acting on the pipe. The friction resistance is then determined by multiplying the interface friction coefficient by the normal force. A ‘wavy’ shaped pipeline model is proposed to define an angular deviation influence factor to scale up the calculated jacking force due to pipe misalignment. In the end, comparison between calculated and field measured jacking force is conducted for three different drives in a pipe jacking project to illustrate the effectiveness of the proposed analysis framework.
An oversized pit-in-pit (PIP) excavation, which comprised an octagonal pit outside and two cross-shaped pits inside, was excavated in soil-rock mixed strata, Shenzhen, China. There were two shield ...tunnels connected to the north and south of the PIP excavation after the main structures completed. Extensive instruments were adopted throughout the construction process to guarantee the safety of the project. Based on the massive field data, the performance of the ground settlement, retaining structures and adjacent building deflection were investigated. Field data indicate that the influence zone of ground settlement in depth was above the stiff clay layer. The maximum lateral displacement (
δ
hm
) of the retaining structures occurred at 0.4
H
e
(
H
e
is the excavation depth), and
δ
hm
decreased when the excavation depth was over 0.5
H
e
. The maximum ground settlement
δ
vm
occurred at 0.2
H
e
which gradually decreased with
d
(
d
is the distance from the monitoring point to the excavation edge). This large discrepancy of the ground settlement induced 3.13‰ tilting of the adjacent buildings. The ground settlement influence zone was 1.7
H
e
away from the pit edge (
d
≤ 1.7
H
e
). A half-3D numerical model was established to investigate the influence of different excavation sequences. The results show that the maximum principal stress (
σ
m
) of the cover plate increased to peak value due to the excavation of subsoil, which indicated that the sidewall construction and subsoil excavation should be carried out simultaneously to reduce the stress concentration of the cover plate. TD excavation can effectively minimize the ground and building settlement, while the excavation may induce uneven displacement of the interior supporting columns. Push in failure of the sidewalls may occur during the construction which was the combined result of unloading and increase in the excavation depth.
Shield thrust is a critical operational parameter during shield driving, which is of vital significance for adjusting operational parameters and ensuring efficient and safe propulsion of shield ...tunneling machine. In this paper, a novel hybrid prediction model (CLM) combining attention mechanism, convolutional neural networks (CNN) and Bi-directional long short-term memory (BiLSTM) network is proposed for shield thrust prediction. Correlation analysis based on Maximal Information Coefficient (MIC) between the thrust and other parameters is first conducted to select optimal parameters and reduce input dimension. An attention mechanism is introduced into CNN to distinguish the importance of different features, with the convolution layer and pooling layer further extracting dimension features of the data. Then, a BiLSTM neural network integrating first attention layer is employed to extract time-varying characteristics of the data, with a second attention layer added to capture important time information. Field data during shield cutting bridge piles are investigated to support and validate the effectiveness and superiority of the proposed method. Results show that the proposed CLM model are general enough to avoid overfitting problems and have good performance at prediction. The predicted value match reasonably well the monitoring data, with coefficient of determination (<inline-formula> <tex-math notation="LaTeX">\text{R}^{2} </tex-math></inline-formula>) equaling to 0.85, root mean square error (RMSE) equaling to 0.05, mean absolute error (MAE) equaling to 0.02. The CLM model in this paper can accurately predict the thrust even under complicated construction conditions, which provides reference for similar industrial application.
Saline soil is characterized by high concentrations of soluble salts, which can pose hazards such as frost heaving, uneven thaw settlement, and concrete erosion, especially subjected to freeze-thaw ...(F-T) cycles in the seasonal frozen and frost regions. This study aims at investigating the cement and micro-silica treatments effect on the changes in microstructure, strength property and durability of compacted saline soil, and evaluating the suitability of micro-silica as potential industrial waste materials for altering the mechanical behaviors of saline soil in comparison with the use of cement as traditional binder. Unconfined compression tests, oedometer tests, and freeze-thaw cycle tests were conducted on the untreated and treated saline soil stabilized by cement alone, micro-silica alone, and mixtures binders with cement-micro-silica (CMS). Furthermore, the microscopic characteristics were analyzed by scanning electron microscope and X-ray diffraction test. Tested results indicates that the cement is committed to improving the strength of saline soil, and the micro-silica contributes to improve the F-T cycle durability. The performance of CMS-treated saline soil with unconfined compressive strength of 1.763 MPa and coefficient of collapsibility of 0.056 is superior to that of cemented and micro-silica-treated saline soil alone. Besides, the stabilization with CMS achieved promising results with 3% cement and 4% micro-silica admixture, achieving the purpose of recycling micro-silica and exhibiting the excellent durability with strength loss of 50% due to F-T cycles. The formation of cementitious compounds originated from pozzolanic reactions between cement and micro-silica can effectively improve the behaviors of saline soil.
Deep excavations are prone to result in excessive ground surface settlement displacement of surrounding existing structures, which could cause severe economic damage, even casualties. Hence, the ...optimization of pile parameters and evaluation of the stability of the excavation are of paramount importance. This paper aims to evaluate the security of deep excavation and optimize the parameters of supported piles in granular soils. An excavation case in granular soils is used to evaluate the stability of deep excavation using displacement least squares method. The stability of case history, Changqingqiao subway station, using pile and inner support system is evaluated by using the least square method. Subsequently, the finite element method is used to optimize the critical parameters of the supported piles, and it needs to be emphasized that the correctness and reasonability of the finite element (FE) models are evaluated according to field measurements. The optimum pile diameter and embedment ratio for single- and double-row retaining pile are 1.0 m and 0.4. The maximum vertical displacement of surrounding soil and horizontal displacement of piles can be calculated by the equations obtained in this research which can provide useful guidance for the designing of deep excavation.
The application of reinforced concrete has been used in various engineering and architecture fields. Stress relaxation and creep are two crucial time-dependent behaviours of concrete. The influence ...of two behaviours is closely related to the service life of the reinforced concrete structure. However, the research on experimental relaxation behaviour has rarely been extensively studied because of the complicated procedures. Meanwhile, fly ash is commonly utilised to partially replace cement to reduce the greenhouse effect. As a result, this study is committed to examining the creep and relaxation behaviour of fly ash concrete. The concrete creep and relaxation tests were designed to maintain a constant stress and strain levels, respectively. The creep and relaxation tests were conducted at the same time to minimise the shrinkage and ageing effects. The stress and strain levels were selected as 20% and 60% of concrete compressive strength to investigate creep and relaxation in linear and nonlinear cases. By comparing computed values of relaxation from the inverse of the compliance function, the estimated relaxation function showed good agreement using the inverse of the compliance function. However, the existing creep model showed a difference in predicting the creep of fly ash concrete. As a result, the existing model is amended to improve the estimation of creep and relaxation of fly ash concrete.
The Su-Xi-Chang area is located in the Yangtze River Delta in southeastern Jiangsu Province, China. More than 2 m cumulative land subsidence has occurred since 1980s. A range of monitoring programs, ...geological investigations, and numerical modeling has been implemented in order to establish a regional rehabilitation plan. In this paper, the column element settlement model (CESM) has been established to investigate the coupling effect of soil self-weight, upper loads, and groundwater withdrawal on land subsidence. The model has been verified by comparing with the land subsidence records in Changzhou and further applied to the investigation area. The results show that extensive groundwater withdrawal is the main cause of the land subsidence. Settlement caused by soil self-weight increases with the depth and decreases with upper loads, while settlement caused by upper loads increases with the intensity of upper loads and decreases with depth. The proportion of ground settlement caused by soil self-weight, upper loads, and groundwater withdrawal is also investigated.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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