Optimized Spacing Of The Longitudinal Reinforcement In CRCP To Avoid Horizontal Cracking

Continuously reinforced concrete pavement (CRCP) is characterized by the absence of transverse contraction joints and the presence of longitudinal and transverse reinforcement. The continuous longitudinal reinforcement holds the transverse cracks, caused by the longitudinal shrinkage of concrete, tightly together and thus provides long term performance with minimal maintenance cost. Field investigations on recently constructed CRCP's in Flanders region of Belgium indicated horizontal cracking in the vicinity of the longitudinal reinforcement under the transverse cracks which eventually causes the punch-out distress at the edge of the pavement slab. This paper shows the results of a finite element (FE) study to investigate the effect of varying longitudinal reinforcement on the risk of horizontal cracking in CRCP under typical Flanders conditions. For this purpose, a (3D) FE model of CRCP is developed using a FE package Diana 10.2. The varying longitudinal reinforcement with a most narrow spacing of 125mm in the outer region of the pavement slab is applied while keeping the same CRCP reinforcement ratio. A comparison is made with the conventional longitudinal reinforcement spacing (170mm). Development of concrete stress in the vicinity of the longitudinal reinforcement is plotted against the different longitudinal steel spacing. Findings show that the stress in concrete near longitudinal reinforcement is significantly reduced up to maximum 17% when the narrow spacing is used. In addition, the steel stress in the longitudinal reinforcing is reduced up to maximum 31.75% in the outer region of the pavement slab.

Pore Preservation and Failure Mechanism of Sinian Dengying Formation Carbonate Reservoirs: A Case Study of Two Ultradeep Wells in the Sichuan Basin, Western China

Despite being one of the most important factors in deep oil and gas exploration, the preservation mechanisms of ultradeep carbonate reservoirs remain poorly understood. This study performed thin-section, geochemistry, field emission scanning electron microscopy, fluid inclusion, and basin model analysis of samples from two boreholes over 8,000 m deep in the Sichuan Basin to determine the pore features and preservation mechanism of the Sinian (Ediacaran) Dengying Formation carbonate reservoirs. The reservoir of CS well #1 is characterised by pore diameters larger than a centimetre (average porosity 7.48%; permeability 0.8562 mD), and the pores are mainly filled with dolomite or bitumen. In contrast, the reservoir of MS well #1 is predominantly composed of micron-scale residual pores (average porosity 1.74%; permeability 0.0072 mD), and the pores are typically filled with dolomite, bitumen, and multistage quartz. The burial thermal histories suggest that both reservoirs were subjected to high pressure (i.e., pressure coefficient > 1.5 ) before the Late Cretaceous. However, the pressure coefficient of the reservoir of MS well #1 has decreased to less than 1.0 owing to strong structural adjustment this well since the Late Cretaceous, which allowed other ore-forming fluids to enter and fill the pores, resulting in further compaction of the pores. In contrast, the pressure coefficient of CS well #1 is 1.1–1.2, which effectively prevented other ore-forming fluids from entering and filling the pores. The findings show that the dynamic adjustment of the Dengying Formation palaeo-gas reservoir indirectly affects the preservation or failure of the reservoir. The occurrence and geometry of bitumen in the Dengying reservoir exhibit good consistency with the pressure changes in both boreholes. In particular, bitumen with an annular shape and contraction joints in reservoir pores is widespread in CS well #1, which is attributed to the continuous preservation of palaeo-gas fields. Conversely, bitumen with a broken particle shape is located among the epigenetic minerals widespread in MS well #1, which is attributed to failure and depletion of the palaeo-gas fields.

Evaluation of Premature Cracking in Urban Concrete Pavement

This study investigated the causes for premature, transverse cracking on urban jointed plain concrete pavements in Illinois. A field survey of 67 sections throughout Illinois coupled with ultrasonic evaluation was completed to synthesize the extent of premature cracking on urban JPCP. The visual survey showed some transverse and longitudinal cracks were a result of improper slab geometry (excessive slab length and width). Ultrasonic tests over the contraction joints determined some notched joints had not activated and adjacent transverse cracks were likely formed as a result. Three-dimensional finite-element analyses confirmed that cracking would not develop as a result of normal environmental factors and slab-base frictional restraint. The concrete mixture also did not appear to be a contributing factor to the premature cracks. Finally, the lack of lubrication on dowel bars was determined to potentially be a primary mechanism that could restrain the transverse contraction joints, produce excessive tensile stresses in the slab, and cause premature transverse cracks to develop.

The Effect of Shear Sliding of Vertical Contraction Joints on Seismic Response of High Arch Dams with Fine Finite Element Model

The contraction joints of arch dams with and without shear keys are simplified to be with no-slip condition and with relative sliding condition, respectively. Based on the Lagrange multiplier method, a contact model considering the manner of independent cantilever dead load type with no-slip condition and relative sliding condition is proposed to model the nonlinearities of vertical contraction joins, which is special to the nonlinear analysis of arch dams considering the manner of dead load type. Different from the conventional Gauss iterative method, the strategy of the alternating iterative solution of normal force and tangential force is employed. The parallelization based on overlapping domain decomposition method (ODDM) and explicit message passing using distributed memory parallel computers is employed to improve the computational efficiency. An existing high arch dam with fine finite element model is analyzed to investigate the effect of shear sliding of vertical joints on seismic response of the arch dam. The result shows that the values of maximum principal tensile stress under relative sliding condition are significantly greater than those under no-slip condition.

Seismic Stability Sensitivity and Uncertainty Analysis of a High Arch Dam-Foundation System

Parameter uncertainty associated with concrete arch dams always arises from modeling assumptions and the lack of knowledge or information of the engineering geological situations, especially in the seismic stability analysis of arch dams. In this research, a high arch dam is selected as a case study for probabilistic analysis of the seismic stability performance. The arch dam abutment and the dam are coupled as a system. A comprehensive approach considering contraction joints, boundaries of the probable sliding rock mass and the dam-foundation interface is presented. The contact nonlinearity is solved by using the dynamic contact model with Lagrange multiplier method. The main parameters of the probable sliding block are considered as random variables containing the friction coefficients and cohesions. Both the slippage and sliding area ratio are chosen as the engineering demand parameters (EDP). The sensitivity analysis is performed to reveal the relative influence of each parameter separately by the approximate incremental dynamic analysis (IDA) method. The friction coefficients are shown to be more crucial than the cohesions on the dam’s resistance to seismic instability. The sliding area ratio can be better used for unveiling the sliding process of the arch dam of concern, while the slippage is useful for one to judging the stability of the arch dam under seismic hazards. The Latin hypercube sampling (LHS) with approximate moment estimation is used to investigate the parameter uncertainty to the seismic stability performance of the high arch dam. The results provide a useful reference for using the median/mean-parameter model to accurately estimate the median/mean response of the dam.

A Comparative Study of Cantilever- and Integral-Type Dead Loads on the Seismic Responses of High Arch Dams

The actual dead load of an arch dam should be applied gradually through staged construction and sequenced grouting. However, the cantilever- and integral-type dead loads commonly used in the analysis of arch dams represent simplified versions of the actual loading. In this paper, these two types of dead loads, i.e. cantilever and integral types, are presented based on the Lagrange multiplier method considering the nonlinear behaviors of contraction joints. Based on the finite element method and an appropriate contact model together with artificial viscoelastic boundary conditions, a dynamic analysis model of a dam–foundation–reservoir system is established in consideration of the interactions between the arch dam and foundation, the opening and closing of contraction joints, and the radiation damping effect of the far-field boundary. Taking a 300 m high arch dam in the strong earthquake area of West China as an example, a fine mesh finite element model with a total of approximately 3.5 million degrees of freedom is established. The separate effects of the cantilever and integral dead loads on the static and dynamic responses of the dam are studied. The results demonstrate that the distribution and magnitude of the contraction joint opening width and maximum tensile stress are different under the two different dead load simplifications.