PURPOSES : The purpose of this study was to investigate the behaviors of the middle slab in a double-deck road tunnel subjected to construction equipment loading from such as a concrete pump car, concrete transmixer, and lifting crane. METHODS: The major construction processes of a middle slab include concrete placement, concrete transportation, and lifting of materials near the emergency passageway section. During the concrete placement, the middle slab is subjected to construction loading due to the presence of the concrete pump car and fully loaded concrete transmixer. During the concrete transportation, the middle slab is subjected to loadings from both the fully loaded and empty concrete transmixer. The emergency passageway section of the middle slab is subjected to crane loading during lifting work. The magnitudes and geometries of these construction loadings are determined and the stresses and deflections of the middle slab under these loadings are analyzed using finite element models of the middle slab. The behaviors of the middle slab under the design truck loadings are also analyzed to compare the results with those under construction loadings. RESULTS : The stresses and deflections of the middle slab under construction loadings are comparable to those under the design truck loadings. Higher stresses can be observed when the concrete transmixers cross paths at the expansion joint section of the middle slab. The behaviors of the middle slab under the construction loadings during concrete placement are very similar regardless of the section types of the middle slab such as the normal, expansion joint, and emergency passageway sections. CONCLUSIONS : When the middle slab is designed, the construction loadings should be considered to determine the primary design loads and to verify the usability of a variety of construction equipment.

The objective of this study is to analyze the behavior and failure mode of the brackets that support middle slabs in the double-deck tunnels by conducting laboratory experiments. In the double-deck tunnels, the middle slabs are supported by the brackets connecting to the tunnel lining. The brackets are subjected to the loads due to the weight of middle slabs and traffic moving on the middle slabs. Since the damages of brackets are directly associated with the safety problems such as falling down of middle slabs, the appropriate design of brackets is one of the most important factors when designing double-deck tunnels. In this study, the reinforcement design of concrete bracket was performed based on the concrete structure design guide, and the load capacity was evaluated by conducting laboratory loading tests. A small scale concrete bracket specimen was fabricated using the scale factor of 0.5. The reaction wall is normally needed to simulate the tunnel lining in this kind of test; however, two brackets were attached symmetrically to a column, which was assumed to be tunnel lining, to be able to conduct the tests without using the reaction wall. When the bracket specimen was fabricated, the lining part was fabricated first and after curing of the lining part, two brackets were fabricated at the same time at both sides of the lining part. In the tests, the loads were applied to both brackets simultaneously using a loading frame and the displacements were measured at different locations. The main behaviors of the bracket systems such as the vertical displacements of brackets and the displacements at the interfaces between the brackets and lining were measured and the horizontal displacements of the specimen were also measured at the bottom of the lining part to confirm if there was any slip or rotation of the specimen during the tests. The experimental analysis results showed that the initial damage of the specimen was observed at the interface between the bracket and lining with appearing the gap and the failure of the specimen was reached with cracking in the brackets. The load capacity (safety factor) of the bracket specimen to the initial damage based on the design load was 2.5 and to the failure was 3.3.

PURPOSES : The purpose of this study is to investigate the stresses of the middle slab in a double-deck tunnel owing to the slab lift to replace the underlying elastic pads during maintenance workMETHODS: The middle slab was divided into three different sections: typical section, expansion joint section, and emergency passageway section. Finite element analysis models of these three sections of middle slab were developed, and the stress distribution and maximum stresses were obtained using the models when the middle slab was lifted to replace the underlying elastic pads. Various slab lifting methods were examined in this study such as one-, two-, and multiple-point lifts, distributed lifts, and one or both slab side edge lifts.RESULTS: When the slab side edge is lifted, the longitudinal stresses of the slab are almost the same as the principal stresses. This implies that the governing stresses are the longitudinal stresses. The maximum stresses with both-edge lifts are generally smaller than those with one-edge lifts at all three sections of middle slab.CONCLUSIONS: If the middle slab in a double-deck tunnel is lifted for maintenance, the slab should be lifted at multiple points along the longitudinal direction to reduce the tensile stresses.

PURPOSES : The purpose of this study is to investigate the fundamental behaviors such as stresses and deflections of the middle slab in a double-deck tunnel for the development of a middle slab design guide. METHODS : The middle slab has been divided into the following three different sections as according to its structural differences: the normal section, expansion joint section, and emergency passageway section. The normal section of middle slab represents the slab supported by brackets installed continuously along the longitudinal direction of tunnel lining. The expansion joint section refers to a discontinuity of middle slab due to the existence of a transverse expansion joint. The emergency passageway section has an empty rectangular space in the middle slab that acts as an exit in an emergency. The finite element analysis models of these three sections of middle slab have been developed to analyze their respective behaviors. RESULTS: The stresses and deflections of middle slab at the three different sections decrease as the slab thickness increases. The emergency passageway section yields the largest stresses and deflections, with the normal section yielding the smallest. CONCLUSIONS: The stress concentrations at the corners of the passageway rectangular space can be reduced by creating hunch areas at the corners. The stresses and deflections in the emergency passageway section can be significantly decreased by attaching beams under the middle slab in the passageway area.

The stresses occurred in the middle slab at the areas of the emergency passageway in a double-deck tunnel are analyzed when the slab is lifted to replace bearing pads placed between the middle slab and supporting bracket as a maintenance process. The middle slab can be lifted at several different points near the emergency passageway areas and the stresses of the middle slab depend on the lifting points. This study presents the effect of the lifting location of the middle slab on the stress occurrence for the maintenance work of replacing bearing pads under the middle slab near the emergency passageway areas.