Friction characteristics of confined inflatable structures

Abstract

Abstract:The availability of high-strength fabrics and progress in the development of large-scale inflatable technology made possible the creation of temporary and quickly deployable structures for protection of underground infrastructure. Inflatable structures are relatively lightweight and portable, and can maintain the required rigidity while in operation. These benefits have prompted the development of inflatable structures for use in confined spaces, such as tunnels and large-diameter pipes to act as barriers for containing flooding with minimal infrastructure modification. This work presents experimental results obtained from the evaluation of frictional characteristics of the fabric material that constitute the structural membrane of confined inflatable structures developed for protection of underground transportation tunnels and other large conduits. Friction tests at coupon level and slippage tests in a reduced-scale inflatable structure were performed in order to evaluate the frictional characteristics of Vectran webbings. Tests at coupon level were performed to determine the friction coefficient for different surface types and conditions. Tests with the reduced-scale inflatable structure contributed to the understanding of the friction characteristics at system level when subjected to different pressurization or depressurization sequences designed to induce slippage. Test results indicate that friction coefficient values at coupon level are about 29 percent higher than values derived from reduced-scale tests.

Large-scale inflatable structures for tunnel protection: a review of the Resilient Tunnel Plug project

“…1) Uniaxial tensile tests were used to determine the ultimate tensile strength of specimens of Vectran webbing used to produce the outer layer of the full-scale plug. 2) Friction testing of Vectran webbing was also necessary to determine the plug's ability to maintain axial stability within the tunnel during operation under dry and wet conditions [89]. 3) Shear tests were used to determine the level of shear forces that are present in the draping and flexibility of a macro fabric comprised of Vectran woven webbings and to determine the ability of the material to conform to a three-dimensional surface [90].…”

“…One of the most critical outcomes from quarter-scale testing was the fine-tuning of friction factors assumed in calculating the required length of the cylindrical body of the final full-scale plug. Testing at quarter scale also allowed inducing plug slippage to verify the minimum pressure differential required between the internal plug pressure and the external floodwater pressure; such testing was not conducted at full scale because of the additional time and expense associated with testing plug slippage at that scale and the possibility of damage to the plug [89]. Figure 7 illustrates the quarterscale plug during preparation and flooding simulations.…”

“…Unlike the single-layer design, in the threelayer, the loads originated at the different stages of the preparation and pressurization of the plug were carried by the different fabric layers of the membrane. In the quarter-scale tests (1.22 m tunnel diameter) completed during this phase, the inflatable plug was taken safely to the reference pressure of 468 kPa while holding a flooding pressure of 330 kPa without slipping [88,89]. As a reference, the reduced-scale studies carried out in [32,35,36] included tunnel diameters in the range of 0.2 m to 0.4 m for pressures in the range of 10 kPa to 50 kPa.…”

Finite Element Simulation of Large-Scale Confined Inflatable Structures

“…A possible way to improve the membrane distribution in the simulations is to produce a gradual release of membrane material during the inflation process as carried out in the experiments [7][8][9][10][11][12][13][14]. In order to produce a gradual release of the membrane, a better control of the membrane was implemented during the deflation by introducing pre-folds held by passive restrainers, as explained in Chapter 6.…”

“…The feasibility of using a more robust membrane as well as the implementation of a lateral deployment instead of a ceiling deployment was evaluated in [10,11]. The evaluation of frictional characteristics of the inflatable when subject to flooding pressures were evaluated in reduced scale experiments reported in [12]. A key aspect found in the experimental work was that the level of conformity of the inflatable to the tunnel perimeter plays an important role in the sealing capacity of the inflatable.…”