Rigid Facing Research Articles

In situ acoustic characterization of a perforated panel on a cavity by means of PU measurement and model fitting

The in situ characterization of materials is a crucial challenge in room acoustics, as laboratories measurement cannot always be applied in consultancy practices. In particular, there is a lack of method to characterize in situ systems with perforated facings, which are commonly encountered systems in room acoustics. In this paper, the in situ characterization of a rigidly-backed porous material behind a rigid perforated facing by means of pressure–velocity measurements is presented. The method includes an inverse impedance model fitting based on measurement in a limited frequency range. The applicability of this method was studied by measuring a variety of perforated facings, whether in front of an air cavity or backed by a porous layer, and comparing the obtained impedance model parameters to reference values. Good agreement was observed between the retrieved parameters and the references, with the errors in all retrieved parameters moving mass, facing thickness, cavity depth, porous layer thickness and porous layer flow resistivity not exceeding 15%.

In situ characterization of wall linings with perforated facings

The in-situ characterization of acoustic materials is one of the main challenges in room acoustics. Previously, the characterization of a single porous layer backed by a hard wall was successfully done by combining pressure-velocity measurements near the surface of the material with an impedance model fitting approach. In practice however, most porous materials are mounted behind a membrane or a rigid perforated facing. By again combining pressure-velocity measurements and a model fitting procedure, this work studies the possibility to characterize such systems. This was done by measuring a variety of perforated facings and membrane facings, whether in front of an air cavity or backed by a porous layer and comparing the obtained impedance model parameters to the reference values. Good agreement was observed between the retrieved parameters and the references, with error in retrieved moving mass, facing thickness, cavity depth, porous layer thickness and porous layer flow resistivity not exceeding 15%.

Influence of facing conditions on the dynamic response of back-to-back MSE walls

This paper presents an experimental study of shaking table tests on two back-to-back mechanical stabilized earth (MSE) walls with full-height rigid facing and modular block facing, respectively, to investigate the influence of facing conditions on the dynamic response. The reduced-scale MSE wall models were designed according to the similitude relationships considering model geometry, reinforcement stiffness, and input motions. The back-to-back MSE wall models were constructed using poorly graded backfill soil and geogrid reinforcement, and then were excited using a series of sinusoidal input motions with increasing acceleration. The threshold acceleration where acceleration amplification factors suddenly increase significantly for the back-to-back MSE walls with modular block facing is smaller than that for the full-height rigid facing walls. The full-height rigid facing walls have smaller facing displacements than those for the modular block facing walls under the same motions and can resist stronger earthquakes in terms of facing displacements. For the back-to-back MSE walls with full-height rigid facing, incremental reinforcement tensile strains increase significantly with increasing input acceleration, while the reinforcement strains of the modular block walls are similar under different input motions for the conditions investigated.

Low Compressibility at the Transition Zone of Railway Tracks Reinforced with Cement-Treated Gravel and a Geogrid under Construction

In the transition zone of railway tracks, track irregularities occur frequently due to differential settlement, which arises from the difference between the vertical supporting stiffness of the abutment and the backfill. This is disadvantageous because it increases the maintenance requirements and deteriorates the ride quality. To address this challenge, this study proposes a strategy involving the application of cement-treated gravel reinforced with geogrids and rigid facing walls. The reinforced subgrade for railways (RSR), which can reduce residual settlement through the initial construction of the backfill reinforced with geogrids and the subsequent development of the rigid facing wall, was constructed at the transition zone with cement-treated gravel as the backfill material. The long-term behaviors during and after construction on the RSR for a period of 16 months were evaluated by analyzing the surface and ground settlements, horizontal earth pressure, and geogrid strain. The minor net settlement of the reinforced backfill converges at the early stage of subgrade construction, and the horizontal earth pressure was approximately reduced to the level of 54–63% of the Rankine active earth pressure.

Numerical Analysis of the Deformation Behavior of Geogrid-Reinforced MSE Wall Having FHR and SPT Wall Facing

The mechanically stabilized earth (MSE) wall has been widely used globally for several decades now. The study on MSE wall is continuously growing as well as various innovations on its designs and techniques. The natural complexity of soil behavior makes the study on MSE wall system challenging for researchers. One of the factors that affect the deformation behavior of MSE wall structure is the wall facing system. Hence, this study is undertaken to investigate the deformation behavior of geogrid-reinforced MSE wall, having full height rigid (FHR) and segmental panel-type (SPT) wall facing, using finite element method (FEM) in Plaxis 2D program and small-scale experimental study. Both numerical and experimental models are using discrete geogrids reinforcement with three different reinforcement length ratios of 1H, 0.7H and 0.5H (where H is the wall height). The results from the series of numerical analysis and experimental tests showed that the vertical displacement on top of the MSE wall and the horizontal displacements of the FHR facing were smaller than those of the SPT wall facing, regardless of the reinforcement length. In addition, the reinforcement length has minimal effect on settlement for MSE wall with FHR facing but is more visible for MSE wall with SPT wall facing. The magnitude of the reinforcement effect may not be great in this study because the MSE wall models are only 0.60m high. But it is expected that the higher wall height might induce greater reinforcement length effect.

Field monitoring of vertical stress distribution in GRS-IBS with full-height rigid facings

This paper presents a case study of the first geosynthetic reinforced soil-integrated bridge system (GRS-IBS) with full-height rigid facings in China. Open graded gravel and biaxial geogrid were used for the GRS-IBS. Steel frames and three-dimensional (3D) vegetation nets were used as temporary facing support during construction of the GRS abutments. Full-height rigid facings were cast in place on strip foundations. Field monitoring results of vertical stress distribution for different construction stages and loading conditions are presented and discussed. For both bridge dead load and truck loads, measured incremental vertical stresses under the beam seat increase significantly with increasing elevation, especially for higher applied vertical stress. The calculated incremental vertical soil stresses using the Boussinesq solution are in reasonable agreement with the measured values, while the 2 : 1 stress distribution method overestimates the incremental stresses in the lower section of the abutment. The transferred vertical stresses from bridge load application for the GRS abutment with full-height rigid facing are larger than those for the GRS abutment with modular block facing near the top of the abutment, but are smaller near the bottom.

Experimental study on the load bearing behavior of geosynthetic reinforced soil bridge abutments with different facing conditions

This paper presents an experimental study on reduced-scale model tests of geosynthetic reinforced soil (GRS) bridge abutments with modular block facing, full-height panel facing, and geosynthetic wrapped facing to investigate the influence of facing conditions on the load bearing behavior. The GRS abutment models were constructed using sand backfill and geogrid reinforcement. Test results indicate that footing settlements and facing displacements under the same applied vertical stress generally increase from full-height panel facing abutment, to modular block facing abutment, to geosynthetic wrapped facing abutment. Measured incremental vertical and lateral soil stresses for the two GRS abutments with flexible facing are generally similar, while the GRS abutment with rigid facing has larger stresses. For the GRS abutments with flexible facing, maximum reinforcement tensile strain in each layer typically occurs under the footing for the upper reinforcement layers and near the facing connections for the lower layers. For the full-height panel facing abutment, maximum reinforcement tensile strains generally occur near the facing connections.

Wear Based Lifetime Estimation of a Clutch Facing using Coupled Field Analysis

Repetitive use of the clutch, over a period of time, causes the friction material at the contact surfaces (clutch facing and flywheel/pressure plate) to wear, thus deteriorating its performance and usable life. The working life of a rigid clutch is the limiting factor when it comes to extracting maximum performance from a dual mass flywheel system, which is used in a lot of modern vehicles nowadays to lower fuel consumption and improve ride quality. In this study, we investigate the influence of different groove patterns on wear in rigid clutch facings and estimate their life using a comprehensive finite element model. The wear is calculated and analysed for five different groove patterns across two different inorganic materials, namely FTL180 and TF1600-MC2, using Archard’s Adhesive Wear Model. Coupled multi-physics elements are employed in the analysis to capture the effect of frictional heat generation on wear. We found that the Waffle pattern offered a decrease of 10.4% in volumetric wear loss, a 5.78% decrease in maximum wear thickness and an increase of 11.51% in the average working life is used in city like conditions with frequent engagements. This work sheds light on the impact of groove patterns on clutch facing wear and opens a new path for the design and development of more resilient rigid clutches.

A Study of the Effects of Geosynthetic Reinforced Soil and Reinforcement Length on GRS Bridge Abutment

The geosynthetic reinforced soil (GRS) bridge abutment with a staged-construction full height rigid (FHR) facing and an integral bridge (IB) system was developed in Japan in the 2000s. This technology offers several advantages, especially concerning the deformation behavior of the GRS-IB abutment. In this study, the effects of GRS in the bridge abutment with FHR facing and the effects of geosynthetics reinforcement length on the deformation behavior of the GRS–IB are presented. The numerical models are analyzed using the finite element method (FEM) in Plaxis 2D program. The results showed that the GRS–IB model exhibited the least lateral displacements at the wall facing compared to those of the IB model without geosynthetics reinforcement. The geosynthetics reinforcement in the bridge abutment with FHR facing has reduced the vertical displacement increments by 4.7 times and 1.3 times (maximum) after the applied general traffic loads and railway loads, respectively. In addition, the numerical results showed that the increase in the length-to-height (L/H) ratio of reinforcement from 0.3H to 1.1H decreases the maximum lateral displacements by 29% and the maximum vertical displacements by 3% at the wall facing by the end of construction. The effect of the reinforcement length on the wall vertical displacements is minimal compared to the effect on the wall lateral displacements.

Stabilization of soil nailed slope by flexible materials

The soil slopes alongside the roads, embankments etc. often lead to mishaps as they are prone to slide or collapse due to their instability. Soil nailing is remedial measure to such unstable soil slopes and thus to prevent such mishaps. In this research, a physical model of soil nailed slopes has been established and is tested for stress and strain with different flexible facing materials under the application of load using a hydraulic jack. Then the settlement and displacement of the soil nailed slopes with different facing materials is also calculated and compared. The several flexible facing materials used were HDPE Geomembrane Sheet, Geocomposite and Biaxial Geogrid and were compared with the soil slope without facing. This research shows that different flexible facing materials have different behaviour in terms of strain and displacement under the similar magnitude of load. And it is obtained that flexible facing materials can be a good replacement to rigid facing materials for non-critical structures and an economical and effective way to strengthen existing soil slopes and stabilize them with as they are less costly than the rigid materials. Among all flexible materials that used in this research Geocomposite has high strength of 1.23 N/mm2 and less vertical and horizontal displacement.

Experimental study on the behavior of MSE wall having full-height rigid facing and segmental panel-type wall facing

Abstract The amount of the lateral displacements on the mechanically stabilized earth (MSE) wall depends on the reinforcement extensibility and length, reinforcement-to-facing connection, and the wall facing, among others. In this study, the deformation behavior of MSE wall models was focused considering two types of wall facing and three types of reinforcement. A series of small-scale model tests were undertaken on the MSE wall having a full-height rigid (FHR) facing and a segmental panel-type (SPT) wall facing. At the same time, the models were using discrete geogrids, geosynthetic strips, and steel rods as reinforcement. The results showed that the geogrids-reinforced MSE wall with FHR facing exhibited the highest load capacity with the least vertical displacements. The MSE wall models with steel reinforcements generally exhibited the least lateral displacements at wall facing than those with geosynthetics reinforcements. Finally, the results showed that MSE wall models with FHR facing have generally lesser lateral displacements at the wall facing compared to those with SPT wall facing.

Interaction mechanisms in small-scale model MSE walls under the strip footing load

The effect of preloading on mechanically stabilised earth (MSE) has remained an aspect difficult to quantify in design, particularly when considering different reinforcement types, stiffness values, and facing rigidity. This study analyses several scaled model tests on MSE walls under a strip footing load with a single unloading-reloading cycle. Scaled models were constructed as part of this investigation to expand the evaluation of previously constructed full-scale tests. The strip footing load and wall deflections were measured and compared with analytical models. The failure mechanism of the soil, before and after the strip footing load, was included in the study via the particle image velocimetry (PIV) method. The results indicate that the bearing capacity of a strip footing is higher for a rigid facing than for a flexible facing. PIV analysis results for the first and second loading step formed two failure lines with the angle (π/4 + φ/2). The deflection values in the second loading step, however, were smaller than those reached during the first loading in small-scale tests. Good agreement was observed between the proposed analytical method and experimental results for the second loading step, after taking into account the preloading effect.

Design Theory and Method of Geo-Synthetic Reinforced Soil Retaining Wall Combined with a Gravity Retaining Wall or Full Height Rigid Facing

Geo-synthetic reinforced soil retaining wall (GRS-RW) combined with a Gravity Retaining wall (GRW) facing or Full High Rigid (FHR) facing is a new type of retaining wall. This type of retaining wall is used to get full advantages of GRW and reinforced soil retaining wall (RS-RW) and to avoid their drawbacks. The design method based on the principle of working strain considers the backfill in the limit state but the reinforcement not in the limit state; while in traditional design method based on the tensile strength of reinforcement, consider both backfill and reinforcements in the limit state and it cannot reflect the influence of reinforcement stiffness. In this paper, numerical analyses were performed to evaluate the stress and strain of both reinforcement and backfill. From the analyses, deformation of the retaining wall, the working performance of GRS-RW with GRW facing, and contribution of geo-grids to GRS-RW with a GRW facing, were evaluated. Analyses are performed for determining the force between GRS-RW with a GRW facing and reinforced soil. Analytical methods, for the calculation of soil pressure acting on the back of GRW, based on the principle of working stress are obtained by comparative analysis between the working performance characteristics of common GRS-RW and GRS-RW with GRW facing. A new analytical method for determining the force between GRS-RW with a GRW facing and reinforced soil “E” is proposed. By comparative study between theoretical and numerical analysis results, method 1 and method 2 are recommended for determining the “E”. A method for determining the tension in the reinforcement of GRS-RW with a GRW facing based on the principle of working strain is also presented in this paper.

Load sharing characteristics of rigid facing walls with geogrid reinforced railway subgrade during and after construction

Reinforced subgrade for railways (RSR) is a construction method in which reinforced subgrade is constructed first and a rigid facing wall later to minimize the residual settlement after the service of a roadbed. The RSR was designed and constructed at Osong railway test line in Korea. In this study, load sharing capacities from the reinforced subgrade to the rigid facing wall of it were evaluated through long-term measurement, extending 22 months from the start of roadbed construction to the completion of track construction. Under the condition of 0.4 m geogrid vertical spacing installation, the load sharing proportion of horizontal earth pressure of the rigid facing wall was 9%–22% in the lower part, and lesser in the upper part. The strain of geogrid during construction was 0.607%, which was relatively lower than the designed geogrid tensile strain of 5%. The change in geogrid strain after construction was closely correlated with temperature change in the soil.

Non-Newtonian couple-stress squeeze film behaviour between oscillating anisotropic porous circular discs with sealed boundary

The thrust of this paper is to investigate theoretically the non-Newtonian couple stress squeeze film behaviour between oscillating circular discs based on V. K. Stokes micro-continuum theory. The lubricant squeezed out between parallel porous and rigid facings is supposed to be a concentrated suspension which consists of small particles dispersed in a Newtonian base fluid (solvent). The effective viscosity of the suspension is determined by using the Krieger-Dougherty viscosity model for a given volume fraction of particles in the base fluid. For low frequency and amplitude of sinusoidal squeezing where cavitation as well as turbulence are unlikely, the governing equations including the modified Reynolds equation coupled with the modified Darcy's equation are derived and solved numerically using the finite difference method and a sub-relaxed iterative procedure. The slip velocity at the porous-fluid interface is directly evaluated by means of the modified Darcy's law considering laminar and isothermal squeezing flow. For a given volume fraction, the couple stress effects on the squeeze film characteristics are analyzed through the dimensionless couple stress parameterℓ˜considering sealed and unsealed boundary of the porous disc. The obtained relevant results reveal that the use of couple stress suspending fluids as lubricants and the effect of sealing the boundary of the porous matrix improves substantially the squeeze film behaviour by increasing the squeeze film force. On the other hand, side leakage flow calculated in the sealed case remains constant in comparison to that of open end (unsealed) porous disc for all values of couple stress parameter and volume fraction of particle.

Geogrid Reinforced Soil Walls with Marginal Backfills Subjected to Rainfall: Numerical Study

Altering natural landforms without impacting stability has become quintessential due to unprecedented infrastructure development. Geosynthetic reinforced soil wall (GRSW) as a retaining structure is a congenial option addressing land scarcity and right of way challenges. However, with dearth of good-quality backfill soil and prohibitive transportation costs, engineers are being forced to use native low-permeable marginal soils for constructing geosynthetic reinforced soil walls. Adverse climatic changes leading to erratic rainfall have triggered numerous failures in such soils due to their inefficiency to dissipate excess pore water pressure. The objective of the present paper is to evaluate applicability of different backfill soils for GRSW. Seepage and stability analyses were conducted to appraise the behaviour of a geogrid reinforced soil wall with rigid facing of height 9.6 m having 6° batter during rainfall. The effects of backfill soil types with fines content of 0%, 20% and 40% on seepage behaviour and stability were assimilated under moderate rainfall. It was ascertained that failure occurred faster when the backfill soil with 20% fines was considered. For backfill soil with 40% fines, a significant portion of rainfall was observed to simply disappear as runoff. In the section with sand backfill, failure did not occur as water drained off faster than rainfall infiltration, restraining mounting of water table.

Geosynthetic-reinforced soil structures for railways and roads: development from walls to bridges

The development and construction of various types of geosynthetic-reinforced soil (GRS) structures for railways, roads and others, mainly for railways, for the last 35 years in Japan is described. In the 1980s, GRS retaining wall (RW) with full-height rigid (FHR) facing was developed. The FHR facing is constructed firmly connected to reinforcement layers after the reinforced backfill and subsoil has deformed sufficiently. In the early 1990s, GRS Bridge Abutment supporting one end of a simple girder at the top of the FHR facing was developed. In the early 2000s, GRS Integral Bridge was developed, which structurally integrates both ends of a continuous girder to the top of the FHR facings of a pair of GRS RWs. The total wall length of these GRS structures became about 185 km by June 2019 with no problematic case. The use of FHR facing, the staged construction of FHR facing and the structural integration for GRS Integral Bridge are the three major breakthroughs for the development of these GRS structure technologies.

EFFECT OF WALL ASPECT RATIO ON SEISMIC RESPONSE OF NARROW MECHANICALLY STABILIZED EARTH WALLS

Increasing population and expanding urban development in limited spaces involves construction of Narrow Mechanically Stabilized Earth (NMSE) walls having an aspect ratio (ratio of reinforcement length, L, to wall height, H) below 0.70. When constructed in seismically active zones, these walls are subject to seismic ground motions. The purpose of this paper is to present the results of small scale shaking table tests on NMSE walls with rigid facing. A series of reduced scale (1/8 of the prototype model) shaking table tests are performed on a 1-dimensional shaking table. The modeled walls have aspect ratio (L/H) of 0.20, 0.30 and 0.40. The model is shacked using ramped sinusoidal base accelerations with incrementally increasing displacement amplitude (i.e. actuator stroke) and constant frequencies to generate an equivalent base acceleration ranging from 0.05 g to 0.70 g or until failure occurs. Ground motion frequency of 2.5 Hz is used. The results show that at input accelerations ranging from 0.25g to 0.45g yielding occurs and the NMSE walls behaves as a rigid body. Subsequently, excessive deformations occur due to the pull out of the top reinforcement layers. An amplification factor of 2.50 times the input ground motion is measured at the surface of the NMSE models. Furthermore, the average design acceleration for the model walls ranges from 1.02 to 1.35 of the input base acceleration.

Life cycle assessment of a geosynthetic-reinforced soil bridge system – A case study

Road infrastructures are a very important component of the world's total transportation network. Investment in its construction and maintenance is significant on a global scale. The paper presents some results from an environmental study of a geosynthetic-reinforced soil integrated bridge system. The Pavlovski potok stream in Slovenia was used as a demonstration case for this study. It is the first GRS bridge system with full-height rigid (FHR) facings in Europe. It was constructed at the end of 2014. The goal of these analyses was to compare two different types of bridges: the new GRS bridge system, which is comprised of a simple girder partially structurally integrated to FHR facings of GRS bridge abutments and a conventional reinforced concrete road bridge. The results of an environmental life cycle assessment (LCA) show that the GRS bridge system has a much lower environmental impact than an equivalent bridge conventionally built with reinforced concrete.

Seismic responses of the steel-strip reinforced soil retaining wall with full-height rigid facing from shaking table test

To investigate the seismic response of the steel-strip reinforced soil retaining wall with fullheight rigid facing in terms of the acceleration in the backfill, dynamic earth pressure in the backfill, the displacements on the facing and the dynamic reinforcement strain distribution under different peak acceleration, a large 1-g shaking table test was performed on a reduced-scale reinforced-earth retaining wall model. It was observed that the acceleration response in non-strip region is greater than that in potential fracture region which is similar with the stability region under small earthquake, while the acceleration response in potential fracture region is greater than that in stability region in middle-upper of the wall under moderately strong earthquakes. The potential failure model of the rigid wall is rotating around the wall toe. It also was discovered that the Fourier spectra produced by the inputting white noises after seismic wave presents double peaks, rather than original single peak, and the frequency of the second peak trends to increase with increasing the PGA (peak ground amplitude) of the excitation which is greater than 0.4 g. Additionally, the non-liner distribution of strip strain along the strips was observed, and the distribution trend was not constant in different row. Soil pressure peak value in stability region is larger than that in potential fracture region. The wall was effective under 0.1 g-0.3 g seismic wave according to the analyses of the facing displacement and relative density. Also, it was discovered that the potential failure surface is corresponds to that in design code, but the area is larger. The results from the study can provide guidance for a more rational design of reinforced earth retaining walls with full-height rigid facing in the earthquake zone.