scholarly journals Impact mechanisms of granular and viscous flows on rigid and flexible barriers

2017 ◽  
Vol 54 (2) ◽  
pp. 188-206 ◽  
Author(s):  
C.W.W. Ng ◽  
D. Song ◽  
C.E. Choi ◽  
L.H.D. Liu ◽  
J.S.H. Kwan ◽  
...  
Keyword(s):  
Earth Pressure ◽  
Viscous Flows ◽  
Rigid Barrier ◽  
Geotechnical Centrifuge ◽  
Flow Energy ◽  
Mountainous Regions ◽  
Barrier Energy ◽  
Flexible Barrier ◽  
Barrier Type ◽  
Flexible Barriers

Structural countermeasures such as rigid and flexible barriers are commonly installed in mountainous regions to intercept mass-wasting processes. Without sufficient and reliable comparable physical data, the study of impact mechanisms remains difficult and not well understood. In this study, a newly developed flexible model barrier together with a rigid barrier are used to simulate either dry granular or viscous liquid impacts on these model barriers in a geotechnical centrifuge. The novel flexible barrier is made of four instrumented cables controlled by spring mechanisms to replicate a bilinear prototype loading response. Tests revealed that regardless of barrier type, both dry granular and viscous flows could have similar frontal dynamic impact coefficients around unity. Compared with the kinetic energy of flow mass (∼10 MJ), only 249 kJ of flexible barrier energy capacity was mobilized. This implies that debris-resisting barriers may only be required to intercept the dynamic flow front as the subsequent flow energy may mainly be dissipated through internal shearing. Attributing to the large deformation of the flexible barrier, the granular static load acting on the flexible barrier could be 39% lower than that on the rigid barrier, resulting in an active failure mode and a lower earth pressure.

Estimating total resisting force in flexible barrier impacted by a granular avalanche using physical and numerical modeling

2016 ◽  
Vol 53 (10) ◽  
pp. 1700-1717 ◽  
Author(s):  
Wesley Ashwood ◽  
Oldrich Hungr
Keyword(s):  
Debris Flow ◽  
Current Practice ◽  
Earth Pressure ◽  
Total Force ◽  
Test Results ◽  
Promising Tool ◽  
Flexible Barrier ◽  
Flow Parameters ◽  
Dry Granular Flow ◽  
Flexible Barriers

Flexible barriers are a promising tool for protection against extremely rapid landslides such as debris flow and debris avalanches. With landslide impacts of any size, the total force induced within the barrier and transferred to the anchorage is a fundamental question to design. Current practice limits the investigation to flow parameters, neglecting the behavior of the structure, which can vary significantly. This paper describes steps taken to quantify the total force induced within a flexible barrier. It describes laboratory experiments of dry granular flow against rigid and flexible barriers with observations of resisting force and other filling processes that provide an understanding of the behavior and possible flow–structure interaction for larger scale rapid landslides. Results from the experiments suggest that for granular flows with high discharge the current practice sufficiently quantifies the total force, and for those with lower discharge, the total force is better characterized by active lateral earth pressure calculations. Test results were also used to validate an adaptation to an existing depth-integrated numerical model for landslide mobility to quantify the total force. This model was then used to estimate the resisting forces induced within a full-scale flexible barrier impacted by a controlled debris flow.

Earth pressures exerted on an induced trench cast-in-place double-cell rectangular box culvert

2012 ◽  
Vol 49 (11) ◽  
pp. 1267-1284 ◽  
Author(s):  
Olajide Samuel Oshati ◽  
Arun J. Valsangkar ◽  
Allison B. Schriver
Keyword(s):  
Earth Pressure ◽  
Test Results ◽  
Overburden Pressure ◽  
Centrifuge Testing ◽  
Geotechnical Centrifuge ◽  
Drag Forces ◽  
Field Instrumentation ◽  
Earth Pressures ◽  
Box Culvert ◽  
Base Contact

Earth pressure data from the field instrumentation of a cast-in-place reinforced rectangular box culvert are presented in this paper. The instrumented culvert is a 2.60 m by 3.60 m double-cell reinforced cast-in-place rectangular box buried under 25.10 m of fill constructed using the induced trench installation (ITI) method. The average earth pressure measured across the roof was 0.42 times the overburden pressure, and an average of 0.52 times the overburden pressure was measured at mid-height of the culvert on the sidewalls. Base contact pressure under the rectangular box culvert was also measured, providing field-based data demonstrating increased base pressure resulting from downward drag forces developed along the sidewalls of the box culvert. An average increase of 25% from the measured vertical earth pressures on the roof plus the culvert dead load (DL) pressure was calculated at the culvert base. A model culvert was also tested in a geotechnical centrifuge to obtain data on earth pressures at the top, sides, and base of the culvert. The data from the centrifuge testing were compared with the prototype structure, and the centrifuge test results agreed closely with the measured field prototype pressures, in spite of the fact that full similitude was not attempted in centrifuge testing.

The Effects of Upstream Flexible Barrier on the Debris Flow Entrainment and Impact Dynamics on a Terminal Barrier

2021 ◽  
Author(s):  
Hervé Vicari ◽  
C.W.W. Ng ◽  
Steinar Nordal ◽  
Vikas Thakur ◽  
W.A. Roanga K. De Silva ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Impact Force ◽  
Dynamic Pressure ◽  
Pressure Coefficient ◽  
Flexible Barrier ◽  
Impact Forces ◽  
Flexible Barriers ◽  
The Impact ◽  
Bed Entrainment

The destructive nature of debris flows is mainly caused by flow bulking from entrainment of an erodible channel bed. To arrest these flows, multiple flexible barriers are commonly installed along the predicted flow path. Despite the importance of an erodible bed, its effects are generally ignored when designing barriers. In this study, three unique experiments were carried out in a 28 m-long flume to investigate the impact of a debris flow on both single and dual flexible barriers installed in a channel with a 6 m-long erodible soil bed. Initial debris volumes of 2.5 m<sup>3</sup> and 6 m<sup>3</sup> were modelled. For the test setting adopted, a small upstream flexible barrier before the erodible bed separates the flow into several surges via overflow. The smaller surges reduce bed entrainment by 70% and impact force on the terminal barrier by 94% compared to the case without an upstream flexible barrier. However, debris overflowing the deformed flexible upstream barrier induces a centrifugal force that results in a dynamic pressure coefficient that is up to 2.2 times higher than those recommended in guidelines. This suggests that although compact upstream flexible barriers can be effective for controlling bed entrainment, they should be carefully designed to withstand higher impact forces.

scholarly journals Effects of dynamic fragmentation on the impact force exerted on rigid barrier: centrifuge modelling

2019 ◽  
Vol 56 (9) ◽  
pp. 1215-1224 ◽  
Author(s):  
C.W.W. Ng ◽  
C.E. Choi ◽  
D.K.H. Cheung ◽  
Y. Cui
Keyword(s):  
Volume Fraction ◽  
Impact Force ◽  
Inertial Particles ◽  
Size Segregation ◽  
Centrifuge Modelling ◽  
Rigid Barrier ◽  
Flow Energy ◽  
Dynamic Fragmentation ◽  
Large Particles ◽  
The Impact

Bi-dispersity is a prerequisite for grain-size segregation, which transports the largest particles to the flow front. These large and inertial particles can fragment upon impacting a barrier. The amount of fragmentation during impact strongly influences the force exerted on a rigid barrier. Centrifuge modelling was adopted to replicate the stresses for studying the effects of bi-dispersity in a granular assembly and dynamic fragmentation on the impact force exerted on a model rigid barrier. To study the effects of bi-dispersity, the ratio between the diameters of small and large particles (δs/δl), characterizing the particle-size distribution (PSD), was varied as 0.08, 0.26, and 0.56. The volume fraction of the large particles was kept constant. A δs/δl tending towards unity characterizes inertial flow that exerts sharp impulses, and a diminishing δs/δl characterizes the progressive attenuation of these sharp impulses by the small particles. Flows dominated by grain-contact stresses (δs/δl < 0.26), as characterized by the Savage number, are effective at attenuating dispersive stresses of the large particles, which are responsible for reducing dynamic fragmentation. By contrast, flows dominated by grain-inertial stresses (δs/δl > 0.26) exhibit up to 66% more impulses and 4.3 times more fragmentation. Dynamic fragmentation of bi-disperse flows impacting a rigid barrier can dissipate about 30% of the total flow energy.

Field performance, centrifuge testing, and numerical modelling of an induced trench installation

2008 ◽  
Vol 45 (1) ◽  
pp. 85-101 ◽  
Author(s):  
Rodney P. McAffee ◽  
Arun J. Valsangkar
Keyword(s):  
Numerical Modelling ◽  
Pressure Distribution ◽  
Earth Pressure ◽  
Field Performance ◽  
Overburden Pressure ◽  
Centrifuge Testing ◽  
Geotechnical Centrifuge ◽  
Earth Pressures ◽  
Prototype Structure ◽  
Box Culvert

The field performance of an induced trench installation is compared to the results of centrifuge testing and numerical modelling. The measured vertical pressure at the crown of the pipe in the field ranged from 0.24 to 0.36 times the overburden pressure. The horizontal earth pressures measured in the field at the springline level determined a coefficient of lateral earth pressure between 0.39 and 0.49. The culvert was monitored over a period of 2 years following completion of embankment construction indicating no measurable changes in earth pressures and deformations. A model box culvert simulating the prototype height of soil cover, the pipe width, and the thickness of the compressible layer was tested using a geotechnical centrifuge. The prototype structure was also evaluated using numerical modelling to predict full earth pressure distribution and deformations. A comparison of field data, centrifuge testing, and numerical modelling shows that the Marston–Spangler theory used in designing induced trench culverts is conservative. The theory however, does not address or predict the nonuniform pressures on the top, sides, or bottom of the pipe, and therefore numerical analysis should be used to estimate the complete pressure distribution.

scholarly journals Analysis of Vertical Earth Pressure Acting on Box Culverts through Centrifuge Model Test

2021 ◽  
Vol 12 (1) ◽  
pp. 81
Author(s):  
Inyeop Chu ◽  
Sang-Kyun Woo ◽  
Sang Inn Woo ◽  
Joonyoung Kim ◽  
Kicheol Lee
Keyword(s):  
Model Test ◽  
Earth Pressure ◽  
Centrifuge Model Test ◽  
Gravitational Acceleration ◽  
Soil Pressure ◽  
Geotechnical Centrifuge ◽  
Centrifuge Model ◽  
Cover Depth ◽  
Box Culvert ◽  
Vertical Earth Pressure

Due to the lack of surface space, most structures are heading underground. The box culvert is underground infrastructure and serves to protect the buried structure from the underground environments, but it has a different characteristic from other structures in that the inner space is empty. Therefore, in this study, the vertical earth pressure which is the most significant effective stress acting on a box culvert was measured by conducting a geotechnical centrifuge model test. A box culvert was installed following the embankment installation method, and the vertical earth pressure acting on it was measured considering the cover depth, gravitational acceleration, and loading and unloading conditions. The soil pressure measured was greater than the existing theoretical value under high cover depth and the unloading condition, which is considered as the variability of many soils or the residual stress acting under the loading condition. Finally, a goodness-of-fit test was conducted as a part of variability analysis. The measured earth pressure was found to be considerably larger than the existing theoretical value, and the variability was large as well. This means the existing theoretical equation is under-designed, which should be reflected in future designs.

scholarly journals Laboratory tests for the optimization of mesh size for flexible debris-flow barriers

2015 ◽  
Vol 15 (12) ◽  
pp. 2597-2604 ◽  
Author(s):  
C. Wendeler ◽  
A. Volkwein
Keyword(s):  
Grain Size ◽  
Debris Flow ◽  
Laboratory Tests ◽  
Mesh Size ◽  
Field Measurements ◽  
Maximum Diameter ◽  
Small Scale ◽  
Dimensionless Numbers ◽  
Flexible Barrier ◽  
Flexible Barriers

Abstract. Flexible barriers can be used within channelized riverbeds as an effective and efficient alternative to protect from debris flows. Their retention capability strongly depends on the size of the mesh openings and the gap between the lower barrier edge and the channel's floor. The question is now whether there is a relation between the grain size distribution of the debris material and the openings of a flexible barrier. Small-scale laboratory tests were performed to study these loading aspects of flexible debris-flow barriers for the Milibach river (Canton Berne, Switzerland). In situ debris material has been used to quantify the influence of different mesh sizes and the gap between the lower barrier edge and the riverbed compared to the d90 grain size and the flow height, where d90 is the maximum diameter of 90 % of the grains. It was possible to study the filling process and the retaining behaviour of the barriers as a function of the mesh size. A reasonable retention was reached with the net having a mesh size and a basal gap smaller than or equal to d90. These relations could be transferred to the field. A dimensional analysis reveals possible dimensionless numbers that can be used to scale the laboratory results. The findings are supported by the results of similar laboratory tests using debris material from different locations and by the available field measurements.

scholarly journals ENERGY DISSIPATING MODES AND DESIGN RECOMMENDATION OF H-SHAPED STEEL BAFFLES SUBJECTED TO BOULDER IMPACT

2021 ◽  
Keyword(s):  
Element Model ◽  
Steel Beams ◽  
Structural Behaviour ◽  
Flexible Barrier ◽  
Compression Members ◽  
Shear Buckling ◽  
Protective Structures ◽  
Flexible Barriers ◽  
Design Recommendation ◽  
The Impact

Flexible barriers are one of the most effective protective structures, which have been widely used for the mitigation of rockfalls. As the only compression members in a flexible barrier system, steel posts maintain the integrity of the interception structure to keep the function of the system. Due to the random trajectories of rockfalls, steel posts may be impacted by boulders directly. The impact scenario may result in the failure of the post and even the collapse of the system. In this paper, firstly, steel baffles were proposed to be an additional structural countermeasure to avoid the direct impact of posts. Secondly, numerical method was adopted to study the structural behaviour of steel baffles under direct boulder impact. Then, an available published experimental test of H-shaped steel beams under drop weight impact loading by others was back analyzed to calibrate the finite element model. Finally, numerical simulations were carried out to investigate the energy dissipating modes and energy dissipating efficiency of the H-shaped steel baffles. The simulation results show that there are three typical energy dissipating modes of H-shaped baffles subjected to boulder impact, namely flexural, local compression buckling and shear buckling. Local compression buckling is the most efficient energy dissipating mode. The thickness of the web of an H-shaped baffle is suggested to be 4 mm and 6 mm for the rated dissipating energy of 50 kJ and 100 kJ, respectively.

scholarly journals Large Scale Physical Modelling Study of a Flexible Barrier under the Impact of Granular Flows

2018 ◽  
Author(s):  
Dao-Yuan Tan ◽  
Jian-Hua Yin ◽  
Wei-Qiang Feng ◽  
Jie-Qiong Qin ◽  
Zhuo-Hui Zhu
Keyword(s):  
Debris Flows ◽  
Large Scale ◽  
Impact Force ◽  
Granular Flows ◽  
Physical Modelling ◽  
Flexible Barrier ◽  
Impact Forces ◽  
Flexible Barriers ◽  
Open Question ◽  
The Impact

Abstract. Flexible barriers are being increasingly applied to mitigate the danger of debris flows. However, how barriers can be better designed to withstand the impact loads of debris flows is still an open question in natural hazard engineering. Here we report an improved large-scale physical modelling device and the results of two consecutive large-scale granular flow tests using this device to study how flexible barriers react under impact from granular flows. In the study, the impact force directly on the flexible barrier and the impact force transferred to the supporting structures are measured, calculated and compared. Based on the comparison, the impact loading attenuated by the flexible barrier is quantified. The hydro-dynamic and hydro-static approaches are also validated using the calculated impact forces.

Discrete-element investigation of influence of granular debris flow baffles on rigid barrier impact

2016 ◽  
Vol 53 (1) ◽  
pp. 179-185 ◽  
Author(s):  
Raymond Pak Hei Law ◽  
Clarence Edward Choi ◽  
Charles Wang Wai Ng
Keyword(s):  
Debris Flow ◽  
Discrete Element ◽  
Row Spacing ◽  
Dynamic Force ◽  
Flow Front ◽  
Flume Experiments ◽  
Rigid Barrier ◽  
Flow Energy ◽  
Slit Size ◽  
Peak Impact Force

Granular debris flow baffles are commonly installed in front of rigid barriers to dissipate flow energy and reduce the required barrier impact capacity. Despite the engineering value of baffles, their influence on rigid barrier impact is still not well understood. A previously calibrated discrete element method (DEM) model using a series of flume experiments was adopted to study the effectiveness of installing baffles in front of a rigid barrier. Froude scaling was used to characterize the flow front. Different baffle configurations were examined, namely number of rows, spacing between successive rows (L), and baffle height. Results reveal an optimum row spacing of L/D = 3 (D is the slit size). Row spacing less than L/D = 3 leads to increased peak dynamic force from overflow impacting the barrier, whereas row spacing greater than L/D = 3 results in increased peak dynamic force from the granular debris flow front. Increasing spacing greater than L/D = 3 allows the dispersion of debris between rows and decreases the effectiveness of the second row. Adopting baffle heights greater than 1.5 times the approach flow depth (h) reveals little influence on the peak impact force induced on the barrier.

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