Model Test Research Research Articles

Physical model analysis of stability coefficient for tetrapod innovation

Beach protection is vital to reduce the damage to shorelines and coastal areas; one of the artificial protections that can be utilized is the tetrapod. However, much damage occurred when using a traditional tetrapod due to the lack of stability coefficient (KD). Therefore, this research aims to increase the stability coefficient by providing minor modifications to the cape of the tetrapod, such as round-caped or cube-caped. The modification seeks to hold the drag force from the wave and offer a good interlocking in between the tetrapod. This research applied physical model test research using a breakwater model made from the proposed innovative tetrapod with numerous variations in dimensions and layers simulated with several scenarios. The analysis was carried out by graphing the relationship between the parameters of the measurement results and the relationship between dimensionless parameters, such as wave steepness H/gT2, and other essential parameters, such as the KD stability number and the level of damage in %. The result shows that the modified and innovative tetrapod has a more excellent KD value than the conventional tetrapod. In addition, the innovative tetrapod with the cube-shaped has a recommended KD value greater than the round shape. This means that for the modified tetrapod structure and the same level of security, the required weight of the tetrapod with the cube cap will be lighter than the tetrapod with the round cap. These findings have significant practical implications for coastal protection and engineering, potentially leading to more efficient and cost-effective solutions.

The model test research of medium-low specific speed Francis pump-turbine

Abstract In the last few years, the pumped storage power station grows vigorously. As a result, the higher demand have been put forward in relevant technical fields. This article mainly discusses the model test research of medium-low specific speed Francis pump-turbine. Furthermore, the pump-turbine model test method of performance, cavitation, pressure pulsation, complex characteristics, and the rest auxiliary test is expounded and studied, with a view to optimizing pump-turbine model test method and further improving test rate. It can provide the favorable condition for the pump-turbine unit design and power station continuously operation.

Model test research on arch dam displacement monitoring based on distributed strain sensing

Distributed optical fiber strain sensing technology can realize the full distributed monitoring of arch dam deformation, but the strain is directly measured instead of displacement. Therefore, it is necessary to study the displacement transfer of such complex structures as arch dams according to strain measurement. In this paper, Bayesian Optimized Long-short-time Memory Neural Network (BO-LSTM) and distributed optical fiber monitoring are innovatively combined to establish a three-dimensional model for measuring dam strain by optical fiber, which realizes the transformation between strain and displacement. The feasibility of different spatial resolutions is discussed by using BO-LSTM, and the strain input and displacement output are selected by using pure arch method. The results show that the strain–displacement transformation of arch dam can be realized accurately based on the BO-LSTM transformation model. The accuracy of the model is improved by screening strain values by analogy pure arch method.

Model test research and application on control method of cooperative pressure relief by directional roof cutting for roadways with strong dynamic pressure

Model test research and application on control method of cooperative pressure relief by directional roof cutting for roadways with strong dynamic pressure

Non-contact model test and numerical simulation of plastic zone in sandy soil foundation

Reasonable determination of the ultimate bearing capacity of the foundation is of great significance in engineering applications. Based on the self-developed non-contact testing device for the plastic zone of shallow foundation, this paper carries out model test research on the plastic zone of sandy soil shallow foundation and analyzes the development law of plastic zone under the action of foundation load. The main advantages and functional characteristics of the foundation plastic zone test system are that it can realize the non-contact test of displacement deformation of soil, the dynamic development process of shear deformation, and the plastic zone of model foundation can be obtained intuitively. The development process, morphological boundary characteristics, and foundation failure mode of the plastic zone of the sand foundation are obtained. The plastic zone of the foundation starts from the edges of both sides of the bearing plate; with the increase of the load, the plastic zone gradually develops downward and approaches to the center line, and finally crosses through at the bottom until the local shear failure of the foundation occurs. The measured plastic zone is a symmetrical spindle shape with thin ends and a bulge in the middle; the sand on both sides of the bearing plate partially bulges, forming a “V” shaped shear failure zone, and the bottom of bearing plate forms a triangular compression zone, the foundation failure mode of sandy soil represents a typical punching shear failure mode. In order to study the distribution characteristics of the plastic zone range of foundation under different foundation loads and foundation widths, the Universal Distinct Element Code (UDEC) based on the discrete element method is used for numerical simulation research. By conducting parameterized numerical simulation test for the plastic zone of foundation and analyzing the results, with the changes in the foundation load and the foundation width, the variation law of (1) the depth of the plastic zone on the foundation bottom, (2) the width of the plastic zone on both sides of the foundation, (3) the ratio for the depth of plastic zone to the width of foundation, (4) the ratio for the width of plastic zone to the width of foundation and (5) the ratio for the width of plastic zone to the depth of plastic zone is obtained. The research has significant guiding significance for the study of the development law of plastic zone and foundation design.

Application of Fixed-Wing UAVs to Develop Digital Terrain Model on Coastal Peatland Bengkalis Island

Destructive abrasion is currently occurring in Teluk Papal Village. The coast of Teluk Papal Village has a humus soil structure with soil conditions with a type of peat that is relatively easy to decompose. The cause is along the coast because of the absence of coastal protection plants (mangroves). To prevent the increasing abrasion rate, a comprehensive plan is needed by involving relevant stakeholders in both short and long-term planning. One of the efforts in controlling the abrasion rate is the construction of breakwater buildings. Before the construction is carried out, a study is needed to support the breakwater construction. One of the supports is to make a topographic or contour map. The field data acquisition process uses Unmanned Aerial Vehicle (UAV) technology. This data processing technique uses photogrammetric data processing techniques with the stages of flight path planning, measurement of Ground Control Point (GCP), and Benchmark points, which are then tied to BIG's CORS points to produce higher control point accuracy, Dense Cloud Point to create Digital Elevation Model (DEM) or Digital Terrain Model (DTM), and orthophoto embellishment. Furthermore, horizontal and vertical position accuracy tests were conducted using the calculation method issued by BIG regulation No. 15/2014 to provide information on how far the accuracy of the resulting map is. The results of the Digital Terrain Model (DTM) and orthophoto data accuracy test research based on the results of the accuracy test obtained a LE90 value of 0.6757 meters, then for the CE90 value of 0.1543 meters so that it meets the map requirements at a scale of 1:2500 at class 1 horizontal accuracy and class 2 vertical accuracy.
 Keywords: Digital Elevation Model, Ground Control Point, Orthophoto, Topography, Unmanned Aerial Vehicle

Model Test Study on the Transmission Law of Explosion Stress Wave in Rock Mass with Filling Joints

In order to study the propagation and attenuation law of explosive stress wave in rock mass with filling joints, and consider the influence of different crustal stress conditions, different strength mortar is used to simulate rock mass and joints, and the multi-functional simulation test device of geotechnical engineering is used to carry out explosive model test research, the influence characteristics of different in-situ stress conditions on the attenuation of explosive stress wave in rock mass with different thickness filling joints are analyzed, and obtain the transmission law of stress wave. The results show that: when the explosion stress wave propagates in the joined rock mass, the thicker the filling joint is, the greater the attenuation range of the stress wave energy and the samller the transmission coefficient; In-situ stress will change the attenuation of explosive stress wave in rock mass. With the increase of in-situ stress, the transmission coefficient of stress wave in intact rock mass and joined rock mass will increase. When the local stress is fixed, the transmission coefficient of stress wave in joined rock mass also increase gradually with the increase of explosion load.

Model test and numerical simulation research on the mechanical response law of lager span and small interval tunnels constructed by CD method

In order to study the mechanics response law of lager span and small interval tunnels during the construction process, this paper took the Jinan Southeast Second Ring Engineering-Daling Tunnel as the research object, and developed a large-scale 3D visible and assemble geomechanical model test system. Based on that, we carried out a model test and numerical simulation of the construction progress of the Daling Tunnel, and we studied the mechanics response law by monitoring the deformation and stress changes of the surrounding rock in real time. Combined with the results of the model test and the numerical simulation, the mechanical characteristic response law of the construction process of the lager span and small interval tunnels was revealed, and we found that: 1) The deformation of the surrounding rock of the lager span and small interval tunnels showed a change law of “slow settlement-rapid settlement-tending to be gentle”. And the stress release of surrounding rock shown a change law of “load accumulation-load release-tending to be stable”; 2) The excavation of the section ③ caused the largest settlement of the vault surrounding rock, which accounted for about 18.5% of the settlement value. The order of the influence degree of the surrounding rock deformation of the vault was ③＞②＞④＞①, which were almost the same with the law of the stress release of the surrounding rock; 3) The excavation of the tunnel ② caused the largest convergent deformation of the surrounding rock of the side wall, accounting for about 26.4% of the total convergent deformation. The order of the degree of influence of excavation on the deformation of the surrounding rock of the side wall was: ②>④>③>①, which were almost the same with the law of the stress release of the surrounding rock. The technical methods and conclusions formed in this experiment have important guidance and reference significance for related projects.

Model Test and Numerical Simulation Research of Reinforced Soil Retaining Walls under Cyclic Loads

The stress diffusion characteristics of reinforced soil retaining walls (RSW) with concrete-block panels under cyclic loads are studied. The distribution of the vertical dynamic earth pressure caused by an external load and the analysis of stress diffusion angles were studied using a model test and the numerical simulation model of the reinforced soil retaining wall was established to analyze the change in the stress diffusion angle. We then changed the parameters to investigate the influencing factors of the stress diffusion characteristics. The results showed that: the average value of the peak vertical dynamic earth pressure caused by an external load at the loading position of the RSW was a nonlinear distribution, decaying from top to bottom and increasing with the increase in the loading amplitude, while the change in the loading frequency number of loading cycles had no obvious rule. The results of model test and numerical simulation agree with each other. The diffusion angle of the stress caused by the external load of the reinforced body was basically between 50° and 65° in the range from 1.8 m to 1.2 m, the diffusion angle at the top was slightly larger than the middle, and the diffusion angle away from the wall was larger than the diffusion angle close to the wall. The main factors affecting the stress diffusion in reinforced soil retaining walls are the coefficient of reinforcement of the soil and the dynamic stress amplitude; the stress diffusion angle increased with an increase in the coefficient of the reinforcement of the soil and the dynamic stress amplitude. The conclusion of this paper can provide a reference for the design of reinforced soil structures.

Model test research on creep characteristics of discontinuous structural surfaces slope

The rock slopes in nature are mainly cut by joints, which are in a non-persistent state in the rock mass. The creep mechanical characteristics of discontinuous structural surfaces have a significant and complicated influence on slope stability. Based on the analysis of the characteristics of a rock slope in Western Hubei before and after instability, the geological prototype of the slope is generalized, and the mechanical model of the discontinuous structural surfaces is established. Based on the uniaxial compression creep test, the phase creep characteristics of discontinuous structural surfaces are analyzed. The instantaneous strain in the creep process of discontinuous structural surfaces decreases greatly, and then increases slowly. The creep strain increases with the increase of stress. A viscoelastic-viscoplastic element that can describe the viscoelastic and the viscoplastic properties and damage variables are introduced, and an improved Nishihara damage creep constitutive model is constructed. The Levenberg-Marquardt (L-M) algorithm and global optimization method are used to verify the improved Nishihara damage constitutive model. After verification, comparing the experimental values and the predicted values of the damage constitutive model, the results show that the improved Nishihara damage constitutive model can better simulate the creep process of discontinuous structural surfaces. The author hopes that this study can provide reference for the study of creep characteristics of discontinuous structural surfaces in the future.

Numerical Simulation of Hydraulic Characteristics of Spillway Tunnel with Gradually Expanding Outlet and Lower outlet height

Using a practical and efficient overall three-dimensional turbulent numerical model of the spillway tunnel, the numerical simulation of the hydraulic characteristics of the spillway tunnel with the gradually expanding outlet and lower outlet height is carried out. The calculation results show that when the gate is fully open, there is pressure flow in the whole tunnel of the spillway tunnel, and the flow state is stable; when the gate is not fully open and the water level is low, the flow state in the tunnel is unstable, and the free and pressure flow occur alternately. When the gate is at a small opening, the flip bucket raises the water level at the outlet, and the lower outlet height causes insufficient air supply in the cave, which is prone to cavitation. The lift distance is small, and it is easy to scour the slope of the hole. The lower outlet height at the outlet of the spillway tunnel further exacerbates the complexity of the hydraulic characteristics in the back arc section, which should be paid attention to during design and construction, and it is necessary to carry out hydraulic model test research.

Model Test Research on the Mechanical Characteristics of Tunnel Lining Structures under Local High Water Pressure in Concealed Karsts

Mountainous karst areas contain many hidden karsts around highway tunnels. During the stormy rain season, concealed karsts connected to surface are recharged by surface water. Consequently, the water level of the corresponding caverns rises sharply, posing an imminent threat to the safety of the lining structure of the operating tunnel. This paper uses similar model experiment methods from a highway tunnel in southwestern China to discuss the contact pressure between the lining and surrounding rock, internal lining force, and change law of the failure mode when the local high water pressure acts on the sidewall. Results showed that at increasing external water pressure, the contact pressure between the lining and surrounding rock in the hydraulic pressure area decreased, whereas the contact pressure at other parts increased. Consequently, the axial force distribution maintained a “horseshoe shape” whose maximum value was proportional to the position of the external water pressure. Moreover, the pressure had a more dramatic influence on the bending moment of the lining that even changed its direction. Furthermore, the right side wall fractured when the water pressure acted on the left side wall, making the left side appear under the load. However, the longitudinal penetrating cracks were the same as the sidewall dislocation during the operation of the tunnel. These findings have specific reference significance for the design of traffic tunnels in karst areas.

Computer simulation and model test study on influence of water immersion degree on wind power generation pile stress

The force of foundation piles in collapsible soil is a complex and important issue. Different degrees of collapsibility will have different effects on the force of foundation piles. In order to analyze and discuss the distribution and change law of the axial force and negative friction resistance of the foundation pile in moe detail, this paper summarized the existing research results on the influence of immersion collapsibility on the development of the axial force and negative friction of the foundation pile, and through model test research, the strain of the loaded foundation pile and the unloaded foundation pile under the same site conditions were measured as the site was wet.The test shows that the degree of collapsibility is positively correlated with the force of foundation piles in collapsible loess site. The presence or absence of a load on the top of the pile has a greater impact on the development process of the pile's force during the immersion of the site; but it has little effect on the distribution of the pile side friction when the site is fully immersed and saturated.

Experimental investigation of wave reflection at a wave energy converter breakwater

The wave energy converter breakwater innovation model with an overtopping mechanism with an impermeable single smooth slope was investigated experimentally in the laboratory. Investigations were carried out to determine how the relative freeboard and slope influence the reflection waves. This research is interesting because the main objective of this model is actually to capture overtopping waves to be collected in the reservoir and used as energy conversion, therefore besides the occurrence of wave overtopping through the model peak, one important parameter which is also interesting to know is how the effect of the relative freeboard and slope of this model to the reflection waves in front of the model. The physical model test research was conducted on a two-dimensional wave flume. The single smooth impermeable slope wave energy converter breakwater model is made of a size that can be mobilized by the flume. Several parameters of the model are varied, such as the slope angle and height of the freeboard model. In hydraulic parameters, variations such as incident wave height and wave period are also carried out. The results showed that the 1: 2 and 1: 2.5 slope models generally produce a greater reflection than the 1: 3 slope model. For the effect of the relative freeboard, it is found that the greater the value of the structure relative freeboard, the greater the wave reflection coefficient, with the range of wave reflection coefficient values obtained in this study are 0.1-0.7.

Urban Environment Evaluation and Analysis Based on Street View Image

The real and intuitive reconstruction of the city street scene can not only give the viewer an immersive feeling, but also serve as a way to display information. As a mass data, it also provides unique decision-making ideas for recording phenomena, discovering rules and predicting results. This paper proposes a green visual rate to measure the green apparent area of urban street trees. For complex urban street landscapes, the green apparent area index can well reflect the visualization degree of green area of street trees and urban environment under street scenes. Research to Skesfehervar, Hungary as an example, it carried out the street tree green apparent area calculation model test research in different characteristics of road sections, different street scenes under the authenticity and adaptability.

Development and Application of Model Test System for Reconstruction and Expansion of Existing Shallow Single-Hole Tunnel into Twin-Arch Tunnel

In this study, we developed a tunnel excavation model test system to investigate the deformation and mechanical response of the surrounding rocks and tunnel structure during the reconstruction and expansion of an existing shallow single-hole tunnel into a twin-arch tunnel. A model test was conducted to study the variation in the ground surface settlement characteristics, surrounding rock pressure, and internal stresses of the supporting structure and midwall during the construction process. The influence of the excavation distance on displacements and structural stress between the faces of the left and right tunnels was analysed using numerical software. A comparison between the model test results and the monitoring and measurement construction results revealed a fairly consistent ground surface settlement, indicating that the system is stable and reliable and can be widely applied to laboratory model test research on tunnel excavation. Results show that the excavation of the first tunnel had a significant effect on the stability of the surrounding rock within the distance of a single-tunnel span behind the tunnel face. When the excavation distance between the two tunnels exceeded twice the length of the single-tunnel span, its effect on the stresses and deformation of the reconstructed twin-arch tunnel was negligible.

Seismic model test research on the combination of rigidity with flexibility of tunnel portal in high intensity seismic areas

Taking the soft rock portal section of the Baiyunding Tunnel as the research background, it is proposed that the combination of rigid and flexible anti-vibration measures can more effectively improve the seismic performance of the tunnel. Through shaking table model test, the seismic effects of structural reinforcement, installation of shock absorbing joint, and the combination of rigid and flexible anti-vibration measures are compared and analyzed. The test data shows that: only structural strengthening measures are taken, the minimum increase percentage of the structural safety factor of the tunnel portal section is between 30.40% and 62.28%; only shock absorbing joint are installed, and the minimum increase percentage of the safety factor of the tunnel portal section is between 41.86% and 53.30%; the combination of rigid and flexible anti-vibration measures is adopted, the minimum increase percentage of the structural safety factor of the tunnel portal section is between 85.20% and 140.99%. The combination of rigid and flexible anti-vibration measures has a significant effect on resisting earthquake vibration and reducing forced displacement, and the effect of shock absorption is the best. The research results can provide a reference for improving the seismic performance of traffic tunnels in high seismic intensity areas.

Laboratory Model Test Research on Mechanical Characteristics of Anchor in Loess Tunnel under the Action of Pull‐Out Load

The deformation mode of loess surrounding rock of anchor under the action of pull‐out load and the shear stress distribution law of loess anchor and loess interface under the condition of different lengths anchor are studied by using the laboratory self‐made model test chamber and micro anchor pullout instrument. A total of three tests are carried out for the selected test anchor. Three deformation modes of loess surrounding rock under the action of pull‐out load are obtained according to the test results. It is proposed that the maximum shear stress of loess anchor under the action of pull‐out load appears in the section 25 times the anchor diameter from the anchor head, and the shear stress in the middle and rear part of the anchor body can only be brought into full play when the length‐to‐diameter ratio of the anchor body is 110 or more. Based on the displacement solution of Mindlin problem, the drawn conclusion is compared with the theoretical solution of shear stress and axial force of loess anchor under the action of pull‐out load. The results compared are basically consistent, indicating that the conclusion has strong engineering practice, which can provide technical basis for the design and optimization of the system anchor in the sidewall of loess tunnel.

Geomechanics model test research on automatically formed roadway by roof cutting and pressure releasing

The N00 mining technology is a new coal mining method of automatically formed roadway (AFR). The roadway is created by roof cutting and pressure releasing (RCPR). Compared with the traditionally longwall method, this new technology does not require excavating mining roadways and reserving protective coal pillars (no-pillar). In order to make an in-depth study on the law of the mining pressure behavior, the first working face of N00 mining technology around the world is taken as the engineering background in this manuscript. A three-dimensional geomechanics model test system is independently developed for the N00 mining technology and the model test is carried out. Combined with numerical comparative analysis, the law of surrounding rocks stress evolution and overlying strata movement of AFR is obtained. The variation law of roof and floor convergence deformation of AFR has obvious zoning characteristics, which can be divided into four significant stages. These stages are the pressure releasing stage, the dynamic pressure deformation rising stage, the dynamic pressure deformation stabilizing stage, and the compaction stabilisation stage, respectively. The overload test results indicate that the key damaged parts are the shoulder corner of solid coal side, and the gangue rib of AFR. The research results can be used as a reference for theoretical research, engineering design and field application of the N00 technology.

Study on the deformation and fracture laws of surrounding rock of a TBM tunnel in a deep composite stratum

To solve the key problems of tunneling and excavation, deformation and rupture of surrounding rocks in TBM tunnel model test research in deep composite stratum was conducted. This research employed a combined strategy of physical model test and numerical simulation for studying the deformation and fracture laws of the surrounding rock in a vertical section of a TBM tunnel in deep composite strata. In this study, the main research results are 1) The “soft and hard unevenness” and “combination effect” of the composite stratum affected the overall bearing capacity of the tunnel resulting in failure at a shallower buried depth or a lower stress concentration factor. 2) When the model was only excavated and unloaded, the plastic zone was basically near the periphery of the tunnel, resulting mainly in shear failure. In the lower layer of the composite stratum tunnel, the plastic zone due to its higher strength parameters was smaller than that in the upper layer. 3) Under the premise of the axial loading and surrounding constraints, the deformation and failure mode of the TBM tunnel in the deep composite strata exhibited “X”-type failure characteristics. The vertical section of the partially excavated rock mass revealed that the rock mass at the top layer of the tunnel caused a sudden and integral shear sliding of the palm face along the oblique direction upward 50°. This research provides significant and important guidelines for solving the problems of safety in TBM tunnel construction in a deep composite stratum.