Results Of Physical Model Tests Research Articles

3D Numerical Model Validation Using Experimental Test Data for Patrind Hydropower Project

Whilst numerical modelling is commonly used for simulation to check the design of water conveyance, sluicing and spillway structure design, the numerical modelling has rarely been compared with the physical model tests. The objective of this research presented in this paper was to examine the validity and suitability of the numerical computational fluid dynamics (CFD) modeling method within an ANSYS Fluent/CFD R 18.2 software and compare its results with a fully instrumented and well-run physical model test at the 1:45 scale, carried out for Patrind Hydropower Project located in Pakistan. The physical model test was conducted for confirmation and optimization of a natural de-sanding basin, and diversion of suspended sediment-rich flood waters using a bypass tunnel. The numerical simulation was able to reproduce physical model test results and data gathered over a 7-year project operation to an acceptable level of accuracy. A detailed explanation of the approach used in numerical modelling together with analysis of simulation diagrams of ANSYS Fluent/CFD is also presented. The research shows that a 3D numerical model with accurate boundary conditions and mesh size can replace the need for physical model tests.

Experimental study on overtopping dam-break of a tailing reservoir under extreme conditions.

There is a high risk of dam breakage in tailing reservoirs under extreme conditions. Once a dam breaks, it causes serious pollution to the surrounding ecological environment. To explore the effects of a tailings dam break under extreme conditions (flood conditions, drainage failure, flood discharge failure, and dam saturation), the mechanism underlying an overtopping dam break must be accurately understood. In this study, fine-grained tailings and perlite were selected to create composite model sand, and a prototype tailing reservoir was restored at a scale of 1:200. Furthermore, the dam-break process and results were analyzed and summarized by performing an overtopping dam-break test on the tailing reservoir under extreme conditions. The results show that the tailing discharge process has a high sand content, strong sand-carrying capacity, and high speed. The amount of model sand discharge accounted for 15.13% of the total storage capacity, and the amount of tailings deposition in the downstream area accounted for 95.21% of the discharge, which were both greater than the results of similar physical model tests and actual tailings dam failure accidents. An overtopping dam break in a tailing pond is a progressively destructive process. The dam break mechanism can be divided into two stages: prior breach penetration and subsequent breach horizontal expansion. In the process of a tailings dam break, the motion state of the tailings particles is transformed between the bed-load and suspended-load movement states. These results can provide important reference for the reinforcement of mine management and the formulation of preventive measures, which are essential to improving the safety of tailings reservoirs and protecting the ecological environment.

Aeration strength analysis of overflow weir in siphon well based on numerical simulation of water–air two‐phase flow

AbstractThe phenomenon of water aeration is serious after the overflow weir in the siphon well at the cooling water circulation system of coastal power plants. At present, designing special hydraulic structures is an effective way to reduce the intensity of aeration. In this paper, three engineering structure schemes were designed, and the three‐dimensional Realizable k–ε turbulence model was used. The volume of fluid method was introduced to capture the free water surface, and the unstructured grid was used to construct the two‐phase turbulent flow field. The aeration concentration and pressure distribution, obtained by numerical simulation, were basically consistent with the physical model test results. The results showed that the flow field at the orifice plates of cases 1 and 2 changed drastically, and the turbulent kinetic energy downstream of the orifice plate decreased with the increase of the number of holes. As for case 3, it showed that the high‐speed water flow fell into the water cushion pool, tumbling and sucking up a lot of air, and the turbulent kinetic energy and Reynolds stress were significantly greater than the other two cases. The hydraulic structure changed the cavitation characteristics of the downflow water, and the sequence of aeration concentration of the horizontal section was case 3 > case 1 > case 2. The aeration concentration was only 9.18%–17.86% in case 2. The aeration concentration at stable time is expressed as a function of the relative water depth y/y90 and the turbulent diffusion coefficient D. The distribution formula of aeration concentration was established, and its validity was verified by literatures. The results of this study will provide a certain reference for in‐depth analysis of water–air mixing motion characteristics, and simultaneously, it will have a guiding significance for the design of siphon well defoaming engineering.

Model Test of Surrounding Rock Temperature Field under Different Drainage Structures and Insulation Conditions in High Cold Tunnel

Improper layout of drainage structures and inadequate insulation measures in high-altitude cold areas have resulted in varying degrees of frost damage in numerous tunnels during operation. To address this issue and propose a viable drainage structure layout scheme, this paper analyzes and studies the temperature field distribution characteristics of the lower surrounding rock and drainage structure around high-altitude cold tunnels, as well as the layout of the central drainage ditch and anti-cold water leakage hole. Based on physical model test results of cold area tunnels, the distribution characteristics of the temperature field around the tunnel drainage structure under different insulation conditions are obtained, and a control equation of temperature change along the depth direction is proposed. By comparing and analyzing the differences in temperature field and water flow characteristics of drainage structures under different insulation methods, the setting conditions of different drainage structures are determined. Furthermore, the function relationship between the freezing depth of the lower surrounding rock of the tunnel arch and the air temperature inside the tunnel is established, and the curve of the on-site tunnel freezing depth change is predicted. This study provides valuable insights into the design and construction of drainage structures and insulation measures for high-altitude cold tunnels, ultimately contributing to the prevention of frost damage and ensuring safe and efficient tunnel operation.

Mechanical behavior of soft rock roadway reinforced with NPR cables: A physical model test and case study

Deep soft rock roadways are prone to large deformations and failure when reinforced with traditional rockbolts owing to the stiffness mismatch between soft rocks and rockbolts. Thus, a novel rockbolt named “negative Poisson’s ratio (NPR) bolt/cable” that maintains a constant support force during loading is used to reinforce deep soft rock roadways to prevent large deformations. In this study, a large-scale physical model test was conducted to reveal the mechanical performance of NPR cables in soft rocks and obtain the mechanical properties of reinforced rock masses. The test results show that the rock mass reinforced with the NPR cable underwent progressive failure and exhibited the characteristics of a constant-resistance yielding-pressure under external loading, suggesting that NPR cables operate well with soft rock masses. Moreover, on-site investigations confirmed that the effective control of NPR cable supports slow and large deformations of soft rock roadways. An analytical model was developed to verify the physical model test results. The study findings can serve as a reference for theoretical model studies and field applications of NPR cables to prevent large deformations.

Numerical Analysis and Experiments on Heavy Oil Heating of Shipwrecks

Analyze the change of oil temperature flow times during the heating process of wreck heavy oil and the temperature gradient change in the radiation area of the heating source. Using the result guide the heating process of low-temperature underwater oil recovery operations on the wreck. fluid software was used for the analysis process of the numerical simulation, and the physical model test is a simulation test of low temperature underwater electromagnetic heating of heavy oil. In this way, data related to the heating process of heavy oil can be obtained. from the numerical analysis results and the physical model test results, it can be concluded that the numerical simulation results are similar to the experimental verification results. The result can be used for engineering guidance. Due to the physical properties of heavy oil, the oil temperature decays faster during the heating process and the radiation effect of heat source is small, using the electromagnetic heater heats the heavy oil in the oil tank, and the heavy oil can be heated to meet the requirements of the pumping operation in a short time. The calculation model parameters are derived from actual operations. Numerical calculations and physical test results are of great significance to engineering guidance and can guide the underwater cryogenic oil pumping operation of shipwrecks.

Modelling hydro-mechanical coupled behaviour of unsaturated soil with two-phase two-point material point method

Material point method (MPM) offers an effective approach for analysing large-deformation problems, such as landslides that often involve unsaturated soil. Several MPM formulations for unsaturated soil have been reported in the literature, but they assumed that water retention ability and permeability function are independent of soil deformation. Furthermore, most studies used a single set of material points, so they cannot simulate some processes (e.g., the infiltration of free water into unsaturated soil). To address these problems, a two-point MPM formulation has been extended from saturated to unsaturated soils, considering the influence of porosity change on the water retention curve and permeability function. The information of solid and liquid phases is carried by two individual sets of material points, assuming zero air pressure. The elastoplastic mechanical behaviour is modelled by the Drucker-Prager model using Bishop’s stress. The MPM simulations were compared with the results of physical model tests (for large-deformation problems) and finite element analysis (for small-deformation problems). It is evident that the proposed MPM formulation is able to capture various hydro-mechanical problems well. In particular, the computed failure processes of unsaturated soil slope under rainfall are consistent with results from physical model tests.

Tunnel stability analysis of coral reef limestone stratum in ocean engineering

The islands and coasts in the South China Sea have developed coral reefs, which are the basis for the development of ocean resources and the construction of ocean engineering. However, the biogenetic coral reef limestone in the sea has the physical properties of much porosity, low strength and low density, which is obviously different from the traditional geological rock mass during the underground engineering construction. So in this paper, surrounding rock stability of coral reef limestone stratum in tunnel excavation is studied by physical model tests and numerical simulation. Firstly, according to the similarity theory, quartz sand, barite powder, high strength gypsum, calcareous sand and cement are selected to configure the similar materials of coral reef limestone by the orthogonal ratio test and physical mechanics test. Secondly, the triaxial geomechanical model tests of tunnel excavation in coral reef limestone stratum are carried out. The influence of tunnel shape, support method and rock strength on the tunnel stability is studied by analyzing the variation laws of displacement and stress of the surrounding rock. Finally, the numerical calculation of tunnel excavation in coral reef limestone stratum is conducted and the results of physical model tests are verified. The influence of tunnel depth on the surrounding rock stability is further studied. The results show that: (i) Compared with the horseshoe shaped tunnel, the displacement of the circular tunnel at the haunch and springer is significantly increased, and the stress concentration phenomenon occurs. (ii) The stress release rate and displacement of surrounding rock decrease significantly when the anchor support is added or the strength of reef limestone increases. (iii) The stress release rate and displacement of surrounding rock increase with the tunnel depth, so the support strength of surrounding rock should be increased.

Shear behaviour of infilled rock joints under different boundary conditions

The use of commercial software for the analysis and design of rock slopes, underground structures, mining projects, foundations of infrastructure projects, piles and so on is becoming more commonplace. However, such software sometimes has limitations and cannot be used directly for determining the strength and deformation behaviour of rock joints when they are subjected to external loads due to construction. Correct predictions of the strength and deformation behaviour of rock joints are important for safe, economical and sustainable design. The strength and deformation behaviour of unfilled and infilled rock joints were numerically studied using the commercial software Universal Distinct Element Code (Udec) under different boundary conditions (constant normal stiffness (CNS) and constant normal load (CNL)). The numerical results were compared with experimental results of physical model tests. The strength predicted by the numerical model was in close agreement with the experimental results at low initial normal stress and for CNL boundary conditions, as asperity degradation during the shearing process was almost same throughout the test. However, the numerical model did not correctly predict the shear strength of rock joints under CNS boundary conditions and at high normal stress under both CNL and CNS conditions because Udec does not consider the effect of asperity degradation during shearing. The Udec code was thus modified for applicability under both CNL and CNS boundary conditions and at high initial normal stress at CNL boundary conditions. Comparison of the predicted and experimental results indicated most predictions to lie in the 95% confidence band.

Performance of Subbase Layer with Geogrid Reinforcement and Zeolite-Waterglass Stabilization

Some laterite soil is an inferior material for engineering applications such as road and highway pavement, dam construction and filling material. Laterite soil stabilization is required to increase its strength for field application purposes. The potential use of zeolite and waterglass as stabilizing agents is their pozzolanic properties. This study aims to analyze the strength and bearing capacity of laterite soil stabilized by waterglass-activated zeolite and reinforced with geogrid. The soil sample was prepared with a zeolite percentage of 4, 8, 12, 16 and 20%, and waterglass as much as 2, 4 and 6% with curing times of 0, 7, 14 and 28 days. Furthermore, the physical model test was carried out in the container with the optimum composition obtained from the compressive strength (UCS) and California bearing test (CBR) test. The stabilized subbase layer with geogrid reinforcement was placed on a subgrade layer with a substandard CBR value. The results showed that the compressive strength (UCS) of stabilized soil with a curing time of 7 days was found significantly increased. The CBR value also increased with the content of additive and curing time compared to the untreated soil. The physical model test results showed that the performance of stabilized laterite soil with additives and reinforced by geogrid (ZW-geogrid) as a subbase layer provides more optimal performance in carrying the load compared to the sand-gravel mixtures material. Doi: 10.28991/CEJ-2022-08-02-05 Full Text: PDF

Study of the mechanism of water inrush in karst tunnel based on transparent rock mass physical model test

Water inrush is the main geological disaster occurred during karst tunnel excavation, which will cause huge economic losses and casualties. Therefore, it is important to investigate the water inrush mechanism of karst tunnel surrounding rock mass for preventing water inrush disasters in karst tunnel construction. Herein, Xinjie Tunnel of Kaili Ring Expressway in Guizhou Province is chosen as an object, where a large water-filled karst cave may locate on the upper right side of the tunnel cross section according to the geological survey report. Then taking the typical tunnel cross section as the prototype, a three-dimensional geomechanical model of Xinjie tunnel is made by using transparent rock mass material based on similarity theory, on which laboratory water inrush physical model tests are performed. Based on laboratory physical model test results, the mechanism of water inrush in karst tunnel is investigated, from which it indicates that the groundwater mainly flows through the fissures of the tunnel surrounding rock during water inrush process, and the water inflow rate mainly depends on the initial water pressure of the water-filled karst cave. When water pressure increases from 0.1MPa to 0.2MPa, the water inflow increases by 84.4%, but the increase rate of water inflow will slow down when water pressure further increases. Compared with the previous level of water pressure, the water inflow only increases by 7.2%. Hence, in the excavation of karst tunnel, it is necessary to seal the fractures by grouting timely and release the water pressure of the karst cave for preventing water inrush accident. The research results will provide important guiding significance for the excavation of karst tunnel.

Study on quantitative characterization method of measurement accuracy of geostress technology and equipment

In view of the shortcomings of existing research, the definition, quantitative characterization of all elements and its application of geostress measurement accuracy are studied. On the basis of the summary and classification of the measurement accuracy research in past decades, the definition of geostress measurement and its accuracy are given from the perspective of closed-loop measurement, different from the definition of taking rock mass as measurement object. The function and significance of the measurement accuracy research is also clearly pointed out. The quantitative characterization idea and procedure of geostress measurement accuracy are introduced. A physical model test device is provided, and the coordinate setting and the method of reducing the uncertainty of measurement accuracy representation by coordinate conversion are explained. 2D and 3D accuracy characterization formulas of all stress component which including single indexes of average-mode and maximum-mode are given first in the world, and the calculation method of angle error is discussed, the relationship between characterization modes and technical requirements is explained. Taking the measurement accuracy characterization of the physical model test results of early USBM borehole deformation gauge(USBM-type gauge) and CSIRO hollow inclusion strain cells(CSIRO HI cells) as example, the quantitative characterization process of measurement accuracy is shown, the characterization indexes are compared with the original ones, and the overall measurement error of the single index of the maximum-mode of the two test technology is 10% and 27%, respectively.Accuracy indexes of different dimension test methods are calculated and compared for the first time, and the data show that the overall measurement accuracy of the former is much better than the latter.

Kajian Hidrolika Aliran Bangunan Pelimpah Samping (Side Channel Spillway) Bendungan Beringin Sila Kabupaten Sumbawa

The construction of the Beringin Sila dam is a priority to provide irrigation water and meet raw water requirements in the Utan and Buer districts. To address this issue, the Beringin Sila Dam is one of the government's efforts to build equitable infrastructure to support national water and food safety. The hydraulic analysis of the physical design of the Beringin Sila dam is one of the planning rules for the dam. The goal of the analysis of the physical model of the Beringin Sila dam is to evaluate and propose the best alternative to improve the overall hydraulic performance based on initial planning. The hydraulic analysis of the physical model of the Beringin Sila dam was carried out with the initial planning of the series 0 using the standard stage method on the transition channel and the chute way. The physical model test results show that the design of the dam is safe to flow the Q100th and Q1000th discharge because the conditions of the transition channel are not crossflow, the chute way channel is supercritical and there is no capitation and vibration flow.

Physical Model Test of Artificial Freezing-Inclined Shaft

Based on the vertical straight artificial freezing engineering in Northern Shaanxi, a three-dimensional (3D) physical simulation test system was developed, consisting of six parts, which are simulation box, shaft model, loading system, freezing system, external environment simulation system, and data acquisition system. The physical model and actual test results show that the 3D physical simulation test system is reasonable and reliable. The test model results show that the distance from the freezing pipe significantly affects the freezing wall temperature. For the case of four adjacent, two adjacent tangential freezing, and two adjacent axial freezing pipes, the cooling rates were 1.37, 2.79, and 1.96°C/h, respectively. The field measurement showed that the proximity to the freezing pipe increases the cooling rates. The cooling rates of points 1k#, 2k#, and 3k# were 25.61, 25.32, and 25.35 mm/d, respectively. The increment rates of vertical and horizontal freezing pressures with temperature were 8.78 and 2.97 kPa/°C, respectively. Furthermore, the freezing pressure time fitting formula was given. The calculated results of temperature and freezing pressure are consistent with the measured results, indicating the reasonability and reliability of the 3D physical simulation test scheme of the artificial freezing-inclined shaft in this work.

Numerical simulations of the failure process of anaclinal slope physical model and control mechanism of negative Poisson’s ratio cable

Occurrence of toppling failure has been prominent due to the increasing of infrastructure construction, such as road slopes, dams, and hydroelectric stations. Many scholars have done research on the toppling failure characteristics, but paid less attention to the comparison of numerical simulations and physical models in order to propose reasonable and effective stability control methods. Based on previous tests on physical model and field investigations, a numerical model of an anaclinal slope using the three-dimension distinct element code (3DEC) software has been built to simulate the failure process of the physical model. Based on the prominent mechanical properties of the engineering-scale and model-scale negative Poisson’s ratio (NPR) cables, a numerical simulation model of the NPR cable has been developed. The numerical model has been used to simulate the effects of different types of model-scale cables on controlling the deformation of the anaclinal slope. The numerical results show that standard cables, i.e., Poisson’s ratio (PR) cables, cannot control the large deformations of the slope, and the slope finally fails. On the opposite, NPR cables can absorb the deformation energy and maintain the stable constant resistance force during the tensile process. This thereby allows avoiding tensile breakage of cables under the effect of large deformations of the slope and driving the slope towards a new equilibrium state. Through the comparison between the numerical simulation results and the physical model test results, the accuracy and rationality of the numerical simulations have been proven. The numerical model developed in this study can be used for future research works on the failure mechanism of anaclinal slopes and the control effect of NPR cables. It thereby lays a foundation for applying the NPR cables to control the toppling deformations of similar anaclinal slopes.

Dynamic ice force estimation on a conical structure by discrete element method

This paper aims to numerically estimate the dynamic ice load on a conical structure. The Discrete Element Method (DEM) is employed to model the level ice as the assembly of numerous spherical particles. To mimic the realistic fracture mechanism of ice, the parallel bonding method is introduced. Cases with four different ice drifting velocities are considered in time domain. For validation, the statistics of time-varying ice forces and their frequencies obtained by numerical simulations are extensively compared against the physical model-test results. Ice properties are directly adopted from the targeted experimental test set up. The additional parameters for DEM simulations are systematically determined by a numerical three-point bending test. The findings reveal that the numerical simulation estimates the dynamic ice force in a reasonably acceptable range and its results agree well with experimental data.

ROUGHNESS FACTOR FOR MULTI-LAYER ARMOUR AS OVERTOPPING ESTIMATOR

Nowadays one of the most challenging problem for engineers is to adapt existing coastal structures to climate changes. Wave overtopping is highly sensitive to the increasing extreme water depths due to higher storm surges coupled with sea level rise. One way to face these problems for rubble mound breakwaters is to add one or more layers to the existing armour. Prediction of wave overtopping of coastal structures is presently obtained from empirical formulae in EurOtop (2018). For the case of overtopping over multi-layer armour, no validated method exists, so prediction must be based upon assumptions and judgement, with related uncertainties. This study is focused on the effects of different types of armour, the number of layer and other structural characteristics on the roughness factor f. The main effects of porosity and roughness will be investigated. This paper analyzes the results of several new physical model tests of different rubble mound breakwaters reproduced at the new medium scale random wave flume of the Department of Engineering of Roma Tre University.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/8cOdqkqQ-9s

Experimental and Numerical Studies on Pull-out Behavior of Granular Anchor Pile Foundation Embedded in Sandy Soil

The granular anchor pile foundation (GAPF) is an improved foundation technique used to withstand compressive as well as tensile forces and effectively reduce the settlement of soil. In this paper, the behavior of a GAPF system was studied in sandy soil. Pull-out load tests were conducted on GAPF by varying different parameters viz. length of pile (250 mm, 350 mm and 450 mm), L/D ratio (7.5, 10 and 12.5) and group of piles (spacing 2D, 2.5D and 3D). The test results indicate that the pull-out capacity decreases with the increase in L/D ratio from 7.5 to 12.5. The group effect resulted in increased uplift load in comparison to that of a single GAP tested. Finite element analysis using PLAXIS 3D software had also been carried out to validate the results of physical model tests. On comparison of numerical and model study results, a reasonable agreement has been found.

Response of dual-row retaining pile walls under surcharge load

Deep foundation pits are usually located in densely built-up areas, and its stability is affected by adjacent structures. A few studies have considered the effect of surcharge load on the stability of foundation pits; such effect may lead to excessive deformation or even collapse. To determine the mechanical response of dual-row pile walls (DRPWs) in foundation pits under the action of surcharge loading, a physical scaling model test and numerical simulation were conducted, and a method to determine the influence of overloading was provided. Five physical scaling model test schemes were proposed; electronic displacement gauges, strain gauges, and pressure sensors were installed to test the static response of a DRPW under excavation and surcharge load. The effects of loading distance and load magnitude on the bending moment, pile head displacement, and pile shaft deformation of DRPWs were also investigated. The relationship between overload and the mechanical response of DRPWs was quantified, and the results of physical model tests were verified by numerical simulation. Results showed that surcharge loading has a negative effect on the stability of DRPWs in foundation pits, and the deformation of DRPWs is negatively correlated with the loading distance of surcharge load. The critical value of the loading distance of surcharge load is 0.5 times the excavation depth. When the loading distance is less than the critical value, the overload causes remarkable displacement and inner force of the DRPW. Moreover, the deformation of the DRPW is positively correlated with the surcharge loading magnitude. With the increase in vertical loading, the displacement of soil increases nonlinearly, and the circular sliding surface through the excavation bottom is finally formed. The results of this study provide some references for the design and construction of DRPWs.

Analysis of the Limit Support Pressure of a Shallow Shield Tunnel in Sandy Soil Considering the Influence of Seepage

The objective was to optimize the existing solution for the limit support pressure of a tunnel face. Firstly, based on the numerical simulation results, the existing three-dimensional analytical solution for pore water pressure distribution is expanded to a three-dimensional solution considering the pore water pressure distribution in the upper formation behind the tunnel face. Then, according to the results of physical model tests, a failure model considering the failure range in the upper formation behind the tunnel face is established, and the newly established three-dimensional solution for pore water pressure is introduced into the model, and then the limit effective support pressure of the tunnel face considering seepage is obtained by the method of soil–water joint calculation. Finally, the calculation results in this paper are compared with the experimental results, numerical simulation results and existing theoretical solutions. The major findings are as follows. The distribution of pore water pressure in the front and back strata above the tunnel face is basically symmetrical. The limit effective support pressure of the tunnel face will increase linearly with an increase in the hydraulic head difference between the tunnel face and the ground surface. The calculated results of the new limit equilibrium theory are obviously larger than those of the existing theory and numerical simulation and closer to the results of the physical model tests. Therefore, the new limit equilibrium model can better predict the limit effective support pressure of the tunnel face considering seepage and provide a reference for actual projects.