Model Test Device Research Articles

Development of a trench cutting re-mixing deep wall method model test device

The trench cutting re-mixing deep wall (TRD) is a new type of underground waterproof curtain. Mixing uniformity is the key index affecting the efficiency and quality of this method. However, because of many influencing factors, existing theories cannot be used to express the relationship between various factors and mixing uniformity. By analyzing the cutting and mixing process of the TRD method, the main factors affecting the uniformity of the mixing were obtained. A model test device was designed and manufactured, based on Buckingham’s pi theorem. The validity of the model test device was verified through a comparative analysis of model and field test results. The model test device was demonstrated to be able to simulate the mixing process of the TRD method. The results provide guidance for promotion and better application of the TRD method.

Design and application of multifunctional physical model test device for movement and accumulation process of rapid long-runout landslide

There are many factors affecting the movement and accumulation process of rapid long-runout landslide. During the developing the physical model test device, it is necessary to meet the needs of multi-factors, so as to achieve multi-functional purposes. The device is 3.40 m long, 0.56 m wide and 1.35 m high in initial state (vertical angle=20° and horizontal angle=0°). The design includes three modules: volume adjustment of slide body, slope adjustment of upper slide groove and horizontal angle adjustment of horizontal slide groove. Two kinds of materials, 3 mm thick stainless steel plate and 8 mm thick tempered glass, are used as the processing raw materials, leading to good durability. Moreover, the universal wheel is installed in the form of component assembly to facilitate the handling of the experimental instrument. Based on sand and pebble granular materials, the physical model tests with respect to the movement and accumulation process of rapid long-runout landslide are preliminarily carried out by using the developed device. The effects of slope, horizontal angle, height of sliding body and base material on sliding distance are briefly analyzed.

Development of a lever type multi-functional plane strain model test device

The lever type multifunctional plane strain model test equipment is mainly composed of the basic frame, loading system, data acquisition and measurement system, and auxiliary device. Its biggest feature is the “multiple use of one machine”, which means a variety of geomechanical tests can be carried out with one equipment. The load is carried out by the principle of double lever amplification. The load can be altered by changing the counterweight at the end of the rod. Since the counterweight is determined, the load is constant. Equipped with an automatic device integrating mining, chip removal, support and monitoring, it can realize quantitative mining, timely chip removal, temporary support, real-time monitoring, improve automation and intelligence of model test, which is closer to the simulated engineering practice. The equipment has excellent mechanical properties and can meet the needs of different geotechnical engineering research.

Experimental Study of Pile Installation and Cyclic Behaviour in Yellow River Silt

The pile foundation is often affected by friction fatigue during pile installation and cyclic loading. In order to study the fatigue behavior of it, the installation and cyclic experiments were carried out using pile foundation model test device. The effects of cycle numbers, cumulative displacement on the pile load performance were studied in the experiments. The results show that the friction fatigue appears with different degrees on pile installation and cyclic process. During installation from soil surface, the soil plug increases and eventually remains constant, and the pile head load increases with the increase of penetration displacement, while the horizontal stress on pile shaft decreased with the increase of h/R because of lower relative displacement. In the cyclic load stage, pile head load and base resistance stresses decrease rapidly in the 5 cycles and gradually restore to 68% and 112% respectively, while the horizontal stress reduces to stable in cyclic load and the fatigue behavior is more significant with lower value of h/R due to the higher degree of soil particle breakage.

Performing captive model tests with a hexapod

In this study, a hexapod, six-degree of freedom (DOF) platform has been implemented to perform the captive model tests. With this novel device, a physical ship model can be forced to produce independent or coordinated motions in six-DOF that cannot be accomplished by a traditional one. This paper starts with the demonstration of the principle of the novel captive model test device. The motion relations between the driving legs of the testing platform and the physical ship model have been derived, based on which the mathematical model of hydrodynamic force has been established. Next, the testing procedures have been given by performing hydrodynamic coefficients tests of a rectangular frame and two ship models using the novel test device. Finally, the test results are compared with the theoretical values to verify the reliability of the device. The test device proposed in this paper provides a novel alternative to the traditional captive model test devices. It can identify the complex hydrodynamic coefficients of the mathematical model simultaneously in a single device, which is of great significance for the efficient prediction of hydrodynamics performance of given ships and offshore structures.

Centrifugal model tests on face failure of earth pressure balance shield induced by steady state seepage in saturated sandy silt ground

When tunnelling in a stratum with a high level of water (e.g., tunnelling below the river) by earth pressure balance shield, seepage due to the difference of hydraulic head between the ground and the shield’s chamber can result in the failure of tunnel face. In order to investigate the failure of the tunnel face induced by the steady state seepage, a centrifuge model test device was developed and a series of the centrifugal model tests was performed. With the increase of the horizontal displacement of the tunnel face, it is found that the effective support pressure firstly decreases steeply to the limit effective support pressure and then increases gradually to a steady value. It is also found that the limit effective support pressure approximately increases linearly with the increase of the difference of hydraulic head between the ground and the chamber. Two available theoretical methods were compared with the measurement. In the limit state, a wedge-prism failure mechanism occurs in front of the tunnel face, and the failure zone has expanded to the ground surface. On the condition of a steady-state seepage, the pore pressure in the limit state μlim gradually increases from the tunnel face to the far ground. The results of this paper may help to guarantee the face stability of the shield tunnels in a stratum with a high water level.

Experiment and numerical simulation on seepage failure of sand caused by leakage of underground water pipe

Underground water pipe leakage accident is a serious threat to the city road and people's life safety, the internal mechanism is necessary to carry out related study. In this paper, numerical simulation technology and model test device was used for researching on the effect of different factors on the seepage failure of sand. The research shows that the evolutionary process of sand seepage failure induced by underground water pipe leakage can be divided into three stages: unfluidized stage stable cavity stage and fluidized stage. At the initial stage, the pressure distribution at different height reaches a peak with the increment of water pressure and flow rate. When the water pressure and flow rate is beyond the peak, cavity would occur at leakage hole. Under the action of seepage force, the cavity would dissipate at the surface of soil, and the distribution of fluidized bed pressure would maintain a stable state. Moreover, the smaller the leakage diameter, the greater the critical water pressure is. In a numerical test of a wedge angle of 62 degrees, F (upward drag force) is equal to the W (weight of wedge), which indicates the cavity reaches a force balance. The wedge with an angle of 62 degrees is significant to the sample model used in numerical simulation.

Numerical calculation model investigation on response for connector assembly of a free-standing hybrid riser with experimental validation

In order to provide efficient and reliable method for structural design and optimization of upper assembly and lower assembly of a free standing hybrid riser, a numerical calculation model and model test device for the upper assembly and lower assembly of a free-standing hybrid riser were established independently based on similarity criterion and correlative elastic-plastic mechanics theories and methods. The static and dynamic numerical calculations and corresponding tests for the upper assembly and lower assembly of a free-standing hybrid riser were carried out. The results show that the deviation between numerical simulation results and experimental results is less than 6.83%, and the dynamic test results coincide with the dynamic results of numerical simulation. The results of the above study demonstrate that the accuracy and reliability of numerical results for static and dynamic responses of the upper assembly and lower assembly and suggestions on further optimization for upper assembly and lower assembly of a free standing hybrid riser are given based on numerical simulation and test results. These results provide guidance for structural optimization of the upper assembly and lower assembly of a free-standing hybrid riser.

Study on Active Earth Pressure of Sheet Pile Model Test on Foundation Pit Engineering

In recent years, building density in the city is increasing as the promoting of urban modernization. Deep foundation pit excavation and bracing is a topic in geotechnical engineering, including strength and stabilization of soil mechanics, and transmutation and sedimentation of deep foundation, and common effect between soil and shoring structure. The paper based on the design and fabrication of indoor model test device. This paper respectively explored the destroy mechanism of cantilever and anchored sheet pile support structure on the soil pressure under the different loads, and comprehensively carried through cantilever and anchored sheet pile support test under four-grades excavation depth and four-grades load combination, and specially researched the transformation of soil pressure. At the same time, the piles spacing changed among 3cm, 4cm and 5cm. Theoretical results showed that the active earth pressure increased with the increase of load and excavation depth. Model test results showed that the earth pressure behind the piles increased with the increase of excavation depth and the load. The biggest earth pressure was 19.38kPa when loading 40kPa. The changing curves of soil pressure were similar when piles spacing was 3cm and 4cm. Earth pressure after the piles was negative when piles spacing exceeded 4cm, which illustrated that active earth pressure had changed into passive soil pressure.

In contact observation of model synovial fluid lubricating mechanisms

This paper examines the fundamental mechanisms of synovial fluid lubrication in artificial joints. Film thickness measurements were made for bovine serum solutions in a model test device. In contact imaging was also carried out to aid interpretation of these results. The results indicated that two types of film are formed; a boundary layer of adsorbed protein molecules, which are augmented by a high-viscosity fluid film generated by hydrodynamic effects. The high-viscosity film is due to inlet aggregation of protein molecules forming a gel which is entrained into the contact preferentially at low speeds. As the speed increases this gel appears to shear thin, giving much lower lubricant film thickness. Results suggest that protein-containing fluids do not obey classical Newtonian EHL models.

Use of Vacuum for the Stabilization of Dry Sand Slopes

Vacuum is proposed as a means for rescuing soil slopes showing signs of impending failure. Two aspects associated with the proposed method were studied; namely, the theory of airflow through dry soils and the effectiveness of vacuum for enhancing the stability of soil slopes. A model test device was developed, and two series of tests were carried out using this device. One was a series of tests on pore-air pressure distributions in dry sand slopes, and the second series involved dry sand slope stability tests. The results revealed that a vacuum (negative pore-air pressure) even as small as −0.4 kPa significantly increased the stability of the model slopes with dimensions of 0.9×0.5×0.28 m (length×width×height). The pore-air pressure distributions in the model slopes were simulated using a finite-element partial differential equation solver, FlexPDE. Fick’s law and mass conservation were used to formulate the airflow through dry soils. Good agreement was achieved between the experiment results and the numerical simulations. A computer routine, called Slope-Air, was developed for slope stability analysis using Bishop’s simplified method and considering the pore-air pressure distributions in the slope. The calculated factors of safety of the model slopes at failure were consistent with the results of the model slope stability tests.

Experiment Study of the Uplift Mechanism of Disk Piles

Based on the analysis of the uplift mechanism theory of the disk piles, a model test device was designed to study the uplift bearing capacity and deformation behavior of the disk piles and to compare with the equivalent diameter piles. Uplift loading tests were carried out on the equivalent diameter pile, the single-disk pile and the double- disk pile respectively. Through the test, it was proved that the uplift bearing capacity of the disk piles was much better than the equivalent diameter pile. The bearing capacity of the single-disk piles was better than the double-disk piles in the test. This was mainly related to the embedded depth of the upper disk was not enough and the specific failure mode. So, a reasonable design was necessary.

Effect of vacuum degree and aeration rate on sludge dewatering behavior with the aeration-vacuum method

Due to large-scale dredging operations, a large amount of sludge is inevitably produced. Large areas of land are occupied when the dredged sludge is discarded in the disposal site as waste material. The sludge dewatering with aeration-vacuum (SDAV) method is suit for treating the sludge with high water content and high clay content in the disposal site. The water in the sludge can be discharged out. The volume of the sludge can be reduced quickly, and the recycling of the land can be accelerated by this method. Most importantly, this technique is an efficient way to deal with clogging problems when pumping water from high water content, high clay content dredged sludge. Vacuum degree range tests, the aeration rate range tests, and the influencing factors of sludge dewatering behavior tests were conducted with a self-developed SDAV model test device. Sludge samples were taken from the South-to-North Water Diversion East Line Project in Huai’an White-Horse Lake disposal site, Jiangsu Province, China. The optimal range of vacuum degree and aeration rate were obtained through the test results, and the mechanisms for how the two factors work and how they affect the sludge dewatering behavior were analyzed. The suitable vacuum degree range in SDAV is below 50 kPa, and the suitable aeration rate is about 1.0 m3/h. The low-vacuum degree contributes to reduce the adsorption effect of micro-channels on soil particles in filter material and to maintain the arch structures. Aeration has the effects of expansion, disturbance, changing Reynolds number, and dynamic sieve separating. The pump quantity of water per meter of filter tube (Δm) has different change rules as the vacuum degree changes under different aeration rates. The reason is that the formed arch structures’ conformation and permeability differ greatly under different combined-conditions of vacuum degree and aeration rate. The optimal combined-condition for dewatering the sludge is 35 kPa with 1.0 m3/h.