Laboratory Model Tests Research Articles

Laboratory Model Test for Heavy Metal-Contaminated Soil Remediation Using PVDs

Laboratory remediation experiments were carried out through the use of Prefabricated Vertical Drains (PVDs) to remediate soil contaminated with heavy metals. In the ground with lower permeability, the extraction of contaminants and the transmission of fluids are difficult; thus, to improve the injection or extraction of surfactants and to overcome difficulties due to micro pores in the soil, PVDs were used. For band-type drains, experiments comparing the effectiveness of filters coated with reactive material with the effectiveness of uncoated filters were conducted, and for cylindrical-type drains, experiments comparing the effects of the injection of surfactants were carried out. The heavy metal contaminants used in the experiments were Cu, Pb, and Cd, and concentrations over time were measured to assess the remedial efficiency. In the experiments, the initial concentrations were determined in consideration of the Korean Soil Contamination Warning Standards. The results from the experiments showed that the removal rates for Cd and Cu were 40% while that for Pb was 35% in the case of extraction alone. In the case of extraction with the application of reactants, the removal rates for Cu and Cd were 60% while that for Pb was 55%. In the case using both the reactant coating and cleansing agent injection, the removal rates were 74%, 65%, and 58% for Cd, Cu, and Pb, respectively.

사질토 지반에 설치된 조립식 지주옹벽(AER)의 안정성에 관한 실험적 연구

Assembled Earth Retaining wall (AER-wall is used here) using back pile (back supporting beam is used from here) has been developed at Pusan National University. Both cost and time have been significantly reduced because AER-wall can be fabricated in a shop. Also its stability has been improved with a back supporting beam reducing earth pressure. In this study, the test results were analyzed after laboratory model tests were performed. The lateral displacement of AER-wall significantly decreased with both inclined wall and back supporting beams. As a result, the stability of AER-wall and effect of back supporting beam have been analyzed and verified.

실내모형시험을 통한 상대밀도가 다양한 사질토 지반에서의 하수도관 파손에 따른 지표침하의 영향범위에 관한 연구

도심지 지반함몰 현상의 대부분이 노후된 하수관에 의해 발생한다는 것은 이미 잘 알려진 사실이다. 따라서 관 파손의 위치와 주변 지반의 상대밀도가 지반의 거동에 미치는 영향을 알아보기 위해 실내모형시험을 수행하였다. 관 파손은 관 둘레에 대해 20% 파손된 것으로 가정하여 관 상부에 파손이 발생한 경우와 하부에 발생한 경우로 고려하였다. 느슨한 지반과 조밀한 지반을 상대밀도 30%, 70%로 조성하여 관 파손의 위치에 따른 지반 거동을 측정하였을 뿐만 아니라, 유한요소해석을 이용하여 실내모형시험 결과와 비교 분석하였다. 관 하부가 파손되어 누수가 발생되는 것이 상부가 파손되는 것보다 더 큰 지반 거동을 유발하는 것으로 나타났을 뿐만 아니라, 느슨한 지반에서 더 큰 지표침하량이 발생하는 것을 알 수 있었다. It is well known that water leakage from decrepit sewer pipe mainly causes frequent occurrence of ground subsidence in urban area. Thus, laboratory model tests were carried out to investigate ground behaviour according to location of sewer fracture and various relative densities of surrounding soil. The portion of fractured pipe was assumed to be 20% compared to the circumference of pipe, and to be positioned at the top and bottom of the pipe. Ground conditions were made as loose sand (<TEX>$D_r=30%$</TEX>) and dense sand (<TEX>$D_r=70%$</TEX>). In addition, comparison and analysis with results of model tests were carried out by Finite Element analysis. As a result, not only water leakage from the bottom of pipe (scenario 2) caused greater ground behaviour than leakage from the top of pipe (scenario 1), but also much greater surface settlement occurred when the ground condition is loose.

Behavior of eccentrically inclined loaded footing resting on fiber reinforced soil

A total of 104 laboratory model tests on a square footing subjected to eccentrically inclined loads supported by sand reinforced with randomly distributed polypropylene fibers were conducted in order to compare the results with those obtained from unreinforced sand and with each other. For conducting the model tests, uniform sand was compacted in a test box at one particular relative density of compaction. The effect of percentage of reinforcement used, thickness of the reinforced layer, angle of inclination of load to vertical and eccentricity of load applied on various prominent factors such as ultimate load, vertical settlement, horizontal deformation and tilt were investigated. An improvement in ultimate load, vertical settlement, horizontal deformation and tilt of foundation was observed with an increase in the percentage of fibers used and thickness of reinforced sand layer under different inclinations and eccentricities of load. A statistical model using non-linear regression analysis based on present experimental data for predicting the vertical settlement (<TEX>$s_p$</TEX>), horizontal deformation (<TEX>$hd_p$</TEX>) and tilt (<TEX>$t_p$</TEX>) of square footing on reinforced sand at any load applied was done where the dependent variable was predicted settlement (<TEX>$s_p$</TEX>), horizontal deformation (<TEX>$hd_p$</TEX>) and tilt (<TEX>$t_p$</TEX>) respectively.

The volume of settlement trough change with depth caused by tunneling in sands

The Volume of the settlement trough is essential for estimating the settlement caused by tunneling. Generally, the volume of the settlement trough was recognized as a constant which was equal to the volume of the ground loss in the tunnel buried in clay. According to observation data from both laboratory and field tests, the volume of the settlement trough caused by tunneling in sands changed with depth, although the mechanism behind the volume change has not yet to be understood. In the present study, a largescale laboratory model test was conducted to investigate the volume change of the settlement trough with depth caused by tunneling in sands. The results show that the volume of the settlement trough decreased significantly with a decrease in depth. Based on the data from both literature and the current study, a modified model was proposed to estimate the settlement caused by tunneling in sands considering variation of the volume of settlement trough with depth.

Behavior of Geosynthetic Reinforced Soil Foundation Systems Supported on Stiff Clay Subgrade

A series of laboratory model tests was performed to investigate the behavior of geosynthetic reinforced stiff clay foundation systems under circular loading. The footing consisted of a rigid circular steel plate with a diameter of 150 mm. Five different series of tests were performed in both homogeneous (clay or sand) and layered configurations. The tests used planar geogrid and three-dimensional geocell reinforcements. Test results indicate that both types of reinforcements substantially improve the performance of the stiff clay foundation bed. A maximum threefold improvement was observed in bearing pressure, depending on the reinforcement type. However, geocell was found to be the most advantageous soil reinforcement technique, giving maximum performance improvement.

Behavior of polymer columns in soft clayey soil: A preliminary study

Deep soil mixing with cement and cement-lime mixtures has been widely used for decades to improve the strength of soils. In this study, small-scale laboratory model tests of polymer columns in soft clayey soil were conducted to evaluate the feasibility of using various polymeric compounds as binders in deep soil mixing. Floating and end bearing polymer columns were used to examine the load-settlement relationship of improved soft clayey soils for various area replacement ratios. The results indicate that polymer columns show good promise for use in deep mixing applications.

Bearing capacity of shallow strip foundation on geogrid-reinforced sand subjected to inclined load

Laboratory model test results for the ultimate bearing capacity of shallow strip foundation on multi-layered geogrid-reinforced dense and loose sand subjected to centric inclined load have been presented. The angle of friction for the dense sand and loose sand was 41 and 34 degrees, respectively. The tests have been conducted using biaxial geogrid layers as reinforcement with the embedment ratio (Df = depth of embedment of the foundation, B = width of foundation) varying as 0, 0.5, 1, and the load inclination (α) varying from 0 to 20° in 5° increments. The inclined load to the model foundation was applied by a specially designed machine. Based on the laboratory model test results, an empirical reduction factor has been developed to estimate the ultimate inclined load per unit area from the ultimate bearing capacity with vertical centric loading. The non-dimensional reduction factor is a function of Df, B, α, and df (df = distance between the ground surface and bottom geogrid layer).

Settlement Analysis of Saturated Tailings Dam Treated by CFG Pile Composite Foundation

Cement fly ash gravel (CFG) pile composite foundation is an effective and economic foundation treatment approach, which is significant to building foundation, subgrade construction, and so forth. The present paper aims at investigating the settlement behaviors of saturated tailings dam soft ground under CFG pile composite foundation treatment, in which FEM and laboratory model test were utilized. The proposed findings demonstrate that CFG pile treatment is effective in reinforcing saturated tailings dam and loading has little influence on settlement of soil between piles. The variation of soil between piles settlement in FEM has a good agreement with the laboratory model test. Additionally, the cushion deformation modulus has a small effect on the composite foundation settlement, although the cushion thickness will generate certain influence on the settlement distribution of the composite foundation.

Ground Improvement Using Granular Pile Anchor Foundation

The use of granular pile is one of the effective and efficient methods of ground improvement because of its ability in improving the bearing capacity and reducing the settlement of different soft soils. Conventional granular piles cannot be used as tension members to offer resistance under pull out loads. Granular Pile Anchor (GPA) is one of the recent ground improvement technique in devised for resisting pull out forces. In a granular pile anchor, the footing is anchored to a mild steel plate placed at the bottom of the granular pile through a reinforcing rod or a cable.The main objective of the present study is to investigate the effect of relative density of fill material, granular pile diameter on the pull capacity of the granular pile anchor and the comparison of encased and non-encased granular pile has been done. The laboratory model tests using GPAF system revealed that the pull-out capacity of the granular pile anchor increased with increasing relative density of the granular material. There was a maximum percentage increase of 35% in the ultimate load when the relative density was increased from 50 to 70% for 50mm diameter pile. It was also revealed that the pull-out capacity of the granular pile anchor increased with increasing diameter of the granular pile anchor. The increase of 35% was also obtained when the diameter was increased from 30mm to 50mm at a relative density of 70%. For the encased pile, maximum increase in the percentage ultimate pullout load was obtained for pile diameter of 30mm and it was about of 13.2%.

Physical Modeling of Supersonic Flow Over Bodies with Plane and Axisymmetric Shape

One of the major stages in methods development of internal ballistic performance calculation for propulsion (thrust, density impulse, the fuel burning rate, pressure-chamber, etc.) is a simulation of the structure and definition of the gas encircling flow parameters. During the operation of the engine by supersonic flowing, the verification of the developed mathematical models on the basis of a comparison with experimental data is required due to the complexity of the intra-chamber processes and changes in performance duct tract geometry. Field tests of the engines are conducted to obtain the necessary data on the main parameters of the process, but it is due to the high material costs. A comparative analysis of numerical and experimental data obtained by laboratory model tests is the most efficient way to obtain objective experimental data. This paper presents the results of an experimental study of one of the main parameters of supersonic air stream over bodies with plane and axisymmetric shape in the range of Mach number M=(2÷5).

Response of laterally loaded pile in soft clay on sloping ground

This paper presents the results of static lateral-load test carried out on a single aluminium model pile embedded in soft clay (consistency index, Ic = 0.42) on a sloping ground. A series of laboratory model tests had been carried out on the instrumented aluminium pile with outer diameter of 25.46 mm on a sloping ground of varying slopes (1V:1H, 1V:1.5H, 1V:2H, 1V:3H and 1V:5H) and with varying embedment length-to-diameter ratio (L/D) of 20, 25 and 30. To quantify the effect of slopes, the tests were also carried out on a horizontal ground surface. From the experimental results, the lateral load-carrying capacity of the pile, load–deflection response of the pile at pile head, effect of slopes and embedment length on pile capacity and bending-moment profile along the pile shaft were studied. The experimental results have been compared with those obtained from finite element analysis PLAXIS 3D and found to be in good agreement.

Stress Analysis of CFG Pile Composite Foundation in Consolidating Saturated Mine Tailings Dam

Cement fly-ash gravel (CFG) pile is a widely used ground reinforcement technique. This paper aims to address the mechanical characteristics of CFG composite foundation in consolidating saturated mine tailings (MTs) dam. The field static load tests were employed to explore the bearing capacity of the CFG composite foundation, and finite element (FE) models in three dimensions validated through comparison with experimental results were used to discuss the pile-soil stress distribution and pile-soil stress ratio of the CFG composite foundation. The results indicate that the distribution of earth pressure and pile stress is relatively homogeneous and stable over depth and load, while the development of CFG composite foundation bearing capacity is insufficient, in which the developed bearing capacity of CFG piles is less than 50% of its characteristic value. Additionally, compared with the laboratory model test results, the pile-soil stress ratio decreases with the increasing of the load in FEM results proved to better conform to the actual engineering conditions. Furthermore, the deformation modulus and thickness of cushion exert significant influence on pile-soil stress ratio and integral bearing capacity of CFG composite foundation.

Ultimate bearing capacity of rectangular foundation on geogrid-reinforced sand under eccentric load

Laboratory model test results for the ultimate bearing capacity of rectangular surface foundations supported by multi-layered geogrid reinforcement and subjected to eccentric loading have been presented. Based on the model test results a reduction factor has been developed, which is a function of width-to-length ratio (B/L), eccentricity ratio (e/B), and reinforcement depth ratio (d/B) of the foundation. The reduction factor can be used to estimate the ultimate bearing capacity of an eccentrically loaded foundation from the ultimate bearing capacity of a vertically loaded foundation.

쇄석다짐말뚝 주변지반의 지반정수산정을 위한 민감도 분석

연약지반 개량목적으로 쇄석다짐말뚝에 대한 연구는 많이 진행되어 왔다. 하지만 이러한 연구들은 수치해석 및 실내모형실험을 토대로 도출해 낸 결과이며, 연성말뚝(기초의 강성이 작아 유연한 기초)의 벌징파괴에 대해 효율적으로 적용할 수 있는 방안에 대한 연구는 없는 실정이다. 이 연구는 SPT 시험의 N치로 추정된 지반물성치의 변화에 따른 쇄석다짐말뚝의 등단면 및 변단면의 하중-침하량 관계에 대한 민감도를 분석하였다. 정재하시험의 하중-침하량 결과에 기초하여 수치해석 시 지반에 대한 지반 물성치를 추정하였다. N치가 3이하인 매우 연약한 점토층의 탄성계수는 700~2000kPa, 푸아송비는 0.40~0.48의 값이 합리적인 것으로 판단되었다. The GCP (Granular Compaction Pile) for the improvement objective of soft ground has been frequently studied. However, these studies were the results deduced on the basis of the numerical analysis and the laboratory model tests, and there was no study method to apply the effects of the bulging failure of a flexible pile. In this study, the sensitivity of the load-settlement curves of the uniform and the tapered GCP dependant on the geotechnical parameters estimated from N value of standard penetration test (SPT) was analyzed. It was estimated reasonably that, in the very soft clay soil (N=3 or less), elastic modulus was 700~2000 kPa and Poisson's ratio was 0.40~0.48.

Experimental investigation of lateral displacement of PVD-improved deposit

Laboratory model tests were conducted to investigate the effect of surcharge loading rate on the magnitude of lateral displacement of prefabricated vertical drains (PVDs) improved deposit. The test results indicate that under the condition that the system had sufficient factor of safety (FS) (<TEX>$FS{\geq}1.2$</TEX>), for the similar model ground under the same total applied surcharge load, the lateral displacement increases with the increase of loading rate. The test results have been used to check the validity of a previously proposed method for predicting the maximum lateral displacement, and it shows that the data points are around the middle line of the predicted range, which supports the usefulness of the proposed method. The basic idea of the prediction method is an empirical relationship between the normalized lateral displacement (NLD) and a ration of load to the undrained shear strength of the deposit (RLS). The model test results offer some modifications of the NLD-RLS relationship: (1) instead of a bilinear relationship, NLD-RLS relationship may be entirely nonlinear; (2) the upper bound value of RLS for the proposed method can be used may be limited to 2.1 instead of the originally proposed value of 3.0.

Experimental Study on Contact Erosion Failure in Pavement Embankment with Dispersive Clay

AbstractSoft subgrades are not strong enough to provide the required degree of compaction for a pavement embankment’s foundation. Therefore, it is required to treat the subgrade soil or construct a working platform on top of the soft subgrade to ensure proper compaction of the subsequent layers. The constriction sizes of the granular materials used for a working platform are comparatively higher to restrict the erosion of overlying embankment materials. This condition would lead to severe material loss in the embankment layer in cases where the embankment is constructed with dispersive soil, which becomes structurally unstable in wet conditions and appears to disperse in water. This paper investigates the contact erosion failure at the foundation of a pavement embankment constructed with dispersive soil as a result of groundwater fluctuation. Experimental studies were conducted on a laboratory model test apparatus designed to simulate the conditions in the pavement embankment’s foundation. The experimenta...

Three-dimensional slope stability problem with a surcharge load

Abstract. A semi-analytical solution for the three-dimensional stability analysis of the ultimate uniform patched load on top of a slope is developed by the limit analysis using kinematically admissible failure mechanisms. The failure mechanism which is assumed in the analytical solution is verified by three-dimensional strength reduction analyses and laboratory model test. Furthermore, the proposed method and the results are further compared with some published results for illustrating the applicability of the proposed failure mechanism.

Model tests on methods to improve dewatering efficiency for sludge-inflated geotextile tubes

ABSTRACT: Geotextile tubes made of woven geotextile materials have been widely applied to dewater waste sludge such as digested bio-solids, sewage sludge, dredged materials, industrial solid wastes, fly ash and coal slurry. However, the dewatering process of single geotextile tubes is time consuming. Two methods to accelerate the dewatering process of slurry in geosynthetic tubes were studied using laboratory model tests. The first method was to stack one tube on top of another and use the weight of the top tube to preload the bottom one. The second method was the vacuum method proposed in this paper to use vacuum pressure to consolidate the slurry in the geosynthetic tube. A 2.0-mm-thick woven polypropylene geosynthetic sheet was selected for the geotextile tubes. The deformation, pore water pressure and tensile forces monitored during the model tests against time are presented and analysed in this paper. The properties of the soil after consolidation were also measured and compared. The model test data showed that the vacuum method resulted in a lower water content and higher deformation rate than the two-layer stacking geotextile tube method. Compared with the stacking method, the vacuum method could reduce the risk to the geotextile sheet from explosion.

Experimental investigation of joint filling materials performance on preventing seepage in lined open concrete canal (laboratory and field model)

Seepage is one of the most serious problems of water loss in the irrigation canals. In Iraq, most projects of concrete lining irrigation canals suffer from seepage losses phenomena through joints. The loss of water due to seepage from irrigation canals constitutes a substantial part of the usable water. The aim of this study is to reduce or prevent the seepage by using new alternative joints filling materials. The methodology in this study follows two main categories for calculating and studying the seepage and efficiency of some alternative materials, hoping to apply a new filling joint material, and assessing their performance to prevent seepage. The first category was done by constructing a trapezoidal concrete canal model. The joints filling materials used in this research were : cement-sand mortar, cement-sand mortar with Styrene Butadiene Rubber (SBR), cement-sand with Krystol Internal Membrane (KIM), and Setseal B (liquid polymer with powder). The average percentage of seepage losses was reduced to about 11.3, 29, and 89% when using cement-sand mortar and SBR, cement-sand mortar and KIM, and Setseal B respectively, as joints filling material instead of cement-sand mortar (the initial filling material). While when using Setseal B as a coating material for 9 months duration give no seepage (zero seepage). The second category was carried out by field study, which was done on a branch of irrigation concrete Setseal B as a coating layer was applied on the existing cement-sand joints of the canal (based on the results of the laboratory model tests). It has been tested for 3 weeks. The average reduction percentage in water losses was about 62.5%, by comparing it with using cement-sand mortar only as joints filling material.