Behaviour of a square model footing on loose sand reinforced with braided coir rope

The effectiveness of horizontally placed braided coir rope reinforcement on the strength improvement and settlement reduction of loose sand is investigated for modeling footings using plate load tests in the laboratory. The influence of parameters such as depth of reinforcement embedment, length, number of layers and number of plies of braided coir rope was examined. The model test results indicate that up to about a six-fold improvement in strength and about ninety percent reduction in settlement (vertical displacement) can be achieved through the use of the proposed reinforcing method. The optimum value of embedment depth of a single layer of braided coir rope reinforcement was identified as 0.4 times the footing width. It was also found that optimal benefit was realized for a length ratio equal to about 3 and by reinforcing the zone of soil directly beneath the model footing upto a depth equal to about 0.6 times the width of footing. Increase in the number of layers within the significant depth leads to a proportionate increase in strength improvement ratio, while the optimal settlement reduction is realized with three layers of braided coir rope reinforcement. Regression analysis carried out with limited experimental data suggests the possibility of developing a predictive model to quantify the strength improvement.     

Effect of geotextile reinforcement on the mechanical behavior of sand

Laboratory triaxial compression tests were carried out in order to determine the stress–strain and dilation characteristics of geotextile-reinforced dry beach sand. The mechanical behavior of the composite material was investigated through varying the number of geotextile layers, type of geotextile, confining pressure, and geotextile arrangement. In order to study the effect of sample-size on the results, tests were performed on samples with two different diameters. The results demonstrated that geotextile inclusion increases the peak strength, axial strain at failure, and ductility. However, it reduces dilation. Such improvements in the behavior of reinforced sand are more pronounced for small-size samples. Failure envelopes for reinforced sand were observed as bilinear or curved. Bulging between layers was detected in reinforced samples which failed.     

Strip footing on geocell reinforced sand beds with additional planar reinforcement

The results from laboratory model tests on strip footings supported by geocell reinforced sand beds with additional planar reinforcement are presented. The test results show that a layer of planar geogrid placed at the base of the geocell mattress further enhances the performance of the footing in terms of the load-carrying capacity and the stability against rotation. The beneficial effect of this planar reinforcement layer becomes negligible at large heights of geocell mattress.     

Behaviour of model footing on bamboo mat-reinforced sand beds

Soil reinforcement is one of the most common and cost-effective methods among ground-improvement techniques. Recently, sustainable and natural materials for soil reinforcement have attracted the attention of soil engineers. Bamboo is considered to be one of the most effective materials for soil reinforcement due to it’s excellent mechanical and engineering properties. This paper discusses the results of laboratory model studies conducted on sand beds reinforced with traditionally woven bamboo mats. An improvement in the bearing capacity of about 2.5 times was seen when the reinforcement was placed at the optimum depth. The effective spacing of the reinforcement between two layers of bamboo mats was found to be equal to the optimum depth value, i.e., 0.3B. An improvement in the bearing capacity of about seven times was observed when four layers of reinforcement were placed at a spacing of 0.3B. The results obtained from the present study reveal the excellent capacity of bamboo mat for soil reinforcement.     

Seismic behaviour of reinforced embankments in dynamic centrifuge model tests

A series of dynamic centrifuge model tests was conducted to investigate the effects of reinforcement on the seismic behaviour of hillside embankments consisting of sandy soils and resting on stiff base slopes. In total, three types of seismic reinforcements, namely, large-scale gabions, drainage-reinforcing piles, and ground anchors with pressure plates, were employed in the tests. The test results showed that: (1) the seismic performance of both lower and higher embankments was remarkably improved by installing large-scale gabions at the toe as they restrained the completion of the formation of sliding planes; (2) the installation of drainage-reinforcing piles at the embankment toe was rather effective in reducing the overall earthquake-induced deformation due to their high permeability and restraint effect against sliding displacement at the reinforced region; and (3) the embankments improved by ground anchors with pressure plates were not vulnerable to earthquake-induced damage due to their constraint effects even under high water table conditions. The improvement effects by the above-mentioned three types of reinforcements were presented by evaluating the global safety factors based on the results of a series of triaxial compression tests.     

Effect of reinforcement form on the bearing capacity of square footings on sand

This paper presents the results of laboratory model loading tests and numerical studies carried out on square footings supported on geosynthetic reinforced sand beds. The relative performance of different forms of geosynthetic reinforcement (i.e. geocell, planar layers and randomly distributed mesh elements) in foundation beds is compared; using same quantity of reinforcement in each test. A biaxial geogrid and a geonet are used for reinforcing the sand beds. Geonet is used in two forms of reinforcement, viz. planar layers and geocell, while the biaxial geogrid was used in three forms of reinforcement, viz. planar layers, geocell and randomly distributed mesh elements. Laboratory load tests on unreinforced and reinforced footings are simulated in a numerical model and the results are analyzed to understand the distribution of displacements and stresses below the footing better. Both the experimental and numerical studies demonstrated that the geocell is the most advantageous form of soil reinforcement technique of those investigated, provided there is no rupture of the material during loading. Geogrid used in the form of randomly distributed mesh elements is found to be inferior to the other two forms. Some significant observations on the difference in reinforcement mechanism for different forms of reinforcement are presented in this paper.     

Shear behaviour of methane hydrate bearing sand with various particle characteristics and fines

It is recognized that methane hydrate (hereafter referred to as MH) is trapped in the sand sediments of alternating sand and mud layers in the turbidite of the Nankai Trough, Japan. The existence of fines within the marine sediment significantly affects its mechanical and physical properties. A series of plane strain compression tests at high pressures were performed in order to investigate the effect of the particle characteristics and fines content of the host sands on the shear behaviour of MH bearing sands. MH bearing sands were artificially produced using rounded glass beads and three other silica sands with different fines contents. A high-pressure low-temperature testing apparatus was equipped with a camera to observe deformation of the specimens during shearing and particle image velocimetry analysis was conducted on pictures taken during the experiments. The experimental results show that strength enhancement due to the bonding effect in MH bearing sand increases with the level of fines content. Values for both the cohesion and friction angle of MH bearing sand composed of Toyoura sand increased along with increasing MH saturation. However, in the case of MH bearing glass beads, only the value for cohesion increased when MH was formed. The maximum shear strain of MH bearing glass beads was mostly concentrated near the shear band. While the maximum shear strains of the three other MH bearing sands were concentrated within the shear band, some was widely distributed in the region outside of the shear band. A rise in the degree of MH saturation increased the angle and narrowed the width of the shear band, regardless of the fines content.     

探讨土工格栅加筋砂土加固机理

以路基浅层处理为研究对象,通过室内模型试验对土工格栅加筋体的局部应力—应变分布以及剪切破坏状况进行了研究,并得出科学结论,从而对加筋砂土的变形破坏以及补强材料的加固机理有了更加全面深入的认识。     

加筋土坡的可能滑移模式和基于库仑理论的稳定分析方法

加筋土坡因其填方量少、工期短、经济安全等优势在国内外已得到广泛应用,故其稳定性分析也显得尤为重要。目前,已有多位学者将极限分析上 限定理运用于加筋土坡的稳定性分析中,并假定水平条块速度间断面。然而在其分析过程中,构造的速度场并不符合位移协调条件。提出了由于筋材的隔断 作用形成的斜向界面破坏模式,并计算相应速度场式,分别提出主动、库仑、被动三种滑移模式。通过计算比较发现,在加筋间距较密时,库仑模式总是相 应安全系数最小的控制工况。实际工作中,可以只使用这一概念清晰、计算简便的方法分析加筋土坡的稳定性。为方便工程设计快速获取安全系数或筋材间 距,将土坡各参数进行无量纲化,绘制了安全系数图,并与Michalowski设计图表进行对比,验证了该算法的有效性。且针对多个实际工程算例进行验算, 验证了库仑模式上限法的可行性。     

Two dimensional experimental study for the behaviour of surface footings on unreinforced and reinforced sand beds overlying soft pockets

This paper presents results of a comprehensive investigation undertaken to quantify the efficiency of using reinforcement layers in order to enhance the bearing capacity of soils that are characterised by the existence of localised soft pockets. Small-scale model experiments using two dimensional tank were conducted with beds created from well graded sand with mean particle size of 300 μm but prepared with different dry densities. A relatively softer material was embedded at predetermined locations within the sand beds so as to represent localised soft pockets. Various arrangements of soil reinforcement were tested and compared against comparable tests but without reinforcement. In total 42 tests were carried out in order to study the effect of the width and depth of the soft pocket, the depth of one reinforcing layer and the length and number of reinforcing layers on the soil bearing capacity. The results show clearly that the ultimate bearing capacity reduces by up to 70% due to the presence of a soft pocket. It was also noted that the proximity of the soft pocket also influenced the bearing capacity. Reinforcing the soil with a single layer or increasing the length of reinforcement is not as effective as was anticipated based on previous studies. However, bearing capacity increased significantly (up to 4 times) to that of unreinforced sand when four layers of reinforcement were embedded. The results suggest that rupture of the bottom reinforcement layer is imminent in heavily reinforced sand beds overlying soft pockets and therefore its tensile strength is critical for successful reinforcement.     

Influence of anisotropic stress states on the thermal volume change of unsaturated silt

This study is focused on understanding the influence of anisotropic stress states on the thermal volume change of unsaturated, compacted silt specimens. A thermo-hydro-mechanical true-triaxial cell was used that permits control of the temperature on all six boundaries of a cubical soil specimen as well as control of the suction within the specimen to provide drained conditions during mechanical loading and temperature changes. Six non-isothermal tests were performed as part of this study, each involving suction application, consolidation to a given isotropic or anisotropic stress state, heating and cooling in stages under drained conditions, and unloading. Specifically, tests having minor to major principal stress ratios of 1.0, 0.7, and 0.5 were performed on specimens having initial degrees of saturation of 0.7 and 0.8, complementing tests on the same soil under similar stress states but saturated conditions published in a previous study. Although compressive thermal axial strains were measured in both the major and minor stress directions, a greater thermal axial strain was observed in the direction of the major principal stress for stress ratios less than 1.0. However, similar thermal volumetric strains were observed in all of the tests regardless of the stress state. A small effect of inherent anisotropy was observed due to the formation of the specimens using compaction. Specimens with a lower initial degree of saturation experienced greater thermal volume changes than specimens closer to saturation, possibly due to thermal collapse of the air-filled voids during heating or thermally accelerated creep after application of a given plastic strain during mechanical loading. An empirical relationship to consider the effects of anisotropic stress states and variable saturation was incorporated into an established elasto-plastic model developed for saturated soils under isotropic conditions, and a good fit was obtained between the measurements and predictions.     

Impact of repeated loading on mechanical response of a reinforced sand

Pavements constructed over loosely compacted subgrades may not possess adequate California bearing ratio(CBR)to meet the requirements of pavement design codes,which may lead to a thicker pavement design for addressing the required strength.Geosynthetics have been proven to be effective for mitigating the adverse mechanical behaviors of weak soils as integrated constituents of base and sub-base layers in road construction.This study investigated the behaviors of unreinforced and reinforced sand with nonwoven geotextile using repeated CBR loading test(followed by unloading and reloading).The depth and number of geotextile reinforcement layers,as well as the compaction ratio of the soil above and below the reinforcement layer(s)and the compaction ratio of the sand bed,were set as variables in this context.Geotextile layers were placed at upper thickness ratios of 0.3,0.6 and 0.9 and the lower thickness ratio of 0.3.The compaction ratios of the upper layer and the sand bed varied between 85% and 97% to simulate a dense layer on a medium dense sand bed for all unreinforced and reinforced testing scenarios.Repeated CBR loading tests were conducted to the target loads of 100 kgf,150 kgf,200 kgf and 400 kgf,respectively(1 kgf = 9.8 N).The results indicated that placing one layer of reinforcement with an upper thickness ratio of 0.3 and compacting the soil above the reinforcement to compaction ratio of 97%significantly reduced the penetration of the CBR piston for all target repeated load levels.However,using two layers of reinforcement sandwiched between two dense soil layers with a compaction ratio of 97%with upper and lower thickness ratios of 0.3 resulted in the lowest penetration.     

Testing the impact of targeted team building on project team communication using social network analysis

Communication and teamwork are key determinants of whether a project will be delivered successfully. Team building is often used as a way of improving patterns of team interaction. This research tests the impact of a standardised and repeatable team building protocol on communication in a project team. It builds on the theory that increasing the interconnection within a team communication network will lead to enhanced project outcomes. A longitudinal Social Network Analysis approach was used to diagnose the patterns of communication in a project team, inform planning of the team building intervention, and test the impact of the intervention on team communication. Over a three-month period, the team building resulted in a significant change to project team members' comfort discussing personal matters, and the frequency with which they discussed personal and work-related matters.     

土工格室对路堤沉降影响的有限元分析

通过研究土工格室如何对软土路堤进行加筋,并且应用ANSYS有限元软件来数值模拟土工格室增强土体的强度。通过添加土工格室前后情况对比,改变土工格室的添加层数进行分析,研究了铺设土工格室对软土路堤的沉降影响以及最优的铺设层数。结果表明,添加土工格室能限制路堤的沉降,使土体稳定性整体提高。     

Reflections on Rodney Turner's impact and the future of the field: An interview with Aaron Shenhar,Jeffrey Pinto and Graham Winch

In this interview with Aaron Shenhar, Jeffrey Pinto and Graham Winch, we probe the influence of Rodney's work on the field as it is, in terms of how it is developing now, and how it will develop into the future. Based on three questions asked by the interviewer Martina Huemann we get insights about 1) What these three leading scholars consider to be Rodney Turner's major contributions 2) How their work intersects with or has been influenced by Rodney's, and finally, 3) Which important issues and trends they see for the future of the field?     

Effects of prestressing the reinforcement on the behavior of reinforced granular beds overlying weak soil

The effects of prestressing the reinforcement on the strength improvement and settlement reduction of a reinforced granular bed overlying weak soil are being investigated through a series of laboratory scale bearing capacity tests. The influences of parameters such as strength of underlying weak soil, thickness of granular bed, magnitude of prestressing force, direction of prestressing forces and number of layers of reinforcement are being examined. Finite element analyses are carried out using the FE program PLAXIS to study the effect of prestressing the reinforcement. Results obtained from finite element analyses are found to be in reasonably good agreement with the experimental results.     

Mechanical role of reinforcement in seismic behavior of steel-strip reinforced earth wall

In the current design practices of steel-strip reinforced earth walls (SSREWs), the length of the reinforcing material is determined based on the equilibrium between the reinforcement tension and the earth pressure acting on the wall. Here, the resistance of the reinforcing material laid in the active failure zone (AFZ) is not considered. Moreover, the mechanical role of the reinforcing material against the integrity of the SSREW has not been sufficiently verified. Regarding the seismic stability of SSREW, although it is investigated by treating the entire reinforced earth wall as a rigid body, this inspection method is for gravity-retaining walls, and the difference in the seismic behavior between the SSREW and the rigid body is not clear. In this study, therefore, dynamic centrifuge model tests on 6 types of SSREWs were conducted to clarify the following items: (1) the basic earthquake behavior of a SSREW, (2) the mechanical role of the reinforcing material laid in the AFZ and (3) the mechanical role of the reinforcing material against the integrity of the SSREW. The results indicated that the reinforcing material laid in the AFZ can restrain the amount of deformation of the wall during earthquakes. Furthermore, the more stable the AFZ is, the smaller the maximum wall displacement will be.     

Effect of gas-oil contamination on the mechanical behavior of sand-woven geotextile interface: Experimental investigation and constitutive modeling

The accurate estimation of the frictional resistance of interfaces between soils and geosynthetics plays a central role in stability and serviceability of geosynthetic reinforced earth structures. Contamination with hydrocarbons generally impairs soil geotechnical properties; however, its effect on the behavior of soil-geosynthetic interfaces has seldom been examined precisely. For this reason, an extensive series of direct shear tests was performed to investigate the consequence of gas-oil contamination on the mobilization of shear strength and volume change response of gas-oil contaminated angular sand in contact with woven geotextile (WGTX). Complementary tests on the interfaces between glass beads as a replicate for sands with high degree of sphericity and roundness in contact with WGTX were also performed to explore the effect of particle shape. Gas-oil contamination is observed to causes decrease of the peak and critical state friction and dilation angles in both the sand-WGTX and glass bead-WGTX interfaces. However, gas-oil contamination-induced decrease in the frictional efficiency in the glass bead-WGTX interfaces was greater than that in the angular sand-WGTX interfaces. Calibration of a state-dependent sand-structure interface model against the laboratory data of gas-oil contaminated soils-WGTX interfaces results in a reasonable agreement between the model simulations and the laboratory data.     

A laboratory investigation on the impact resistance of a woven geotextile

This paper focuses on the impact resistance of geotextiles when subjected to impact loadings induced by dropping of stones. Such scenarios occur when geotextiles are used as a protective measure for fine granular material where is prone to be washed away. Usually, these geotextiles are restrained by placement of stones on top of them. A laboratory testing program is performed to expose a woven geotextile under dropping of a concrete block with various dropping energies and geometries. The induced damage on the geotextiles is inspected after the drop. Results indicate that as the drop energy increases, not only the possibility of puncturing of geotextiles increases but, in case of puncturing, the punctured area of geotextile expands as well. In addition, it is found that the geometry of the concrete block, where it collides on the geotextile, plays an important role on the survivability of geotextiles. In addition, PIV analysis has been performed to better understand the deformation pattern of the geotextile under impact loading. Based on the PIV results a simple scheme is suggested to estimate the drop energy threshold that the geotextile can survive under certain block geometry.