Showing papers in "Geotechnical and Geological Engineering in 2009"
TL;DR: In this paper, the effect of changes in shrinkage pattern on the swell-shrink behavior of compacted expansive soils was studied and the results showed that there may be an immediate equilibrium state attained by the soil in terms of swell shrink potential if suction at the shrinkage cycles was less than the past suction; otherwise, the equilibrium state was accompanied by fatigue of swelling.
Abstract: Laboratory cyclic swell–shrink tests were carried out on compacted expansive soil specimens to study in detail the effect of changes in shrinkage pattern on the swell–shrink behaviour of compacted expansive soils. Compacted soil specimens were allowed to swell and either shrank fully or partially shrank to several predetermined heights in each cycle. The tests were carried out at a surcharge pressure of 50 kPa. The test results revealed that shrinkage of compacted saturated soil specimens to predetermined height in each shrinkage cycle provides similar conditions as that of the controlled suction tests with an increasing number of swell–shrink cycles. The water content of soil specimens and hence soil suction was found to remain nearly constant for each pattern of shrinkage. For soil specimens equilibrated to a given swell–shrink pattern, suction at the end of shrinkage cycles was changed from a higher suction to a lower suction, and also from a lower to a higher suction. The experimental results showed that there may be an immediate equilibrium state attained by the soil in terms of swell–shrink potential if suction at the shrinkage cycles was less than the past suction; otherwise, the equilibrium state was accompanied by fatigue of swelling. The volumetric deformation of the soil specimen subjected greater shrinkage was found to be much larger than the corresponding vertical deformation. The compressibility index of microstructure, κm, was determined for several shrinkage patterns. It is shown that κm is heavily influenced by suction at the end of shrinkage cycles.
111 citations
TL;DR: In this article, the authors used Finite Element method to investigate the dynamic response and damage of subway structures under internal blast loading in New York City, where they focused on small-diameter single-track tunnels.
Abstract: Public transit systems have become one of the targets of terrorist attacks using explosives, examples of which are the 1995 attack on Paris subway and the 2004 attack on Moscow subway. Considering the intense threats of terrorist attacks on subway systems in metropolitan areas, explicit three-dimensional Finite Element method was used to investigate the dynamic response and damage of subway structures under internal blast loading. The study was motivated by the fact that explosion in subway structure may not only cause direct life loss, but also damage the subway structure and lead to further loss of lives and properties. The study based on the New York subway system, and investigated the influences of various factors on the possible damage of subway tunnel, including weight of explosive, ground media, burial depth and characteristics of blast pressure. A mitigation measure using grouting to improve ground stiffness and strength was also analyzed. Considering the amount of explosive terrorists may use, the present study focused on small-diameter single-track tunnels, which are more vulnerable to internal blast loading and are common in New York City. Blast pressure from explosion was applied to lining surface assuming triangle pressure–time diagram, and the elasto-plasticity of ground and lining as well as their nonlinear interaction was taken into account in the numerical model. It is found from the numerical study that maximum lining stress occurred right after explosion, before the blast air pressure reduced to the atmospheric one, and it was more dependent on the maximum magnitude of air pressure than on the specific impulse, which is the area below the pressure–time curve. Small tunnels embedded in soft soil, with small burial depth, might be permanently damaged even by modest internal explosion that may be perpetuated by terrorists.
97 citations
TL;DR: In this paper, granulated blast furnace slag (GBFS) and GBFS-cement (GBFSC) were utilized to overcome or to limit the expansion of an artificially prepared expansive soil sample (sample A).
Abstract: Expansive clays undergo swelling when subjected to water. This can cause damage, especially to light weight structures, water conveyance canals, lined reservoirs, highways, and airport runways unless appropriate measures are taken. In this study, granulated blast furnace slag (GBFS) and GBFS-cement (GBFSC) were utilized to overcome or to limit the expansion of an artificially prepared expansive soil sample (sample A). GBFS and GBFSC were added to sample A in proportions of 5–25% by weight. The effects of these stabilizers on grain size distribution, Atterberg limits, swelling percentage and rate of swell of soil samples were determined. GBFS and GBFSC were shown to successfully decreasing the total amount of swell while increasing the rate of swell.
87 citations
TL;DR: In this article, the results of geotechnical and mineralogical investigations on lime-treated soft clay soil from Idku City, Egypt, where high organic matters of about 14% exist were presented.
Abstract: This paper presents the results of geotechnical and mineralogical investigations on lime-treated soft clay soil from Idku City, Egypt, where high organic matters of about 14% exist. Lime was added in the order of 1%, 3%, 5% and 7% by weight and laboratory experiments after 7, 15, 30 and 60 days were conducted including the mineralogical and microstructural examinations, grain size analysis, plasticity limits, unconfined compressive tests, vane shear tests and oedometer tests. The results indicate that soft clay soil of high organic content of 14% can be stabilized satisfactorily with the addition of 7% lime. The results also demonstrate that the changes in the mineralogical contents and soil fabric of high organic lime-treated soft clay improve soil plasticity, strength and compressibility.
81 citations
TL;DR: To determine the changes in hydraulic properties of MSW in bioreactor landfill with time and decomposition, a series of constant head permeability tests were performed to determine variation of permeability of MSw with degradation.
Abstract: Bioreactor landfills are operated for rapid stabilization of waste, increased landfill gas generation for cost-effective energy recovery, gain in landfill space, enhanced leachate treatment, and reduced post closure maintenance period. The fundamental process of waste stabilization in bioreactor landfill is recirculation of generated leachate back into the landfills. This creates a favorable environment for rapid microbial decomposition of the biodegradable solid waste. In order to better estimate the generated leachate and design of leachate recirculation system, clear understanding of the permeability of the Municipal Solid Waste (MSW) with degradation and the factors influencing the permeability is necessary. The objective of the paper is to determine the changes in hydraulic properties of MSW in bioreactor landfill with time and decomposition. Four small-scale bioreactor landfills were built in laboratory and samples were prepared to represent each phase of decomposition. Then, the changes in hydraulic properties of MSW in bioreactor landfill with time and decomposition were determined. A series of constant head permeability tests were performed on the samples generated in laboratory scale bioreactor landfills to determine variation of permeability of MSW with degradation. The test results indicated that the permeability of MSW in bioreactor landfills decreases with decomposition. Based on the test results, the permeability of MSW at the first phase of degradation was estimated as 0.0088 cm/s at density 700 kg/m3. However, with degradation, permeability decreased to 0.0013 cm/s at the same density, for MSW at Phase IV.
68 citations
TL;DR: In this article, the authors focus on the characteristics of two soils, Osorio sand and Botucatu residual sandstone, which can be converted to well acceptable materials for this purpose, if stabilized with cement.
Abstract: Soil stabilization with cement is a good solution for the construction of subgrades for roadway and railway lines, especially under the platforms and mostly in transition zones between embankments and rigid structures, where the mechanical properties of supporting soils are very influential. These solutions are especially attractive in line works where other ground improvement techniques are extensive and, therefore, very expensive. On the other hand, the economic and environmental costs of such works should be optimized with good balances between excavation and embankment volumes. For this purpose, the improvement of locally available soils can bring great advantages, avoiding a great amount in borrowing appropriate material, as well as the need of disposing huge volumes in deposits. This paper focus on the characteristics of two soils, Osorio sand and Botucatu residual sandstone, which can be converted to well acceptable materials for this purpose, if stabilized with cement. The study of soil stabilization with cement relies on the quantification of the influence of percentage of cement and porosity adopted in the admixing process for different state and stress conditions. This influence will be evaluated from the analysis of unconfined compression strength (UCS or q u ) test results. This experimental framework will enable a good definition of mechanical parameters used in design of foundations and subgrades of railways platforms and for their execution quality control.
68 citations
TL;DR: In this article, a three-dimensional solution is proposed for totally or partly submerged backfill, which gives the normal stresses along the vertical and horizontal axes, with the effect of a surface load on the backfill.
Abstract: The determination of the stress state in backfilled stopes is an important step for assessing the behaviour of mine openings and for designing barricades. Most previous analyses have considered only the 2D case (plane strain condition) and neglected the effect of pore water pressure. In this paper, a three-dimensional solution is proposed for totally or partly submerged backfill. The new solution gives the normal stresses along the vertical and horizontal axes, with the effect of a surface load on the backfill. The solution is validated using laboratory experimental results taken from the literature. The good agreement obtained between the proposed analytical solution and laboratory test results indicates that this new solution provides a realistic evaluation for both the total and effective stresses in vertical backfilled stopes.
59 citations
TL;DR: In this article, the authors present a solution to evaluate the stress state in submerged or partially submerged backfilled stopes, where water is present in mine stopes and its effect should be assessed.
Abstract: The rapid increase of backfill use in underground mines requires a better understanding of the interaction between the fill material and the surrounding rock mass. This is a fairly complex issue as backfill materials are weak compared to the rock mass. This difference in the mechanical behavior induces a stress transfer along the contact area. Previous work conducted on backfilled trenches and mining stopes has shown that basic arching theory can be used to estimate earth pressures in narrow, vertical openings. In this regard, most existing solutions have been developed for dry backfills. However, in many cases, water is present in mine stopes, so its effect should be assessed. In this paper, the authors present a solution to evaluate the stress state in submerged or partially submerged backfilled stopes. The proposed analytical solution is validated against numerical modeling results.
55 citations
TL;DR: In this article, a parametric study of an embankment on soft soils reinforced with stone columns is performed using a computer program based on the finite element method, which incorporates the Biot consolidation theory (coupled formulation of the flow and equilibrium equations) with constitutive relations simulated by the p-q-θ critical state model.
Abstract: A parametric study of an embankment on soft soils reinforced with stone columns is performed using a computer program based on the finite element method. The cylindrical unit cell formulation is used by modeling one column and its surrounding soft soil with confined axisymmetric behaviour. The computer program incorporates the Biot consolidation theory (coupled formulation of the flow and equilibrium equations) with constitutive relations simulated by the p–q–θ critical state model. The following parameters are analysed: the replacement area ratio, the deformability of the column material, the thickness of the soft soil, the deformability of the fill and the friction angle of the column material. Based on the results of this study, a new design method is proposed, relating the settlement improvement factor to the two factors that revealed major influence: the replacement area ratio and the ratio between the deformability of the soft soil and the deformability of the column material.
47 citations
TL;DR: In this article, the authors analyzed data from 348 landslides in Nicaragua, and 19 in other Central American countries to describe landslide characteristics and search for possible correlations and empirical relationships, including the relationship between the height of fall and run-out distance for rock falls, slides, debris flows and debris avalanches.
Abstract: Statistical analyses of landslide deposits from similar areas provide information on dynamics and rheology, and are the basis for empirical relationships for the prediction of future events. In Central America landslides represent an important threat in both volcanic and non-volcanic areas. Data, mainly from 348 landslides in Nicaragua, and 19 in other Central American countries have been analyzed to describe landslide characteristics and to search for possible correlations and empirical relationships. The mobility of a landslide, expressed as the ratio between height of fall (H) and run-out distance (L) as a function of the volume and height of fall; and the relationship between the height of fall and run-out distance were studied for rock falls, slides, debris flows and debris avalanches. The data show differences in run-out distance and landslide mobility among different types of landslides and between debris flows in volcanic and non-volcanic areas. The new Central American data add to and seem consistent with data published from other regions. Studies combining field observations and empirical relationships with laboratory studies and numerical simulations will help in the development of more reliable empirical equations for the prediction of landslide run-out, with applications to hazard zonation and design of optimal risk mitigation measures.
47 citations
TL;DR: In this paper, the effect of nonplastic fines on undrained cyclic pore pressure response of sand-silt mixtures was investigated using around 289 stress-controlled cyclic triaxial tests on specimens of size 50 mm diameter and 100 mm height.
Abstract: Literature regarding the pore pressure generation characteristics and in turn the cyclic resistance behaviour of silty sand deposits is confusing. In an attempt to clarify the effect of nonplastic fines on undrained cyclic pore pressure response of sand–silt mixtures, an experimental programme utilising around 289 stress-controlled cyclic triaxial tests on specimens of size 50 mm diameter and 100 mm height was carried out at a frequency of 0.1 Hz. Specimens were prepared to various measures of density through constant gross void ratio approach, constant relative density approach, constant sand skeleton void ratio approach, and constant interfine void ratio approach to study the effect of nonplastic fines on pore pressure response of sand–silt mixtures. The effect of relative density, confining pressure as well as the frequency and magnitude of cyclic loading was also studied. It was observed that the pore pressure response is greatly influenced by the limiting silt content and the relative density of a specimen corresponding to any approach. The influence of other parameters such as relative density, confining pressure and magnitude of cyclic loading was as usual but an increase in frequency of cyclic loading was seen to generate excess pore pressure at a higher rate indicating an impact load type of behaviour at higher frequency. Utilising the entire test results over a wide range of parameters a new pore pressure band for sand–silt mixtures in line with Lee and Albaisa (1974) has been proposed. Similarly another pore pressure band corresponding to 10th cycle of loading as suggested by Dobry (1985) and up to a shear strain of around 25% has been proposed. These two bands can readily be used by researchers and field engineers to readily assess the pore pressure response of sand–silt mixtures.
TL;DR: In this article, the effects of the column diameter on the compressibility of fibrous peat were investigated and the results indicated that compressibility index decreased with increasing diameter of the cement column.
Abstract: This paper presents the compressibility of fibrous peat reinforced with cylindrical cement columns. The effects of the cement column diameter on the compressibility have been investigated in this study. The results indicated that compressibility index C
c
and C
α
decreased with increasing diameter of the cement column. Specimens with 45 mm (area ratio = 0.09) diameter and 60 mm (area ratio = 0.16) diameter of cement columns were cured for 7, 14 and 28 days, after which they were subjected to Rowe Cell consolidation test. Results are also presented from tests conducted on groups of cement columns using four (area ratio = 0.04) and nine (area ratio = 0.09) columns of 15 mm diameter each to investigate the influence of the number of cement columns on compressibility of peat. Apart from that various proportions of cement were used to form cement columns in order to study the influence. Based on the results obtained, it shows that cement columns can successfully reduce the compressibility of fibrous peat.
TL;DR: In this paper, a simple method of Digital Elevation Model (DEM)-based earthquake-induced shallow landslide susceptibility analysis was described, and the correlation of shallow landslides generated by the Niigataken Chuetsu-oki Earthquake in 2007 with landslide susceptibility values suggests that the method proposed by Uchida et al. (2004) can be around 80% accurate in delineating the probable locations of earthquake induced landslides.
Abstract: This paper describes a simple method of Digital Elevation Model (DEM)-based earthquake-induced shallow landslide susceptibility analysis. Considering topographic effects in amplification of earthquake ground motion, Uchida et al. (2004) have developed a topographical parameter based empirical description of landslide susceptibility during an earthquake. In this research, the method proposed by Uchida et al. (2004) was utilized in raster GIS and shallow landslide susceptibility analysis was performed in the study area of Nishiyama Town of Kashiwazaki City, Niigata prefecture, Japan. The correlation of shallow landslides generated by the Niigataken Chuetsu-oki Earthquake in 2007 with landslide susceptibility values suggests that the method proposed by Uchida et al. (2004) can be around 80% accurate in delineating the probable locations of earthquake-induced landslides. By calibrating landslide data and landslide susceptibility values in a small site within the study area, a final landslide susceptibility map was prepared for the whole study area. The resultant susceptibility map is very useful for regional scale planning.
TL;DR: In this paper, the shaking table tests are conducted on small scale nailed embankment slopes to study their behavior under dynamic conditions, and the results of the numerical analyses are found to be reasonably close to the corresponding experimental results.
Abstract: The shaking table tests are conducted on small scale nailed embankment slopes to study their behavior under dynamic conditions. Medium grained local sand with a water content of 3% is used in the study. The embankment slope is constructed using the controlled-volume compaction method. Three slope angles, 30°, 35° and 40° with a constant slope height of 18 cm are considered for the embankment. Each slope is reinforced with six number of hollow aluminum nails in two rows. The ratio of the length of nail to slope height (0.82) is same for all model slopes. The nails are inserted at three different inclinations. Three strain gauges are glued to each nail to obtain local strains during shaking. The accelerations at the base and the crest of the model slopes are monitored to find the acceleration responses of the embankments during the input ground motions. The numerical simulation of the model tests is performed by a commercial program called FLAC. The results of the numerical analyses are found to be reasonably close to the corresponding experimental results.
TL;DR: In this paper, an analytical expression is derived for the factor of safety of the rock slope incorporating most of the practically occurring destabilizing forces as well as the external stabilizing force through an anchoring system.
Abstract: In this paper, an analytical expression is derived for the factor of safety of the rock slope incorporating most of the practically occurring destabilizing forces as well as the external stabilizing force through an anchoring system. The slope stability is analyzed as a two-dimensional problem, considering a slice of unit thickness through the slope and assuming negligible resistance to sliding at the lateral boundaries of the sliding block. A detailed parametric study is presented to investigate the effect of surcharge on the stability of the rock slope for practical ranges of governing parameters such as inclination of the slope face, inclination of the failure plane, depth of tension crack, depth of water in tension crack, shear strength parameters of the material at the failure plane, unit weight of rock, stabilizing force and its inclination, and seismic load. For the range of parameters considered in the present study, it is found that the factor of safety of the rock slope decreases with increase in surcharge; the rate of decrease being relatively higher for lower values of surcharge. It is also observed that for a specific surcharge, the factor of safety depends significantly on all other parameters, except for unit weight of rock and higher values of inclination of stabilizing force to the normal at the failure plane. For any combination of these variables, the surcharge plays a vital role in the stability. A perfectly stable slope at relatively low surcharge can become unsafe with the increase in surcharge. The deterioration in the stability can be quite rapid, depending on the combination of the factors under consideration. The analysis and the general expression proposed herein can be used to carry out a quantitative assessment of the stability of the rock slopes.
TL;DR: In this paper, a backpropagation artificial neural network (ANN) model is developed to predict the secant friction angle of residual and fully softened soils, using data reported by Stark et al. (J Geotech Geoenviron Eng ASCE 131:575-588, 2005).
Abstract: A backpropagation artificial neural network (ANN) model is developed to predict the secant friction angle of residual and fully softened soils, using data reported by Stark et al. (J Geotech Geoenviron Eng ASCE 131:575–588, 2005). In the ANN model, index properties such as liquid limit, plastic limit, activity, clay fraction and effective normal stress are used as input variables while secant residual friction angle is used as output variable. The model is verified using data that were not used for model training and testing. The results also indicate that the secant residual friction angle of cohesive soils can be predicted quite accurately using liquid limit, clay fraction and effective normal stress as input variables with R
2 = 0.93. The sensitivity analysis results indicate that plastic limit and activity have no appreciable effect on ANN predicted secant friction angles. The secant friction angle predictions of the ANN model were also compared with those of Stark’s et al. (2005) curves and the empirical formulas suggested for the same data sets by Wright (Evaluation of soil shear strengths for slope and retaining wall stability with emphasis on high plasticity clays, 2005). The comparison shows that the ANN model predictions are very close to those suggested by the Stark et al. (2005) curves but much better than the prediction of Wright’s (2005) empirical equations. The results also show that ANN is an alternative powerful tool to predict the secant friction angle of soils.
TL;DR: In this article, the influence of various soil parameters, such as strain level, confining stress, void ratio, plasticity index, organic content and secondary consolidation time on shear modulus, G, and damping ratio, DT, is discussed.
Abstract: The paper presents results from a laboratory investigation into the dynamic properties of natural intact and model organic soils by means of resonant-column tests. The natural intact organic soils were sands, cohesive soils and peats with varying content of calcium carbonate. The model organic soils were formed in laboratory by mixing kaolinite and paper pulp. The influence of various soil parameters, such as strain level, confining stress, void ratio, plasticity index, organic content and secondary consolidation time on shear modulus, G, and damping ratio, DT, is presented and discussed. The test results on natural organic soils show that only high organic contents (OC ≥ 25%) have significant influence on G and DT at both small and high shear strains. For the model organic soils, however, a significant influence of even lower values of organic content (5% ≤ OC ≤ 20%) on G at small strains and DT at both small and high strains is observed.
TL;DR: In this article, the free-swell and swelling pressure of five compacted clays, covering low to high plastic clays have been investigated in respect to compaction states and the swelling pressure was compared with collapse pressure threshold.
Abstract: Expansive soils have received attentions of several investigators in the past half of century in the problematic soils context. Volume change behavior of unsaturated compacted soils in presence of water and change of degree of saturation was observed in two form of heave or collapse. Low water content and low density compacted soils in presence of enough surcharge pressure lose stability and collapse, because of their metastable and susceptible structure to change of degree of saturation. Free-swell and swelling pressure of five compacted clays, covering low to high plastic clays have been investigated in respect to compaction states and swelling pressure was compared with collapse pressure threshold. The results of experiments were utilized in two Artificial Neural Networks to predict free-swell percent and swelling pressure of a soil sample based on index properties and compaction state.
TL;DR: In this paper, the authors analyzed the stability of solid waste slopes within the bioreactor landfills, as a function of time and decomposition, using finite element program PLAXIS and limit equilibrium program STABL.
Abstract: A bioreactor landfill is operated to enhance refuse decomposition, gas production, and waste stabilization. Some of the potential advantages of bioreactor include rapid stabilization of waste, increased landfill gas generation, gain in landfill space, enhanced leachate treatment, and reduced post closure maintenance period. Due to the accelerated decomposition and settlement of solid waste, bioreactor landfills are gaining popularity as an alternative to the conventional Subtitle D landfills. However, the addition of leachate to accelerate the decomposition changes the physical and engineering characteristic of waste and therefore affects the geotechnical characteristics of waste mass. The changes in the physical and mechanical characteristics of solid waste with time and decomposition are expected to affect the shear strength of waste mass. The objective of this paper is to analyze the stability of solid waste slopes within the bioreactor landfills, as a function of time and decomposition. The finite element program PLAXIS is used for numerical modeling of bioreactor landfills. Stability analysis of bioreactor landfills was also performed using limit equilibrium program STABL. Finally the results from finite element program PLAXIS and limit equilibrium program STABL are compared. GSTABL predicted a factor of safety of more than 1 in all the cases analyzed, whereas PLAXIS predicted a factor of safety of less than 1 at advanced stages for a slope of 2:1. However, the interface failures between solid waste and landfill liners have not been considered in this paper.
TL;DR: An application of the information coming from the 3D model is shown to define the characteristics of the optimal excavation machines (the type and disposition of tools on the head and the necessary engine power) for the future developments of the Underground Metro System.
Abstract: This paper introduces a 3D geological and geotechnical model of the subsoil of the city of Turin managed by means of a Geographical Information System (GIS). The 3D GIS of the subsoil of Turin represents a useful decision-support tool in the underground management for engineering purposes and it’s here proposed as base geological elaborate to support future underground work in the city. In the final part of the paper, an application of the information coming from the 3D model is shown to define the characteristics of the optimal excavation machines (the type and disposition of tools on the head and the necessary engine power) for the future developments of the Underground Metro System.
TL;DR: In this article, the results of a study of grain crushing in road construction and its effect on road behaviour were presented. But they did not consider the effect of particle breakage on road performance.
Abstract: This paper presents the results of a study of grain crushing in road construction and its effect on road behaviour. Sieve analyses of field samples confirmed that grain crushing occurs during compaction of the base layer despite the good quality of aggregates used. Laboratory testing indicated that grain crushing reduces the resilient modulus of the aggregate material by half and increases the permanent deformations by onefold to threefold depending on the state of density and stresses considered. Road design and analyses undertaken to delineate the effect of grain crushing on performance showed that particle breakage yields a significant increase in rutting and longitudinal and alligator cracking of roads.
TL;DR: In this article, the influence of the process of the leaching out of Tunis soft soil on its geotechnical parameters is a focal point in this research, since it appears to happen in a two steps with increasing sensitivity.
Abstract: In Tunis City, the sensitivity of the marine deposits at shallow depth (z = 0–20 m) varies significantly. The influence of the process of the leaching out of Tunis soft soil on its geotechnical parameters is a focal point in this research. This process leads finally to moderate levels of sensitivity for Tunis clays since it appears to happen in a two steps with increasing sensitivity. The “hard water” leaching out and the dispersive action of organic matter (humus) lead unexpectedly to higher but still moderate level of sensitivity as measured on many Tunis sites. These sensitivity variations result from the combination of leaching out with hard ground water and high content of organic matter. This sensitivity attracted our attention and remains of high interest for the study of the behaviour of the Tunis soft clay.
TL;DR: In this paper, the effect of clear spacing (s) between the anchors, for different combinations of embedment ratio (λ) of anchors and friction angle (ϕ) of soil mass, was examined in detail.
Abstract: The ultimate uplift resistance of a group of multiple strip anchors placed in sand and subjected to equal magnitudes of vertical upward pullout loads has been determined by means of model experiments Instead of using a number of anchor plates in the experiments, a single anchor plate was used by simulating the boundary conditions along the planes of symmetry on both the sides of the anchor plate The effect of clear spacing (s) between the anchors, for different combinations of embedment ratio (λ) of anchors and friction angle (ϕ) of soil mass, was examined in detail The results were presented in terms of a non-dimensional efficiency factor (ξγ), which was defined as the ratio of the failure load for an intervening strip anchor of a given width (B) to that of a single strip anchor plate having the same width It was clearly noted that the magnitude of ξγ reduces quite extensively with a decrease in the spacing between the anchors The magnitude of ξγ for a given s/B was found to vary only marginally with respect to changes in λ and ϕ The experimental results presented in this study compare reasonably well with the theoretical and experimental data available in literature
TL;DR: In this paper, the authors developed a ratio of cut-slope lengths to cutslope heights based on the performances of unsupported natural and artificial cuts and some stability analyses, and showed that road cuts on cliffs of hard rocks need a horizontal to vertical ratio of 0.25:1.
Abstract: Road construction in the Blue Nile basin is largely determined by geotechnical factors. The area is characterized by steep slopes and has a history of landsliding. The geological formations range from Mesozoic sedimentary to Tertiary volcanic rocks making the stratigraphic makeup sensitive to deformation and failure. The heterogeneity of these rocks also means it is difficult to depend on results of stability analyses alone for road design and construction. As an alternative, ratios of cut-slope lengths to cut-slope heights have been developed in this study based on the performances of unsupported natural and artificial cuts and some stability analyses. Hence, road cuts on cliffs of hard rocks need a horizontal to vertical ratio of 0.25:1. Slopes made up of weak rocks can remain stable at a threshold angle of 45°. For heterogeneous slopes, it is advisable to use different road cuts depending on material makeup, and the degree of weathering and consolidation.
TL;DR: In this article, a pseudo-static analysis has been presented to investigate the stability of soil nailed vertical/nearly vertical excavations, where the failure surface is assumed as the arc of log-spiral passing through the toe of the excavation and intersecting the ground at right angle.
Abstract: In this paper, a pseudo-static analysis has been presented to investigate the stability of soil nailed vertical/nearly vertical excavations. The failure surface is assumed as the arc of log-spiral passing through the toe of the excavation and intersecting the ground at right angle. The horizontal and vertical seismic forces are taken in terms of horizontal and vertical seismic coefficients. The internal failure mode of the nailed cut is considered either by pull-out or rupture or excessive bending whichever is critical. Expression for the factor of safety is derived using moment equilibrium method. Results have been arranged in tabular form considering ranges of the design parameters usually occur in practice. A typical table for the design of nailed excavation with driven nails is presented in the paper. Analytical results have been compared with the findings of model tests and reasonably good agreement has been observed.
TL;DR: In this article, an analytical method has been proposed to predict the ultimate uplift capacity of single vertical piles embedded in sand considering arching effect, which takes into consideration of various pile and soil parameters such as length (L), diameter (d), angle of internal friction of soil (ϕ), soil pile friction angle (δ), and unit weight of soil(γ).
Abstract: An analytical method has been proposed to predict the ultimate uplift capacity of single vertical piles embedded in sand considering arching effect. The present analysis takes into consideration of various pile and soil parameters such as length (L), diameter (d) of the pile, angle of internal friction of soil (ϕ), soil pile friction angle (δ) and unit weight of soil (γ). A modified value of coefficient of lateral earth pressure in uplift has been developed considering the arching effect of soil. A comparative assessment of the uplift capacity of piles predicted by using proposed theory and the existing available theories is made with the existing field and model test results. It has been observed that the present model considering the arching effect predicts the results closer.
TL;DR: In this paper, a more effective and economical technology, namely Overburden Grout Injection Technology (OGIT), is recently developed in China and Australia by injecting waste material into the bed separations during long-wall mining to achieve subsidence control.
Abstract: Increasingly, mine subsidence is becoming a major issue of community concern. Among the measures of subsidence control, a more effective and economical technology, namely Overburden Grout Injection Technology (OGIT), is recently developed in China and Australia by injecting waste material into the bed separations during longwall mining to achieve subsidence control. The OGIT is proposed for the subsidence control in West Cliff Colliery located at the Southern Coalfield of the Sydney Basin, Australia. The three-dimensional finite element code COSFLOW is applied to investigate in a detail the bed separation developing with longwall mining and the effect of grout injecting into the separations in order to guide the subsidence control design when using the OGIT in West Cliff Colliery longwall mining practice.
TL;DR: In this article, a method for computing the aisle temperature field using 3D FEM is given, and the computation accuracy is verified by contrasting the computed and site measured results, the back propagation neural networks are also applied to the temperature prediction using self-developed Neural Network-Expert System software, the predicted results are also very satisfactory.
Abstract: The ground freezing construction technique is one of the most effective and widely applied site construction methods in soft soil areas, like Shanghai. Some elevation-inclined refrigeration pipes are arranged for the artificial freezing excavation of the Pudong-side first-storey connection aisle, which is designed to connect two adjacent tunnel lanes of Shanghai East-Fuxing-Road tunnel project. No advanced research results could be found for computing the temperature field of tunnels and aisles frozen with inclined refrigeration pipes. Anyhow the computation of the relevant temperature field is of high importance for the safe and economical excavation of the above-mentioned aisle. In this paper, a method for computing the aisle temperature field using 3D FEM is given, and the computation accuracy is verified by contrasting the computed and site measured results. The back propagation neural networks are also applied to the temperature prediction using self-developed Neural Network-Expert System software, the predicted results are also very satisfactory. The mechanism during freezing and aisle excavation will be discussed on the basis of 3D FEM simulation. The authors believe that studying the parameter-sensitivity of temperature field is very important for the optimum selection of parameter values. So, in this paper, the parameter-sensitivity of temperature field is also discussed. In order to obtain the optimum frozen wall thickness, the relation between the frozen wall thickness and the initial freezing brine temperature is studied. At the end, an excavation pre-control plan is proposed by means of fuzzy logic theory for improving the excavation safety. The research result of the current paper is very helpful for projects that will be excavated by freezing construction technique.
TL;DR: In this article, the effect of two different combinations of a spring mounting base and a rubber pad sandwiched between the machine base and its concrete footing block was examined experimentally and two different modes of resonance were clearly observed and the peak amplitudes of vibrations were associated always with the second mode; the predominant frequencies associated with the peak amplitude of vibrations (second mode) were significantly greater than those without the employment of any isolation system in which case only a single mode of resonance was observed.
Abstract: The effect of two different combinations of a spring mounting base and a rubber pad sandwiched between the machine base and its concrete footing block was examined experimentally The machine was subjected to steady state horizontal harmonic excitation with the help of the Lazan mechanical oscillator Experiments were performed by inserting a spring cushioning system between the machine base and its concrete footing In addition, two additional series of experiments were carried out by placing a rubber pad either just above or below the spring cushioning system It was clearly noted that an employment of a spring cushioning system, as an active isolation measure, becomes the most effective when the rubber pad is kept just below the machine base For different combinations of the spring mounting base and rubber pad, two different modes of resonance were clearly observed and the peak amplitudes of vibrations were found to be associated always with the second mode; the predominant frequencies associated with the peak amplitude of vibrations (second mode) were found to be significantly greater than those without the employment of any isolation system in which case only a single mode of resonance was observed It is expected that the study will be beneficial for assessing the performance of the machine foundations with the employment of springs and rubber pad
TL;DR: In this paper, a methodology that can be employed to simulate radionuclide migration through unsaturated soils, under laboratory conditions, has been developed and reported, with the help of a specially designed half-cell setup to study diffusion characteristics of inactive forms of Cs+, Sr+2 and Co+2 in two different types of soils, corresponding to their different compaction states.
Abstract: In this paper, a methodology that can be employed to simulate radionuclide migration through unsaturated soils, under laboratory conditions, has been developed and reported. This was achieved with the help of a specially designed half-cell setup to study diffusion characteristics of inactive forms of Cs+, Sr+2 and Co+2 in two different types of soils, corresponding to their different compaction states. It has been noted that the apparent diffusion coefficient strongly depends on the volumetric water content of the soil. However, increase of the apparent diffusion coefficient for higher volumetric water contents is found to be much less as compared to the lower volumetric water contents.