Showing papers in "Geotechnical and Geological Engineering in 2002"

Practical pedotransfer functions for estimating the saturated hydraulic conductivity

Abstract: The saturated hydraulic conductivity k is one of the most important and widely used geotechnical parameters, commonly involved in a diversity of applications. The value of k depends on many factors, which can be divided into three classes: properties of the fluid, pore size distribution, and characteristics of the solid surfaces. Because the latter two are not necessarily constant within a given deposit, the hydraulic conductivity may vary significantly in space. Engineers and scientists need indications about how changing factors may affect the actual k value. In this paper, the authors propose some simple expressions, based on pedologic properties, to estimate the value of k. Using experimental results of their own and taken from the literature, it is shown that the proposed pedotransfer functions can be used for quickly estimating the k value for granular and plastic/cohesive soils. Such expressions can be employed, with a useful chart format, for the preliminary design phase of a project, and also for estimating the range of k values to be anticipated within a given deposit.

Bearing capacity of strip foundation on geogrid-reinforced sand

Abstract: Results of small-scale laboratory model tests to determine the ultimate bearing capacity of a strip foundation supported by sand with multiple layers of geogrid reinforcement are presented. Tests were conducted with only one type of geogrid and a sand compacted to one relative density. The embedment ratio of the foundation was varied from zero to 0.6. It is found that, for the given reinforcement-depth ratio, the bearing capacity ratio with respect to ultimate load increases with embedment. The relationship between the bearing capacity ratio at ultimate load and at limited levels of settlement (less than or equal to 5% of foundation width) is also presented. The bearing capacity ratio at limited levels of settlement is smaller than the value at ultimate load.

Geogrid-reinforced railroad bed settlement due to cyclic load

Abstract: Results of large-scale laboratory model tests conducted to determine the permanent settlement due to cyclic load of the railroad bed for a proposed high-speed train route extending from Seoul to Pusan in South Korea are reported. The possibility of using geogrid layers as reinforcement to reduce settlement of the subbase layer was investigated. Based on the present model test results, it appears that practically all permanent settlement due to cyclic load is completed after application of 105 cycles of load. The most beneficial effect of reinforcement is derived when one layer of geotextile and one layer of geogrid are placed at the interface of the subgrade soil and subbase course.

The artificial neural network as a tool for assessing geotechnical properties

Abstract: Geotechnical properties are controlled by factors such as mineralogy, fabric and pore water: dynamic properties which can change in response to the environment and human intervention. Their interactions are difficult to establish by statistical methods alone due to their interdependence. Based on the application of an artificial neural network, a methodology has been developed for predicting geotechnical properties utilising their Relative Strength of Effect (RSE) and Potential Relative Strength of Effect (PRSE). The PRSE reveals the trend in the neighbourhood of the focus point and has been found to be less sensitive to any noise existing within the data set. An application is illustrated using sandstone data published by Hawkins and McConnel (1991) whereby the possible influence of petrological characteristics on their geotechnical properties has been assessed.

Determination of hydraulic conductivity of sand-bentonite mixtures for engineering purposes

Abstract: Pollution of the environment due to leakage from waste repositories is a well-known and wide spread problem. Emphasis has therefore been put on design of liners for such repositories, focusing on hydraulic conductivity and its variation with time, liner composition, water content, compaction etc. The paper addresses the hydraulic conductivity of sand/bentonite mixtures, especially the variation of the hydraulic conductivity as a function of bentonite content, compaction and degree of saturation. In order to better understand the variation of the hydraulic conductivity of a sand–bentonite mixture a new parameter k1 has been proposed. The parameter reflects the amount of bentonite per pore volume and can easily be calculated based on the amount of bentonite and the dry density of the soil mixture. Thereby, the hydraulic conductivity can be predicted as a function of different degres of compaction. This method can be used for engineering purposes to predict the hydraulic conductivity at an early stage of a design to get an idea of the required design and hence, cost.

Risk considerations for crown pillar stability assessment for mine closure planning

Abstract: Evaluation of the long-term surface stability of crown pillars overlying underground mines is an important component of mine closure planning The definition of a crown pillar, as well as a brief discussion of the assessment of the probability and consequence of crown pillar failure are given in this paper Techniques for stability assessment using mechanistic, empirical and numerical simulation techniques are discussed Consequence assessment is discussed, but is still subjective and difficult to quantify Where crown pillars are suspected to be marginally stable or unstable either at the time of the investigation or over the long term, and where the consequence of failure is medium to high, the closure plan for the site must include proposed rehabilitation alternatives Selection of the optimum solution depends largely upon financial considerations, but also upon the common public expectation that the result of mine closure planning be a ‘permanent’ solution that does not restrict public access or future land use on the site

The effects of tidal buffering on acid sulphate soil environments in coastal areas of New South Wales

Abstract: One-way floodgates installed on flood mitigation drains in regions affected by acid sulphate soils restrict carbonate/bicarbonate buffering, thereby creating reservoirs of acid water (pH < 4.5) that discharge during the ebb tide. The drain water quality and hydrodynamic conditions prior to and following floodgate modifications that allowed for controlled saline intrusion are described with reference to data collected from intensively drained and floodgated coastal lowlands located in southeastern New South Wales, Australia. Cl:SO4 ratios taken from groundwater samples depicted an acidic environment with little soil buffering capacity. Prior to modification, water quality upstream of the one-way floodgate was consistently acidic (average pH 4.6) with high concentrations of aluminum and iron that fluctuated with precipitation. Over a two-week period before modifications, floodgate leakage permitted alkaline water to intrude upstream of the floodgate and react with H+ ions. This period showed the strongest supporting field evidence for tidal buffering via modified floodgates. After installing vertical lifting, two-way floodgates average drain water pH increased to 5.89 and aluminum and iron concentrations decreased by more than 30%. A large rainfall (131.8 mm) during the post-modification period caused acidic groundwater flushing, however, in comparison to the pre-modification period, recovery time and average pH were markedly improved. Preliminary investigations of groundwater salinity in response to tidal intrusion has shown that electrical conductivity fluctuates with rainfall and it is predominately limited to 10 m perpendicular to the drain.

Laboratory investigations on rotary diamond drilling

Abstract: Extensive laboratory drilling investigations were conducted on a wide variety of rocks to study the inter-dependence of machine as well as rock parameters on the performance of the drilling operation. Detailed physical and mechanical properties of all the rock types were determined to study the influence of the rock properties on the drilling performance. The effect of PEO (poly-ethylene-oxide) added to the drilling water was also studied. Slake durability tests were conducted in plain water as well as a PEO mixed water medium to observe the effects of PEO on the surface properties of the rock. An attempt is also made to understand the different modes of wear of impregnated diamond bits in the rotary drilling operation.

Applicability of piezocone and dilatometer to characterize the soils of the Venice Lagoon

Abstract: The effectiveness of two geotechnical investigation tools—the piezocone and the dilatometer—to characterize the soils forming the shallowest deposits of the upper quaternary basin of the Venice lagoon soil is examined in this study. For this purpose, the results of a comprehensive site and laboratory investigation carried out recently over a small lagoon area—the Malamocco Test Site—are used to evaluate the applicability of the most widely used charts or correlative equations to characterize soil profile and estimate the main geotechnical properties of these soils, when applied to the interpretation of CPTU and DMT results. The particular interest of this site—apart from its unquestionable historical relevance—is the presence, apparently without any regular pattern in depth and site, of a predominantly silty fraction combined with clay and/or sand, thus forming an erratic interbedding of various types of sediments. This case represents therefore the opposite condition of that which has been normally utilized in the past to calibrate the two devices, namely the presence of particularly homogeneous natural deposits or artificially sedimented homogeneous layers of sand or clay. The Malamocco Test Site may therefore be considered as test benchmark for the applicability of the two devices to characterize highly heterogeneous silty deposits.

Development of a pulverized fly ash suspension grout

Abstract: A Greek lignite fly ash was selected because of its hydraulic properties and was pulverized to produce a specific surface of 8300 cm2/g, and a gradation with D15, D50, and D85 equal to 1.3 μm, 6 μm and 20 μm, respectively. The pulverized fly ash suspension properties were optimized by adding a suitable superplasticizer and a suitable accelerator at optimum dosages. The experimental evaluation of suspension properties included sedimentation tests, viscosity'measurements, rheological properties, setting times and development of strength with time. Groutability and effectiveness were evaluated by injecting selected suspensions into clean sands. Pulverization improves remarkably the behavior of fly ash suspensions. Suspensions with water to solids ratios of 1.5:1 and 2:1 by weight and containing additives, behave as Bingham fluids, have apparent viscosity lower than 70 cP, bleed capacity lower than 5%, initial setting time lower than 24 h, and can be injected into relatively coarse sands. These characteristics are comparable to those obtained for ordinary and microfine cement suspensions, showing that pulverized fly ash suspensions can be used for permeation grouting.

Exploration of underground strata conditions for a traffic bypass tunnel using ground penetrating radar system - a case study

Abstract: A ground-penetrating radar (GPR) survey was carried out in connection with the construction of a traffic bypass tunnel between Saraikale Khan and Dr. Zakir Hussain Marg in Delhi. Five boreholes were drilled in this area to correlate and confirm the GPR signatures with borehole data. This Note covers the correlation of the borehole data with GPR signature to explore the real subsurface strata conditions for the construction of the bypass tunnel.

A non-linear stress-stiffness model for geomaterials at small to intermediate strains

Abstract: A double exponential fitting model (DEFM) capable of expressing the non-linear stress-stiffness relationship of geomaterials has been proposed by Shibuya et al. (1997). The model comprises two material constants; the elastic stiffness at very small strains and the strength, together with other free parameters to determine the complete stress-stiffness relationship. In this paper, the capability of the original function used for DEFM in simulating the tangent stiffness-stress relationship of geomaterials is first discussed. Second, the methods for determining the free model parameters, as well as its conversion to obtain a stress-strain relationship are proposed. The applicability of DEFM to predicting non-linear stress-stiffness relationship is examined in detail in a total of forty-nine fitting cases of compression test data on sedimentary rock, artificial soft rock and soft clay. It is found that the DEFM is effective in expressing the non-linear stress-stiffness relationship of various kinds of geomaterials at small to intermediate strains, say less than 0.5%. The superiority of this model compared to other fitting models currently in use is also demonstrated in some of the fitting cases.

Seismic reliability analysis of earth slopes under short term stability conditions

Abstract: Different models were developed for evaluating the probabilistic three-dimensional (3-D) stability analysis of earth slopes and embankments under earthquake loading The 3-D slope stability model assumed is that of a simple cylindrical failure surface The probabilistic models evaluate the probability of failure under seismic loading considering the randomness of earthquake occurrence, and earthquake induced acceleration and uncertainties stemming from the discrepancies between laboratory-measured and in-situ values of shear strength parameters The models also takes into consideration the spatial variabilities and correlations of soil properties The probabilistic analysis and design approach is capable of obtaining the 2-D and 3-D static and dynamic safety factors, the probability of slope failure, the earthquake induced acceleration coefficient, the yield acceleration coefficient, the earthquake induced displacement, and the probability of allowable displacement exceedance taking into account the local site effect The approach is applied to a well known landslide case: Congress Street Landslide in Chicago A sensitivity analysis was conducted on the different parameters involved in the models by applying those models to the Congress Street landslide considering different levels of seismic hazard Also, a sensitivity analysis was carried out to study the sensitivity of computed results to input parameters of undrained shear strength, and corrective factors A comparison was made between the different models of failure The parametric study revealed that the hypocentral distance and earthquake magnitude have major influence on the earthquake induced displacement, probability of failure and dynamic 2-D and 3-D safety factors

Faulting and slope failures in surface coal mining—some examples from North East England

Abstract: The shallow terrestrial Coal Measures strata of North East England have been faulted and tectonised by geological events (orogenies), and are divided by faulting and the River Tyne valley into the Northumberl and and Durham coalfields. The type of faulting is almost exclusively normal faulting, with close spacings and complex geometries being prevalent. These coalfields are generally overlain by glacial deposits. Surface coal mining, as a mechanised operation, has been carried out in this region for about the last 60 years. The earliest workings were on a relatively small scale, and faulting and geologically complex ground was avoided as far as possible; but with time, the introduction of progressively larger excavation plant has led to ever larger and deeper surface mines, and working in faulted ground has become commonplace. Detailed ground investigations by drilling and geophysical logging are carried out to prove the geological structure. The gradient of bedding dips usually determines whether the coal should be mined by opencast dip or strike cuts, or by open-pit working, but the choice of excavation face alignments with respect to faulting can be critical. Faces aligned near parallel with faults tend to suffer failures, whereas faces aligned near perpendicular to faults tend to be stable. The types of slope instabilities which are associated with normal faulting comprise planar failures (including bi-planar and multi-planar), toppling failures, tetrahedral wedge failures and complex endwall failures. Endwalls formed against faults are especially likely to become unstable, and can become very problematic if located close to mining area boundaries where important natural or infrastructure features may exist. Several case studies are included to illustrate these points.

Geomechanical properties of sandy soil near Scanzano Jonico (Basilicata, Italy)

Abstract: The soils of the Ionian coastal zone, except those in proximity to Taranto where overconsolidated clays outcrop, are not currently well known from the perspective of their physical characteristics and mechanical behaviour. This note report a series of data from laboratory and on site tests (SPT and CPT) that have made it possible to undertake interesting quantitative comparisons as well as verifying some correlations proposed in the literature. The results show how to deal with, at least for more obviously sandy soils, medium and/or high density sands, to which can be attributed friction angles even of the order of 40° and greater, while the soils nearer the surface show notable variability related to the presence of soils with finer grain size distribution.

Making an impermeable clay core from a flysch mudrock

Abstract: A flysch mudrock was used for the construction of the core of the Evinos embankment dam. The thinly bedded, slightly weathered and intensely folded mudrock was thoroughly investigated in order to prove its suitability to form an impermeable core. Proper winning and placing methods could produce an adequately impermeable homogeneous and plastic core material. The resulting material had a fines content (d < 0.076 mm) around 50%, low plasticity, high strength and small permeability. After a trial fill, placement procedures were finalised and the core was successfully built with small variations in its properties. A substantial increase in the depth of the borrow pit did not influence the core quality. The instrumentation results during construction and for the subsequent three years, showed that design assumptions were greatly validated and a clay material of low permeability was produced.

Productivity optimisation in weak sedimentary formations for improved coal production and roof stability—an approach

Abstract: Far-field peak particle velocity (PPV) measurements were made in the roof while blasting in coal development drivages at Tandsi Mine, Western Coalfields Limited, India. The roof was fragile at this mine and was posing constant support problems for mining, resulting in low productivity. The PPV measurements have been used to decipher the damage zone in the roof. The extent of damage obtained has been compared to establish the threshold limits for the damage zone. Conversely, the maximum charge per delay that can be exploded is calculated and a suitable blast design has been recommended for maintaining the roof stability and pull. A roof vibration predictor equation has been developed that shows a consistent trend indicating that it may have future use in a similar geo-mining setup. The blast pattern recommended has reduced the damage extent, though marginally, but helped in improving pull. Critical PPV for incipient rock damage in underground coal mine development drivages under fragile roof were computed. The PPV level for incipient crack growth was found to vary from 500 to 800 mm/s while for overbreak it varied from 800 to 1200 mm/s. It was also observed that the location of cut holes, charge concentration and firing sequence were found to be responsible for the difference in their damage potential.