This paper proposes two special tools for design of steel sheet pile walls, based on a combination of a subgrade reaction model and the transfer matrix method. In the first tool a plastic hinge is generated when the ultimate moment in the retaining structure is exceeded and earth pressures are redistributed until new equilibrium is found. The program computes the rotation of the plastic hinge, which can be checked with the rotation capacity of the sheet pile in accordance with Annex E of ENV 1993-5 (CEN, 1997). The second tool can be used to study the amount of loss of strength and stiffness due to oblique bending of sheet pile walls composed of double U-sections and to examine the effectiveness of possible measures to reduce the oblique bending. Application possibilities of both tools are illustrated with a typical example.
The new design procedure for steel sheet pile walls from Eurocode 3 part 5 (CEN, 1997) demands the development of simple design tools with a short calculation time which take effects due to the generation of plastic hinges and oblique bending into account. Analysis of plastic hinges is interesting because it involves a possible material saving up to 30% (Van Tol and Kort, 1997) and a tool to study oblique bending is useful to investigate the possible loss of stiffness and strength of the sheet pile. Subgrade reaction models are popular for simple retaining wall design because they give the designer insight in the soil-structure interaction problems, have a short calculation time and offer the possibility to account for rather complicated construction stages. With the second tool the amount of loss of strength and stiffness due to oblique bending can be determined as well as measures to reduce the oblique bending.
Many unstable slopes with active or potentially active slides are limiting factors in urban planning, and urban, traffic and other development on the Danube river bank (right) in Yugoslavia from Belgrade to the state border. Because of complex lithological structures, neotectonics, erosion and other current geodynamical processes in the area, a multidisciplinary approach to investigations is required and particularly needed for any local remedial or protection measures. Our numerous papers on engineering geological investigations on unstable slopes clearly show that we have not enough experience in the determination of groundwater table fluctuations, although its presence is one of the key active factors in slope stability. This paper puts an emphasis on the hydrogeological activities and methodology of a reliable, quality determination of the groundwater regime in the landslide body as a basis for geotechnical modelling of slope stability, all for the purpose of planning the Golden Hill farm estate development near the town of Smederevo, Yugoslavia, i.e. preparing optimum measures of protection.
For the purpose of determining geotechnical parameters for local land development, vineyard raising, construction of access communications, subsidiary buildings, an optimum irrigation system and drainage systems in the overhumid zones in the area of Golden Hill farm estate near Smederevo, which is fully situated in the central part of the "Plavinac" landslide, a program of specific, dedicated, hydrogeological and engineering geological investigations, in the office and in the field, was first defined and then implemented. In the final phase the ground stability was to be modelled using different groundwater tables, and protection measures of the level of a detailed design were to be planned in order to arrange and develop the land on an area of about 31 hectares.
A new elasto-plastic constitutive model for unsaturated collapsible soil implemented in a finite element program able to simulate complex loading conditions including variable suction during loading. The numerical model has been applied for the prediction of a pile test installed in a collapsible soil in Southeast Brazil. The pile test consisted of initial loading followed by unloading-reloading, soil inundation and further reloading. The numerical simulation of the test was able to predict quite well the whole load-settlement curve including the measured soil collapse, although this has been slightly overestimated.
Predictions of pile capacity and pile displacements are usually carried out using empirical methods based on CPT or SPT data. These methods have a number of drawbacks, and do not take into account, for instance, variations in water content (suction) due to inundation or precipitation, but just external loading changes. Predictions of the response of unsaturated soils subjected to complex soil loading has experienced great advances with the elasto-plastic critical state models recently proposed (e.g., Alonso et al., 1990; Josa et al., 1992; and Wheleer & Sivakumar, 1995). However the collapsible and expansible behaviour associated with these soils still makes difficult accurate predictions. The present paper presents numerical analysis of a pile load test (Villar et al, 1995) using an elasto-plastic critical state model for unsaturated collapsible soils (Futai et al.,1998; Silva Filho, 1998). The pile test analysed is non-conventional and could not be analysed by constitutive models that do not consider the influence of suction.
SOIL AND PILE LOAD TESTS
Some soil properties (Vilar et al., 1995; Machado and Villar, 1998) are described in Figure 1. The bulk weight, Figure 1b, increases with depth and, consequently, the voids ratio, Figure 1c, in the range 0.7 Ð 1.0 decrease with depth.
Understanding the operational variables in electrokinetic remediation of aquifers is not sufficient to put the remediation method to practical use. This is because the method is relatively new, though an inovative technique in the aquifer remediation. In order to investigate theoretically the operational variables of the electrokinetic remediation, a mathematical model has been constructed based on the physico-chemical mass transport process of heavy metals in the pore water of contaminated aquifers. Transport of the heavy metals is driven not only by the hydraulic flow due to the injection of the purge water but also by the electromigration due to the application of an electric potential. The electric potential between the anode and the cathode is considered an important operational variable in electrokinetic remediation. From model simulations of Cu2+ (as a heavy metal), it is confirmed numerically that the remediation starts from the upstream anode and the heavy metal is gradually transported to the downstream cathode.
The increase in need for water supply enhances the need to clean up contaminated groundwater and soil. Many new techniques for the remediation of the groundwater and soil have been proposed. Among them, one of the most cost-effective technologies is the in-situ electrokinetic remediation. Though investigation of the electrokinetic remediation is done not only experimentally but also theoretically, the understanding to obtain the mathematical model is quite insufficient. This study aims to investigate the operational variables of the remediation using a mathematical model based on physico-chemical mass transport theory to simulate the nonsteady characteristics of the electrokinetic remediation. The in-situ electrokinetic method is simply realized by burying the electrodes (anode and cathode) into the treatment zone of the aquifer, which is saturated with the groundwater or the purge water, and by applying a fixed low voltage direct current between the electrodes.
Geotextiles are often included in engineered earth systems, where they are used as a filter material to reduce the movement of soil particles into drains, and as a reinforcing material to increase the strength of soils subjected to loads. In both instances, the ability of the material to transmit water is of importance since soil strength tends to decrease as moisture content increases. If the inclusion of geotextiles reduce the ability for moisture to migrate as planned, they may not be accomplishing their intended purpose and, instead, may be worsening rather than improving the system. Conversely, in systems that are designed to prevent water movement, the inclusion of a fabric that attracts moisture may be undesirable and counter to the design. A series of tests were conducted on three geotextiles to evaluate their ability to conduct water under unsaturated conditions. It was found that the geotextiles tended to be hydrophobic and did not begin wetting until pore suctions were near zero or positive. It was found that the unsaturated hydraulic conductivity of the geotextiles was high when nearly saturated, but that the conductivity decreases rapidly as saturation fell. The fabrics also tended to exhibit a very high level of hysteresis that results in significantly different abilities to conduct water depending on whether the fabric is drying or wetting. A series of three tests, transmissivity, moisture content versus matric potential and unsaturated hydraulic conductivity, were conducted on the materials evaluated. This required the development of a suitable TDR methodology for use on a very thin material.
Geotextiles are increasingly being applied in a large variety of engineering uses, such as in the separation, drainage and reinforcement of soils. These uses are in roads, landfill covers and liners, and in embankments and foundations.
This paper investigates the mechanism of slope displacement using the results of long-term monitoring of the unstable behavior and failure of a large excavated rock slope with an elevation difference about 300 m. The study also evaluates the influence of joint sets on slope behavior through numerical analysis. Then fundamental points regarding the stability of large excavated rock slopes are introduced as follows. The stability of a large excavated rock slope is greatly influenced by the joints and weak layers in the rock, and the relationship between their positions and the positions of the excavated surface. It is important not to fail to notice signs of instability caused by the influences of them early through long-term monitoring started in the early stages of excavation. Based on such monitoring, the need of actions should be determined such as additional investigations, stability analysis, and design modifications and changes.
This paper focuses on a case of failure of a large excavated rock slope with a height (an elevation difference) about 300 m. First, the behavior of each part of the slope is analyzed based on the displacement measurements obtained during a period of about 10 years before the failure. Next, each cross section of the slope is modeled by elasto-plastic equivalent continuum analysis to illustrate that the measurements are explainable. And how the unstable behavior of the slope occurred according to the topographical and geological conditions of the respective cross sections is examined.
SLOPE DEFORMATION BEHAVIOR BASED ON LONG-TERM MEASUREMENT
Geological structure The slope involved in this case study consists of late Paleozoic to early Mesozoic olistostrome: limestone, shale, tuff, and sandstone. The alterations of shale and tuff include lenses of sandstone, and these layers are overlain by olistoliths of limestone.
The behavior of EPS block under dynamic loading remains one of the main concerns in geotechnical applications for this material. Laboratory tests were carried out to determine the resilient modulus of elasticity of EPS material, which is one of the most important properties needed in mechanistic methods of pavement design. The resilient modulus is usually determined in the laboratory from cyclic triaxial tests. However, because the confining pressure has little effect on the behavior of EPS material (Zou and Leo, 1998, Horvath, 1995, Preber et al. 1994, and Eriksson and Trank, 1991), a series of cyclic unconfined compression tests of EPS specimens were carried out instead. Cylindrical specimens with 50mm diameter and 50 mm height, and with a density of 20 kg/m3, were used for the tests. The effects of static and dynamic stress level, and load cycles on the resilient modulus and deformation of EPS material, were investigated. Test results indicated that the resilient modulus of EPS decreases with an increase in static stress, but remains constant as the dynamic stress increases.
A rigid closed-cell cellular plastic foam, Expanded Polystyrene (EPS), has been used successfully as a subgrade replacement material for pavement construction, especially for poor quality subgrade. In flexible pavement structures, the mechanical properties of the asphalt concrete, the base course, and the soil subgrade, have a considerable influence on the response of the whole pavement to dynamic traffic loading. The design procedures for flexible pavements presented in the AUSTROAD (APRG Report No.8, 1993) and AASHTO Guide for Design of Pavement Structures (AASHTO Guide 1993) utilize the mechanical properties of the asphalt concrete, base course and soil subgrade. This is considered to be a required input for determining the stress-strain characteristics of pavement structures subject to traffic loading.
According to the features of displacement-time curves on tunnel, the possibility to use displacement acceleration form curve model as a stability criterion of rockmass is analyzed. By means of GM(1,1) model of Grey system, the stable displacements and the ultimate convergence displacements of rockmass are predicted. The formula of predicting unstable time with tangent angle is established.
It is well known that there are many Grey systems in reality, which are complex systems formed by both known and unknown factors or indefinite factors. To define all of factors, and erect corresponding mathematical model for these systems is almost impossible. We can avoid these difficulties completely, according to a group of tested data in a happened time-series, begin from time-series analysis method and establish mathematical model, which is applied to forecast future action of systems directly. That is the character of Grey system. The change of displacement convergence in tunnel rockmass is a Grey system in fact. This system composed of known factors (such as the geometrical figure, dimension, mechanical performance) and many unknown factors (such as mechanical state of rockmass-support system, rockmass mechanical performance). By means of the Grey system, we can predict the future development tendency according to measurement data, and pre-control the rockmass to avoid fatal accident and significant property loss. We select the displacement convergence of tunnel rockmass as the basic physical parameter for predicting, because the measurement is more convenient, and original data more reliable. Utilizing the Gray theory model GM(1,1), the stable displacement and ultimate displacement can be predicted. Therefore the result of stability analysis is given to spot engineering timely, on the other hand, some predicted data such as initial stress, and elastic modulus can be used for stability analysis.
Two kinds of improvement of soil properties are dealt with. To simulate the mechanical stabilization, clay was mixed with sand. Specific (unstable) behaviour was observed at the binary system (sand : clay = 1 : 1) at low shearing stress level which is explained by macroporosity. Critical ratio sand: clay = 5 : 1 was found when the increase of sand contents did not affect the behaviour. Chemical improvement was modelled by mixing sand with portland cement (2 % to 8 % by weight). A bonding surface was defined. The extent of debonding may be described by a ductility index. Brittle shear behaviour is typical for bonded sand, ductile behaviour (loose sand was used) for debonded sand. The model material (sand + cement) depicts well the behaviour of naturally cemented soils where the cementation is, however, nonhomogeneous as a rule.
For the ground improvement, the treatment of structural units and the increase of bonding seem the most viable. Both interventions are, to some extent, interrelated: by implanting some additional bonds, the granulometrical composition should be changed. The nature of structural units may be affected by mixing fine soil (clay) with coarse soil (sand). Such a mixture may reproduce the whole spectrum of soils encountered in situ – sandy clays, loams, clayey sands. Clay-sand mixtures thus deserve wider attention than merely as a procedure of mechanical soil improvement. The last sentence equally applies to sand-cement mixtures (chemical improvement). They may be considered as a way of soil properties improvement but also as a model of structural bonding.
Clay-sand mixture was produced by dry mixing of powdered clay and dry sand in the proportions S:C = 0:1 to 1:0. Theory of such mixtures was developed by Voight and Reuss (Omine et al., 1998).
This paper describes the development of coefficient of lateral earth pressure at rest, K0 in soft kaolinbentonite mixtures. The presence of montmorillonite in bentonite increases the consistency limits and consequently enhances the activity of the soil mixture. Ko values of a series of reconstituted kaolinbentonite mixtures were observed continuously during one - dimensional consolidation during loading as well as unloading cycles. The samples were consolidated under a constant hydraulic gradient of 0.2 kPa/mm in a purposely built consolidometer and measurements from flush diaphragm transducers gave the total vertical stress and total lateral stress on the sample. The equipment used has previously been described in Ting, Sills and Wijeyesekera (1994). Experimental observations confirm that K0 increase linearly with decreasing void ratio as reported by Ting et al (1994) for soft kaolin soils. The increasing montmorillonite content results in a lowering of the angle of friction, which in turn increases the value of K0. The value of K 0 was observed to initially decrease with time during secondary consolidation. These observations provide an answer to a query raised by Schmertman (1983) which had remained unanswered to date. During unloading, K0 values were observed to increase with increasing over consolidation ratio (OCR).
The coefficient of earth pressure at rest, K0, is an essential design parameter in soil mechanics and its evaluation is important for problems related with foundations, excavations, retaining walls, friction piles and numerical modelling. Therefore the estimation of an incorrect value of Ko can seriously affect the soil deformation parameters (Wijeyesekera, 1994). Donath (1891) defined k0 as the ratio of the total horizontal stress to the total vertical stress (sh/sv) when under a condition of zero lateral strain.
KAOLIN - BENTONITE MIXTURES
The kaolin used was Speswhite China Clay, marketed by English China Clays Ltd.