Showing papers on "Lateral earth pressure published in 1993"

The coefficient of earth pressure at rest

Abstract: Laboratory experiments on undisturbed specimens of a large number of soft clay deposits, as well as previous measurements on clays and granular soils, were used to examine and explain the magnitude...

An introduction to the mechanics of soils and foundations: through critical state soil mechanics.

Abstract: Introduction to geotechnical engineering basic mechanics essentials of material behaviour the structure of the Earth description and classification of soils pore pressure, effective stress and drainage laboratory testing of soils compression and swelling critical state strength of soil peak states behaviour of soil before failure cam clay stiffness of soil consolidation behavious of natural soils ground investigation steady state seepage stability of soil structures using bound theorems limit equilibrium method stability of slopes earth pressures and stability of retaining walls bearing capacity and settlement of shallow foundations piled foundations geotechnical centrifuge modelling.

Load reduction on rigid culverts beneath high fills: long-term behavior

Abstract: Three full-scale tests with the imperfect ditch method are described. The imperfect ditch method involves installing a compressible inclusion above rigid culverts to reduce the vertical earth pressure. Superlight expanded polystyrene blocks are used as the compressible material. In the first test, the instrumented culvert was a 1.95-m diameter concrete pipe beneath a 14-m-high rockfill embankment. In the second test, a 1.71-m diameter concrete pipe was used beneath a 15-m-high rock fill, and in the third, the culvert is a cast-in-place concrete box culvert with a 2.0-m width beneath 11 m of silty clay. The culverts were built between 1988 and 1989, and the instrumentation measured earth pressure, deformation, and temperature. The full-scale measurements show considerable reduction in the vertical earth pressure: that on top of the pipes in the granular fill was reduced to less than 30 percent of the overburden and that on the box culvert beneath the clay fill was reduced to less than 50 percent of the overburden. The deformation of the expanded polystyrene was 27 percent in the rock fill and 42 percent in the clay. The long-term observations show that there is no increase in earth pressure on and deformation of the pipes beneath the rock fill. There is a slight increase in deformation of the expanded polystyrene in the clay. Use of this method in Norway has realized cost reductions of the order of 30 percent and has made it possible to use concrete pipes beneath higher fills.

Earth Pressure and Earth-Retaining Structures, Second Edition

Abstract: Part 1: Fundamentals 1. Soil behaviour 2. Soil properties 3. Wall construction and movement, and the development of earth pressure 4. Water and retaining structures 5. Global and local instability Part 2: Design 6. Wall selection 7. Introduction to analysis 8. Avoiding failure 9. Gravity walls 10. Embedded walls 11. Composite walls 12. Appendix: 'classical' earth pressure theory 13. Appendix: earth pressure coefficients

Analysis of the arching action in granular mass

Abstract: When the lining of a tunnel is more flexible than the surrounding soil, the pressure applied to the lining is in general far smaller than the value estimated from the weight of the overburden. Pressure applied to an underground conduit or a trapdoor is also smaller than the weight of overburden. Similarly, earth pressure applied to a retaining wall or to the timbering of an open cut, and particularly to the lower part of the wall or the cut, is sometimes smaller than the values estimated from the theory of earth pressure. Some studies of this arching action to the soil assume that the soil remains in an elastic state; others assume a plastic soil model with a Tresca yield criterion. In this Paper the stress distribution in the soil is analysed assuming that the soil is in a state of plastic equilibrium and that Mohr-Coulomb's failure hypothesis is satisfied. Results are compared with those obtained by measuring the inner air pressure of models made of vinyl tubes or bags buried in dry sand or gravel. Si l...

Behavior of cantilever retaining walls

Abstract: Current methods for retaining‐wall analysis are based on the classical theoretical formulations of Rankine or Coulomb, with the assumption that sufficient lateral yield will occur to mobilize fully active conditions behind the wall. This leads to relatively simple equations for active pressure distributions. The effects of the deformation parameters of the backfill and foundation subsoil, construction sequence, wall flexibility and other complex initial conditions are not taken into consideration. In this paper the finite element method is employed to investigate the behavior of concrete cantilever retaining walls. The analyses reveal that the wall and soil movements are of considerable importance in predicting the lateral earth pressures. The results indicate that the lateral pressures acting on the wall stem are generally close to the active condition only in the top two‐thirds of the wall stem. Based on this study, a simplified design procedure is proposed for estimating the lateral earth pressures in ...

Skew effects on backfill pressures at frame bridge abutments

Abstract: The abutments of frame bridges are integrally connected to the deck without expansion joints. Active soil pressures are normally considered in design despite the movement of the abutments into the soil from thermal expansion of the deck. Many abutments are located on a skew, but possible effects of this skew on the backfill soil pressures are not considered in design. To improve the knowledge of soil pressures behind a skewed integral abutment for use in designing this type of bridge, soil pressures were measured on an installed project for 33 months. The soil pressure measurements were taken using total pressure cells in the backfill on each side of the centerline for both abutments of a 20-degree skewed bridge in Maine. A total of 16 pressure cells plus temperature indicators have been monitored four times a day using a data acquisition system since October 1989. Expansion of the deck causes the pressure to increase well above the active conditions on the upper part of the abutment wall. Skew effects on the pressures that develop near the deck level behind the abutment wall of an integral abutment are substantial. When the greatest deck expansion occurs, the pressures at 3 m (10 ft) from centerline on the obtuse side reach almost three times the value at the corresponding distance on the acute side. The horizontal variation of pressure is greater than the vertical variation. A design envelope is proposed.

Estimation of in situ lateral stresses in soils by cone-penetration test

Abstract: A simple method for the estimation of in situ lateral stress in soils using the results of a cone‐penetration test (CPT) is described and illustrated. The method is based on the dependence of cone‐penetration‐test sleeve friction on lateral stress. It recognizes that insertion of the cone causes soil disturbance, so the normal stress on the friction sleeve must differ from the initial in situ value. The lateral earth pressure on the sleeve during penetration is assumed equal to the Rankine passive pressure value. Field test results show that the method gives estimates of lateral stress that compare well with values determined by other procedures, such as the self‐boring pressuremeter, the flat‐plate dilatometer, laboratory tests on undisturbed samples, and the Brooker and Ireland correlations. The method in its present form requires separate assumption or determination of the overconsolidation ratio of the soil.

A study of soil nailing in sand

Abstract: This dissertation is concerned with a study of soil nailing, in particular the interaction mechanism between the soil and a nail and the failure mechanism and suitable design procedure for nailed slopes in sand. The interaction mechanism of a nail was studied by carrying out a number of pull-out tests, direct shear tests of nailed sand and interface tests using two uniform sands. Major parameters of the tests were flexibility, surface roughness and diameter of a nail. From the tests, it was found that: (1) flexibility of a nail significantly influences the interaction mechanism. Both the interaction parameter and apparent friction coefficient differ between a flexible and a stiff nail. Theoretical consideration indicates that the mobilization of nail forces is dominated by the relative stiffness between soil and nail. (2) a smooth-surface nail produces smaller bond friction than the critical state friction angle and mineral-to-mineral angle of the soil. This is due to the very thin rupture surface developed around the nail. On the other hand, a rough-surface nail was observed to produce two to four times larger bond friction than the direct shear friction angle of sand, due to the thick rupture surface developed and the dilatancy of the soil. (3) increasing the diameter of a nail produces a smaller apparent friction coefficient. Restrained dilatancy was found to play an important role. (4) the pull-out test, direct shear test of nailed sand and interface test produce different values of apparent friction coefficient , due to the different amount of restrained dilatancy effect around the nail (or reinforcement). The overall behaviour of nailed slopes was studied by carrying out a comprehensive series of centrifuge tests. Excavation of soil was simulated by draining water from two rubber bags in front of the facing wall. The centrifuge tests have provided much useful information on the mechanics of soil nailing. From the tests, it was found that: (1) draining of the water significantly influences both the earth pressure on the facing wall and the displacements of the nailed slope. Horizontal displacements of the facing wall were decreased by increasing the length and/or friction (bond) of the nail. (2) earth pressures on the facing wall do not exhibit a simple hydrostatic distribution. The deviations of the earth pressure are not negligible especially near the top and bottom of the facing wall. (3) roughness and bending stiffness of the facing wall considerably influence the stability and displacement of the nailed slope, respectively. (4) the observed failure surfaces were well described by a logarithmic spiral passing through the toe of the facing wall. (5) fairly good predictions for the failure acceleration were made using stability analysis of the nailed slopes based on the limit equilibrium method, provided an accurate friction angle for the sand and pull-out resistance of each nail could be determined. The factor of safety F5 of the nailed slopes was estimated by comparing the total available force and the total required force based on the observed failure surfaces.

Field Behavior of Instrumented Geogrid Soil Reinforced Wall

Abstract: An earth-reinforced retaining wall utilizing geogrids with full-height precast concrete wall facing is instrumented. Measurements include movements of wall faces, lateral earth pressure, vertical stress in the soil mass, strains in the soil mass, and strains along the geogrids. A comparison is made between observed behavior and design assumptions and calculations. Based on this comparison, the following statements can be made: (1) Computation of maximum tension in the geogrids using the standard design procedure is in general satisfactory; (2) a part of the lateral earth pressure is transferred to the full-height concrete facing, which is not considered in the design; (3) the distribution of vertical stress measured in the reinforced soil mass is nonlinear with the lowest value at the wall facing and this is contrary to the linear distribution assumed in the design calculations.

A literature review of the geotechnical aspects of the design of integral bridge abutments

Abstract: The report presents a literature review of the behaviour of integral bridge abutments and the effects on the surrounding ground. Based on this review there is evidence to indicate that cyclic thermal movement of an integral bridge abutment results in an increase in earth pressure up to the limiting value K(sub p) acting behind the abutment wall. The pressure depends on the magnitude of the induced soil shear strain resulting from wall movement towards the backfill or retained soil together with the number of movement cycles. The rate of increase of pressure would appear to be dependent on the magnitude of the shear strain which is dependent on the bridge span subjected to thermal movement and the abutment height. Typically earth pressures may take 5 to 10 years or more of seasonal cyclic movement to reach the limiting value K(sub p). Cyclic thermal movement of an integral abutment may also affect the general stability of the foundations and underlying soils, particularly spread footings. Horizontal sliding of shallow spread footings may occur, if insufficient restraint is provided by the abutment backfill or retained soil, and this could result in elasto-plastic soil behaviour beneath the foundation leading to unacceptable settlement or ground instability. In practice, however, many hundreds of integral bridge abutments have been constructed in Europe and North America with little or no sign of structural distress. The possible reason for the satisfactory performance of these bridges is that they have relatively moderate spans and the induced shear strains behind the abutments are such that any increase in pressure can be redistributed in the structure and surrounding soil. Longer span bridges, in which the induced shear strains are potentially large are unlikely to be able to allow redistribution of the associated higher pressures. Increase in earth pressures above the design value and up to the limiting pressure value K(sub p) could then occur, together with foundation movement, resulting in structural distress. Tentative guidance on the likely magnitude of induced soil strain, soil behaviour and parameters to be used for the design of an integral bridge abutment are presented in this report. (A)

Earth pressures under general wall movements

Abstract: In this paper, the finite element method is used to investigate the variation of horizontal earth pressure behind a rigid retaining wall for two categories of wall movements: (1) rotation about a point below its base (RBT mode); and (2) rotation about a point above its top (RTT mode). Triaxial tests and direct shear tests have been conducted to determine the hyperbolic parameters employed in the analyses. Numerical findings are compared with experimental results and traditional theories, and good agreements have been achieved. It is found that the mode of wall movement has a significant effect on the generation of earth pressure. For a wall under translational movement (T mode), the intensity and distribution of active earth pressure are in good agreement with Coulomb's solution. The RT (rotation about top), RB (rotation about base) and T modes are the three limiting movement modes that could occur to a rigid wall. (A)

Vertical Earth Loads on Buried Engineered Works

Abstract: The theory of vertical earth loads on buried engineered works is extended with a closed-form solution to include ditch geometries with backslopes and wide ditch bottoms, as well as works buried under fills. A variable horizontal stress ratio that is a function of the backslope angle is proposed to accurately model the effects of the minor principal stress arch. Parametric studies of the effect of ditch slope, ditch-bottom width, and friction angle upon the vertical earth load are explained. Without including the effects of sloped ditch geometries, the vertical soil load may be underestimated. The theory is applied to narrow underditches as a means to lessen earth load. The theory explains full-scale experimental observations and is readily broadened to include positive projecting structures buried in fills. An iterative design procedure is suggested for structures that are buried under fills, incorporating the minor principal stress arch and structural stiffness. Ditch geometry is an important construction control for both slope safety and the estimation of the load on buried works; these two constraints must be optimized in design.

Reliability of earth pressure measurements adjacent to a multi-propped diaphragm wall

Abstract: Field monitoring data from one panel of a multi-propped diaphragm wall in a stiff fissured clay have been analyzed to investigate their internal consistency. Measured total earth pressures have been assessed in the light of measured prop loads and wall rotations. The raw earth pressure data are shown not to satisfy the fundamental requirements of equilibrium, and to fit poorly with measured wall rotations. However net earth pressure distributions have been constructed which do show consistency with all the other data. These imply that the measured earth pressures, while giving the right general picture, may be over or under recording by up to a factor of two. (A) For the covering abstract see IRRD 860485.

Influence of seepage flow on the passive earth pressures

Abstract: This paper presents a method which allows a rigorous solution of the earth pressure, and which takes seepage forces into account. This method is based on a variational approach. It is a rigorous one in regard to the limit equilibrium method as it makes no assumptions with respect to the shape of the slip surface and the normal stress distribution along this surface. The variational limit equilibrium method is equivalent to the upper-bound method in limit analysis for a rotational log-spiral mechanism, hence the solution obtained is an upper-bound one for a rigidly perfect plastic material obeying Hill's maximal work principle. Details are provided of the method used to calculate passive earth pressures, and the pore water pressure distribution. For the covering abstract see IRRD 860485.

Structural Stiffness Influence on Soil Consolidation

Abstract: Several papers have been written about the influence of structural stiffness on soil consolidation. Most dealt with the soil as an elastic-medium, flexible beam on a Winkler medium with adequate interface finite element between the structure and soil, foundation element stiffness matrix, and three-phase spatial structure. The present technical note considers the effect of settlement caused by cohesive soil consolidation on the structure and the effect of the change in structure forces on the process of consolidation. It also considers the direct pressure from the foundation on the soil, as well as the pressure spread according to Boussinesq's equation from one foundation to another.

Observed and predicted response of a braced excavation in soft to medium clay

Abstract: A test section was established next to a 5.5 m braced excavation in made ground consisting mainly of partially weathered clay elements. A sewer trunk line had to be installed at Pietrafitta (Central Italy), where the Italian Electricity Board (ENEL) is building a new thermo- electric plant. Surface ground movements, strut loads, sheet-pile deflections and strains were measured. The relationships between the in situ observations and the construction sequences showed the strong influence of the construction activities on the sheet-pile performance. The measured ground and bracing system responses are compared with results from standard design procedures and finite element analysis. The empirical relationships by Peck (1969) and the method by Mana and Clough (1981) were used to predict the ground response, while the free earth support method and the Peck (1969) earth pressure envelopes were used to evaluate the loads in the bracing system. A plane strain, total stress finite element analysis was carried out by modelling the excavation geometry, the construction sequences and the soil-sheet pile interface. The FEM (Finite Element Method) capability of accounting for the construction procedures provides a much closer evaluation of the deflection profile, if compared with the predictions obtained by the classical design methods. The ground-surface settlements are matched better by the empirical relationships than by the finite element method, probably because of soil non-linearity or strain localisation phenomena not accounted for in the analysis. The standard design analyses appear to underestimate the loads measured in the bracing system, while a better prediction is obtained through finite elements, in spite of the simple soil model selected. (A) For the covering abstract see IRRD 859983.

Statically admissible earth pressure and bearing capacity calculations

Abstract: A calculation method for plane earth pressure and bearing capacity problems is presented. The method is based on the theory of plasticity and statically admissible figures of failure, which may however more appropriately be labelled stable stress figures. The numerical calculations are carried out as finite-difference calculations applying Koetter's equation. Use is made of curves of discontinuity, with the normal stresses acting parallel to the curve not being identical on both sides of the curve. The method is applicable for investigation of failure problems for a great number of geotechnical structures. So far a spreadsheet program has been developed for the design of free and anchored sheet walls. The method is considered to be a more sound approach than the kinematically admissible methods dominating the standard calculation procedures used in geotechnical practice. (A) For the covering abstract see IRRD 860485.

Mobilisation of stresses in deep excavations: the use of earth pressure cells at sheung wan crossover

Abstract: A 30 m deep excavation built as part of the Hong Kong Mass Transit Railway Island Line, utilising diaphragm walls, has been monitored using jackout earth pressure cells, inclinometers, piezometers, strut load cells and settlement points. Measurements of horizontal effective stress at the diaphragm wall face indicate that passive pressure in the completely decomposed granite is mobilised more quickly than expected for dense cohesionless material and points to the need for consideration of cohesion or passive stress relief in similar excavations. (A) For the covering abstract see IRRD 859983.

Active earth pressure reducing pneusol: experimental tests

Abstract: "Pneusol", a combination of old tyres and soils, is a material developed by the LCPC that has a number of areas of applications. These include retaining structures, stiffening of slopes, and lightweight embankments arching. Used behind a retaining wall, this material can reduce the active earth pressure on it. This paper presents results of tests on small-scale three-dimensional models which show how this "pressure-reducing" effect influences the critical height of failure of the structure. A double layered sand/pneusol earth fill structure is also studied. The parameters investigated included: a) the spacing between the layers; b) the number of ties between the tyres; c) the number of tyres per layer; and d) the thickness of the sand layer. The results indicate that the stabilizing effect of pneusol becomes greater as the number of tyres per layer increases, and as the thickness of sand between the layers decreases. For the covering abstract see IRRD 860485.

Transmitted Swelling Pressures on Retaining Structures

Abstract: The main objectives of this paper are to describe a finite element model to simulate the lateral swelling behavior of expansive soils as a function of soil suction change in the soil domain and to compare the results of the numerical model with results obtained by others in a large-scale experimental study. To achieve these objectives, a mathematical model using the well known Finite Element Method, FEM was developed. Also, a computer program called LATEX2D was developed for the mathematical model and a quadrilateral isoparametric finite element was employed in the analysis. The strain due to swelling is related to soil suction changes within the depth. The large-scale laboratory tests were simulated in the numerical model. The observed and the estimated lateral pressures found by the numerical modeling were then compared to the experimental results. The lateral pressure distributions from the numerical model compared closely with the results of the large-scale experiments. Thus, it was concluded that by developing proper material properties of the expansive soils, the lateral pressures on the retaining structures can be predicted fairly well for engineering purposes.

Excavated soil and sand discharger for small-bore pipe laying device

Abstract: PURPOSE:To discharge excavated soil and sand continuously without installing a soil and sand force-feed equipment into an excavator body, to maintain soil- discharge capacity even when propulsion length is lengthened and to stop ground-water in a facing completely even during the stoppage of excavation in a small-bore pipe laying device by a method of propulsion construction. CONSTITUTION:Excavated soil and sand 26 from a facing are transferred to a first isolation chamber 13 in an excavator body 2, and soil and sand are discharged to the second isolation chamber 14 side through an on-off valve 15 while controlling earth pressure in the first isolation chamber 13 by an earth pressure detector 18. The outside air is sucked into a soil discharge pipe connected to a soil-discharge pipe connecting section 20 from the opening section 19 for sucking air of the second isolation chamber 14 by a vacuum suction system installed on the ground, air quantity is adjusted by an opening regulator 21, and soil and sand discharged to the second isolation chamber 14 side are carried on the ground by vacuum pressure in the soil discharge pipe and air force.

Ground vibration reducer

Abstract: PURPOSE:To lower the propagation of ground vibrations without damaging stability at the time of an earthquake and stability to earth pressure by installing a cushioning material having excellent vibration reducing properties and high compression load bearing capacity onto the vertical surface of the buried footing section of a structure. CONSTITUTION:A ground vibration reducer 2 is mounted into space formed between the underground external wall 1A of a structure 1 and the ground G. The ground vibration reducer 2 is composed of cushioning materials 3 brought into contact properly with a plurality of surfaces in the underground external wall 1A and a shell-shaped plate member 4 supporting an external surface on the ground side so as to be connected and receiving the earth pressure of the ground. The cushioning material 3 is formed of an anisotropic elastic body, and a shear spring constant in the vertical direction is brought to one third of a compression spring constant in the horizontal direction. The cushioning material 3 is given the compression spring constant in the horizontal direction and compression load bearing capacity so as to resist earth pressure in the horizontal direction working at all times and reaction, etc., and a free design is enabled. Accordingly, the vertical component of ground vibrations transmitted over the structure 1 can be reduced largely.