Lateral earth pressure

About: Lateral earth pressure is a research topic. Over the lifetime, 5334 publications have been published within this topic receiving 62552 citations.

Calculation Models For Dam Foundations With Geotextile Coated Sand Columns

Abstract: As against conventional column foundations, coated columns can be used as ground improvement in very soft soils. The radial support is guaranteed through the composite between the geotextile coating and the surrounding soil, while the geotextile is under ring tension forces. Therefore this foundation system will be employed widely to found buildings, especially embankments on very soft or organic soils like peat. Numerical and analytical models for calculation and design of the new foundation system will be reflectet. INTRODUCTION By the foundation of buildings on soft soils often an improvement of the soft soil with the already known column foundations was carried out for example compacted sand columns or vibro displacement granular piles. In very soft soils like peat this columns normally can not be used, because the horizontal support in this soils is not sufficient. By the new foundation method ‘geotextile coated sand columns’, sand columns are inserted down to the bearing layer. These columns are coated with a geotextile of polyester threads, which guarantees the filter effect and the horizontal support. By using this new developed system a safe and flexible foundation on very soft soils with low settlements, especially for dams or traffic roads embankments, can be achieved. CONSTRUCTION PROCEDURE Two construction methods are developed by the Josef Mobius Baugesellschaft GmbH, Hamburg, Germany, which are called the excavation method and the displacement method. By the excavation method a casing with a diameter between 0,8 m and 1,5 m is vibrated into the ground and after that the soil in the casing is excavated. Opposite to that by the displacement method a steel tube with a much smaller diameter of about 0,6 m to 0,8 m is placed into the subsoil. According to the displacement principle, the two base flaps of the casing are closed and displaces the soft soil to the sides of the casing. Then the geotextile with a somewhat larger diameter as the column is inserted into the casing. This is delivered from the factory and cut in length on the construction site. On the one hand this is due to the construction, on the other hand it ensures the partial mobilisation of the passive earth pressure, which increases the horizontal support. After inserting the geotextile and the filling of the column the casings are pulled using vibration, which causes compaction of the sand-gravel mixture in the column. BEARING BEHAVIOUR The geotextile coated sand columns are a bearing component, although the column must be horizontally supported. In contradiction to a conventional not coated column, where the horizontal support of the soft soil σh,s,tot must be equal to the horizontal pressure σh,c in the column, geotextile coated columns can be used as soil improvement in very soft soils, due to the radial supporting effect of the coating σh,geo = f(Fr) combined with the surrounding soft soil σh,s,tot. At the same time the coating is demanded to ring tension forces Fr. So the horizontal support of the soft soil σh,s,tot, which depends on the vertical pressure on the soft soil σv,s, can be much smaller, and a large settlement reduction is given due to the load concentration over the sand columns. Finally a load-dependent equilibrium state, with a flexible and self-regulating bearing behaviour is reached. At the same time a settlement acceleration is observed, since the columns behave as large vertical drains. After construction time, only small settlements will occur. 1 Dr. Marc Raithel, Geotechnique Consultants Kempfert +Partner, Mannheim, Germany 2 Prof. Hans-Georg Kempfert, Institute of Geotechnique, University of Kassel, Germany CALCULATION METHODS Numerical calculation using FEM For the numerical calculation the program PLAXIS (Finite Element Code for Soil and Rock Analyses) was used. An advantage of this program is the possibility to use several soil models. For the soft soil the Soft Soil Model (SSM), a model of the Cam-Clay type was used. For the sand and gravel of the column material the Hard Soil Model (HSM), a modified model on the basis of the Duncan/Chang model, was used. The calculation of the bearing and deformation behaviour leads to a three-dimensional problem. The program PLAXIS allows only calculations with an axial symmetric model or a cross model. In practice a threedimensional calculation model is hardly used. Therefore in the numerical analysis the problem is simplified and the calculation is split up into two separate models. By the examination of a single column (according to the ‘unit cell concept’) and the use of an axial symmetric calculation model the ring tension forces for the design are determined. To investigate the deformation behaviour of the whole system, for example a dam foundation, a cross model is used. The coating can not be simulated directly, because the columns must be substituted by walls of equal area ratio. Therefore a substitute shear parameter is defined, which is used for the column material after activation of ring tension forces. The definition and derivation of the substitute shear parameter as well as comparative calculations are shown in Raithel (1999) and Raithel and Henne (2000). Analytical Calculation model Assumptions and boundary conditions The analytical, axial symmetric calculation model (according to the ‘unit cell concept’) with the essential boundary conditions is shown in figure 1.

Expansion of Cylindrical Probes in Cohesive Soils

Abstract: The present study shows that the cylindrical expansion tests can not only solve foundation problems by empirical method but are also a means to study the undrained behavior of cohesive soils. On theoretical grounds, it has been shown that the undrained stress-strain curve of the soil can be derived from the pressure meter curve. New testing techniques have been developed, much more sophisticated than the classical ones. The following information has been obtained on a few cohesive soils: horizontal at rest pressure; undrained stress-strain curve of the undisturbed soil for strains up to 5% and in situ undrained cohesion, which appears higher than those determined by classical methods.

Earth Pressure on Retaining Walls Near Rock Faces

Abstract: The present study examines the lateral earth pressure transferred to a rigid retaining wall by granular fill confined between the wall and an adjacent rock face. The centrifuge modeling technique is used to test small models in which rotation of the wall about its base can be controlled, thus allowing observation of changes in pressure from the at‐rest to the active condition. Janssen's silo pressure equation may be reasonably used for estimation of the atrest pressure, using an earth pressure coefficient, K=1-sinΦ. Significant variations from the estimated pressure may occur next to the wall as a result of small variations in placement conditions. A conservative approach may be to use a decreased Φ value in calculating K. In the active condition, progressive failure in the soil results in a decreased Φ, which should be used when estimating wall pressure. These estimates may be obtained from stress characteristic solutions, or from the silo pressure equation in which a K value compatible with the values o...

Vibratory compaction of coarse-grained soils

Abstract: The variation of the coefficient of earth pressure in normally consolidated and overconsolidated soil and the effect of soil compaction on the change of the horizontal effective stress are discusse...