Analysis of Excavation-induced Deformation with Different Soil Models
Abstract: The monitored case of deep excavation works located in the centre of Warsaw is described and back analysed as a boundary value problem with the finite element method. The excavation was carried out in over-consolidated clayey layers under the support of braced diaphragm walls. Accurate simulation of such soil-structure interaction problems requires advanced soil constitutive models – especially for the pre-failure range of small strains. On the other hand, such models should not be very complex and their material parameters should be relatively simple to obtain from laboratory and in situ surveys. By means of a case study, this paper examines several simple elasto-plastic constitutive models for the simulation of the behaviour of soil layers. The influence of such characteristics of the soil behaviour, as anisotropy and non-linearity of stiffness, is studied in the paper. The discussion concerns the problems related to the application of the models for a practical example. The comparison is focused on the obtained and measured displacements of the neighbouring building and diaphragm walls.
Modelling the effect of recent stress history on the deformation of overconsolidated soils
The aim of the research was to study the behaviour of overconsolidated soils subjected to small changes of strain or stress appropriate to the investigation of ground movements around excavations, retaining walls or foundations, and to develop a constitutive soil model that can predict such behaviour. The principal feature of soil behaviour investigated was the effect of recent stress history, defined by 9 the angle of rotation between the previous and current stress path directions. Stress path triaxial tests were carried out on both reconstituted and undisturbed samples of speswhite kaolin and London clay. The tests, which followed on from previous work by Richardson (1988), examined details of the influence of recent stress history, which was found to have a significant influence on the stress-strain response of the soil for the current loading path. The data from the tests together with a re-evaluation of the existing experimental data and a limited investigation of the effect of recent stress history in 3D stress space, enabled the main features of the soil behaviour to be identified. The stress-strain response of the soil was found to be highly non-linear, inelastic and dependent on recent stress history; if the stress path rotation was 18O, i.e. a complete reversal, the soil stiffness was at a maximum and was at a minimum for no rotation. As the loading path continued the influence of the recent stress history gradually diminished until it was no longer evident. Recent stress history also affects strain paths and effective stress paths measured during drained and undrained loading respectively. The significance of mean effective pressure and overconsolidation ratio was also investigated. Soil models which can predict this behaviour need to include at least one kinematic yield surface which allows plastic straining inside the state boundary surface. A two-surface yield model of this type, formulated by Al Tabbaa (1987) was evaluated. The predictions of this model did not compare well with several important aspects of the experimental observations and it was shown that an additional kinematic surface is necessary to model non-linearity, inelasticity and the recent stress history effect. A new three-surface model based on the two-surface model was developed, within the framework of Critical State soil mechanics, which successfully predicts all the main features of the soil behaviour. It is described by eight parameters which are all soil properties and, with one exception, all have a clear physical meaning.
The Inca Occupation of the South Coast of Peru
like the others, however; it forks into several nearly parallel ravines of which the largest are Huayuri, Rio Grande-Palpa, Ingenio (called Collao in ancient times), Nasca proper (the ancient Caxamarca), Taruga, and Poroma. Due to peculiarities of the local topography, the irrigated areas in Ica and the ravines of Nasca are located inland, at the foot of the mountains, rather than at the mouths of the rivers as is more usual in Peruvian coastal valleys. No sharp natural or cultural boundary separates the valley of Chincha from the valleys of Cafiete (ancient Huarco and Runahuana), Asia, and Mala, the next valleys going up the coast to the northwest. At the other end of the area we are considering, however, there is a sharp break; beyond Yauca the Andean foothills reach out to the sea, natural conditions are quite different, and there are important differences in the archaeological picture as well. The historical sources which mention the south coast are not particularly helpful, except in so far as they provide us with a few dates. To begin with, no chronicler gives an explicit account of the political organization of the south coast at the time it came into contact with the Incas. It can, perhaps, be inferred from Cabello Balboa's statements about common policy toward the Inca invaders that there was some sort of political connection between the valleys of Mala, Cafiete, and Chincha, but the connection need have been no more than a temporary military alliance. Cabello makes no mention at all of Pisco. The valleys of Ica, Nasca, and 125