Numerical Analysis of Dry Excavation Using a Tie Back Wall Under Static and Dynamic Load
Deep excavations are common in urban areas, nearby existing constructions. The support systems have the main function of preserve the stability and control soil displacements close to the excavation. Settlement control of nearby structures is an essential aspect during design and construction. Settlements prediction is usually made by empirical methods and in some cases also by numerical modeling. The paper presents a numerical modeling of a dry excavation by Plaxis program. The program allows the prediction of stress and deformation behavior of different geotechnical constructions using the Finite Element Method. The excavation has been modeled in five stages, in order to reproduce the construction phases. The numerical modeling was capable to reproduce satisfactorily the horizontal profile of the displacements of the diaphragm wall. In relation to settlements, the shape of the settlement profile was quite similar
Shape of ground surface settlement profiles caused by excavation
There are two general types of settlement profiles induced by excavation, the spandrel type and the concave type. Based on a regression analysis of the field observations of settlement curves with predominantly cohesive subsurface conditions, an empirical method for predicting the spandrel and concave settlement profiles is proposed. The proposed method is verified through several case histories. For comparison, the results obtained from other empirical methods are also presented. The proposed method provides a fairly good prediction of ground surface settlement and yields better prediction of angular distortion than other empirical methods for the concave- and spandrel-type settlement profiles. Furthermore, the relationship of cantilever area and deep inward area of wall deflection is established which can be used as the first approximation to predict the type of settlement profile.Key words: prediction, excavation, settlement profile, spandrel, concave.
Measured Performance of Braced Excavation
This paper documents the measured performance of a test section of braced excavation for a subway. The excavation was 37 ft wide and 58 ft deep, and five levels of struts were installed. The subsoil consists of fill, silt, till and rock. The water table was from 6 ft to 8 ft below ground surface. The instruments installed were slope indicators, piezometers, and strain gages. The typical horizontal inward movement of the sheeting was 5 in., and the maximum movement on one sheeting was 9 in. A maximum surface settlement of 7 in. occurred outside the excavation. Large drops in pore pressure occurred in the soil over a distance (greater than 70 ft) far back from the excavation. The strut loads measured showed a wide variation but the average maximum values, except in the top strut, were less than half the design loads. The maximum strut loads occurred at an intermediate state of excavation. Details of construction procedure greatly influenced the behavior of the braced excavation.