Online Database of Deep Excavation Performance and Prediction

Deep excavations can comprise one of the most challenging design and construction geotechnical problems. Many factors affect their performance including soil strength, ground-water, building surcharges, construction methods, and construction techniques. Engineers are confounded with the complex problem of predicting behavior while producing a safe and economical design. Typical parameters of interest are design wall moments, bracing forces, wall displacements, and ground or building settlements. Many authors have compiled case histories that quantify maximum observed displacements in various publications. Often, these publications include benchmarking of observed behavior otherwise known as Class “C” predictions. Few authors have compiled Class “A” predictions where performance predictions are presented before the actual project is completed. This publication presents a recently developed online database of deep excavation prediction and performance available to engineers in an effort to make performance and modeling information more accessible. In addition, the performance and benchmarking of nearly 39 deep excavations is briefly presented, focusing mostly on inclinometer recorded wall deflections

Measured performance of slurry walls

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2002.Includes bibliographical references (p. 355-361).This thesis evaluates the measured performance of 29 slurry wall supported excavations in Boston, Chicago, Washington DC, and San Francisco - most of which have been constructed since 1980. Each of these case studies includes data on the initial site conditions (soil profile and properties, groundwater conditions and location of adjacent facilities etc.) and designs for support of the excavations. The main goal is to relate construction records to the measured performance of the lateral earth support systems. The principal parameters of interest are the induced ground deformations (and their effects on adjacent structures) and observations of groundwater flows. The actual monitoring data always include inclinometer measurements of lateral deflections within the diaphragm wall and/or adjacent soil. However, other information such as surface settlements, building settlements, heave of the sub-grade or piezometric data were only archived for some of the projects (nearly all in Boston). Even fewer projects contain measurements of structural forces in either the diaphragm wall or bracing system. These data have been grouped according to the soil profile, toe fixity of the wall and type of bracing system (tie-back anchors, prestressed cross-lot and top-down). Most of the projects have succeeded in allowing only small wall deflections, often less than 0.2% to 0.3% of the total excavation depth, and similar magnitudes of the maximum surface settlements. Larger wall movements did occur in several projects but have been linked to either inadequate bracing (poor tieback design or inadequate pre-stressing of rakers), lack of toe embedment or ground softening inside the excavation (installation of drilled caissons or load bearing elements). Unexpectedly large surface settlements in one project (Dana Farer) were clearly linked to ground loss during tieback installation. Several other reported cases of leakage (through panel joints and/or tiebacks) have been repaired by grouting. Given the limited availability of archival data, the thesis has focused on the interpretation of lateral deflections. Wall deformations have been sub-divided into rigid body translation, rigid body rotation and bending modes. Empirical correlations have been proposed for estimating each of these components.b y Dimitrios C. Konstantakos.M.Eng

Control of Ground Movements for a Multi-Level-Anchored, Diaphragm Wall During Excavation

An excavation up to 23m deep for the Dana Farber research tower in the Longwood medical area of Boston, was supported by a permanent perimeter diaphragm wall extending into the underlying conglomerate and up to 6 levels of prestressed tiebacks anchored in the rock. The lateral earth support system was very successful in limiting wall deflections to less than ±15mm on each of the four sides of the excavation. However, ground surface settlements up to 65mm occurred on two sides and were attributed to ground losses that occurred when tiebacks were installed through overpressured sand layers at depths of 15-18m. Finite element simulations are able to describe consistently the effects of the different excavation and support sequences on each side of the project using backfigured soil properties, while surface settlements can be explained by including local ground losses within the analyses