Geotechnical Engineering Online Library

A numerical method, PEI (Pile behavior in Expansive soil upon Infiltration) developed at the University of Ottawa can be used as a tool for the prediction and interpretation of the mechanical behavior of piles in expansive soils taking account of the influence of matric suction changes associated with water infiltration. This program is employed in back analyses of the in-situ single pile test results for a case study at the Colorado State University (CSU) field test site, which has expansive soil deposits. Four single piles were drilled into the expansive shale of the Pierre Formation west of Fort Collins, Colorado. The piles were 350 mm in diameter and were installed to a depth of 7.6 m. During installation, slope indicator-type VS embedment strain gauges were embedded on the piers at a depth of 1.8 m, 3.1 m, 4.3 m and 5.5 m below the ground surface. Water content variations of the surrounding soil along the pile depth were measured periodically from 1995 to 2004, in addition to other measurements, which include pile axial force distribution and pile head displacement. Extensive analysis regarding this case study with respect to the mechanical behavior of pile associated with changes in water content is available in the literature. In this paper, this case study is illustrated in an innovative way to understand the influence of matric suction on the mechanical behavior of the pile using the program PEI. In addition, in-situ measurements of both pile head displacements and pile axial force distribution are compared with the results of numerical simulations using the PEI. Analyses of the results show that measured in-situ and numerical results are in good agreement. The results of this study are of significant interest for the practicing engineers who routinely design pile foundations in expansive soils.

The collapse of the soil structure due to wetting is called hydroconsolidation and it occurs only once under constant loading, in cases of perturbation of the soils moisture content. It is encountered usually in non-sedimentary soils such as anthropogenic fills and residual materials. This paper presents an interpretation of hydroconsolidation settlements in a building of the historical centre of Thessaloniki followed after a rise of the water table. The interpretation is based on the results of laboratory evaluation of hydroconsolidation properties, in conjunction with in situ measurements of settlements.

St Isaac’s Cathedral in St. Petersburg was completed in 1858 after 40 years of construction; it is today the fourth largest domed Cathedral in Europe. The soil is a relatively soft saturated sediment and carries this 3155 MN structure that is 100 meters high with an imprint of 92 m by 100 m. It is founded on a 7.5 m thick mat of granite and limestone blocks resting on relatively short timber piles of different lengths. The Cathedral has progressively experienced significant deformation including differential settlement causing cracks in the pillars and tilting of the porticoes. The paper summarizes the available geotechnical engineering and engineering geology aspects of the soil on which the Cathedral is built as well as classical issues such as foundation ultimate capacity and settlement analysis through simple calculations and numerical simulations. It also includes some less classical issues such as the influence of microbial activity on the behavior of the Cathedral through the changes the microbes and their activity create in the engineering properties of the soil and in the groundwater composition. The paper concludes with the results of a numerical simulation of the soil and the foundation under load and a comparison with the limited measurements that have been collected.

The growing demand for public and sustainable transportation in heavily urbanized areas like Singapore requires construction of an increasing number of Metro Lines. Complicated technical challenges are associated with such an activity and settlement prediction models play a key role in assessing the tunnelling-related risk assessments and planning mitigation techniques. Although a significant amount of research has been performed to study the settlements induced by side-by-side twin tunnels, the settlement prediction of stacked tunnelling has been, relatively, limited. In this paper, stacked tunnelling induced settlements are predicted using 2D numerical simulation. The extensive data from the instrumentation measurements collected during the construction of a stacked configuration tunnel in Singapore Downtown Line MRT tunnels have been used to study the validity of the principle of superposition for stacked tunnels. Key observations are presented by comparing empirical, numerical and actual field settlement data. Using the Monte-Carlo simulation technique, the empirical trough parameter is back-calculated to fit the actual settlements observed in Kallang formation. This could be used for future settlement predictions in similar ground conditions.

The excavation system performance and ground movement behavior for the cut-and-cover excavation for the Downtown Line 2 Cashew Station in Singapore is presented. The information presented includes ground settlement profiles, wall deflection profiles, strut loads, and ground water monitoring behavior. Construction activities and remedial measures that were undertaken are also presented. Comparisons of the measured wall deflections and the ground surface settlements are also performed against the empirical methods/charts from the literature. It is hoped that this case study will provide useful reference and insights for future projects involving excavation in the Bukit Timah Granite residual soils.