Predicting RC Frame Response to Excavation-Induced Settlement

Abstract

In many tunneling and excavation projects, free-field vertical ground movements have been used to predict subsidence and empirical limits have been employed to evaluate risk. Validity of such approaches given the reality of two-dimensional ground movements and the influence of adjacent applied loads has been largely unknown. This paper employed analytical and largescale experimental efforts to quantify these issues, in the case of a reinforced concrete frame structure adjacent to an excavation. Nearly half of all soil and building movements occurred prior to installation of the first tie-back, even when conservative practices were applied. Freefield data generated a trough half the size of that recorded near the building frames. Empiricallybased relative gradient limits generally matched the extent and distribution of the damage. Application of various structural limits also generally reflected global experimental response but did not fully identify local damage distribution. Fully free-field data or failure to include accurate two-dimensional soil displacements under-predicted building response by as much as 50% for low-rise concrete frames without grade beams.

Impact of modeling architectural detailing for predicting unreinforced masonry response to subsidence

“…Good correlations between the experimental results and expected empirical damage levels are reported in detail elsewhere [20]. A full discussion of scaling and further description of the testing is provided in the following references [18][19][20]. Given the complexity of masonry modelling, the authors felt it was incumbent to employ a model for this study that had been verified under relevant loading conditions.…”

Solutions for Model-Scale, Tied-Back Anchors and Sheet Pile Walls

“…Measurements were taken with each excavation level and before and after the post-tensioning of the tieback anchors ( fig. 2) [22]. …”

Manufacturing, assembly, and testing of scaled, historic masonry for one-gravity, pseudo-static, soil-structure experiments

“…Details herein are reported for the excavation at design grade. These corresponded to excavation depths of 1.22 in Test 4, and 1.09m in Test 5 (see [24] for a detailed description of the excavation process). At the end of testing, the cumulative displacements and cracking occurring throughout the excavation process were recorded for benchmarking.…”

“…The two tests (Test 4 and Test 5) reported herein for verification were part of a six-test program some of which is reported elsewhere [24]. The scale-model Tests 4 and 5 each included two unreinforced brick walls (named West and East), which were respectively supported by shallow and deep footings.…”

“…To illustrate material selection and development, a portion of a larger testing program [22,24] to consider building response to adjacent excavation is herein described. A common urban scenario was selected, including a load-bearing, unreinforced masonry (URM) building with a semicontinuous, shallow foundation ( Figs.…”