Browsing by Subject "Expansive soil"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item The behavior of drilled shaft retaining walls in expansive clay soils(2013-08) Brown, Andrew C.; Gilbert, Robert B. (Robert Bruce), 1965-Drilled shaft retaining walls are common earth retaining structures, well suited to urban environments where noise, space, and damage to adjacent structures are major considerations. The design of drilled shaft retaining walls in non-expansive soils is well established. In expansive soils, however, there is no consensus on the correct way to account for the influence of soil expansion on wall behavior. Based on the range of design assumptions currently in practice, existing walls could be substantially over- or under-designed. The goal of this research is to advance the understanding of the effects of expansive clay on drilled shaft retaining walls. The main objectives of this study are to identify the processes responsible for wall loading and deformation in expansive clay, to evaluate how these processes change with time, and to provide guidance for design practice to account for these processes and ensure adequate wall performance. The primary source of information for this research is performance data from a four-year monitoring program at the Lymon C. Reese research wall, a full-scale instrumented drilled shaft retaining wall constructed through expansive clay in Manor, Texas. The test wall was instrumented with inclinometers and fiber optic strain gauges, and performance data was recorded during construction, excavation, during natural moisture fluctuations, and during controlled inundation tests that provided the retained soil with unlimited access to water. In addition to the test wall study, a field assessment of existing TxDOT drilled shaft retaining walls was conducted. The main process influencing short-term wall deformation was found to be global response to stress relief during excavation, which causes the wall and soil to move together without the development of large earth pressures or bending stresses. Long-term wall deformations were governed by the development of drained conditions in both the retained soil and the foundation soil after approximately eight months of controlled inundation testing. To ensure adequate wall performance, the deformations and structural loads associated with short- and long-term conditions should be combined and checked against allowable values.Item A case study of pavement failures in Central Texas due to expansive soils(2014-12) Jouben, Andrew James; Gilbert, Robert B. (Robert Bruce), 1965-The volumetric strains induced in the subgrade of a pavement or light foundation by the swelling and shrinking of expansive soils routinely cause distress, and ultimately failure of the structure. Additionally, shallow embankment slope failures have also been shown to cause damage to pavements throughout Central Texas. As such, the main objective of this project was to correlate observed field pavement distresses, attributed to expansive soil movement, to results obtained from laboratory forced ventilated swell-shrink tests. Additionally, the author wished to analyze if edge distresses could be attributed to shallow slope stability failures. This research was conducted with the cooperation of the Capital Area Pavement Engineering Council (CAPEC); a multi-agency entity with the goal of mitigating or eliminating historical pavement distresses with roadways constructed over highly expansive soils. Forced ventilated swell-shrink tests were conducted on specimens from six specific test section locations. In general, the magnitude of shrinkage strains measured in the laboratory were larger for specimens obtained from severely distressed roadway sections.Item Driven piles in central Texas expansive soils(2011-12) Signor, Clayton Avery; Gilbert, Robert B. (Robert Bruce), 1965-; Rathje, Ellen M.Expansive soils cause more damage to structures annually than a combination of other major natural disasters. Because of the cost to our society, all means and methods need to be fully explored to mitigate the problems associated with expansive soils. This study will present a foundation design approach that is under utilized in this application, driven piles. The main objective of the study is to present pile test results and analysis from four driven pile project sites in three types of expansive soils found in central Texas: Del Rio formation, Taylor/Navarro formation, and expansive alluvium. Observations of the pile driving operations will be reported to highlight pile design considerations like predrilling and open versus close-ended pipe piles and the type of equipment involved. High strain dynamic pile tests were conducted on each of the four studies with rigorous signal matching analysis from the CAse Pile Wave Analysis Program (CAPWAP). Ultimate pile capacities ranged from 73 to 311 kips with an average of 61% of the total capacity coming from the pile shaft and were two to six times the structural capacity needed. Static design methods under-predicted, dynamic formulas over-predicted, and wave equation analysis conducted with GRLWEAP closely modeled test results. Average unit skin frictions ranged from 0.55 to 4.7 ksf. Restrike pile tests of 1 to 17 days after initial driving reported 30 to 100% shaft capacity gain. All open-ended pipe piles driven produced soil plugs ranging from 4 to 14 feet thick, and it was observed that harder driving conditions produced thinner soil plug thicknesses. Small diameter, thick-walled, open-ended pipe piles reached penetration of twice the depth of designated zone of seasonal moisture change without problem. The observed production rate of the driven piles was on average 8 minutes which implied daily production of 15 to 40 piles. Predrills or augered holes should be specified for underground obstructions found in soil investigation. Future studies on pile-supported foundations should measure localized movement correlated with seasonal moisture changes in expansive soil, or active zone, to confirm long-term performance. Also uplift forces need to be observed from tests on fully-instrumented and loaded driven piles to determine required pile embedment length below the active zone to withstand movement.