Lateral Spreading of Soft Soils - WisDOT Research

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Title: A Framework for 3D Nonlinear Ground-Foundation Analysis Author(s): Lu, Jinchi; Elgamal, Ahmed; Shantz, Thomas Year: 2009 Source/URL: 2009 GeoHunan International Conference, pages 189-196; http://tris.trb.org/view.aspx?id=900844 Description: 8 pages Contents: Three-dimensional nonlinear finite element simulations are becoming increasingly feasible for transportation geotechnical applications. This paper presents a robust and versatile framework that helps streamline the use of finite elements for seismic response of soil-structure systems. In this regard, a Windows-based graphicaluser-interface OpenSeesPL is developed for pile-ground interaction analysis. Particularly suited to seismic applications, the open-source computational platform OpenSees is employed throughout. OpenSeesPL allows convenient studies of three-dimensional seismic (earthquake) and/or push-over pile analyses. Various ground modification scenarios may be also addressed by appropriate specifications of the material within the pile zone. To illustrate the capabilities of OpenSeesPL, two studies are presented in this paper. Lateral spreading effects on pile foundations are modeled, followed by an investigation of ground remediation in a mildly sloping silt stratum. Along with the insights gained from these studies, the reported effort aims to highlight the analysis framework capabilities and range of potential applications. Title: Geogrid-Reinforced Roadway Embankment on Soft Soils: A Case Study Author(s): Vega-Meyer, Reinaldo; Garrido, Roberto Sosa; Piedrabuena, Alberto Ramírez; Larios, Ignacio Narezo; Lapuente, Ramón Pico Year: 2007 Source/URL: Soft Soil Engineering: Proceedings of the Fourth International Conference on Soft Soil Engineering, pages 129-138; http://www.crcnetbase.com/doi/abs/10.1201/9781439833926.pt2 Description: 10 pages Contents: Building earth structures on soft soils is one of the toughest challenges in civil engineering. Due to the fill embankment and surcharges, the settlements associated to the overburden pressures are one of the major concerns in roadway embankment construction. Several methods of support improvement have been in practice for years (e.g. excavation/fill replacement, stone filling, Corduroy, etc.), but recently, geosynthetic reinforcement has been successfully incorporated as an efficient way to improve the weak soil conditions. This paper focuses on a case study that introduces a geogrid-reinforced roadway embankment located in the Texcoco Lake, near Mexico City, Mexico. The structure consists of an embankment with variable heights to be built in two different conditions: dry and saturated. The most critical section was in the saturated zone (lake) where the maximum embankment height was 2.80m and the water level was at 1.80 m, leaving only 1.0m of dry embankment body. The embankment was built on highly compressible saturated clay layers up to 40.0m deep, and moisture of up to 300%. The paper presents project design information, settlement observations, and performance evaluation. The performance of the embankment was observed during and after construction using inclinometers, and deep and surface surveying equipment. A presentation of this performance and results about the predicted vs. actual embankment settlements are included in the paper. Title: Characteristics and Engineering Properties of the Soft Soil Layer in Highway Soil Subgrades Author(s): Hopkins, Tommy C.; Beckham, Tony L.; Sun, Liecheng Year: 2006 Source/URL: Kentucky Transportation Cabinet final report; http://www.ktc.uky.edu/Reports/KTC_06_13_SPR_270_03_1F.pdf Description: 101 pages Contents: The objective of this research was to examine the conditions and characteristics of soil subgrades that had been stabilized using mechanical compaction. Goals of the study are to identify and examine the engineering properties and behavior of the “soft layer’ of material observed at the top of untreated, highway pavement soil subgrades. Alternative methods of preventing, or mitigating, the development of the soft layer are discussed. Evidence is presented that shows that a soft layer of soil frequently develops at the top of untreated, highway soil subgrades. Data are presented that show strengths obtained from mechanical compaction are largely destroyed when untreated compacted soils are exposed to moisture. California Bearing Ratio (CBR) values of compacted clayey soils initially are high but become small when exposed to saturation. In situ CBR values measured at the tops of untreated subgrades, where mechanical compaction was the only means used to stabilize the soil subgrade, were smaller than unsoaked and soaked laboratory Kentucky CBR values. At the 85th percentile test value, the laboratory KYCBR value of compacted, unsoaked clayey specimens was 11.5 while the CBR value of soaked specimens was 3.0. For comparison, the in situ CBR value of untreated subgrades at the 85th percentile test value, as shown in this study, was only 2. Using a bearing capacity model, based on limit equilibrium of layered media, bearing capacity 2
analyses of flexible pavement sections were performed. The analyses show that when the in situ CBR is equal to or below 3, the pavement was unstable, i.e., the factor of safety against failure was 1.0 or below. However, when the in situ CBR value was 6, or greater, the pavement was generally stable and the factor of safety was 1.5, or greater. Chemical admixture stabilization of soil subgrades is the most effective means of maintaining large CBR values during construction and throughout the life of the pavement. In situ CBR values at the 85th percentile of tests performed on the tops of soil subgrades treated chemically with lime kiln dust, hydrated lime, and portland cement and that had been in place for 8 to 15 years were 24, 27, and 59, respectively. At the 85th percentile test value, in situ CBR values of chemically treated subgrades were about 12 to 30 times larger than the in situ CBR value of 2 of untreated subgrades. Title: Time-Dependent Behaviour of Soft Soils During Embankment Construction – A Numerical Study Author(s): Brinkgreve, R. B. J. Year: 2004 Source/URL: Chapter 89 of Numerical Models in Geomechanics, pages 631-637; http://www.crcnetbase.com/doi/abs/10.1201/9781439833780.ch89 Description: 7 pages Contents: In this paper the results of a numerical study are presented in which the construction of an embankment on soft soils is simulated using the finite element method. Three different models are compared: The Mohr-Coulomb model, the Modified Cam-Clay model and a creep model that is based on Modified Cam-Clay. It will be shown that advanced soil models will predict horizontal deformations away from the embankment (lateral spreading) during the consolidation phase, as generally observed in practice, whereas the simple Mohr-Coulomb model will unrealistically predict horizontal deformations towards the embankment (lateral confinement) due to the elastic compaction during consolidation. The key issue is to take sufficient irreversible shear deformation during the consolidation phase into account. Even after consolidation, horizontal deformations may continue to increase. This can only be predicted if creep effects are taken into account. It is shown in which way certain parameters in the creep model influence the computational results and how parameters should be selected in order to make realistic predictions. Title: Design of Short Aggregate Piers to Support Highway Embankments Author(s): White, David J.; Suleiman, Muhannad T. Year: 2004 Source/URL: Transportation Research Board 83rd Annual Meeting; http://www.gfcwest.com/tech_papers/TP29.pdf Description: 36 pages Contents: (Excerpt from page 18 of the PDF) In addition to vertical settlements, lateral spreading of the embankment foundation soils should be given consideration, especially for sensitive structures such as culverts and utilities where lateral spreading effects can be a serious problem (8). During embankment fill placement, stress applied to the foundation soil can result in exceeding the preconsolidation pressure in the foundation soils. When this occurs, continued fill placement results in undrained shear distortion under constant effective vertical stress (36). Case histories show that lateral displacement (Δδ L ) is approximately equal to the vertical settlement (Δδ V ) for undrained loading conditions. For long-term drained conditions, however, lateral displacement has been observed to be a smaller fraction of the vertical settlement (37). Assuming: (1) aggregate pier installation renders the matrix soil into an overconsolidated state as described by Handy (18); (2) stress concentrates on the pier elements; and (3) piers act as a drainage pathway to facilitate a drained response, Equation 15 can be used as a simplified empirical solution to estimate lateral spreading. (15) Title: Settlement Calculations of a Highway Embankment on Soft Ground Author(s): Herle, I.; Herle, V.; Novotna, I.; Karcher, C.; Nybel, K. Year: 1999 Source/URL: Twelfth European Conference on Soil Mechanics and Geotechnical Engineering, pages 1089-94; http://tris.trb.org/view.aspx?id=514772 Description: 6 pages Contents: The settlement of a highway embankment on soft soil is calculated using a standard method of the deformation modulus and compared with a more sophisticated approach using hypoplastic and viscoplastic models. Advantages of realistic soil models are discussed and a comparison with the measured in situ settlement is given. 3
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