Analysis of reinforced embankment on soft and hard groung using working stress k-stiffness method | |
| Author | Ocay, Barry Teatro |
| Call Number | AIT Thesis no.GE-11-04 |
| Subject(s) | Embankments Soils--Reinforcement Soil-structure interaction Reinforced soils Soil stabilization |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Geotechnical and Geoenvironmental Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. GE-11-04 |
| Abstract | In this study, existing design methods for internal stability design of geosynthetic and steel reinforced soil structures that are in accordance with the limit equilibrium concepts were compared with working stress K-stiffness method based on the data obtained from five full-scale reinforced embankments – two were constructed on hard ground and three on soft ground. A common element of this data set is that all the embankments were backfilled with cohesive-frictional soils. These embankments were reinforced with steel wire grids, metallic strips, hexagonal wire mesh and geogrid materials particularly polyester (PET), polypropylene (PP) and high density polyethylene (HDPE). Generally, the reinforcement loads predicted by AASHTO simplified method and FHWA structure stiffness method were consistently higher than those of working stress K-stiffness method and the measured reinforcement loads for all cases of embankments on hard and soft ground immediately after construction and at any periods after the completion of the embankment. However, the original K-stiffness method constantly overpredicted the magnitudes of reinforcement loads immediately after construction for all embankment case histories but load predictions were observed to be inconsistent with the measured loads as ground settlement increased. Moreover, the modified K-stiffness method achieved a good agreement with the measured loads for metallic reinforced embankment on soft and hard ground only at duration immediately after construction. For the case of geogrid and hexagonal wire mesh reinforced embankment, the modified K-stiffness method constantly underpredicted the values of maximum reinforcement load for embankments on soft and hard ground. Subsequently, further modification of K-stiffness method that considers the influence of foundation settlement on the magnitude and distribution of reinforcement load was carried out using the observed data. Furthermore, the load distribution factor, Dtmax, and the reinforcement load prediction approach for geogrid and hexagonal wire mesh reinforced embankments were also modified to be the same as both types of embankment showed the same behavior on the distribution and magnitude of reinforcement loads. A uniform value of Dtmax equal to 1.0 was proposed starting from the normalized depth, (z +S)/(H + S), value of 0.4 to the base of the reinforced embankment. The further modified K-stiffness method resulted to a flexible design method that can be efficiently adopted to estimate the reinforcement loads for embankments backfilled with cohesivefrictional soils on soft and hard ground foundation with confidence as supported by its mean of bias values of 0.91 with COV of 19.40% at any durations after the construction. Moreover, the load prediction gap between AASHTO simplified method and the original K-stiffness method was closed when the influence of facing was neglected for the case of steel wire grid embankment. However, if an incremental precast concrete facing was used instead, the AASHTO simplified method required a closely spaced reinforcement layers which was about 35% less than the spacing required for the original K-stiffness method. For a normalized settlement ratio, S/γH, less than 1.25 where the results obtained using the modified and the further modified K-stiffness method were almost equal, the AASHTO simplified method required a more closely spaced reinforcement layers which was about 70% less than the spacing required for the modified and further modified K-stiffness method. iii On the global equilibrium analysis based on simple statically determinate approach, the AASHTO simplified method and the FHWA structure stiffness method satisfactorily passed the statical equilibrium criterion with a factor of safety against soil wedge failure of about 4.5 and 5.5, respectively. However, the original and modified K-stiffness method failed to satisfy this requirement for cases of embankments with values of global stiffness factor lesser than or equal to 0.396 and with stiff facing element with values of facing stiffness factor lesser than or equal to 0.692. Additionally, the further modified K-stiffness method where the potential deficit on the summation of maximum reinforcement load for every layer due to the contribution of facing stiffness was compensated by the anticipation of post-construction load increase due to foundation settlement satisfactorily passed the global equilibrium check against wedge failure with an average factor of safety of 3.0. |
| Year | 2012 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. GE-11-04 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Geotechnical Engineering (GE) |
| Chairperson(s) | Bergadp. Dennes T.; |
| Examination Committee(s) | Noppadol Phien-wej;Pham, Huy Giao; |
| Scholarship Donor(s) | Asian Institute of Technology Fellowship; |
| Degree | Thesis (M. Eng.) - Asian Institute of Technology, 2011 |