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Predicting permanent deformation behaviour of unbound granular materials
KTH, School of Architecture and the Built Environment (ABE), Transport Science. Swedish National Road and Transport Research Institute (VTI).ORCID iD: 0000-0002-5871-7587
KTH, School of Architecture and the Built Environment (ABE), Transport Science. Swedish National Road and Transport Research Institute (VTI).
2015 (English)In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 16, no 7, 587-601 p.Article in journal (Refereed) Published
Abstract [en]

To reliably predict the permanent deformation behaviour of unbound granular materials (UGM) in a pavement structure, the material parameters of the constitutive models used in design should be evaluated using a multi-stage (MS) loading approach. This paper investigated the prediction of the accumulation of permanent strain in UGM using some current models, extended applying the time-hardening approach, based on MS repeated load triaxial tests (RLTTs). The material parameters of these models were optimised for five different UGM used in pavement construction using the MS RLTT data with a specific set of stress levels. With these models, the accumulations of permanent strain in the same materials for MS RLTTs with a different set of stress levels were predicted. Using this approach, three out of the four models performed very well, which may be further developed for field conditions for better prediction of rutting.

Place, publisher, year, edition, pages
UK: Taylor & Francis Group, 2015. Vol. 16, no 7, 587-601 p.
Keyword [en]
model, multi-stage repeated load triaxial test, permanent deformation, timehardening, Unbound granular materials
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering; Transport Science
Identifiers
URN: urn:nbn:se:kth:diva-162370DOI: 10.1080/10298436.2014.943209ISI: 000355121800002Scopus ID: 2-s2.0-84929952537OAI: oai:DiVA.org:kth-162370DiVA: diva2:797707
Note

QC 20150325

Available from: 2015-03-24 Created: 2015-03-24 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Characterising the Deformation Behaviour of Unbound Granular Materials in Pavement Structures
Open this publication in new window or tab >>Characterising the Deformation Behaviour of Unbound Granular Materials in Pavement Structures
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Unbound granular materials (UGMs) used in the base and sub-base layers of flexible pavements play a significant role in the overall performance of the structure. Proper understanding and characterization of the deformation behaviour of UGMs in pavement structures are, therefore, vital for the design and maintenance of flexible pavements. In this study, the resilient deformation (RD) and the permanent deformation (PD) behaviour of UGMs were investigated for the better understanding and improved modelling of these deformation characteristics. The study is based on a series of repeated-load triaxial (RLT) tests carried out on several UGMs commonly used in pavement structures. Here, the influences of stress level and moisture content - two of the most significant factors affecting the deformation behaviour of UGMs - were analysed. The effects of the grain size distribution and the degree of compaction were also considered.

The study on the RD behaviour indicated that the resilient stiffness (MR)of UGMs increases with the increased bulk stress level, which can be satisfactorily described by the k-θ model. Moisture was found to negatively impact the MR as long as the deformation was mostly resilient with a negligible amount of accumulated PD. Analysis of the influence of moisture on the parameters k1 and k2 of the k-θ model showed that k1 decreases with increased moisture and k2 is relatively insensitive to moisture. Based on these observations, a simple model was developed for the impact of moisture on MR. The performance of this model was comparable to an existing moisture dependent MR model. In contrast, it was further observed that at the later stages of the RLT tests, after a relatively large number of load applications, the MR increased with increased moisture up to the optimum moisture content. This occurred when the RD was accompanied by a significant amount of PD. Further investigation suggested that moisture aided the post-compaction (PC) and possible particle rearrangement that resulted in the increased PD and increased MR. In this case k1 decreased, whereas k2 increased, with increased moisture. The existing MR-moisture model did not work for this behaviour. This suggests that the effect of PC on MRshould be considered in modelling. However, although not explored in this study, it may be possible to simulate this effect of increase in MR with increased moisture due to PC using the proposed model if k2 is expressed as a function of moisture.

The PD characteristics of UGMs were investigated based on the multistage (MS) RLT test. In contrast with the single stage (SS) RLT test, the MS RLT test accounts for the effect of stress history and enables a comprehensive study of the material behaviour under cyclic stresses of various magnitudes. Since the existing PD models cannot be directly applied for the MS loading procedure, a general formulation based on the time hardening concept was derived that can be used to extend the models for the MS loading conditions. Based on this formulation, some of the current models were calibrated and their performance in predicting the PD behaviour in MS RLT tests was compared. The investigation regarding the impact of moisture on PD showed that moisture significantly increases the accumulation of PD. Generally, materials with finer grading showed more sensitivity to moisture with regards to both PD and RD. To characterize the impact of moisture, moisture sensitivity of different grain size distributions and the impact of the degree of compaction on PD with reduced effort, a simple model was proposed. Unlike some of the well-performing existing models, this model can be calibrated using a single MS RLT test without requiring any separate static failure triaxial tests. This model was validated using the MS RLT test data with satisfactory results. The sensitivity of the parameters of this model was studied with respect to moisture content, degree of compaction and grain size distribution. Some reasonable trends for the sensitivity of the parameters to these influential factors were obtained, which suggests that these may be further developed to incorporate into the model.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xxi, 76 p.
Series
TRITA-TSC-PHD, 15:004
Keyword
unbound granular materials, resilient modulus, permanent deformation, moisture, model, multistage, repeated-load triaxial test
National Category
Engineering and Technology Infrastructure Engineering
Research subject
Transport Science; Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-162277 (URN)978-91-87353-68-0 (ISBN)
Public defence
2015-04-08, F3, Lindstedtsvägen 26, KTH Royal Institute of Technology, Stockholm, 13:30 (English)
Opponent
Supervisors
Note

QC 20150325

Available from: 2015-03-25 Created: 2015-03-24 Last updated: 2015-03-25Bibliographically approved

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Rahman, Mohammad Shafiqur

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