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Characterising the Deformation Behaviour of Unbound Granular Materials in Pavement Structures
KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.ORCID iD: 0000-0002-5871-7587
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 [en]
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: urn:nbn:se:kth:diva-162277ISBN: 978-91-87353-68-0OAI: oai:DiVA.org:kth-162277DiVA: diva2:797690
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
List of papers
1. Moisture Influence on the Resilient Deformation Behaviour of Unbound Granular Materials
Open this publication in new window or tab >>Moisture Influence on the Resilient Deformation Behaviour of Unbound Granular Materials
2015 (English)In: International Journal of Pavement Engineering, ISSN 1029-8436Article in journal (Refereed) In press
Abstract [en]

The influence of moisture on the resilient deformation (RD) properties of unbound granular materials (UGMs) was investigated based on repeated load triaxial (RLT) tests. Results showed that the resilient modulus (MR) decreased with increasing moisture for a relatively low number of load cycles (N) where the deformation behaviour was mostly resilient with a negligible amount of associated accumulated permanent deformation (PD). Modelling attempts on this behaviour were quite satisfactory. Furthermore, the MR showed an increasing trend with increasing moisture, up to the optimum, when the N was relatively large with a significant amount of accumulated PD. Above the optimum, the MR generally decreased. Further investigation suggested that moisture aided the post-compaction (PC) and possible particle rearrangement that resulted in the increased PD and increased MR. The existing model did not work in this case indicating that the effect of PC on MR should be considered in modelling.

Place, publisher, year, edition, pages
UK: Taylor & Francis Group, 2015
Keyword
Unbound granular materials, resilient modulus, moisture, repeated-load triaxial test, modelling
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering; Transport Science
Identifiers
urn:nbn:se:kth:diva-162287 (URN)10.1080/10298436.2015.1019497 (DOI)
Note

QP 2015

Available from: 2015-03-24 Created: 2015-03-24 Last updated: 2015-03-25Bibliographically approved
2. Evaluation of Permanent Deformation Characteristics of Unbound Granular Materials by Means of Multistage Repeated-Load Triaxial Tests
Open this publication in new window or tab >>Evaluation of Permanent Deformation Characteristics of Unbound Granular Materials by Means of Multistage Repeated-Load Triaxial Tests
2013 (English)In: Transportation Research Record, ISSN 0361-1981, no 2369, 11-19 p.Article in journal (Refereed) Published
Abstract [en]

Rutting in flexible pavements is often associated with permanent deformation of the unbound granular layer. The current permanent deformation models are applicable only to a single stress path in repeated-load triaxial (RLT) tests, in which the load pulses are of constant amplitude. In this paper, a general approach using the time-hardening concept was introduced to model the permanent deformation of unbound granular materials (UGMs) continuously in multistage (MS) RLT tests, in which load pulses of a range of different amplitudes are applied, to represent field conditions realistically. With this formulation, three existing permanent deformation models were reconstructed, and one of the models was slightly modified, to suit MS loading conditions better. The material parameters of these models were then optimized for three UGMs used in pavement construction with data from MS RLT tests and application of a least squares curve-fitting method to the test data. The goodness-of-fit statistics were computed to evaluate and compare the quality of fit achieved with these models. The shakedown ranges were also calculated for each stress path of the MS RLT tests to compare these models in simulating these ranges. Generally, the time-hardening approach, for which the quality of fit is dependent on the chosen model, was found to work successfully. In this study, the selected models performed quite well, with the modified model showing the closest agreement to the test data. Thus, this approach has the potential to be applied for better modeling and prediction of pavement performance.

Keyword
Shakedown, Pavements
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-143744 (URN)10.3141/2369-02 (DOI)000331850700002 ()
Note

QC 20140327

Available from: 2014-03-27 Created: 2014-03-27 Last updated: 2015-03-25Bibliographically approved
3. Predicting permanent deformation behaviour of unbound granular materials
Open this publication in new window or tab >>Predicting permanent deformation behaviour of unbound granular materials
2015 (English)In: The international journal of pavement engineering, ISSN 1029-8436, 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
Keyword
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:nbn:se:kth:diva-162370 (URN)10.1080/10298436.2014.943209 (DOI)000355121800002 ()2-s2.0-84929952537 (ScopusID)
Note

QC 20150325

Available from: 2015-03-24 Created: 2015-03-24 Last updated: 2015-06-16Bibliographically approved
4. Characterizing the Impact of Moistureon the Permanent Deformation Behaviour of Unbound Gronular Materials
Open this publication in new window or tab >>Characterizing the Impact of Moistureon the Permanent Deformation Behaviour of Unbound Gronular Materials
2014 (English)Manuscript (preprint) (Other academic)
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering; Transport Science
Identifiers
urn:nbn:se:kth:diva-162566 (URN)
Note

Compendium of Papers of the 94th Annual Meeting of the Transportation Research Board, Washington DC, 2015. QS 2015

Available from: 2015-03-25 Created: 2015-03-25 Last updated: 2015-03-25Bibliographically approved
5. A Model for Predicting Permanent Deformation of Unbound Granular Materials
Open this publication in new window or tab >>A Model for Predicting Permanent Deformation of Unbound Granular Materials
2015 (English)In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 3, 653-673 p.Article in journal (Refereed) Published
Abstract [en]

A simple model has been proposed to characterize the accumulation of permanent deformation (PD) in Unbound Granular Materials (UGMs) under cyclic loading of variable magnitudes. The model was developed based on Multi-Stage (MS) Repeated-Load Triaxial (RLT) tests. The material parameters of this model can be evaluated using an MS RLT test. The model was validated by calibrating it for a few UGMs with a range of grain size distributions, moisture contents and degrees of compaction. The calibrated model was further validated by predicting the PD behaviour of some of these UGMs for different stress conditions. Generally, quite satisfactory predictions were obtained with this model with the advantage of reduced effort required for its calibration compared to some existing models. Additionally, the sensitivity of the parameters of this model to moisture, degree of compaction and grain size distribution was investigated with the aim of incorporating them into the model in future.

Place, publisher, year, edition, pages
UK: Taylor & Francis Group, 2015
Keyword
unbound granular materials, permanent deformation, multi-stage repeated-load triaxial test, model, moisture, grain size distribution
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering; Transport Science
Identifiers
urn:nbn:se:kth:diva-162376 (URN)10.1080/14680629.2015.1026382 (DOI)000355728600009 ()2-s2.0-84930761752 (ScopusID)
Note

QC 20150626

Available from: 2015-03-24 Created: 2015-03-24 Last updated: 2015-11-17Bibliographically approved

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