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Moisture Influence on Structural Behaviour of Pavements: Field and Laboratory Investigations
KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The structural behaviour of pavements in cold regions can considerably be affected by seasonal variation in environmental factors such as temperature and moisture content. Along with the destructive effect of heavy traffic loads, climatic and environmental factors can considerably contribute to pavement deterioration. These factors can influence the structural and functional capacity of the pavement structures which, as a result, can trigger and accelerate pavement deterioration mechanisms. Studies on the influence of variation of the environmental factors on the response and behaviour of pavement materials have shown that proper consideration to these factors must be given in realistic pavement design and analysis.

In flexible pavement structures, particularly with a thin hot mix asphalt (HMA) layer, unbound materials and subgrade soil largely contribute to the overall structural behaviour of the pavement system. In unbound materials, moisture content and its variation can significantly affect pavement layer stiffness and permanent deformation characteristics. Therefore, the moisture condition of pavements and its influence on the mechanical behaviour of pavement materials has been of interest among the pavement research community. A proper understanding of moisture transformation in pavement systems and its effects on pavement performance are important for mechanistic pavement design.

The present summary of this doctoral thesis is based on four main parts. The first part of the thesis covers field measurements and findings from a test section along county road 126 in southern Sweden and consists of two journal papers (paper I and II) tackling different aspects of the research topic. This test section is located in a relatively wet ground condition and consists of a thin flexible pavement structure with a deep drainage system. It is instrumented with subsurface temperature, volumetric moisture content and groundwater probes. The mechanical response of the pavement structure was investigated using Falling Weight Deflectometer (FWD) measurements. The second part of the thesis (paper III and IV) are based on laboratory experiments and investigates different recent approaches that have been proposed to apply principles of unsaturated soil mechanics for incorporating seasonal variation of moisture content into the resilient modulus models using matric suction. The third part of the thesis (paper V) builds a bridge that spans between the laboratory and field investigations with an attempt to evaluate one of the predictive models presented in Paper III. The fourth part of the thesis (paper VI) mainly focuses on the laboratory-based investigation of the permanent deformation characteristic of subgrade soils. In this part, the permanent deformation characteristics of two different silty sand subgrade soils were investigated and modelled using the data obtained from repeated load traxial tests.

Paper I mainly focuses on the spring-thaw weakening of the pavement structure. The environmental data collected using different sensors and the FWD tests were used to investigate variations in moisture content with thaw penetration and its influence on the stiffness of unbound layers and the pavement’s overall bearing capacity. Using the backcalculated layer stiffness and corresponding in situ moisture measurements in the unbound layers, a degree of saturation-based moisture-stiffness model was developed for the granular material and the subgrade.

In Paper II, the drainage system of the structure was manually clogged during a three month period in summer to raise the groundwater level and increase the moisture content of the layers. Along with the subsurface groundwater level and moisture content monitoring, the structural response of the pavement was studied. In this research work, the FWD tests were conducted at three different load levels. The stress dependent behaviour of the unbound granular layer and the subgrade soil were further studied using the multilevel loads FWD test data. Additionally, parameters of a nonlinear stress-dependent stiffness model were backcalculated and their sensitivity to in situ moisture content was studied.

In Paper III and IV, series of suction-controlled repeated load triaxial (RLT) tests were conducted on two silty sand (SM) subgrade materials. Several resilient modulus prediction models that account for seasonal moisture content variation through matric suction were summarized and after optimizing the model parameters, the capability of the prediction models in capturing the material response were evaluated.

In Paper V, an attempt was made to evaluate the proficiency of one of the suction-resilient modulus models using the field moisture content and FWD measurements from the Torpsbruk test site. The backcalculated subgrade stiffness dataset at different moisture contents were compared with resilient modulus models obtained from the suction-resilient modulus predictive model.

Paper VI presents an evaluation of several permanent deformation models for unbound pavement materials that incorporate the time-hardening concept using a series of multistage repeated load triaxial (RLT) tests conducted on silty sand subgrade materials. The permanent deformation tests were conducted at four different moisture contents with pore suctions measurement throughout the test. The effect of moisture content (matric suction) on the permanent deformation characteristics of the materials and the predictive model parameters were further investigated.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xiv, 61 p.
Series
TRITA-TSC-PHD, 15:003
Keyword [en]
Falling Weight Deflectometer (FWD), backcalculation, unbound material, subgrade, seasonal variation, moisture content, spring-thaw, drainage, pavement stiffness, field test, pavement instrumentation, resilient modulus, permanent deformation, repeated load triaxial test, unsaturated soil, matric suction.
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering; Transport Science
Identifiers
URN: urn:nbn:se:kth:diva-162076ISBN: 978-91-87353-67-3 (print)OAI: oai:DiVA.org:kth-162076DiVA: diva2:796833
Public defence
2015-04-10, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150324

Available from: 2015-03-24 Created: 2015-03-20 Last updated: 2015-03-24Bibliographically approved
List of papers
1. Investigation of a pavement structural behaviour during spring thaw using falling weight deflectometer
Open this publication in new window or tab >>Investigation of a pavement structural behaviour during spring thaw using falling weight deflectometer
2013 (English)In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 14, no 1, 141-158 p.Article in journal (Refereed) Published
Abstract [en]

The response of an instrumented flexible pavement structure in southern Sweden, subjected to seasonal freezethaw cycles, was investigated during the spring thaw and the recovery periods in 2010. The pavement environmental condition was continuously monitored by measuring subsurface temperature and moisture contents. The mechanical behaviour of the pavement structure was investigated by conducting frequent falling weight deflectometer (FWD) measurements throughout the study period. Considerable decrease in the pavement-bearing capacity was observed as thaw penetrated the pavement structure and consequently moisture content increased in all pavement unbound layers. Highest annual moisture content in the subgrade upper section was registered as thaw penetrated the subgrade and pavement exhibited its weakest structural condition. The analyses of the deflection basin indices and back-calculated unbound layer stiffness from the FWD measurements exhibited a clear correlation with the measured subsurface moisture content. Furthermore, the dissipated energy measured from the FWD timehistory data was calculated, exhibiting its highest annual value during the thawing period. Using the back-calculated layer stiffness and moisture measurements in unbound layers, a degree of saturation-based moisture-stiffness model was developed for the granular layer and the subgrade. This model fell on a unique curve showing promising agreement with the laboratory-based model proposed by Mechanistic-Empirical Pavement Design Guide that analytically predicts changes in modulus due to changes in moisture.

Keyword
falling weight deflectometer, spring thaw, bearing capacity, moisture content' deflection indices, resilient modulus-moisture model, back-calculation
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-119727 (URN)10.1080/14680629.2012.754600 (DOI)000315352600009 ()2-s2.0-84878254877 (Scopus ID)
Note

QC 20130325

Available from: 2013-03-25 Created: 2013-03-21 Last updated: 2017-12-06Bibliographically approved
2. Moisture-Sensitive and Stress-Dependent Behavior of Unbound Pavement Materials from In Situ Falling Weight Deflectometer Tests
Open this publication in new window or tab >>Moisture-Sensitive and Stress-Dependent Behavior of Unbound Pavement Materials from In Situ Falling Weight Deflectometer Tests
2013 (English)In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 2335, 121-129 p.Article in journal (Refereed) Published
Abstract [en]

In an instrumented flexible pavement with a subsurface drainage system, a field study was performed to investigate the influence of water on the response of the pavement structure. The drainage system of the structure was clogged for 3 months; this condition allowed the ground-water to rise and the structure to undergo high moisture conditions. Reopening of the drainage system permitted the structure to approach its previous draining hydrological state. Along with monitoring of subsurface groundwater level and moisture content, the structural response of the pavement was studied by conducting frequent falling weight deflectometer tests with multilevel loads. The stress sensitivity of the unbound layers and the influence of moisture on their stiffness were studied, with the intent of using the data to determine the unbound materials' nonlinear parameters through a backcalculation algorithm. The groundwater level rose rapidly after the drainage system was clogged. This rise in groundwater level significantly affected the overall stiffness of the pavement structure, and the backcalculated stiffness of the unbound layers decreased as their moisture content increased. Furthermore, the unbound layers exhibited stress-dependent behavior to multilevel loads. The subgrade showed a stress-softening response in an unsaturated condition and stress-independent behavior in a saturated state. The granular layer exhibited stress-hardening behavior. Backcalculation of the unbound nonlinear parameters determined by the universal extended k-theta model revealed that the k(1) parameter decreased with increasing moisture content for both the unbound granular layer and the unsaturated fine-grained subgrade material.

Keyword
Falling weight deflectometer (FWD), High-moisture conditions, Non-linear parameters, Pavement structures, Stress independents, Subsurface drainage system, Unbound pavement materials, Unsaturated condition
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:kth:diva-141758 (URN)10.3141/2335-13 (DOI)000329979800013 ()2-s2.0-84882937916 (Scopus ID)
Note

QC 20140221

Available from: 2014-02-21 Created: 2014-02-21 Last updated: 2017-12-05Bibliographically approved
3. Modelling resilient modulus seasonal variation of Silty sand subgrade soils with matric suction control
Open this publication in new window or tab >>Modelling resilient modulus seasonal variation of Silty sand subgrade soils with matric suction control
2014 (English)In: Canadian geotechnical journal (Print), ISSN 0008-3674, E-ISSN 1208-6010, Vol. 51, no 12, 1413-1422 p.Article in journal (Refereed) Published
Abstract [en]

Resilient modulus of unbound materials is an important parameter in the mechanistic design of pavements. Although unbound layers are frequently in a partially saturated state, a total stress approach is conventionally used in modelling the material behaviour and therefore pore pressure effects are not considered. In fine‑grained unbound materials, the saturation state can affect their mechanical behaviour due to pore pressure effects. In this study a modified test procedure and a predictive resilient modulus model that takes into account the subgrade soil matric suction as a stress state variable is presented. Two different silty sand subgrade materials were tested in unsaturated conditions using series of repeated load triaxial tests under controlled pore suction conditions to study its influence on the resilient modulus. The test data were further used to obtain the resilient modulus model regression parameters that accounts for moisture content variations through the matric suction parameter. Generally, the prediction model could effectively capture the resilient modulus behaviour of the subgrades with respect to changes in the normal stress state and the matric suction. Given the completeness of this method, this prediction model is recommended as an improved approach in capturing the moisture content effects on the material stiffness properties.

Keyword
Subgrade, Resilient Modulus, Unsaturated Soil, Matric Suction, Environmental Effects, Moisture Content.
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-151373 (URN)10.1139/cgj-2013-0484 (DOI)000345906600005 ()2-s2.0-84914128543 (Scopus ID)
Note

QC 20150116

Available from: 2014-09-18 Created: 2014-09-18 Last updated: 2017-12-05Bibliographically approved
4. Resilient modulus modelling of unsaturated subgrade soils: laboratory investigation of silty sand subgrade
Open this publication in new window or tab >>Resilient modulus modelling of unsaturated subgrade soils: laboratory investigation of silty sand subgrade
2015 (English)In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 3, 553-568 p.Article in journal (Refereed) Published
Abstract [en]

In flexible pavement structures, stiffness of unbound granular layers and subgrade soil significantly contribute to the overall performance of the pavement system. The stiffness of pavement unbound materials is widely characterised by the resilient modulus, M-r, which is obtained from repeated load triaxial (RLT) tests. Although pavement unbound materials are usually in partially saturated conditions and experience seasonal moisture content and therefore suction variations in the field, their stiffness is conventionally characterised using the total stress approach in which the effect of soil suction is not taken into account. Thus, an enhanced approach in predicting the stiffness of subgrade soils has to account for the partially saturated conditions and incorporate soil suction (i.e. matric suction) in the M-r constitutive models. In this study, several M-r prediction models that take into account the effect of pore suction were investigated. The M-r data set from an experimental investigation of two silty sand subgrade soils that was conducted using a suction-controlled RLT testing apparatus was used to optimise the parameter of these models. The capability of the M-r predictive models in capturing the resilient modulus behaviour of the silty sand subgrade soils and its variation due to seasonal changes in the moisture content (soil suction) were evaluated. It was observed that the M-r models that combine the three fundamental stress state variables (confining stress, deviator stress and matric suction) performed better in capturing the resilient modulus behaviour of the subgrade materials.

Keyword
moisture content, seasonal variation, unsaturated subgrade, resilient modulus, matric suction, repeated load triaxial test
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-162082 (URN)10.1080/14680629.2015.1021107 (DOI)000355728600004 ()2-s2.0-84930753258 (Scopus ID)
Note

QC 20150626

Available from: 2015-03-20 Created: 2015-03-20 Last updated: 2017-12-04Bibliographically approved
5. Evaluating a Model for Seasonal Variation of Silty Sand Subgrade Resilient Modulus with FWD Tests
Open this publication in new window or tab >>Evaluating a Model for Seasonal Variation of Silty Sand Subgrade Resilient Modulus with FWD Tests
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The stiffness of unbound pavement material is one of the main input parameters in mechanisticdesign and analysis of pavement systems. This material property is usually moisture dependentand therefore, most of the unbound pavement layers exhibit seasonal variation in stiffness as thepavement moisture regime changes throughout the year. Therefore, this variation should be takeninto account in any realistic pavement design. In unbound materials with high fine content,change in moisture content can result in change in the stress state due to suction effects. In thisstudy, an enhanced predictive resilient modulus model that accounts for seasonal variation bymeans of suction measurement is presented. A silty sand subgrade was tested using a modifiedRepeated Load Triaxial (RTL) system under different moisture (suction) conditions and a set ofresilient modulus model regression parameters were determined. The capability of the model tocapture seasonal moisture variation effects was further evaluated using field data. A series ofFalling Weight Deflectometer (FWD) tests with multi-level loads were conducted on aninstrumented pavement structure where the moisture content of the subgrade was changed bymanipulating the pavement drainage condition. The resilient moduli obtained from the modelwere compared to the backcalculated stiffness data obtained from FWD tests conducted atdifferent moisture conditions. Overall, a good agreement was observed between thelaboratory-based resilient modulus and the backcalculated stiffness. The resilientmodulus-suction model could efficiently capture the moisture content effects.

Keyword
Resilient modulus, backcalculation, falling weight deflectometer, seasonal variation, moisture content, silty subgrade
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-162084 (URN)
Note

QS 2015

Available from: 2015-03-20 Created: 2015-03-20 Last updated: 2015-03-24Bibliographically approved
6. Permanent Deformation Characteristics of Silty Sand Subgrades from Multistage RLT Tests
Open this publication in new window or tab >>Permanent Deformation Characteristics of Silty Sand Subgrades from Multistage RLT Tests
2015 (English)In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 18, no 3, 236-246 p.Article in journal (Refereed) Published
Abstract [en]

Rutting is one of the main forms of distresses in thin flexible pavement structures, often associated with accumulation of permanent deformation in unbound granular layers and subgrade soils under traffic loading. Realistic prediction of surface rutting requires models that can reliably capture the cumulative plastic deformation of pavement unbound layers under repeated loads. This study presents an evaluation of three models that incorporate the time-hardening concept for prediction of permanent deformation of silty sand subgrade materials. A series of multistage repeated load triaxial (RLT) tests, in which the material underwent a wide range of continuous stress conditions, were carried out on two silty sand subgrades. The RLT tests were conducted at four different moisture contents in which pore suctions were measured throughout the test. In the modelling of the permanent deformations, the effective stress approach was used taking into account the effects of soil suctions. The material parameters of the predictive models were optimised using the RLT test data and the effect of moisture content (matric suction) on the permanent deformation characteristics of the materials and the predictive model parameters were investigated. Generally, it was observed that the modified models that are based on the shakedown approach performed reasonably well in capturing the permanent deformation behaviour of the selected subgrade materials with minor discrepancies between the models. This indicates that using multistage RLT tests can be an efficient approach for characterising the permanent deformation behaviour of subgrade soils.

Place, publisher, year, edition, pages
Taylor & Francis, 2015
Keyword
Permanent deformation, subgrade soil, multistage repeated load triaxial test, moisture content, matric suction, modelling
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-162094 (URN)10.1080/10298436.2015.1065991 (DOI)000395089600005 ()2-s2.0-84937805207 (Scopus ID)
Note

QC 20160310

Available from: 2015-03-20 Created: 2015-03-20 Last updated: 2017-12-04Bibliographically approved

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