PURPOSES : In this study, the applicability of the water content, suction, and suction stress in a resilient modulus prediction model for a subbase was reviewed. METHODS : To compare the applicability of water content, suction, and suction stress models for resilient modulus prediction, the suction stress was determined based on the soil water characteristic curve. The model parameters for each approach were derived from the measured resilient moduli. Finally, the relationships between the degree of saturation and resilient modulus were analyzed using the calculated model parameters. RESULTS : Prediction models of the resilient modulus based on water content and suction demonstrated high correlation with measured values, but overestimated the resilient modulus at saturation levels beyond the laboratory testing range. In contrast, the model accounting for suction stress effectively reduced this overestimation, likely owing to a decrease in suction stress as the suction increased. CONCLUSIONS : Based on the above results, the resilient modulus of subbase materials could be estimated through the change in the degree of saturation and the stress-dependent resilient modulus model using the suction stress proposed in this study.

PURPOSES : In this study, an empirical approach was established to estimate the parameters of the resilient modulus based on various geotechnical properties of subgrade soils. METHODS : Multiple regression analyses were performed to analyze the relationship between resilient modulus (k1) and deformation. The most important factors are the #200 sieve passing ratio, moisture content, and dry unit weight of the soil. The applicability of this approach was verified using selected field data and the literature. RESULTS : The correlation between the results predicted using the prediction equation of the model constant (k1) and the actual k1-value was high. The applicability of the prediction equation was considered high owing to its high suitability with the existing data. The range of values obtained using the constant prediction equation of the proposed model was also judged to be reasonable. In the comparison of the CBR value of the subgrade material of the actual design section and the predicted elastic modulus (k1), almost no relationship was observed between the CBR and the model coefficient (k1). Thus, the estimation of the elastic modulus through CBR is likely to contain errors. CONCLUSIONS : Based on these results, the parameters of the universal model can be predicted using the stress-dependent modulus model proposed in this study.

It has been recognized that the performance of pavements is closely related to the properties of the underlying unbound layers and subgrade. It has also been recognized that unbound pavement materials possess a complex nature and often exhibit nonlinear behaviors [1, 2]. The Mechanistic-Empirical Pavement Design Guide (MEPDG) is founded on the use of resilient modulus as the primary input parameter when characterizing unbound pavement materials [3, 4]. The resilient moduli of unbound materials are typically determined by performing repeated load triaxial (RLT) tests in the laboratory. Due to that laboratory resilient modulus tests require sophisticated equipment and trained operators following complicated test procedures, many transportation agencies may not have access to the laboratory facility and opt to correlate resilient modulus with field tests [5]. The long-term pavement performance (LTPP) program offers a large and diverse database that includes a range of laboratory-derived and field-derived properties for unbound materials of many in-service pavement sections. This study is aimed to utilize LTPP data to develop a correlation between the laboratory-derived resilient modulus and a field-derived parameter, dynamic cone penetration index (DCPI) for unbound aggregate materials. Data extracted from the LTPP database were subjected to a thorough quality check to ensure that the data are of good quality and without errors. One-on-one univariate regression was first performed to examine the significance of different variables, including DCPI and some physical properties such as dry unit weight, water content, plasticity index, percent passing No.200 sieve. The physical properties that show strong correlation were selected to be combined with field test parameter (DCPI) to conduct a multivariate regression analysis. A statistical model was developed for the prediction of resilient modulus of unbound aggregates from the DCP test parameters and physical properties. The model predicted a separate data set that did not participate in the correlation analysis, suggesting the success of applying the DCP test in evaluating the resilient modulus of pavement unbound aggregate materials.

Open-graded aggregate is a material that contains significant distribution with few fine particles and high void content. Therefore, it provides high permeability and bearing load from grain-to-grain contact. As a result, in pavement system, this material is usually used for base and subbase courses which are support the pavement in load-bearing capacity and drainage for serving the life of road. When design pavement system with open-graded aggregate, the importance for engineers is designing base/subbase courses which not only meet the requirement of strength, displacement and drainage but also economy. During decades, there is a few researches about the necessary characteristics of this kind of aggregate. The overall objective of this study is summarize some researches in resilient modulus and permanent deformation of open-graded aggregate for understanding well the factors that need to be considered during design pavement.

재활용된 암버력-토사의 회복탄성계수 예측모델이 개발되었다. 반복삼축시험을 통한 회복탄성계수의 전통적 평가방법은 큰 입경을 가진 자갈에는 실현 불가능하다. 미세한 차이가 있는 비선형 전단탄성계수를 이용하여 회복탄성계수를 산출하는 대체기법을 제안하였다. 현장에서 측정한 최대전단탄성계수와 대형공진주 시험으로 구한 감소곡선을 이용하여 회복탄성계수 예측모델을 개발하였다. 이 예측모델을 김천의 고속도로공사현장에서 재활용한 암버력-토사에 적용하여 모델인자 AE, nE, εr, α를 각각 9618, 0.47, 0.0135, 0.8로 제안하였다.

회복탄성계수(MR)로 표현되는 보조기층 재료의 탄성계수는 연성 포장체의 역학적 설계에 대단히 중요한 물성치이다. 그러나 반복재하식 MR 시험을 일상적 시험으로 적용하기에는 너무 시험과정이 복잡하고, 고가이며, 많은 시험시간을 필요로 한다. 본 연구에서는 보조기층 재료의 변형특성을 고려하여 현장공진주시험(EF-RC)을 이용한 대체 MR 시험법을 개발하였다. 보조기층 재료의 변형특성 평가를 위하여 변형률 크기 및 평균주응력의 탄성계수에 대한 영향을 조사하였다. 제안한 대체 MR 시험법으로 결정된 탄성계수와 반복재하식 MR 시험에서 결정된 회복탄성계수는 서로 잘 일치하여 제안된 기법의 효용성을 확인하였다.

회복탄성계수(MR)로 표현되는 보조기층 재료의 탄성계수는 연성 포장체의 역학적 설계에 대단히 중요한 물성치이다. 그러나 반복재하식 MR 시험을 일상적 시험으로 적용하기에는 너무 시험과정이 복잡하고, 고가이며, 많은 시험시간을 필요로 한다. 본 연구에서는 보조기층 재료의 변형특성을 고려하여 현장공진주시험(EF-RC)을 이용한 대체 MR 시험법을 개발하였다. 보조기층 재료의 변형특성 평가를 위하여 변형률 크기 및 평균주응력의 탄성계수에 대한 영향을 조사하였다. 제안한 대체 MR 시험법으로 결정된 탄성계수와 반복재하식 MR 시험에서 결정된 회복탄성계수는 서로 잘 일치하여 제안된 기법의 효용성을 확인하였다.