| The semi-rigid base is widely used in the asphalt pavement.The construction quality of the base layer is very important to the durability of the pavement structure.The main construction means to improve the quality of the base layer is compaction and curing.At present,there are still some problems in the quality inspection of the base construction,such as compaction quality cannot be controlled in real time,the evaluation method for the uniformity of the base construction is lacking,and drilled core method has damage to the base.As a nondestructive testing equipment for measuring stiffness of construction layers,PFWD is widely used in compaction quality control and strength detection.During this study,the PFWD influence depth and factors affecting Evdof cement stabilized crushed stone were analyzed,the semi-rigid base compaction quality control and the uniformity evaluation method based on Evdindex are put forward.Also,the index and standard for the core timing and the Evdstandard for avoiding coring are determined.To study the action depth of PFWD impact load on the road layers and put forward test parameters,the principle of PFWD is discussed,the dynamic load characteristics of PFWD are analyzed.Then the attenuation margin of the vertical stress in the center of the bearing plate is defined,and the stress attenuation law on the single layer structure is analyzed.Results show that weight,height of the hammer and the radius of the plate affect the maximum load.The load under plate is first increased and then decreased in the form of half sine.The degree of stress attenuation in a single layer structure depends only on the ratio of depth to plate radius.The modulus ratio（E1/E0）has an influence on the attenuation of vertical stress.And Poisson’s ratio almost does not affect the stress attenuation.Finally,the influence depth of different PFWD configurations（hammer weight,plate radius）is recommended in accordance with the stiffness ratio of the tested layer and the underlying layer.To study effccts of compaction degree,water content,thickness and bottom stiffness on Evdof cement stabilized crushed stone,the filling test and PFWD were carried out in the laboratory,and the main influencing factors were found by orthogonal test.The results show that the Evdhas a linear relationship with the compaction degree.Evdwas negatively correlated with water content and the maximum value did not appear near the optimum water content.Evdincreases with the increase of the bottom stiffness and decreases with increasing thickness,which is essentially a weakening of the boundary effect.The influence level of each factor on Evdfrom large to small is:compaction degree>water content>bottom stiffness>thickness.Results indicate that compaction degree and water content should be considered during compaction quality control.To determine the core timing and the standard for avoiding coring,laboratory core drilling test were conducted.It was found that the higher the cement content is,the shorter the curing time is.The gradation type has a great influence on core timing,for the same cement content,the suspend-dense structure has a longer coring age than the framework-dense skeleton.Through the splitting test of standard specimen under different curing temperature,a hyperbolic function model between splitting strength and maturity is established,and the maturity standard for determining the coring time is put forward.Through field PFWD test and core drilling test,a double logarithmic founction between Evdand splitting strength is established and the Evdcriterion for avoiding coring is proposed. |
