International Concrete Abstracts Portal

Construction technology exerts a significant influence on the bearing behavior of pile foundations. Taking an airport expansion project as the engineering background in Lanzhou City, Gansu Province, China, a comparative analysis of the bearing behaviors of dry-bored piles and slurry wall-protected bored piles through static load tests and numerical simulations was conducted. The main conclusions are as follows: Both test piles exhibit a load-settlement curve of the steep-drop type. Compared with dry-bored piles, slurry wall-protected bored piles tend to accumulate sediment at the pile base, leading to increased settlement. In addition, a mud cake tends to form along the shaft of slurry wall-protected bored piles, which restrains the mobilization of shaft friction and further exacerbates settlement. Under identical load and pile length conditions, the end-bearing resistance, degree of shaft friction mobilization, and axial force in dry-bored piles are consistently lower than those in slurry wall-protected bored piles. Different construction technologies affect the load-transfer mechanism of pile foundations. During the drilling of slurry wall-protected bored piles, the surrounding soil is infiltrated by slurry, and a mud cake is formed on the pile shaft—this not only reduces the mobilization of shaft friction but also results in a slower decay of axial force along the pile. The presence of the mud cake increases the vertical displacement of the soil around the pile tip, and the magnitude of this displacement increases with the thickening of the mud cake. Moreover, the vertical displacement of the surrounding soil decreases as the elastic modulus of the mud cake increases.

In this paper, several hundred specimens were compacted and tested to evaluate the potential of beam testing protocols to directly measure four mechanical properties from one beam. Mechanical properties measured through beam testing protocols were compared to properties of plastic mold (PM) device specimens and were found to be comparable once specimen densities were corrected. Mechanical properties were also used to quantify mechanical property relationships, often used as pavement design inputs. When compared to traditionally recommended mechanical property relationships, relationships between elastic modulus and unconfined compressive strength, as well as modulus of rupture and unconfined compressive strength, were overly conservative; however, indirect tensile strength and unconfined compressive strength relationships from the literature were accurate. This paper also assessed an elevated-temperature curing protocol to simulate later-life pavement mechanical properties on laboratory specimens. Mechanical properties of laboratory specimens that underwent accelerated curing were shown to be comparable to 10- to 54-year-old cores taken from Mississippi highways.

The behavior of precast concrete tunnel lining (PCTL) segments reinforced with glass fiber-reinforced polymer (GFRP) bars under punching loads is one area in which no research work has been conducted. This paper reports on an investigation of the punching-shear behavior of GFRP-reinforced PCTL segments induced by soil conditions, such as rock expansion or the geotechnical conditions surrounding a tunnel. Six full-scale rhomboidal PCTL specimens measuring 1500 mm (59 in.) in width and 250 mm (9.8 in.) in thickness were constructed and tested up to failure. The investigated parameters were: 1) reinforcement type (GFRP or steel); 2) reinforcement ratio (0.46 or 0.86%); 3) stirrups as shear reinforcement; and 4) segment length (2100 or 3100 mm [82.7 or 122 in.]). The experimental results are reported in terms of cracking behavior, punching-shear capacity, deflection, strain in the reinforcement and concrete, and failure modes. The results reveal that the GFRP-reinforced PCTL segment was comparable with its steel counterpart with the same reinforcement ratio and satisfied serviceability limits. Increasing the reinforcement ratio and decreasing the segment length enhanced the punching-shear strength. The shear stirrups improved the structural performance and increased the punching and deformation capacities of the GFRP-reinforced PCTL segments. In addition, theoretical predictions of the punching-shear capacity using the current design provisions were compared to the experimental results obtained herein. The theoretical outcomes show the suitability of using current FRP design provisions for predicting the punching capacity of PCTL segments reinforced with GFRP bars.

Modular concrete elements are used for retaining walls to provide lateral support. Depending on the retaining wall layout, these precast panels may be interlocking and may be tied into the soil backfill through geosynthetic strips. This study investigates the ultimate pullout load increase, which is possible by adding varied diameter supplementary reinforcement through embedded anchor loops within concrete retaining wall panels. Previous research has investigated supplementary reinforcement around the anchor loops. This paper extends this investigation by evaluating supplementary reinforcement placed through the panel anchor loops. Full-scale panels used in practice have four embedded anchor points. However, only one anchor loop was embedded in the center of the experimental panels. The experimental panels were also cast without any bending reinforcement, as would typically be obtained in the full-scale panels. These reinforcements were purposefully excluded to evaluate the impact of a single-bar reinforcement through the center of the anchor loops. Failures that occurred were loop, panel, and a mixture thereof. Overall, the reinforced panels showed a 14 to 23% increase in the factor of safety.

Over 450 cores were extracted from roadways throughout Mississippi to provide a realistic picture of mechanical properties in later-age chemically stabilized soil. Cores ranged from 10 to 54 years old and were stabilized with either lime-fly ash, cement, or lime. Indirect tensile strength (IDT), unconfined compressive strength (UCS), and elastic modulus (E) tests were used to quantify mechanical properties. Generally speaking, IDT, UCS, and E values tended not to exceed 250, 1500, and 1,500,000 psi (1724 kPa, 10,342 kPa, and 10,342 MPa), respectively, in pavements over 10 years old. Cores were also compared to mechanical property relationships found in the 1993 AASHTO design guide and the Mechanistic-Empirical Pavement Design Guide (MEPDG) and the literature to determine their applicability to later-age pavement properties. Relationships from the literature comparing IDT to UCS were generally good predictors of later-age property relationships; however, relationships between E and UCS were not good predictors of later-age strength as most equations did not account for the decrease in E development over time when compared to UCS.