The formation and development of fatigue cracks in asphalt concrete beams have been extensively studied. Among these studies, however, very few have focused on the effects of geogrids in enhancing the resistance of asphalt concrete to fatigue failure. In addition, findings and conclusions of those studies cannot be effectively applied to most situations in Taiwan. It is therefore necessary to study the formation and development of fatigue cracks in overlaid dense-graded asphalt concrete. Among geogrids used in this laboratory study, two were made of glass fiber with strength of 100 kN/m and 200 kN/m, respectively, and one was made of high-density polyethylene (HDPE) with a strength of 25 kN/m. A series of tests for a beam reinforced with glass geogrids of 100-kN/m strength showed a fatigue life 3 to 5 times that of an unreinforced beam; and for a beam reinforced with 200-kN/m glass geogrids, the fatigue life was 5 to 9 times as long. Beams reinforced with the HDPE geogrids showed a fatigue life equivalent to those reinforced with 100-kN/m glass geogrids. Based on the findings of the laboratory study, an on-site performance study was carried out at a section of the Taiwan Second Freeway (already open for operation) from 80 km 837.5 m to 81 km 262. 5 m. A 10-month rutting-depth measurement was obtained, which confirmed that the improvement from these geogrids over the fatigue life of the pavement overlay so far was obvious and significant.
A combination of the high-vacuum (HV) and dynamic compaction (DC) method (HV+DC method) was used to improve saturated soft foundation. HV and DC were applied alternately and repeatedly to achieve the required level of ground improvement. An in-depth investigation was conducted of the technical requirements, processes, and mechanisms involved in the HV+DC method at the Ningbo Harbor Coal test site near Shanghai, China. Relevant drainage control parameters were identified and optimized to provide the construction parameters, such as compaction energy, spacing, drop number, vacuum dewatering number and location, and wellpoint depth and number, for large area construction. The monitoring during the field trial case study presented here indicates that the method is not only based on sound concepts with rapid stabilization effects and low construction costs but also holds significant promise as an innovative ground improvement method when soft soils are encountered. The application of the HV+DC method increased the cone penetration tip resistance qt of the pond fly ash layer at the Ningbo site more than 2.5 times and that of the clay mud layer more than 1.5 times (compared with unmodified ground) and improved the characteristic value of the bearing capacity of the foundation up to 135 kPa, all of which adequately met the design requirements. For the total area of 400,000 m2 of the main project, this innovative method has saved more than 40% of total cost and approximately 50% of construction time from the original design of the soil cement mixing method.
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