연직배수재 타설 후 장기간 경과된 지반의 통수성능

Discharge Capacity of Prefabricated Vertical Drain Confined In-Clay Under Long-Term Conditions

Abstract

연약점토 지반 개량을 위해 연직배수재 타설 후 선행재하공법이 일반적으로 적용되는데, 현장에서의 시공계획 변경 등으로 인해 연직배수재 타설 후 장기간 방치되는 경우가 종종 발생된다. 따라서 장기간 방치된 조건에서의 연직배수재 열화 현상을 고려하기 위해 구속압으로 적용되는 수온을 각각 30, 35, $40^{\circ}C$를 적용하였다. 그 결과, 시간경과에 따라 배수성능이 급격히 저하되는 경향을 나타냈다. 그리고 현장 원위치 조건, 즉, 점토 구속조건하에서 장기간 통수능 저하 정도를 평가하기 위하여 Miura와 Chai(2000)식을 적용하였다. 그 결과, 온도 변화 조건에서 수행된 통수능 시험결과를 이용한 신뢰성 해석 방법과 Miura와 chai(2000)식을 적용하여 장기 통수능을 평가할 수 있는 것으로 평가되었다.

Typically, soft clay improvement is carried out using installation of PVD and surcharge method. According to circumstances, installed PVD has left for a long time due to the change in construction schedule. Therefore, for simulation of this kind of condition, discharge capacity tests were carried out under a series of temperature condition (30, 35, $40^{\circ}C$). The results indicated that under water confinement, the discharge capacities significantly reduced with elapsed time. And, the empirical equation by Miura and Chai (2000) was used for estimating the long-term in-clay discharge capacity. Based on the test results, it is recommended that in term of long-term discharge capacity, Miura and Chai's equation and reliability evaluation using discharge capacity tests under a series of temperature condition may be used.

Fig. 1. Illustration of discharge capacity test device (Chai and Miura, 1999)

Fig. 2. Comparison of discharge capacity test results under confined-in clay and membrane (Miura and Chai, 2000)

Fig. 3. Comparison of hydraulic gradient affecting discharg capacity (Miura and Chai, 2000)

Fig. 4. Pictures of prefabricated vetical drains

Fig. 5. Discharge Capacity Test Device

Fig. 6. Variation of discharge capacity of PVDs with hydraulic gradients and confined pressure

Fig. 7. Discharge capacity test process with long-term condition

Fig. 8. Variation of discharge capacity of PVDs with elasped time and test temperatures

Fig. 9. Reduction ratio of discharge capacity with elapsed time and test conditions

Fig. 10. Reduction of Discharge Capacity of PVD with Elasped times Under Field Condition

Table 1. Physical Properties of PVDs

Table 2. Discharge Capacity Test Results of PVDs

Table 3. Failure Times with Temperature Under Failure Criterion

Table 4. Performance Prediction Result of PVD (Ordinary Harmonica type)