台北市道路下佈滿管線，時常需要維護、更新或緊急搶修既有管線，為減少用路人不便，工程時間必須避開上下班的尖峰時段，介於早上九點至下午四點，施工廠商必須在時間內進行路面切割、挖掘、埋管、回填、養護、回舖路面，工程緊迫，其中養護的時間佔比相當高，為求時間內通車，廠商經常使用接近初凝的CLSM回填來加速工程進行，這種作法不但可能造成管線周圍回填不實，更增加日後道路塌陷的可能；而按照正確施工程序與材料之廠商，時常為了趕在時間內通車，導致養護時間不足，待車輛經過後路面破損。本研究主要解決上述問題，以不大幅地變更既有之作業程序和使用材料之前提，嘗試在回填CLSM後投入顆粒材料來增加回填層之立即乘載力，達到如期通車效果。
試驗主要找出最適當之CLSM與顆粒材料組合，透過3種水膠比搭配6種顆粒材料比例，以6個齡期進行試驗。室內試驗包含（1）CBR加州承載比試驗（2）抗壓試驗（3）水箱回填試驗，結果顯示，投入過多或過少的顆粒材料皆會影響強度，試驗結果顯示，適合投入之顆粒材料配比為每立方公尺760公斤，經計算CLSM與投入粒料比例約為3：2（體積比）。室內試驗結束後進行PLAXIS分析與現地試驗測試實際效果，結果如預期，既能加速工程進行，也能增加路面乘載力。

There are full of pipelines under Taipei city’s, and it often need to be maintained, replaced or urgently repaired in emergency situation. To reduce the inconvenience of driver, the construction time must avoid the rush hours which between 9 am to 4 pm. Unit in change of construction must do Pavement cutting, digging, buried pipe, backfilling, curing, and resurfacing pavement within a short period of time. The project is urgent and curing takes a lot of time, manufacturers often use initial setting of CLSM backfill to accelerate the project . Generally, initial setting of CLSM backfill not only cause unreasonable backfilling around the pipeline, but also increase the possibility of road collapse in the future. For those manufacturers who follow correct construction procedures and materials they often open to traffic before the time, and when the maintenance times is insufficient, vehicle pass the pavement collapse. This study mainly solves the problems we mentioned above. Without drastically changing the existing operating procedures and materials, we try to increase the immediate loading capacity of the backfill layer by press in gravel to achieve the traffic effect as schedule.
The test mainly finds the most appropriate ratio of CLSM to gravel. Laboratory test includes the （1） CBR California bearing ratio test （2）compression test （3） water tank backfill test. The input of more or less gravel will affect the overall strength. The test results show that 760 kg/m3 gravel content is suitable for this modified CLSM trench backfill method. The volume ratio was about 3 : 2 between CLSM and gravel. Finally, a field test and analysis was conducted to verify the immediate bearing capacity. The results are as expected, can not only accelerate the project but also increase the road bearing capacity.

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