小口徑管線的地下推進工法在都市污水下水道建設上運用的非常廣泛，近年來為適應都市複雜多變的現地環境，引進影響環境層面較小的短管推進工法，運用於都會區污水管線佈設，由於工法援自國外，所採用編列預算的資料也較缺乏，往往無法反應本土環境現況，在建設階段常會導致成本很大之變化，甚致導致爭議。 本研究乃針對短管推進施工所遭遇的現地環境因素加以探討，藉由污水下水道建設的經驗及專業承攬廠商的問卷訪談，使這些影響成本的因素能夠反應量化於預算成本，使之更趨於準確。本研究透過訪談分析將這些因素分為五個主層面為地下管線影響、地質條件影響、區域特性影響、工務程序影響及施工要求影響，分別關連影響短管推進工法中之推進井及推進口設施、管線推進、到達井及到達口設施三部份，在實際問卷調查過程中，針對32位專業承商及業主資深人員發出問卷調查，經問卷統計分析後，獲取有效完整問卷22份。 經過研究的結果，影響成本因素最主要的部份為地下管線，相反的土壤分類、區域形態、施工要求等因素可以被忽略，本研究由短管推進施工標案，推估之影響模式可知，預算經套入本模式修正後，較能符合各案實際需要及合理的結果。 Microtunneling is now commonly used in constructing the sewerage collection system. Due to the lack of experience in the early stage, construction budgets of microtunneling is formulated according only a handful of cost factors. This sometimes resulted in great cost variance during the construction stage, preceded by time-consuming changes or even disputes. The purpose of this work is to summarize the practical experience of using the microtunneling technology for the past two decades and to devise a wide set of cost factor on which a more accurate construction budget can be based. Five aspects of external influence factors are examined, including existing underground utility lines, ground conditions, site locality, project administration and work requirements. The work breakdown structure of microtunneling is comprised of three branches, including those of the entrance work pit, horizontal advancing sections and arrival work pit. Practical experience is obtained by a questionnaire survey, in which 32 experts are surveyed with 20 of them considered complete and valid. The result shows that the key cost factors mostly relate to underground utility lines. In contrast, factors related to ground classification, site locality and client requirements can be omitted. The proposed cost adjustment model is practically useful. With the test case adopted in the study, the budgeted cost can better represented the actual cost incurred in the construction stage.
