臺灣博碩士論文加值系統

本研究是透過現場足尺寸試驗的方式，探討粉土質砂土在冰凍過程中所顯現出的凍脹行為，冰凍試驗之變數包括液態氮之流量大小、冰凍管數目等項目。探討之課題有土壤溫度的變化、凍土周圍土壤之受擠行為和土壓力的變化情形等。試驗之結果顯示冰凍效果會因冰凍管之數量增加而有顯著的增加；冰凍過程中，凍土之成長方式對周圍土壤之擠壓，主要是發生在徑向；減低液態氮流過冰凍管之流量且增加冰凍工法之時間，將使土壤在相同的冰凍土體積下因凍脹所產生之徑向位移量略增。為精確地控制液態氮之流量和冰凍管之溫度，本研究也針對自動化液態氮流量控制之可行性加以探討。
為了減少砂性土壤取樣時造成之擾動，本研究利用液態氮冰凍工法進行地下水位下砂土之冰凍取樣工作，以提昇砂土層不擾動取樣技術並提高分析地層液化潛能之精確性，此次實驗之成果證實冰凍取樣方法之可行性，但是仍有一些問題仍有待解決，如冰凍管溫度及液態氮流量之控制等。此外，未知的地下水狀況也是影響此冰凍取樣工法的一個不確定因素。

A series of full scale liquid Nitrogen (LN) ground freezing tests have been carried out in this research to study the response of soil surrounding a freezing body in silty sand. Parameters studied include the effects of LN flow rate and the number of freezing pipes on the changes of ground temperature and lateral earth pressure within the soil as well as the lateral displscement of surrounding soil. Test results indicate that the effect of ground freezing is significantly increased with the increasing number of freezing pipes. The ground freezing induced lateral displacement of surrounding soil occurs mainly in the radial direction. By reducing the flow rate of LN and increasing the time period of ground freezing, the amount of ground freezing induced radial displacement will be increased at a given volume of frozen ground. The feasibility of automatic control on the flow rate of LN and the temperature of freezing pipe has been evaluated in this research also.
To reduce the sampling disturbance to the sandy soil, the LN ground freezing technique is used to sample the in-situ sandy soil below groundwater table in this research. The preliminary result has shown a promising result of this technique. But there are still some problems to be resulted for the future application, such as the control of temperature on freezing pipe and the flow rate of LN. The unknown groundwater condition poses another uncertainty when applying LN ground freezing to obtain the undisturbed sand samples.

第一章 緒論
1.1研究動機與目的1
1.2研究內容1
第二章 研究背景說明3
2.1冰凍工法的由來3
2.2冷凍工法施工原理與特色4
2.2.1冰凍工法之原理4
2.2.1.1密閉式循環系統（BRINE冷凍系統）5
2.2.1.2開放式循環系統 (LN2冷凍系統)6
2.2.1.3兩種冷凍系統之比較6
2.2.2冰凍工法之特色7
2.3液態氮冷凍工法設計參數8
2.3.1凍結速度9
2.3.2液氮冷凍工法設計所需參數9
2.3.3凍結土層基本理論之計算9
2.3.3.1熱容基本計算9
2.3.3.2熱傳導基本計算11
2.3.4溫度分佈12
2.3.5解凍時間13
2.4液態氮基本認識13
2.5土壤凍結膨脹特性14
2.6砂性土壤凍結特性16
第三章 研究計畫18
3.1研究方法及過程18
3.1.1儀器與模型建立18
3.1.2土壤冰凍模擬實驗19
3.1.3實驗用砂土性質19
3.2儀器組立與周邊設備的介紹
3.2.1液態氮冰凍系統20
3.2.2溫度監測系統22
3.2.3冰凍試驗之地工監測儀器23
3.2.4液態氮流量自動化控制系統24
3.3土壤冷凍試驗流程與操作25
3.3.1實驗目的25
3.3.2場地整理及規劃25
3.3.3溫度監測系統之架設26
3.3.4土壓計之埋設與觀測26
3.3.5傾斜管之埋設與觀測26
3.3.6配管隔熱工程27
3.3.7液態氮流量自動化控制工程27
3.4土壤凍結膨脹實驗之流程27
3.5凍結土壤不擾動取樣之流程29
第四章 試驗結果與分析31
4.1凍脹實驗之溫度紀錄與凍土成長分析31
4.1.1凍脹實驗之溫度記錄31
4.1.2溫度記錄與動土成長分析33
4.2凍脹實驗之溫度紀錄與凍土成長分析34
4.2.1凍脹實驗之土壓力記錄34
4.2.2土壓力記錄結果與凍土成長分析36
4.3凍脹實驗之傾斜管紀錄與凍土成長分析37
4.3.1凍脹實驗之傾斜管記錄37
4.3.2傾斜管記錄結果與凍土成長分析39
4.4冰凍取樣之結果與探討40
4.4.1冰凍取樣之結果40
4.4.2冰凍取樣之結果探討40
第五章 結語與建議42
5.1結論42
5.2建議：43

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