CAJ | 학술논문

多年冻土地基由于大直径钻孔灌注桩桩身混凝土水化热造成桩周冻土融化，而桩体混凝土灌注初期桩土体系不具备冻结强度，导致钻孔灌注桩初期承载力很低。研究低温多年冻土地基大直径钻孔灌注桩未回冻状态的承载力和变形性质，可为工程施工工期安排提供技术依据。结合青藏铁路索南达杰特大桥工程进行低温多年冻土大直径钻孔灌注桩地温测试及现场静载试验，为此设置桩土界面测温孔(SB)、桩侧测温孔(SC，距离桩壁30 cm)以及未受施工扰动的基准地温孔(JZ)。获得夏季灌注桩混凝土入模温度为11℃，不同龄期桩土体系的地温分布，并分析桩土体系的回冻过程。测试数据表明：混凝土灌注完成30d以后，桩顶至地表下2m为正温，地表下2m到桩底桩身表面均为负温，在-0.43℃～-1.26℃范围内变化；灌注50 d以后，桩土界面地温逐渐降低，为-1.0℃～-1.85℃，与未受扰动天然地基地温相比，桩土体系尚未完全回冻。同时进行不同地温条件下基桩的现场静载试验，分析竖向承载力、变形及桩侧摩阻(或冻结力)分布特性。当加载到最大荷载(7600 kN)时，桩顶竖向位移达到4.93 mm，卸载后未恢复的变形为1.01 mm，说明低温多年冻土地基钻孔灌注桩在未完全回冻状态下(试桩龄期30 d)基桩具有较高竖向承载力，且变形量小。
다년동토지기유우대직경찬공관주장장신혼응토수화열조성장주동토융화，이장체혼응토관주초기장토체계불구비동결강도，도치찬공관주장초기승재력흔저。연구저온다년동토지기대직경찬공관주장미회동상태적승재력화변형성질，가위공정시공공기안배제공기술의거。결합청장철로색남체걸특대교공정진행저온다년동토대직경찬공관주장지온측시급현장정재시험，위차설치장토계면측온공(SB)、장측측온공(SC，거리장벽30 cm)이급미수시공우동적기준지온공(JZ)。획득하계관주장혼응토입모온도위11℃，불동령기장토체계적지온분포，병분석장토체계적회동과정。측시수거표명：혼응토관주완성30d이후，장정지지표하2m위정온，지표하2m도장저장신표면균위부온，재-0.43℃～-1.26℃범위내변화；관주50 d이후，장토계면지온축점강저，위-1.0℃～-1.85℃，여미수우동천연지기지온상비，장토체계상미완전회동。동시진행불동지온조건하기장적현장정재시험，분석수향승재력、변형급장측마조(혹동결력)분포특성。당가재도최대하재(7600 kN)시，장정수향위이체도4.93 mm，사재후미회복적변형위1.01 mm，설명저온다년동토지기찬공관주장재미완전회동상태하(시장령기30 d)기장구유교고수향승재력，차변형량소。
by construction,denoted by SB,SC,and JZ,respectively,were set up to obtain the corresponding temperatures. The temperature distributions for the pile-soil system at various ages were obtained when the piles were cast in summer and the initial concrete temperature was 11℃. The refreezing process of the pile-soil system as well as the distribution characteristics of the vertical bearing capacity,vertical deformation and skin friction(or freezing force) of the pile under various ground temperatures were analyzed. Test results show that 30 days after the construction of the pile,the temperature along the pile skin is negative(approximately -0.43 ℃--1.26 ℃) except in the section 0-2 m below the ground surface;50 days after the construction of the pile,it becomes a bit lower(approximately-1.0℃--1.85 ℃. C)ompared with the original undisturbed state,the pile-soil system is not fully refrozen. When a maximum vertical load of 7 600 kN is applied,the vertical pile-head displacement is 4.93 mm while the residual deformation after unloading is 1.01 mm. It shows that the pile has a high vertical bearing capacity and a small deformation under a non-fully refreezing condition with the pile age of 30 days.