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深厚冲积层冻结孔布置分类技术对冻结调控的影响

Classified arrangement technology of freezing holes in deep and thick alluvium and its influence on freezing control

  • 摘要: 冻结孔布置方式不仅决定了能否按期形成设计所需的冻结壁有效厚度和平均温度,还会影响冻结法凿井的速度、安全和施工成本。不合适的布置方式甚至会成为冻结法凿井的安全隐患,因此冻结孔布置方式及其冻结壁形成特性一直是冻结法凿井的理论和技术研究热点和难点。提出深厚冲积层冻结孔按主冻结孔、辅助冻结孔、防片冻结孔3类功能分类设计和布置,可较好地解决主冻结孔及冻结壁主体结构的安全和稳定;根据冻结壁厚度需要及冻结时间均匀布置辅助孔,可明显减少辅助孔数量,提高冻结壁的均匀性和稳定性;根据挖掘荒径变化布置多圈防片孔,可提高冻结调控的灵活性和效果。工程实践表明:以外圈为主冻结孔的布孔方法,有利于主冻结孔和整体冻结壁的安全稳定,可减少冻结孔数量、钻孔工程量、冻结需冷量,提高了冻结的可调性和调控效果,推荐为深厚冲积层冻结孔布置方式的首选。合理的冻结孔布置可为冻结壁安全稳定及冻结调控打下良好的基础,施工过程中通过建立冻结壁形成特性实测分析、工程预报与冻结调控的机制,定期对冻结壁有效厚度、平均温度和井帮温度发展趋势进行分析和预测,提前对防片孔和辅助孔盐水流量、温度进行调控,甚至停止盐水循环,能有效控制井帮温度及冻土扩入荒径量,为掘砌施工创造良好条件。国内外冲积层厚度最大之一的赵固二矿西风井通过采用以外圈为主冻结孔的布孔方式,总的冻结孔数、冻结钻孔工程量、冻结需冷量均显著降低,且冻结壁内部温度和强度的均匀性更好;结合黏性土层井帮稳定性观测,通过主动调控,实现400 m以深井帮温度还可略高于设计调控目标,635 m以深井帮温度接近设计调控目标,冻结壁厚度和平均温度始终满足设计要求,冲积层深部黏性土层井帮温度控制在-11 ℃以上,砂性土层井帮温度在-13 ℃以上;冲积层的冻结壁稳定性良好,冻掘配合好,冲积层深部外壁掘砌速度基本维持在75~80 m/月,冲积层段外壁平均掘砌速度为87.1 m/月,冻结段外壁平均掘砌速度为82.1 m/月。

     

    Abstract: Abstrat;The arangement of freezing holes not only determines whether the effective thickness and average temperature of the freezingwallrequired by the design can be formerd on schetule , but also directly affects the speed, safety and construction cost of the freezing shaftsinking.Improper arrangement will even become the hidden danger.'Therelore , the amrangement of freezing holes and formation characteris-tics of freezing wall are always the hot and difficult points in theory and techmology research. The design and arrangement of freezing holesin deep and thick allwvium can be classified into three types ; main freezing hole , auxiliary freezing hole and spalling-prevention freezinghole, which can solve the problems of safety and stability of main structure of main freezing hole and frezing wall.Arranging auxiliaryholes evenly accordling to the thickness of fromen wall and freezing time can obviously retduce the number of atuxiliary holes and improve theuniformity and stability of the frezing wall.The flexibility and effect of freezing contol can be improved by arranging muliple circles ofspalling-prevention freezing holes accordling to the change of excavation diameter. The enginering practice shows that the holes arrangement method with outer ring as the main frezing hole is beneficial to the sadety and stability of the main freezing hole and the overallfreez-ing wall, which can reruce the mumber of freezing holes , the work amount of drilling holes and the cooling capacity required, improve theadjustability and control effect of freezing, and is recommended as the first choice for the arrangement of freezing holes in deep and thickalluwvium.The reasonable arrangement of freezing holes can lay a good founmdation for the safety and stability of the freezing wall and thecontrol of freezing. In the constuction process, through the establishment of the mechanism of the actual measurenent and analysis of thefomation charactristis of the frezing wall , engineering predliction and frezing control , the development trend of the effective thickness ,average temperalure and the temperature of the frzen wall are analyzel and predlicted on a regular lasis , and the flow and temperature ofsalt water in the spalling-prevention hole and atuxiliary hole are regulated in advance , or even the freezing and freezing cycles are stopped,which can effectively control the temperatur of the shat sidewall and the amount of frozen soil expanding into the excavation section , andcreate good conditions for the excavation.Through the practice and application of the outer ring as the main freezing hole in the West Ven-tilating Shaft of Zhaogu No.2Coal Mine,which passes through one of the deepest alluwvium thickness , the total number of freezing holes ,the work amount of dilling holes and the cooling capacity requiredl are decreased by 10.7%,12.1% and 9.7% respectively , and the uni-fomity of temperature and strength inside the frezing wall is better.Combined with the observation of the stability of the shaft sidewal inthe cohesive soil ayer, through active control , the tempenature of the shaft sidewall below 400 m can be slightly higher than the designedcontrol target.'The temperature of the shaft sidewall below 635 m is close to the designed control target.T'he thickness and average temper-ature of the freezing wall always meet the design requirements.'Tlhe temperature of the shaft sidewall in the deep ohesive soil layer in theallwvium is controlled above -ll ℃ , and the temperature of the shat sidewall in the sandy soil layer is above -13 ℃. The stability of thefrzing wall of the alluvium is god , and the cooperation between freezing and excavation is good. The excavation speed of the deep outerwall of the allwvim is basically maintained at 75 ~80 m per mouth , the average excavation speed of the outer wall of the alluvium sectionis 87.1m per month,and the aveage excavation speed of the outer wall of the freezing section is 82.1 m per month.

     

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