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931.
Steel bar in concrete structures under harsh environmental conditions, such as chlorine corrosion, seriously affects its service life. Bidirectional electromigration rehabilitation (BIEM) is a new method of repair technology for reinforced concrete structures in such chloride corrosion environments. By applying the BIEM, chloride ions can be removed from the concrete and the migrating corrosion inhibit can be moved to the steel surface. In conventional engineering, the concrete structure is often configured with a multi-layer steel mesh. However, the effect of the BIEM in such structures has not yet been investigated. In this paper, the relevant simulation test is carried out to study the migration law of chloride ions and the migrating corrosion inhibitor in a concrete specimen with complex steel mesh under different energizing modes. The results show that the efficiency of the BIEM increases 50% in both the monolayer steel mesh and the double-layer steel mesh. By using the single-sided BIEM, 87% of the chloride ions are removed from the steel surface. The different step modes can affect the chloride ion removal. The chloride ions within the range of the reinforcement protective cover are easier to be removed than those in the concrete between the two layers of steel mesh. However, the amount of migrating corrosion inhibitor is larger in the latter circumstances. 相似文献
932.
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934.
935.
循环温度场作用下PCC能量桩热力学特性模型试验研究 总被引:5,自引:0,他引:5
PCC能量桩是河海大学岩土所开发的一种新型能量桩技术。在常规桩基静载荷模型试验基础上,将PCC能量桩放置在南京典型砂土中,并通过导热管内水体的循环对模型桩体施加温度场,以模拟PCC能量桩在实际运行过程中的承载力特性与受力机制,PCC能量桩先加载至工作荷载(极限荷载的一半),再施加热-冷循环一次,最后加载至极限荷载,测得不同温度下PCC能量桩的荷载-位移关系曲线、桩身应力-应变关系曲线等变化规律。试验结果表明,能量桩换热过程中,热量更容易从桩体传向土体(即夏季模式的热循环);热循环及制冷循环都明显改变了桩顶位移值,且往复循环作用下产生的塑性变形不能完全恢复,其积累变形可能危害上部结构安全;桩身受温度场作用产生的热应力相对较大,且不同约束条件下其变化值有所差异;在制冷循环下,桩底部甚至可能产生较大拉应力。 相似文献
936.
顶管顶进阻力由顶管机的迎面阻力和管节与土体间的摩阻力两部分组成,现有的顶力估算公式都具有一定的适用条件,虽然物理意义明确,但参数取值范围较大,往往估算顶力与实际工程顶力的匹配程度较低,尤其是在三维曲线顶管工程中受曲线段的影响,准确估算顶力的难度更大。以长413.0 m,外径为3.8 m,最小曲率半径为313.7 m的三维曲线顶管工程为研究对象,基于现有的顶力公式估算所需顶力大小并布设中继间,在该工程实测数据的基础上分析顶力组成及其与顶程、顶进曲率半径等影响因素之间的关系和顶管在平面曲线和垂直剖面曲线以不同曲率半径顶进的摩阻力变化规律。分析结果显示,曲线顶管摩阻力附加系数是真实存在的,且工程实测值与经验值有所偏差,但顶管在淤泥或黏土层中顶进时的摩阻力按规程推荐取值能够满足工程实践需求。最后提出了顶力估算及中继间的布置建议,为类似工程提供依据。 相似文献
937.
介绍了加测一个陀螺方位角的地下导线平差方法,根据上海青草沙过江原水管工程地下贯通导线测量中采用GYROMAT-2000型陀螺经纬仪加测一条地下导线边方位角的实例,论证了方法的正确性。 相似文献
938.
In-situ tests and numerical manipulations were conducted for comparison of superior/inferior quality of casing-tube-vacuumized
insulation and polyurethane insulation of freezing apparatuses in relation to non-uniform cold distribution in the multi-coil freezing
layout and the contradiction between large-coil diameter layout of the freezing holes and stability of the headframe base. Tests
show that: (1) under current technology, vacuumized insulation is of short duration due to lack of appropriate applied vacuum; (2)
after the freezing pipe is insulated with polyurethane, the temperature gradient is less than no insulation, and the temperature difference
between insulated and non-insulated apparatuses is stable as the freezing period increases. Finally, it is pointed out that
polyurethane insulation is quite efficient in present technical freezing construction. 相似文献
939.
Eric D. Anderson William W. AtkinsonJr. Timothy Marsh Alexander Iriondo 《Mineralium Deposita》2009,44(2):151-170
The Copper Creek mining district, southeastern Arizona, contains more than 500 mineralized breccia pipes, buried porphyry-style,
copper-bearing stockworks, and distal lead–silver veins. The breccia pipes are hosted by the Copper Creek Granodiorite and
the Glory Hole volcanic rocks. The unexposed Mammoth breccia pipe, solely recognized by drilling, has a vertical extent of
800 m and a maximum width of 180 m. The pipe consists of angular clasts of granodiorite cemented by quartz, chalcopyrite,
bornite, anhydrite, and calcite. Biotite 40Ar/39Ar dates suggest a minimum age of 61.5 ± 0.7 Ma for the host Copper Creek Granodiorite and 40Ar/39Ar dates on hydrothermal sericite indicate an age of 61.0 ± 0.5 Ma for copper mineralization. Fluid inclusion studies suggest
that a supercritical fluid with a salinity of approximately 10 wt.% NaCl equiv. condensed to a dilute aqueous vapor (1–2.8 wt.%
NaCl equiv.) and a hypersaline brine (33.4–35.1 wt.% NaCl equiv.). Minimum trapping temperatures are 375°C and trapping depths
are estimated at 2 km. Sulfur isotope fractionation of cogenetic anhydrite and chalcopyrite yields a temperature of mineralization
of 469 ± 25°C. Calculated oxygen and hydrogen isotope values for fluids in equilibrium with quartz and sericite range from
10.2‰ to 13.4‰ and −60‰ to −39‰, respectively, suggesting that the mineralizing fluid was dominantly magmatic. Evidence from
the stable isotope and fluid inclusion analyses suggests that the fluids responsible for Cu mineralization within the Mammoth
breccia pipe exsolved from a gray porphyry phase found at the base of the breccia pipe. 相似文献
940.
Overcoming Squeezing in the Yacambú-Quibor Tunnel,Venezuela 总被引:2,自引:2,他引:0
Summary The 5 m diameter 23.3 km long Yacambú-Quibor tunnel is designed to carry water through the Andes from the Yacambú dam in the
wet tropical Orinoco basin to the semi-arid but fertile Quibor basin in western Venezuela. The tunnel is excavated in silicified
and graphitic phyllites at depths of up to 1270 m below surface and extreme squeezing problems have been encountered. Construction
involved 8 contracts extending over 32 years with breakthrough being achieved in July 2008. Several excavation methods and
various lining designs were used over the years until the adoption of yielding support permitted the Owner and the Contractor
to agree that only a circular section would be used and emphasis was placed on developing a routine construction procedure,
irrespective of the rock conditions encountered at the face. This paper describes some of the rock engineering issues that
were faced during the construction of this tunnel.
Correspondence: E. Hoek, Consulting Engineer, Vancouver, Canada 相似文献