MC桩组合支护结构稳定性分析

针对按照传统水泥土挡墙稳定性分析方法来计算MC桩组合支护结构稳定性的不足,根据极限平衡理论,结合MC桩组合支护结构的特点,建立了新的抗倾覆稳定性计算方法,分析了不同因素对组合支护结构抗倾覆稳定性的影响。结果表明,C桩宜布置在组合支护结构前侧,转动点位置宜选取在C桩桩端以上,并可适当增加M桩的长度、宽度以及C桩长度来提高稳定性。最后,运用分析的结果和实际工程经验,建议了MC桩组合支护结构的设计参数。     

优化组合预测模型在桥梁变形预测中的应用

为提高桥梁变形预测的精度,探讨不同预测模型在桥梁变形预测中的效果,结合桥梁变形监测数据及组合预测思路,构建桥梁的MC误差修正优化组合预测模型。通过实例验证得出,组合预测较单项预测具有更高的预测精度及稳定性,其中以RBF神经网络组合的预测精度最高;同时,误差优化修正模型进一步减小了预测误差,优化后预测结果的相对误差期望值为0.86%,方差值为0.097 3 mm2,准确预测了桥梁变形,验证了该思路的有效性。     

Accurate and Precise Silicon Isotope Analysis of Sulfur‐ and Iron‐Rich Samples by MC‐ICP‐MS

Silicon isotope determination of sulfur‐rich samples by MC‐ICP‐MS can be challenging because cation‐exchange chromatography used for Si purification does not efficiently remove anionic sulfur species. Results for pure Si standard solutions with addition of sulfate showed shifts of up to +1.04 ± 0.10‰ (2s) in δ³⁰Si. Doping of both standard solutions and samples with S to a fixed S/Si ratio can eliminate the relative change in instrumental mass fractionation due to variable S/Si in samples and also boosts the relative sensitivity of Si by up to 66%. Moreover, Fe hydroxide precipitation during sample processing adsorbs Si resulting in isotopic fractionations. Tests using Fe‐rich samples showed that this could be a major factor for observed shifts in δ³⁰Si. Acidification of the sample and standard solutions to a pH < 1 aggressively dissolved any Fe hydroxide precipitates, even in relatively Fe‐rich samples such as chondrite meteorites. The pH values of the sample solutions were subsequently adjusted to a range of 2–3 by adding ultra‐pure NaOH solutions. The combination of sulfur doping and the pH adjustment protocol ensured a full recovery of Si and proved to be an efficient and reliable method for Si isotope determination of S‐ and Fe‐rich materials.     

MC桩组合支护结构设计与应用研究

水泥土重力式挡墙与混凝土桩组合支护结构（MC桩）近年来开始在支护工程中得到应用,但由于缺乏对其工作机理和变形特性进行研究,实际工程多采用经验设计法,缺乏理论依据。通过对组合支护结构相关问题的研究,特别是对MC桩组合支护结构设计中几个关键问题进行分析,提出了M桩、C桩的设计方法;结合MC桩组合支护结构的特点,建议了新的稳定性计算方法,可供组合支护结构设计时参考。通过将此设计方法应用于实际工程,验证了其可行性。     

Precise and Accurate Determination of Lu and Hf Contents,and Hf Isotopic Compositions in Chinese Rock Reference Materials by MC‐ICP‐MS

In this contribution, we report Hf isotopic data and Lu and Hf mass fractions for thirteen Chinese rock reference materials (GBW07 103–105, 109–113 and 121–125, that is GSR 1–3, 7–11 and 14–18, respectively) that span a broad compositional range. Powdered samples were spiked with a ¹⁷⁶Lu‐¹⁸⁰Hf enriched tracer and completely digested using conventional HF, HNO₃ and HClO₄ acid dissolution protocols. Fluoride salts were dissolved during a final H₃BO₃ digestion, and chemical purification was performed using a single Ln resin. All measurements were carried out on a MC‐ICP‐MS. This work provides the first comprehensive report of the Lu‐Hf isotopic composition of Chinese geochemical rock reference materials, and results indicate that they are of comparable quality to the well‐characterised and widely used USGS and GSJ rock reference materials.     

Accurate Determination of Sr Isotopic Compositions in Clinopyroxene and Silicate Glasses by LA‐MC‐ICP‐MS

The low‐Sr content (generally < 100 μg g^?1) in clinopyroxene from peridotite makes accurate Sr isotopic determination by LA‐MC‐ICP‐MS a challenge. The effects of adding N₂ to the sample gas and using a guard electrode (GE) on instrumental sensitivity for Sr isotopic determination by LA‐MC‐ICP‐MS were investigated. Results revealed no significant sensitivity enhancement of Sr by adding N₂ to the ICP. Although using a GE led to a two‐fold sensitivity enhancement, it significantly increased the yield of polyatomic ion interferences of Ca‐related ions and TiAr⁺ on Sr isotopes. Applying the method established in this work, ⁸⁷Sr/⁸⁶Sr ratios (Rb/Sr < 0.14) of natural clinopyroxene from mantle and silicate glasses were accurately measured with similar measurement repeatability (0.0009–0.00006, 2SE) to previous studies but using a smaller spot size of 120 μm and low‐to‐moderate Sr content (30–518 μg g^?1). The measurement reproducibility was 0.0004 (2s, n = 33) for a sample with 100 μg g^?1 Sr. Destruction of the crystal structure by sample fusion showed no effect on Sr isotopic determination. Synthesised glasses with major element compositions similar to natural clinopyroxene have the potential to be adopted as reference materials for Sr isotopic determination by LA‐MC‐ICP‐MS.     

High‐Precision Measurement of Molybdenum Isotopic Compositions of Selected Geochemical Reference Materials

Here we describe high‐precision molybdenum isotopic composition measurements of geological reference materials, performed using multi‐collector inductively coupled plasma‐mass spectrometry (MC‐ICP‐MS). Purification of Mo for isotopic measurements was achieved by ion exchange chromatography using Bio‐Rad AG^® 1‐X8 anion exchange resin. Instrumental mass bias was corrected using ¹⁰⁰Mo‐⁹⁷Mo double spiking techniques. The precision under intermediate measurement conditions (eighteen measurement sessions over 20 months) in terms of δ^98/95Mo was 0.10‰ (2s). The measurement output was approximately four times more efficient than previous techniques, with no compromise in precision. The Mo isotopic compositions of seven geochemical reference materials, seawater (IAPSO), manganese nodules (NOD‐P‐1 and NOD‐A‐1), copper‐molybdenum ore (HV‐2), basalt (BCR‐2) and shale (SGR‐1b and SCo‐1), were measured. δ^98/95Mo values were obtained for IAPSO (2.25 ± 0.09‰), NOD‐P‐1 (?0.66 ± 0.05‰), NOD‐A‐1 (?0.48 ± 0.05‰), HV‐2 (?0.23 ± 0.10‰), BCR‐2 (0.21 ± 0.07‰), SCo‐1 (?0.24 ± 0.06‰) and SGR‐1b (0.63 ± 0.02‰) by calculating δ^98/95Mo relative to NIST SRM 3134 (0.25‰, 2s). The molybdenum isotopic compositions of IAPSO, NOD‐A‐1 and NOD‐P‐1 obtained in this study are within error of the compositions reported previously. Molybdenum isotopic compositions for BCR‐2, SCo‐1 and SGR‐1b are reported for the first time.     

A Rapid Method for Determining Boron Concentration (ID‐ICP‐MS) and δ11B (MC‐ICP‐MS) in Vegetation Samples after Microwave Digestion and Cation Exchange Chemical Purification

We present in this article a rapid method for B extraction, purification and accurate B concentration and δ¹¹B measurements by ID‐ICP‐MS and MC‐ICP‐MS, respectively, in different vegetation samples (bark, wood and tree leaves). We developed a rapid three‐step procedure including (1) microwave digestion, (2) cation exchange chromatography and (3) microsublimation. The entire procedure can be performed in a single working day and has shown to allow full B recovery yield and a measurement repeatability as low as 0.36‰ (± 2s) for isotope ratios. Uncertainties mostly originate from the cation exchange step but are independent of the nature of the vegetation sample. For δ¹¹B determination by MC‐ICP‐MS, the effect of chemical impurities in the loading sample solution has shown to be critical if the dissolved load exceeds 5 μg g^?1 of total salts or 25 μg g^?1 of DOC. Our results also demonstrate that the acid concentration in the sample loading solution can also induce critical isotopic bias by MC‐ICP‐MS if chemistry of the rinsing‐, bracketing calibrator‐ and sample solutions is not thoroughly adjusted. We applied this method to provide a series of δ¹¹B values of vegetal reference materials (NIST SRM 1570a = 25.74 ± 0.21‰; NIST 1547 = 40.12 ± 0.21‰; B2273 = 4.56 ± 0.15‰; BCR 060 = ?8.72 ± 0.16‰; NCS DC73349 = 16.43 ± 0.12‰).     

Improved Inter‐calibration of Faraday Cup and Ion Counting for In Situ Pb Isotope Measurements Using LA‐MC‐ICP‐MS: Application to the Study of the Origin of the Fangshan Pluton,North China

A laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS) method was developed to obtain precise and accurate Pb isotopic ratio measurements in low‐Pb materials (< 10 μg g^?1) using a combination of Faraday cups and ion counters (FC–IC). The low abundance ²⁰⁴Pb (~ 1.4%) was collected using an IC. A NBS 981 standard solution was used to cross‐calculate the FC–IC gain and to investigate the signal response characteristics of the IC. A significant, continuous and linear decrease in the FC–IC gain was observed within 1 hr, but this drift could be corrected using the calibrator‐sample‐calibrator bracketing method. In addition, a non‐linear response of the IC used in this study was observed and corrected by a non‐linear correction algorithm, which was established by measuring a series of gravimetrically prepared NBS 981 standard solutions (NIST SRM 981). Compared with the conventional arrangement, the use of the newly designed X skimmer cone and Jet sample cone improved the signal intensities from Pb isotopes by a factor of 1.9. Compared with only Faraday cups, using a combination FC–IC array was found to enhance the measurement repeatability (RSD) of ^20xPb/²⁰⁴Pb by approximately one order of magnitude when the ²⁰⁴Pb intensity was < 8 mV. Eight natural glasses and the NIST SRM 612 reference material glass (as a calibration material) were measured to evaluate the new protocol for Pb isotope determination. The analytical results were in agreement with the reference values within 2s measurement uncertainties. For MPI‐DING ATHO‐G (5.67 μg g^?1 total Pb), KL2‐G (2.07 μg g^?1 total Pb) and ML3B‐G (1.38 μg g^?1 total Pb), the typical accuracies of ^20xPb/²⁰⁴Pb were 0.09% of preferred values with precisions of < 0.33% (2RSD). The Pb isotope ratios in feldspars from granodiorite and within mafic microgranular enclaves (MMEs) from the Fangshan pluton, North China, were measured using the present method. The Pb isotopic compositions of feldspars from the whole host granodiorite show that that are radiogenic in the margin zone and gradually become less radiogenic. For the MMEs, the Pb isotopic compositions of feldspars are highly variable and overlap with those of the whole host granodiorite. For single‐grain feldspar, the strong rim‐core‐rim variations of the Pb isotopic compositions and trace elements are interpreted to have been generated via magma mixing. These results suggest that the Fangshan pluton underwent magma mixing of mantle‐derived mafic magmas with felsic magmas, and the proportion of the mafic magma influx decreased over time.     

Combined Separation of Cu,Fe and Zn from Rock Matrices and Improved Analytical Protocols for Stable Isotope Determination

Isotope ratios of heavy elements vary on the 1/10000 level in high temperature materials, providing a fingerprint of the processes behind their origin. Ensuring that the measured isotope ratio is precise and accurate depends on employing an efficient chemical purification technique and optimised analytical protocols. Exploiting the disparate speciation of Cu, Fe and Zn in HCl and HNO₃, an anion exchange chromatography procedure using AG1‐×8 (200–400 mesh) and 0.4 × 7 cm Teflon columns was developed to separate them from each other and matrix elements in felsic rocks, basalts, peridotites and meteorites. It required only one pass through the resin to produce a quantitative and pure isolate, minimising preparation time, reagent consumption and total analytical blanks. A ThermoFinnigan Neptune Plus MC‐ICP‐MS with calibrator‐sample bracketing and an external element spike was used to correct for mass bias. Nickel was the external element in Cu and Fe measurements, while Cu corrected Zn isotopes. These corrections were made assuming that the mass bias for the spike and analyte element was identical, and it is shown that this did not introduce any artificial bias. Measurement reproducibilities were ± 0.03‰, ± 0.04‰ and ± 0.06‰ (2s) for δ⁵⁷Fe, δ⁶⁵Cu and δ⁶⁶Zn, respectively.