地下水开采引起的次压缩对隧道长期沉降的影响

软土地区盾构隧道建成后往往伴随有明显的长期沉降,较大的隧道沉降会严重影响地铁系统的运营及安全。然而,目前对于软土地区隧道长期沉降机制的认识尚不明确。以上海地区地铁盾构隧道1999－2007年间的隧道沉降为例,通过室内试验及现场监测对引起隧道长期沉降的因素,特别对地下水开采引起的软土及砂土层次压缩进行了研究。结果表明,第4含水砂层具有明显的次压缩特性,抽取地下水引起的第4含水层的压缩,特别是其次压缩变形,是引起隧道长期沉降的主要原因之一。因此,严格控制该承压含水层地下水开采是目前缓解上海地铁隧道长期沉降的主要措施。     

ICE‐MARGINAL SEDIMENT DELIVERY TO THE SURFACE OF A HIGH‐ARCTIC GLACIER: AUSTRE BRØGGERBREEN,SVALBARD

Enhanced delivery of water‐saturated, ice‐marginal sediments to the glacier surface is a response to glacier thinning that has the potential to increase both levels of sediment transfer through the glacier hydrological system and total basin sediment yields. Preliminary observations made during summer 2007 at Austre Brøggerbreen, Svalbard, confirm that ice‐marginal debris flows in the upper reaches of the glacier are actively delivering sediments to the glacier surface, which may then be flushed into the glacier's hydrological system. During a four‐day observation period, several stochastic pulses in water turbidity were observed at a single portal where solely supra‐ and englacial drainage emerge at the glacier margin. The erratic suspended sediment fluxes were hypothesized to originate from ice‐marginal sources. Quantitative analysis of continuous turbidity and discharge data confirm that discharge is not driving these turbidity pulses and, combined with observational data, that the most likely origin is the delivery of water‐saturated sediments to the glacier surface from ice‐marginal, debris flows with subsequent transfer to the portal via the glacial drainage system. These observations illustrate the potential importance of the paraglacial component to the overall sediment cascade of deglaciating basins and highlight the need for careful interpretation of turbidity records, where stochastic pulses in turbidity may be attributed to sources and processes other than ice‐marginal sediment inputs.     

Subsurface movement of zinc from contaminated dredge spoils at a periodically flooded site

In 1982, sediments contaminated with zinc, cadmium, and copper were dredged from Lake DePue in Illinois and deposited in a diked sediment disposal area (DSDA) that is flooded annually for at least three months. Data from soil and groundwater samples collected at multiple depths within and adjacent to the DSDA indicate vertical movement of the metals in the subsurface, although groundwater outside of the DSDA was not contaminated with any of the metals. Zinc was elevated in almost all of the wells inside the DSDA. Cadmium concentrations were elevated in shallow wells inside the DSDA, while copper was rarely detected in the groundwater. Comparisons of groundwater samples taken within the DSDA under flooded and unflooded conditions suggest that pH and redox conditions controlled metal solubilities. A comparison between soil cores and sediment cores from Lake DePue suggest that zinc was more mobile than cadmium or copper within the DSDA.     

Amino acid abundances and stereochemistry in hydrothermally altered sediments from the Juan de Fuca Ridge, northeastern Pacific Ocean.

The Juan de Fuca Ridge is a hydrothermally active, sediment covered, spreading ridge situated a few hundred kilometres off the west coast of North America in the northeastern Pacific Ocean. Sediments from seven sites drilled during the Ocean Drilling Program (ODP) Legs 139 and 168 were analyzed for total hydrolyzable amino acids (THAA), individual amino acid distributions, total organic C (TOC) and total N (TN) contents. The aim was to evaluate the effects of hydrothermal stress on the decomposition and transformation of sedimentary amino acids. Hydrolyzable amino acids account for up to 3.3% of the total organic C content and up to 12% of the total N content of the upper sediments. The total amounts of amino acids decrease significantly with depth in all drilled holes. This trend is particularly pronounced in holes with a thermal gradient of around 0.6 degrees C/m or higher. The most abundant amino acids in shallow sediments are glycine, alanine, lysine, glutamic acid, valine and histidine. The changes in amino acid distributions in low temperature holes are characterized by increased relative abundances of non-protein beta-alanine and gamma-aminobutyric acid. In high temperature holes the amino acid compositions are characterized by high abundances of glycine, alanine, serine, ornithine and histidine at depth. D/L ratios of samples with amino acid distributions similar to those found in acid hydrolysates of kerogen, indicate that racemization rates of amino acids bound by condensation reactions may be diminished.     

降雨入渗条件下非饱和膨胀土边坡原位监测

为了对降雨诱发的非饱和膨胀土边坡失稳的机理有较深入的了解,在湖北枣阳选取了一个11 m高的典型的非饱和膨胀土挖方边坡进行人工降雨模拟试验和原位综合监测。监测成果表明：降雨入渗造成2 m深度以内土层中孔隙水压力和含水量大幅度增加,致使膨胀土体的抗剪强度由于有效应力的减少及土体吸水膨胀软化而降低;同时,降雨入渗造成土体中水平应力与竖向应力比显著增加,并接近理论的极限状态应力比,以致软化的土体有可能沿着裂隙面发生局部被动破坏,此破裂面在一定条件下（如持续降雨条件下）可能会逐渐扩展,最后发展成为膨胀土中常见的渐进式滑坡。     

膨胀土地基中隧道施工对群桩影响研究

在膨胀土地基中进行隧道对群桩影响的三维离心模型试验研究,目标地层损失比为2%,着重研究引起的地基沉降槽、桩的附加沉降、附加弯矩、轴力的变化规律。试验得出：隧道开挖沉降槽空间效应明显;隧道开挖从-0.75D至1.25D时,桩附加沉降呈线性增长,隧道开挖至1.25D以后,桩依然沉降明显。前桩与后桩沉降值不同,桩帽会出现倾斜;前桩上部出现负附加弯矩而下部出现正附加弯矩,而后桩仅在下部出现正附加弯矩;前桩附加弯矩最大值出现在隧道轴线附近,且比后桩附加弯矩大得多;前桩附加轴力随着隧道的开挖而增加,且每步最大值在隧道轴线附近。后桩的轴力也随隧道的开挖而增加,但每步最大值出现在桩顶附近。