泥炭质土地层中深基坑变形特征数值模拟与实测分析

本文基于工程实测数据和数值模拟结果,对南宁某深基坑的变形特征进行了分析研究。研究结果表明:泥炭质土地层中,受基坑形状影响,支护结构水平位移存在明显的空间效应,呈角部位移小、中部位移大的特征,可充分利用基坑"角部效应"进行基坑支护结构优化。基坑深层土体水平位移分布形态受支护结构形式、泥炭质土地层分布及监测点所在位置影响较大,宜根据空间位置的不同,合理设计基坑水平支护结构。研究成果可为泥炭质土地层中深基坑的设计和施工提供参考。     

韵律性泥炭土地层中基坑支护设计与施工技术

泥炭质土具有孔隙比大、含水量高、有机质含量高、压缩性高、强度低等特点,韵律性泥炭土地层更甚,在该类地层中施工的锚索往往承载力较低,且徐变较大。根据具体工程实例,总结了泥炭质土层中基坑锚索支护设计的特点及难点,介绍了压灌桩与锚索施工的关键技术,有效地控制了基坑周边建(构)筑物的沉降与变形,为今后在泥炭质土等软土地区基坑支护设计提供参考。     

泥炭土深基坑支护工程高压旋喷扩体锚索施工工艺

结合基坑支护工程实例,介绍了昆明软弱泥炭质土层高压旋喷扩体锚索在深基坑支护工程中的施工工艺及锚固试验。通过不同的施工工艺试验分析,探索针对该场地软弱地质条件下的预应力锚索施工工艺,以确保预应力锚索施工达到设计要求承载力,保证预应力锚索的有效性和基坑支护结构体系的可靠性。     

联合支护体系在深基坑支护中的应用分析

深基坑支护是高层建筑施工中的重要组成部分,基础稳定性对整个建筑结构的安全起着决定性作用。确保基坑稳定的关键在于针对不同地层下合理的支护方案。文章结合工程实际,分析在泥炭土地层软弱基础上采矿用多种联合支护体系对基坑进行降水稳定施工。事实证明,结合各种支护方案的优点针对不同周边环境及地层进行基坑支护是合理可行的。     

昆明软土地区基坑支护设计研究

以具体工程实例为研究背景,分析了昆明软土地区基坑支护设计的特点及难点,并结合以往类似工程设计和实际施工经验,重点对在泥炭质土中设计止水桩、支护桩和锚索进行研究,为今后软土地区基坑支护设计提供了指导性技术参数。     

环梁支撑结构在泥炭土深基坑中的应用研究

以昆明市某超深基坑工程为例,分析探讨了大环梁内支撑结构在深厚泥炭质土层中应用的可行性及变形、应力变化规律。基坑支护结构位移及应力监测结果表明,环形内支撑结构能克服泥炭质土中锚杆锚固力差、易松弛变形等缺点,具有受力性能合理、方便施工且经济等优点,相对于与同类淤泥质软土基坑而言,其变形值相对偏大。本工程的成功经验可供类似基坑工程设计、施工参考。     

泥炭质土层深基坑支护的设计施工例析

本文介绍泥炭质土地层条件下的深基坑支护设计,采用置换水泥土搅拌桩止水和扩径预应力锚杆的方法,从源头保证泥炭质土地层中深基坑的安全和稳定。     

泥炭质土环境下大型环撑基坑变形控制分析

为了研究泥炭质土环境下基坑的变形情况,本文结合昆明某大型环形板撑基坑工程实例,根据基坑土体深层水平位移和基坑周边高架桥桥墩变形监测数据,分析其施工过程中基坑的变形情况。研究表明,该泥炭质土基坑的土体深层水平位移量较大;两道环形板撑施工完成后土体位移的增长速率明显减缓;高架桥桥墩的水平位移和竖向沉降始终未达到监测报警值;本工程所采用的支护桩+支承桩+二道钢筋混凝土环形板撑支护体系能较为有效地控制土体变形。     

昆明泥炭、泥炭质土的力学特性研究

昆明盆地由于阳光充足,水温适宜,又有湖泊、河流、洼地等地貌条件,有利于水生、湿生植物的生长蔓延,向沼泽化辟落发展,所以泥炭、泥炭质土的分布,是有其地区特点的。现建设现代新昆明,有许多建筑必须建设在这样的地基土上,因此,有关昆明泥炭、泥炭质土工程特性及工程应用的研究     

泥炭质土深基坑开挖案例分析

针对泥炭质土深基坑的地质特点,设计采用半盖挖顺筑法施工,地下连续墙+内支撑支护,按照时空效应原理分层开挖,保证了基坑施工安全性和经济性。     

Link between DOC in near surface peat and stream water in an upland catchment

Hydrologic transport of dissolved organic carbon (DOC) from peat soils may differ to organo-mineral soils in how they responded to changes in flow, because of differences in soil profile and hydrology. In well-drained organo-mineral soils, low flow is through the lower mineral layer where DOC is absorbed and high flow is through the upper organic layer where DOC is produced. DOC concentrations in streams draining organo-mineral soils typically increase with flow. In saturated peat soils, both high and low flows are through an organic layer where DOC is produced. Therefore, DOC in stream water draining peat may not increase in response to changes in flow as there is no switch in flow path between a mineral and organic layer. To verify this, we conducted a high-resolution monitoring study of soil and stream water at an upland peat catchment in northern England. Our data showed a strong positive correlation between DOC concentrations at -1 and -5 cm depth and stream water, and weaker correlations between concentrations at -20 to -50 cm depth and stream water. Although near surface organic material appears to be the key source of stream water DOC in both peat and organo-mineral soils, we observed a negative correlation between stream flow and DOC concentrations instead of a positive correlation as DOC released from organic layers during low and high flow was diluted by rainfall. The differences in DOC transport processes between peat and organo-mineral soils have different implications for our understanding of long-term changes in DOC exports. While increased rainfall may cause an increase in DOC flux from peat due to an increase in water volume, it may cause a decrease in concentrations. This response is contrary to expected changes in DOC exports from organo-mineral soils, where increase rainfall is likely to result in an increase in flux and concentration.     

双排桩基坑支护在膨胀土地区的工程应用

以成都望江锦园工程为例,介绍了双排桩支护体系在深基坑支护中的应用,基坑侧壁的变形观测结果表明,双排悬臂桩支护能够有效控制基坑水平位移。     

Geo-engineering properties and settlement of peaty soils at an industrial site (Turkey)

Peats consist of the partly decomposed remains of vegetation, which have accumulated in waterlogged areas. They are often unsuitable for supporting structures of any kind due to their high water content, high compressibility, low shear strength and high degree of spatial variability. The paper reports a preliminary study on peats from industrial sites in the city of Kayseri, Turkey. The soils in the study area are classified as peat to muck. The peats are fibrous at shallow depth and become amorphous as they extend to some 8 m depth. The ranges of geo-engineering properties are generally consistent with those reported in the literature, with some variation due to their higher mineral soil contents. The behavior of the peats is essentially frictional, with high friction and relatively small cohesion. The direct shear tests yielded higher shear strengths than those from the triaxial tests, due to the fact that the peat specimens used in the direct shear tests were rich in fibers and mineral soils. Back analysis of the settlement of heavy rolls of metal wires laid on the peat generally confirmed the consolidation properties of the soil determined in laboratory.     

半圆拱环梁桁架内支撑结构在软土基坑中的应用

随着基坑开挖周边环境越来越复杂,内支撑结构在软土基坑中的应用越来越普遍,其中,圆拱环梁由于受力性能好、平面开阔而得到广泛的应用。通过新型半圆拱环梁桁架结构与复合土钉墙相结合支护型式在中山地区软土基坑中的应用实例,阐述了这种支护结构的技术特点,可供类似基坑支护工程参考。     

厚冲积层深基坑Flac3D数值模拟分析研究

以济南第五医院基坑为实例,利用Flac3D数值模拟技术,建立了深基坑桩锚支护模拟模型。对支护结构进行开挖支护施工过程的三维动态模拟,得到深基坑水平位移、竖直位移和锚杆的内力、土体应力应变等数据,为深基坑支护技术的设计和施工提供指导,并对深入了解桩锚支护作用的机理有较大意义。     

鹤大公路草炭土工程地质特性研究

以吉林东部草炭土为研究对象，分析了草炭土的特殊工程地质性质，研究表明草炭土具有高天然孔隙比、高含水率、高压缩性和低抗剪强度等性质，提出了草炭土地基处理措施。     

Effect of clay content and wetting-and-drying on radiocaesium behaviour in a peat and a peaty podzol

The interaction of radiocaesium with peat under two moisture regimes was studied in laboratory experiments and by growing ryegrass in pot experiments to simulate changing field moisture conditions. A peat untreated and treated with 5% by weight of clay containing 46% illitic minerals, and a peaty podzol naturally containing 4.5% mineral matter on a dry weight basis were contaminated with (134)Cs and incubated. The soils were exposed to 8 wetting-and-drying cycles or kept constantly wet during 40 days. Extraction of the peat with 1 M CH(3)COONH(4) (pH 7) repeated after each wetting-and-drying cycle indicated increasing (134)Cs fixation with time of incubation. The peat treated with clay showed a much higher (134)Cs fixation than that without clay. The pot experiment with the incubated soils showed a (134)Cs transfer to ryegrass of the same order for the peaty podzol as for the peat treated with clay. For the peat untreated with clay the (134)Cs transfer to ryegrass was much greater. Wetting-and-drying the peat, with or without clay, increased the overall yield of grass and the concentration and uptake of (134)Cs over 5 consecutive harvests. K-fertilisation increased the yield of plant material (except for the peat with added clay), decreased the concentration of (134)Cs, but had no significant effect (p=0.05) on the resultant uptake of (134)Cs. Mixing clay with the surface layer of organic soils appears to be an effective means of decreasing radiocaesium transfer to field crops in fallout situations.     

Assessment of dynamic site response of the peat deposits at an industrial site (Turkey) and comparison with some seismic design codes

Peat is an organic soil type with properties of high compressibility and high water content. Peat deposits are often unsuitable for supporting structures of any kind due to their susceptibility to cause a number of geo-engineering problems, such as settlement, slope instability and soil amplification. There are peatlands in Turkey, although these are not so extensive as in other countries, such as Canada, where peatlands are very common. One of the peat deposits in Turkey is located close to the city of Kayseri (Central Anatolia), and industrial structures have been built on these deposits. This paper focuses on one part of a comprehensive research project conducted by the authors on various geo-engineering aspects of the peat deposits in this industrial site, with the main aims to investigate and assess some of the dynamic properties of the peat deposits in this area, to determine and assess their seismic site response and to compare them with the design spectra recommended in the current seismic codes of Turkey and Europe. In the study shear wave velocities of the peat deposits were determined with seismic measurements, and some dynamic properties of the peat were obtained from the resonant column and torsional shear tests. Then site response analyses were carried out and the results were compared with the design spectra recommended for loose-soft soils by the Turkish Seismic Design Codes and European Construction Design Codes. The comparisons suggest that the response spectra of the investigated peat deposits are greater than those recommended in the Turkish Seismic Codes and that at periods of > 0.3–0.5 s the peat will cause an increase in amplification. Although the response spectra of the peat tested show a better agreement with those recommended in the European codes, they show differences at periods of > 1 s.

     

Land management as a factor controlling dissolved organic carbon release from upland peat soils 1: Spatial variation in DOC productivity

The importance of soil storage in global carbon cycling is well recognised and factors leading to increased losses from this pool may act as a positive feedback mechanism in global warming. Upland peat soils are usually assumed to serve as carbon sinks, there is however increasing evidence of carbon loss from upland peat soils, and DOC concentrations in UK rivers have increased markedly over the past three decades. A number of drivers for increasing DOC release from peat soils have been proposed although many of these would not explain fine-scale variations in DOC release observed in many catchments.We examined the effect of land use and management on DOC production in upland peat catchments at two spatial scales within the UK. DOC concentration was measured in streams draining 50 small-scale catchments (< 3 km²) in three discrete regions of the south Pennines and one area in the North Yorkshire Moors. Annual mean DOC concentration was also derived from water colour data recorded at water treatment works for seven larger scale catchments (1.5-20 km²) in the south Pennines. Soil type and land use/management in all catchments were characterised from NSRI digital soil data and ortho-corrected colour aerial imagery.Of the factors assessed, representing all combinations of soil type and land use together with catchment slope and area, the proportion of exposed peat surface resulting from new heather burning was consistently identified as the most significant predictor of variation in DOC concentration. This relationship held across all blanket peat catchments and scales.We propose that management activities are driving changes in edaphic conditions in upland peat to those more favourable for aerobic microbial activity and thus enhance peat decomposition leading to increased losses of carbon from these environments.     

基坑支挡结构设计若干问题探讨

根据基坑开挖应力路径的室内试验和现场实测数据,从土工试验方法、土体强度指标、地基土水平反力系数等方面分析了现在基坑工程支挡结构设计存在的一些问题。研究成果如下:支挡结构设计参数的获取应考虑主动区及被动区地基土的应力路径,并恢复地基土的固结状态。基坑开挖后主动区和浅部被动区土体抵抗剪切破坏的能力大于以常规CU强度指标的计算结果,这有利于工程安全;深部被动区土体抵抗剪切破坏的能力小于以常规CU强度指标的计算结果,对于地基土被动抗力发挥较大的工程,需验算嵌固深度,确保被动抗力小于极限被动土压力。定义了被动区基坑开挖"强影响区",并给出了该区域深度的计算方法。以相应应力路径下的土体割线模量值作为地基土水平反力系数,讨论推导了作用于支挡结构上的分布土反力与支挡结构水平位移的计算公式,其计算结果更接近工程实际。本次研究对以变形控制为主的基坑设计具有较好的指导意义。