PHC静压桩施工监测和信息化施工

静力压桩在工程中的使用越来越广泛,特别是在饱和软粘土地区,伴随压桩产生的挤土效应和超孔隙水压力会对周边环境产生一定的影响.本文结合某具体压桩工程的施工,指出了在工程中应该采取的防护措施,以及因地制宜采取合理压桩顺序的重要性.     

考虑挤土和群桩效应的预制桩安全监控模型

在深入分析密集型静力压入式预制桩挤土效应和群桩效应的机理和不利影响的基础上，建立了确保地基土不因挤土效应而破坏的孔隙水压力监控模型，优化压桩线路和次序的超静孔压监控模型，确保基桩不因桩周土隆起而被拔断的基桩轴力监控模型，确保基桩不因挤土效应而产生弯折破坏以及桩间土不因群桩效应而产生剪切破坏的桩侧土压力监控模型。实测数据表明，在没有采取有效的降排水和卸压预防措施时，沉桩施工容易导致地基土强度失效和基桩拔断破坏。采取袋装砂井排水和碎石桩式降水井降水后。即使是透水性差的软土地基。也可使较大的超静孔压在1d时间内消散70％。     

某PHC静压桩的施工监测和施工优化

在饱和软粘土地区，静力压桩在工程中的使用越来越广泛，但伴随压桩产生的挤土效应和超孔隙水压力会对周边环境产生一定的影响，有时还相当严重。本文结合某具体压桩工程的施工，指出了在工程中应该采取 的防护措施，以及因地制宜采取合理压桩顺序的重要性。     

搅拌桩加固挤土效应及在地铁隧道保护中的应用

在减小地基变形进行的深层搅拌桩加固时,加固本身的挤土效应对隧道变形产生了影响。为此,模拟了搅拌桩（DCM）侧向挤土效应的4种荷载模式,结合实测资料并采用数值试验验证了侧向挤土荷载模式的合理性。进一步应用该模式,通过有限元模拟了搅拌桩的加固挤土效应,分析讨论了不同加固顺序对地面变形,隧道变形以及长期蠕变变形的影响,结论表明,搅拌桩加固对地面环境影响是不可忽略,隧道周围搅拌桩施工顺序对隧道变形影响较大,搅拌桩加固后长期蠕变效应相对加固过程的变形很小。     

静力压桩施工质量控制浅谈

在工程施工过程中，静力压桩作为挤土预制桩的成桩方法之一被广泛应用，本文通过对静力压桩施工中质量控制的分析，提出一些施工控制要点，可为静力压桩规范化施工与提高施工质量提供参考。     

软基路堤拓宽静压PHC管桩挤土效应现场试验

PHC（prestressed high-strength concrete）管桩近年来被广泛应用。PHC管桩为挤土沉桩模式,沉桩过程引起的挤土效应对周围环境产生不利影响并对其可打性和承载特性有重要影响。结合广－清（广州至清远）高速公路扩建工程,通过现场监测超静孔隙水压力和土体水平位移,进行PHC管桩挤土效应研究。水平位移利用固定式测斜仪测量,孔隙水压力使用振弦式孔压计测量,并使用自动系统进行数据采集。研究发现,沉桩过程中引起的超静孔隙水压力变化随深度增加近似呈线性增长,水平方向随距离的增加而减小;挤土效应产生的土体水平位移随距离的增大而减小,随深度增加而减小;挤土效应滞后现象明显,可导致成桩后的桩体倾斜;拓宽地基场地上管桩施工对老路地基影响小,场地条件对沉桩挤土效应影响大,老路路堤对垂直于路基方向的水平位移有约束作用。     

静压单桩挤土位移的有限元分析

在大型通用软件ANSYS平台上,对静力压桩的连续贯入全过程进行有限元模拟,并对静压单桩的挤土位移进行详细地分析,给出了桩土模量比、桩土间摩擦系数、土体泊松比对挤土位移场的影响规律。利用位移贯入法使桩体贯入,考虑了弹塑性本构关系、自重应力场、大变形和桩-土滑动摩擦等复杂问题,更符合静力压桩的实际,具有仿真效果。     

挤土类桩的挤土效应及其防治方法

挤土效应是所有挤土类桩面临的共同问题，它可能造成临近建筑物破坏，地下管线断裂，道路隆起以及工程质量事故。依据挤土类桩挤土效应的形成机理，结合工程实例，提出了减少挤土效应的措施，如预钻排水孔、开挖防挤沟、设置观测点、控制压桩速度等措施，并根据施工地区不同的环境条件提出了合理的压桩顺序。     

开口管桩压入法沉桩土塞效应机理分析

文章基于柱孔扩张理论依据沉桩过程引起大变形的机理得到了管桩挤土过程中塑性区半径解析表达式,分析了开口管桩静力压桩产生的应力场与位移场.分析了由于土塞存在导致的土塞效应对应力场与位移场的影响.     

高铁站场中不同类型桩基沉桩顺序研究

沪宁高铁某站场改建工程在咽喉区的狭窄区域同时出现PHC桩、CFG桩、水泥搅拌桩等多种地基处理方式,为克服PHC桩挤土效应对其他桩的可能影响．分别采用圆孔扩张理论、有限元分析方法及“等量桩”简化方法对PHC桩施工的单桩挤土效应、双桩挤土效应及群桩挤土效应进行了计算分析,获得不同条件下的挤土位移和挤土应力分布规律,进而对该区域基桩的合理施工顺序提出了建议。     

大连临海超大深基坑旋喷桩止水帷幕施工技术

大连临海区域地貌为冲海积阶地,后经人工回填,地质水文条件复杂,既有天然沉积的土层和岩石,又有人工回填的透水性很强的杂填土。其地下水位受海水影响,下部为卵砾石及强风化基岩,基岩面起伏较大。地铁车站超大深基坑开挖采用桩基围护结构加止水帷幕,坑内深井井点方式降水。通过两次试桩及工艺参数优化,高压旋喷桩止水帷幕达到理想效果。     

柴达木盆地西部地区古近纪与新近纪沉积相

利用数十口井的电性、岩性及分析化验资料，将柴达木盆地西部地区古近纪与新近纪沉积相划分为七种相和亚相：洪积锥、水下冲积扇、河道和泛滥平原、滨湖、浅湖、较深湖和三角洲。沉积相的空间展布概括起来分为三大带：（1）阿尔金山前西段陡坡带洪积锥-水下冲积扇-扇三角洲-河道和泛滥平原-湖相 (2)阿尔金山前中段陡坡带洪积锥-水下冲积扇-湖相；（3）昆仑山前洪积锥-河道和泛滥平原-三角洲相。沉积相不仅影响着碎屑岩的成分和结构，而且也影响其物性与含油性。由洪积锥到水下冲积扇，到河道和泛滥平原，到三角洲，到湖相，石英和胶结物含量逐渐升高，岩屑和杂基含量逐渐降低，分选及磨圆变好，颗粒的粒级变细。浅层以河道和泛滥平原及三角洲相的物性最好，深层以三角洲相的物性最好，次为冲积扇，湖相最差。碎屑岩的油气富集以河道、泛滥平原和三角洲相最好，滨浅湖相油气富集最差。     

Climatic Implications of the Late Quaternary Alluvial Record of a Small Drainage Basin in the Central Great Plains

Four late-Quaternary alluvial fills and terraces are recognized in Wolf Creek basin, a small (163 km²) drainage in the Kansas River system of the central Great Plains. Two terraces were created during the late Pleistocene: the T-4 is a fill-top terrace underlain by sand and gravel fill (Fill I), and the T-3 is a strath terrace cut on the Cretaceous Dakota Sandstone. Both Fill II (early Holocene) and Fill III (late Holocene) are exposed beneath the T-2, a Holocene fill-top terrace. The T-1 complex, consisting of one cut and three fill-top terraces, is underlain by Fills III and IV. A poorly developed floodplain (T-0) has formed within the past 1000 yr. As valleys in Wolf Creek basin filled during the early Holocene, an interval of soil formation occurred about 6800 yr B.P. Early Holocene fill has been found only in the basin's upper reaches, indicating that extensive erosion during the middle Holocene removed most early-Holocene fill from the middle and lower reaches of the basin. Valley filling between 5000 and 1000 yr B.P. was interrupted by soil formation about 1800, 1500, and 1200 yr B.P. As much as 6 m of entrenchment has occurred in the past 1000 yr. Holocene events in Wolf Creek basin correlate well with those in other localities in the central Great Plains, indicating that widespread changes in climate, along with adjustments driven by complex response, influenced fluvial activity.     

The Pliocene initiation and Early Pleistocene volcanic disruption of the palaeo-Gediz fluvial system,Western Turkey

In this paper, we report our latest observations concerning a Pliocene and Early Pleistocene record from Western Turkey. The sedimentary sequence described comprises the fluvial deposits of an Early Pleistocene palaeo-Gediz river system and its tributaries prior to the onset of volcanism around Kula and the subsequent lacustrine, volcaniclastic and fluvial deposits associated with the first phase of volcanism (∼1.2 Ma) in this area.Early development of an east–west drainage system in this area resulted from tectonic adjustments to north–south extension and the formation of east–west-oriented grabens. Headward erosion of drainage entering the main Alaşehir graben led to the progressive capture of pre-existing drainage systems as eastward (headward) erosion upstream tapped drainage networks previously formed in internally draining NNE–SSW-oriented basins. Within one of these, the Selendi Basin, part of this evolutionary sequence is preserved as a buried river terrace sequence. Eleven terraces are preserved beneath alluvial fan sediments that are, in turn, capped by basaltic lava flows. Using the available geochronology these terraces are considered to represent sedimentation–incision cycles which span the period ∼1.67–1.2 Ma. Although progressive valley incision is a fluvial system response to regional uplift, the frequency of terrace formation within this time period suggests that the terrace formation resulted from sediment/water supply changes, a consequence of obliquity-driven climate changes. The production of sub-parallel terraces suggests that during this period the river was able to attain a quasi-equilibrium longitudinal profile adjusted to the regional uplift rate. Thus, the incision rate of 0.16 mm a⁻¹ during this period is believed to closely mirror the regional uplift rate.After the onset of volcanism at ∼1.2 Ma, there is a destruction of the dynamic link between fluvial system behaviour and climate change. The repeated damming of the trunk river and its tributaries led to the construction of complex stratigraphic relationships. During the first phase of volcanism the palaeo-Gediz river was dammed on numerous occasions leading to the formation of a series of lakes upstream of the dams in the palaeo-Gediz valley. Variations in lake level forced localised base-level changes that resulted in complex fluvial system response and considerable periods of disequilibrium in profile adjustment. Furthermore, response to these base-level changes most likely disrupted the timing of the incisional adjustment to the on-going regional uplift, thus making the use of this part of the archive for inferring regional uplift rates untenable.     

Alluvial geoarchaeology of an ephemeral stream: Implications for Holocene landscape change in the central part of the Ebro Depression,northeast Spain

La Virgen is an ephemeral tributary of the Ebro River in northeast Spain with a complex alluvial sequence. We analyzed alluvial stratigraphy to develop a model of Holocene fluvial evolution for La Virgen and infer causes of floodplain dynamics. Three alluvial terraces were mapped and described using a combination of geoarchaeological and geomorphological techniques. Stratigraphic ages were estimated using ¹⁴C dating and archaeological remains. Sedimentation in the valley floor commenced in the Neolithic period ca. 6000 BC and continued during the Bronze and Iron ages (ca. 1800–500 BC), the Iberian and Roman periods (ca. 500 BC–AD 500), and the Middle Ages (ca. AD 500–1500). The main terrace (N3) is 14m thick and predominantly composed of sand, silt, and clay that we believe are derived from local hillslopes and represent a long period of human‐induced soil erosion that intensified during the Bronze and Iron ages until the Late Roman period. © 2010 Wiley Periodicals, Inc.     

Evaluating the role of climate and tectonics during non-steady incision of the Yellow River: evidence from a 1.24 Ma terrace record near Lanzhou,China

The competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain. Most of recent studies have attributed terrace formation to climatic changes and held that, even in tectonically active settings, climate variations control cycles of terrace planation and abandonment. Based on field investigations of loess-paleosol sequences, magnetostratigraphy and optically stimulated luminescence (OSL) dating, we develop a new chronology for a spectacular flight of terraces along the Yellow River near Lanzhou, China over past 1.24 Ma. All the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads, suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates. However, the ages of terraces cluster in two relatively short time periods (1.24–0.86 Ma and 0.13 Ma – present). During the intervening time between 0.86 Ma and 0.13 Ma, terraces either did not form or were not preserved. We suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation/preservation. Thus, our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision.     

Distribution and Forming Model of Fluvial Terrace in the Huangshui Catchment and its Tectonic Indication

<正>The Huang Shui River,a main tributary of the Yellow River,crosses a series of tectonically subsided and uplifted areas that show different patterns of terrace formation.The distribution of fluvial terrace of the Huang Shui River is studied through topographic and sedimentologic terrace mapping.Three terraces in the Haiyan Basin,four terraces in the Huangyuan Basin,19 terraces in the Xi'ning Basin(the four high terraces may belong to another river),nine terraces in the Ping'an Basin, five terraces in the Ledu Basin and 12 terraces in the Minhe Basin are recognized.Sedimentology research shows that the geomorphologic and sedimentological pattern of the Huang Shui River,which is located at the margin of Tibet,are different from that of the rivers at other regions.The formation process of the terrace is more complicated at the Huang Shui catchment:both accumulation terrace and erosion terrace were formed in each basin and accumulation terraces were developed in some basins when erosion terraces were formed in other basins,indicating fluvial aggradation may occur in some basins simultaneously with river incision in other basins.A conceptual model of the formation process of these two kinds of fluvial terraces at Huang Shui catchment is brought forward in this paper.First,the equilibrium state of the river is broken because of climatic change and/or tectonic movement,and the river incises in all basins in the whole catchment until reaching a new equilibrium state.Then,the downstream basin subsides quickly and the equilibrium state is broken again,and the river incises at upstream basins while the river accumulates at the subsidence basin quickly until approaching a new equilibrium state again.Finally,the river incises in the whole catchment because of climatic change and/or tectonic movement and the accumulation terrace is formed at the subsidence basin while the erosion terrace is formed at other basins.The existence of the accumulation terrace implied the tectonic subsidence in the sub-basins in Huang Shui catchment.These tectonic subsidence movements gradually developed from the downstream Minhe Basin to the upstream Huangyuan Basin.Dating the terrace sequence has potential to uncover the relationship between the subsidence in the catchment and the regional tectonic at the northeastern Tibetan Plateau.     

利用粒度分析青衣江河流地貌面的新老关系

通过河流阶地的变形特征来分析区域构造活动已得到广泛应用,但同级阶地的对比方法仍存在很多问题,尤其是在缺少标志地层、风化严重的地区。文章通过横穿青藏高原东缘龙门山南段的青衣江河流地貌研究,探讨了粒度分析在阶地、冲积扇面等河流地貌面对比研究中的应用。研究结果表明:河流沉积物中砾石之间基质砂的粒度,很好地区分了同一地区的不同级阶地,粒度呈现出规律的渐变特征;另外,在不同河谷的同级河流地貌面之间存在较大差别,主要与河谷的大小规模相关。这表明,基质粒度的变化反映了河流沉积物随年龄增加而风化程度变大的规律;另一方面,从新到老的河流沉积物剖面中基质的颜色有明显的渐变特征,可以应用于野外初步识别地貌面。这些成果为河流地貌面的对比研究提供了新的简便、可行的方法。     

Pleistocene tectonics inferred from fluvial terraces of the northern Upper Rhine Graben, Germany

This study of fluvial terraces of the River Rhine and tributaries aims to search for indications of Pleistocene tectonic activity. The study area includes the northern Upper Rhine Graben (URG), the Mainz Basin and the adjacent Rhenish Massif with the Middle Rhine Valley. High rates of Quaternary surface processes, large amount of human modifications, relatively slow tectonic deformation and presently low intra-plate seismic activity characterize this area. Therefore, the records of relatively slow tectonic deformation are less well preserved and thus difficult to detect. This study uses the relative position of fluvial terraces to determine the more local effects of fault movements on the terraces and to evaluate their displacement rates and patterns. The research is based on a review of previous terrace studies and new terrace mapping from the eastern Mainz Basin and the bordering URG using topographic map interpretations and field observations. This newly mapped sequence of terrace surfaces can be correlated to other terraces in the vicinity on the basis of relative height levels. Terrace correlation between the western Mainz Basin and Middle Rhine Valley relies on a single chronostratigraphic unit (Mosbach sands) and additional relative height correlations. This is the first study to present a continuous correlation of terraces from the western margin of the URG to the Rhenish Massif and enables the study of the transition from the subsiding graben to the uplifted Rhenish Massif. By means of a longitudinal profile, which ranges from the URG to the Rhenish Massif, the influence of individual fault movements on the terrace levels and the large-scale regional uplift is demonstrated. It is evident from the profile that the uplift of Early to Middle Pleistocene terraces increases northwards, towards the Rhenish Massif. The uplift was diachronic, with a significant pulse occurring first in the northern URG (Lower Pleistocene) and later in the Rhenish Massif (Middle Pleistocene). The largest vertical displacements are recorded for the boundary fault separating the Mainz Basin and the Rhenish Massif (Hunsrück–Taunus Boundary Fault) and for faults bounding the northeastern Mainz Basin. The motions and displacement rates calculated for individual faults indicate deformation rates in the order of 0.01–0.08 mm/year. At this stage, the calculation of displacement rates depends mostly on a single dated stratigraphic unit. Additional dating of terrace deposits is urgently needed to better constrain the temporal development of the terrace sequence and the impact of tectonic movements.