Nonlinear calculating method of pile settlement

To study calculating method of settlement on top of extra-long large-diameter pile, the relevant research results were summarized. The hyperbola model, a nonlinear load transfer function, was introduced to establish the basic differential equation with load transfer method. Assumed that the displacement of pile shaft was the high order power series of buried depth, through merging the same orthometric items and arranging the relevant coefficients, the solution which could take the nonlinear pile-soil interaction and stratum properties of soil into account was solved by power series. On the basis of the solution, by determining the load transfer depth with criterion of settlement on pile tip, the method by making boundary conditions compatible was advised to solve the load-settlement curve of pile. The relevant flow chart and mathematic expressions of boundary conditions were also listed. Lastly, the load transfer methods based on both two-broken-line model and hyperbola model were applied to analyzing a real project. The related coefficients of fitting curves by hyperbola were not less than 0.96, which shows that the hyperbola model is truthfulness, and is propitious to avoid personal error. The calculating value of load-settlement curve agrees well with the measured one, which indicates that it can be applied in engineering practice and making the theory that limits the design bearing capacity by settlement on pile top comes true.

Behavior of raft on settlement reducing piles:Experimental model study

An experimental program is conducted on model piled rafts in sand soil.The experimental program is aimed to investigate the behavior of raft on settlement reducing piles.The testing program includes tests on models of single pile,unpiled rafts and rafts on 1,4,9,or 16 piles.The model piles beneath the rafts are closed ended displacement piles installed by driving.Three lengths of piles are used in the experiments to represent slenderness ratio,L/D,of 20,30 and 50,respectively.The dimensions of the model rafts are 30 cm×30 cm with different thickness of 0.5 cm,1.0 cm or 1.5 cm.The raft-soil stiffness ratios of the model rafts ranging from 0.39 to 10.56 cover flexible to very stiff rafts.The improvement in the ultimate bearing capacity is represented by the load improvement ratio,LIR,and the reductions in average settlement and differential settlement are represented by the settlement ratio,SR,and the differential settlement ratio,DSR,respectively.The effects of the number of settlement reducing piles,raft relative stiffness,and the slenderness ratio of piles on the load improvement ratio,settlement ratio and differential settlement ratio are presented and discussed.The results of the tests show the effectiveness of using piles as settlement reduction measure with the rafts.As the number of settlement reducing piles increases,the load improvement ratio increases and the differential settlement ratio decreases.

Residual settlement calculation of geocell cushion over gravel piles

The calculation of residual settlement of bidirectional reinforced composite foundation, which is composed of geocell cushion over gravel piles, was studied. The geocell cushion was modeled as a thin flexible plate with large deflection. Based on the Kirchhoff hypothesis, the governing differential equations and boundary conditions of the deformation of geocell cushion under working load were founded using von Karman method and solved by Galerkin method. On theses bases, the gravel piles and inter-pile soils were assumed as Winkler ground with variable spring stiffness so as to execute the approximate calculation of the residual settlement of the bidirectional reinforced composite foundation. The calculation method was verified by two laboratory experiments concerning settlement of embankments. One experiment was with just geocell cushion installed to treat the soft clay under embankments; another one was with both geocell cushion and gravel piles installed. The results show that the calculated settlement curve and the maximum settlement are closed to the observed ones.

Settlement mechanism of piled-raft foundation due to cyclic train loads and its countermeasure

In this paper, numerical simulation with soil-water coupling finite element-finite difference（FE-FD） analysis is conducted to investigate the settlement and the excess pore water pressure（EPWP） of a piled-raft foundation due to cyclic high-speed（speed： 300km/h） train loading. To demonstrate the performance of this numerical simulation, the settlement and EPWP in the ground under the train loading within one month was calculated and confirmed by monitoring data, which shows that the change of the settlement and EPWP can be simulated well on the whole. In order to ensure the safety of train operation, countermeasure by the fracturing grouting is proposed. Two cases are analyzed, namely, grouting in No-4 softest layer and No-9 pile bearing layer respectively. It is found that fracturing grouting in the pile bearing layer（No-9 layer） has better effect on reducing the settlement.

Numerical Analysis of the Settlement of Composite Foundation Reinforced with Crushed Stone Grouting Pile and Rigid Bearing Plate

This paper deals with a new type of crushed stone grouting pile with a rigid bearing plate. The load transfer characteristics were analyzed, and a settlement model of the composite foundation reinforced with crushed stone grouting pile and rigid bearing plate was built by FEM program. The effects of replacement ratio of capping plate, replacement ratio of pile, replacement ratio of grout diffusion zone, pile-soil modulus ratio, and serous-soil modulus ratio, on the composite foundation settlement were discussed. It is concluded that the proposed crushed stone grouting pile with a rigid bearing plate is effective in decreasing the settlement of composite foundation.

Settlement of composite foundation with discrete material pile considering modulus change

Based on deeply discussing the deformation mechanism of composite foundation with discrete material pile, firstly, the settlement of composite foundation in rigid foundation conditions was assumed to consist of two parts, an expanding part and an un-expanding part. Then, in view of the differences of deformation properties between the expanding part and the un-expanding part, the relationships between the pile modulus and the applied load in these two parts were respectively developed. Thirdly, by introducing the above relationships into settlement analysis, a new method to calculate displacement of composite foundation with discrete material pile was proposed by using the multi-stage loading theory and the layer-wise summation approach. This method is effective not only for accounting for the effect of variations of pores on deformation modulus of the pile body in different depths, but also for describing the characteristics of different deformation mechanisms of the pile body with varying depth. Finally, the proposed method was used to a practical composite foundation problem, whose theoretical results were presented and compared to those of other methods. The rationality and feasibility of this method are identified through comparative analysis.

Settlement Characteristics of Cement Fly-Ash GravelPile-Plate Composite Foundation of High-Speed Railway

Field tests on settlement characteristics were carried out on the cement fly-ash gravel （CFG） pile-plate composite foundation on Beijing-Xuzhou section of Beijing-Shanghai high-speed railway. The settlements of the piles and the soil between pries were measured and analyzed. The results show that the settlement-time dependency experienced three phases： rapid development phase, stable development phase and stable phase. Therefore, surcharge preloading was necessary to reduce the settlement after construction. The finite element software Plaxis was used to calculate the deformations of the pile top and the soil between piles at the embankment center, as well as the settlements of CFG pile reinforcement area and the underlying stratum under surcharge preloading. The calculation results and the field test results were compared and analyzed. Both the results show that the settlement of the composite foundation mainly occured in underlying stratum. The settlement characteristics of pile-plate composite foundation under high embankment are also concluded.

木栅干栏与高台城垣:工具史视野下青铜时代巴蜀聚落建筑的文化技术探究

本文立足于工具史视野审视青铜时代的巴蜀聚落建筑,阐述以“木栅干栏与高台城垣”为空间特征的聚落建筑文化技术。通过分析以农业栽培及青铜礼器为生业特色的蜀地聚落建筑,以盐泉渔猎及青铜兵器为生业特色的巴地聚落建筑;论述青铜时代巴蜀地区基于生产生活、宗教王权、安全防御等复杂职能的干栏建筑空间逐步走向多样化,同时高台宫室及夯土城垣的大型聚落形态也呈现规模化,并进一步发现其聚落建筑的功能分区明晰,具有显著的轴线及围合性特征;聚落类型可分为木栅城垣与夯土城垣,建筑类型可分为干栏建筑与高台宫室。其中大型祭祀台及宫室区位于聚落核心区域,围绕祭祀台与宫室区形成向心性的仪式空间。这种向心性秩序把青铜时代社会分层系统中类“尖锥体”的等级结构物化于物质空间中,体现了方国联盟集团的共同利益与意志,是青铜时代巴蜀社会制度系统的空间化表达。

考虑桩土作用的单桩承载特性有限元分析

根据某工程的实际检测数据,分析桩基础在竖向受荷状态下的承载性能,通过选择合适的接触面参数,使用ANSYS有限元软件对该工程的单桩静载试验进行数值模拟分析。本文分析不同荷载下的沉降曲线、轴力、桩侧阻力以及桩土相对位移量的曲线。计算结果显示:数值模拟现场单桩静载试验是可行的,模拟沉降曲线和实测值拟合程度较好,并在此基础上分析了桩长、桩径参数对单桩承载性能的影响。

盾构下穿高速公路对既有平行通道桥的影响规律

为探讨盾构下穿高速公路对既有平行通道桥的影响规律,以韩江榕江练江水系连通后续优化工程盾构隧道穿越G78汕昆高速公路路堤为背景,建立三维有限元模型,分析盾构施工对地表沉降、高速公路路基、既有平行通道桥桩基的影响规律。结果表明:1)盾构隧道开挖对地层的影响范围大致为隧道直径的4倍;2)隧道轴线正上方地表沉降值最大,达到5.6 mm,路基最大沉降值发生在隧道轴线正上方,约为5 mm;3)通道桥桩基竖向位移均表现为沉降,靠近盾构侧桩基沉降大于远侧,其中桩基Z1沉降值最大,达到2.4 mm;4)隧道埋深顶面处对应的桩基水平位移较大,受盾构掘进叠加影响,桩基Z1水平位移最大,约为0.37 mm;5)弯矩的最大值出现在隧道埋深位置附近,轴力的最大值出现在桩身中点位置,桩基Z1弯矩和轴力最大。

盾构掘进引起的古建筑变形预测及其控制技术研究

大直径盾构隧道在掘进施工过程中可能会引起土体损失且对邻近古建筑产生不利影响。由于古建筑自身的脆弱性和不可恢复性,其对周围环境的改变非常敏感,因此有必要针对盾构隧道施工期间邻近古建筑的变形特性和控制措施展开研究。基于之江路输水管廊工程,建立了隧道-土体-地基-塔数值模型,开展了盾构施工引起的邻近六和塔变形及其控制技术研究。研究结果表明:随着与盾构隧道距离的减小,地表监测点沉降增大;推力大小的改变对塔身倾斜率和塔基沉降均有影响,土体损失率增大对塔身倾斜率的增大影响显著;布置PVC排桩能有效控制地表沉降;桩长、桩径与桩间距的参数分析表明,桩间距减小对地表沉降和六和塔变形控制最为有效。

高速公路软路基处理技术研究

软土含水率较高,抗剪强度低,容易发生变形,若处治不当,则会在填筑和运营过程中造成较大的沉降甚至路基失稳等病害。为提高高速公路软路基处理效果,文章针对某高速公路软土地基施工中遇到的问题,介绍了几种常用的地基加固技术,并制定了水泥搅拌桩处理软土路基的施工方案,并且通过监测沉降量等指标,证实了这种地基加固技术的可行性与实用性,为类似高速公路软路基处理提供了参考。

复杂地质环境下桥梁钻孔灌注桩施工关键技术研究

钻孔灌注桩作为桥梁工程的基础,由于受复杂地质环境影响较大,其施工工序复杂,施工质量并不可控,从而导致工程事故频发。本研究以新疆某公路桥梁的桩基础工程为背景,计算了其钻孔灌注桩成桩质量的合理性,并通过COMSOL有限元数值模拟软件,计算了单根钻孔灌注桩在不同荷载条件下的应力分布和沉降变形情况。研究结果表明,数值模拟方法能够较好地模拟灌注桩的荷载–沉降变形过程,辅助实际监测结果确定桩的极限承载力,在一定程度上加快施工进程,降低工程风险。

城市道路路基软地基处理过程中的市政工程技术分析

为研究市政工程技术中的双向水泥搅拌桩施工技术在软土地基加固中的应用效果,文章以某滨海地区道路工程为例,分析了施工工艺参数的设定及其对地基加固效果的影响。通过详细的施工步骤和现场沉降监测,结果指出,合理的浆液配置和精确的桩位标定是保证桩体均匀性和地基稳定性的关键因素。同时,沉降监测数据表明,经过双向水泥搅拌桩加固的地基在112天后基本稳定,最大沉降值为43.2mm,低于设计标准50cm;最大水平位移和垂直位移分别为0.06mm和0.22mm,均在允许范围内。说明该技术在提高地基承载力和减少沉降方面具有显著效果。

GEP废弃泥固化桩复合地基在软土地基整治中的应用

软土地基加固一直是工程施工的关键需求,针对传统水泥土搅拌桩的承载力不足、质量不均匀等问题提出一种新型的筋箍预应力(GEP)废弃泥固化桩技术,将流态废弃泥浆进行固化处理,并注入地下形成GEP废弃泥固化桩,旨在解决软土地基整治难题并提升桩身质量,提高软土地基的承载力与稳定性。通过室内试验,确定了GEP桩的设计方案和施工工艺,并通过COMSOL软件对复合地基进行数值模拟,结合现场工程试验,评估其承载力及沉降特性。结果表明,GEP废弃泥固化桩在不同荷载下均展现出优于传统水泥土桩的承载力和沉降控制能力,最大沉降减少了16.87%。此外,GEP技术通过土工格栅的周向约束,显著提高桩体的刚度和承载力。研究结果表明,GEP废弃泥固化桩技术具有良好的应用前景,为软土地基加固和废弃泥资源化利用提供了有效的解决方案。

高速公路软土地基桥梁桩基础的沉降分析

以软土地基的桩基沉降为研究内容,介绍软基区桥梁桩基础沉降特点,并从勘察、设计、施工等角度分析桩基沉降的原因,介绍了沉降分析基础理论以及现行规范的计算原理,并结合试桩试验,提出软土地区桩基设计的基本思路,同时,从设计角度出发,为运营阶段沉降问题的防治提出切实可行的建议。

道路桥梁旋挖灌注桩技术应用

为保证道路桥梁的使用寿命,需提升桩基础的稳定性和承载性,研究以实际工程为例,分析了旋挖灌注桩施工技术。研究结合工程的设计方案和地质勘查结果,确定了灌注桩施工方案,并且选择了合理的施工设备,完成了灌注桩施工,对施工结果进行现场试验后,单桩的桩顶沉降最大值为14.05mm,最小沉降为8.66mm;承载力特征值均在标准结果以上,均高于标准的11000kN,满足施工需求。

双线盾构隧道侧穿既有桥梁桩基沉降变形特征研究

双线盾构隧道侧穿既有桥墩时隧道开挖间距和方式对桥梁桩基沉降变形影响较大。本研究采用有限元分析方法建立三维数值模型,计算了不同先行开挖方式和隧道开挖间距下桥梁桩基的沉降变形。结果表明,远线先行开挖桥梁桩基沉降变形更严重,近线先行开挖桥梁承台倾斜更严重;近线隧道与桥桩间距4 m时,双线隧道间距增大,桥梁承台产生拉伸形变,桩基的弯曲变形程度与隧道间距呈负相关;相比隧道间距为3D(D为隧道直径)时桥梁桩基沉降变形最小。结合数值模拟结果和理论分析,引入双线隧道效应系数m修正了侧穿桥墩桩基沉降的计算公式,结果表明,侧穿桩基沉降双线隧道效应影响程度随着隧道间距的增大而不断弱化。

桩筏互补加固技术在软土地区厂房中的应用

软土地区厂房基础多采用预制桩、灌注桩,由于上部软弱土及施工质量存在缺陷,通常会造成厂区地坪凹陷、开裂等质量问题。通过对某大型厂房项目的不均匀沉降、底板脱空原因研究分析,采用桩筏互补加固技术,大幅度提高了深厚软土区地基承载力,有效减小沉降,同时解决了加固施工过程中涉及的厂区设备多作业空间小,施工不影响厂区正常生产等技术难题,该技术对于深厚软土区、狭小空间加固具有一定的参考意义。

多雨潮湿地区基坑钢板桩支护施工方法研究

通过对多雨潮湿地区在暴雨天气基坑钢板桩内支撑支护的施工方法进行优化,并提出暴雨天气下对基坑的监测监控措施,监测基坑周边建(构)筑物也会产生沉降和位移等数据,暴雨天气后基坑降水施工方法等,其可为基坑钢板桩支护工程施工人员提供参考。