Composting of Food and Yard Wastes under the Static Aerated Pile Method

This work presents the results that were obtained in a commercial composting plant where food (149,690 kg) and yard wastes (144,520 kg) were used as raw materials for its stabilization under the aerated static pile (ASP) method as an alternative to the mechanically mixed windrow method to solve problems of flies and odor nuisance complaints. In a pile of approximately 498 m3, the change in temperature was the main parameter that was evaluated during 49 days of positive forced aeration. Subsequently, a part of the material of the ASP (62 m3) was subjected to a curing period for 44 days recording changes in temperature and humidity. The results of carbon dioxide and volatile ammonia emissions analyses (NH3) and of a bioassay to screen for the presence of phytotoxic conditions showed a very mature compost with an emergence > 90% and a seedling vigor > 95%.

深厚火山灰堆积区大直径灌注桩水平静载试验研究

富含火山灰土层具有特殊的物理力学性质和工程特性,其水平抗力系数的比例系数m的取值不清,途径该地区的高速铁路桩基水平承载特性不明。为此开展了火山灰堆积地区高速铁路桥梁单桩的水平静载试验,分析了该地区桩基的水平承载变形特性,综合分析了不同行业规范对m值折减系数的具体要求,开展了富含火山灰土层m值的取值研究。研究结果表明:富含火山灰土层m值随水平荷载的增大呈非线性衰减,随水平位移的增大而近似呈幂函数形式衰减。获得了单桩水平临界荷载和极限水平承载力,并提出了考虑工作折减系数后的火山灰粉质黏土m的取值建议。研究成果可为我国富含火山灰土层m的合理取值和该地区高铁桥梁桩基水平承载力计算、安全评估提供重要参考。

预制管桩在黏土地质的应用可行性及承载性能研究

本文旨在探讨预制管桩在黏土地质条件下的应用可行性及其承载性能。根据预制管桩设计允许荷载的50%、100%、150%、200%设置了4种循环加载模式,通过锚桩横梁反力装置对试桩施加不同等级的竖向循环压载,观察并分析加载过程中试桩的沉降响应,最终估算出桩基的极限荷载。研究结果表明,在200吨超载条件下,预制管桩在黏土地质中表现出良好的承载性能;根据竖向荷载的加载时间与试桩的沉降量之间的关系,估算出了桩基的极限荷载为262吨。这一结果远高于设计允许荷载(100吨),进一步验证了预制管桩在黏土地质中的高承载能力和稳定性。

大直径超长灌注桩承载特性研究

为明确黄河中下游地区粉土、粉细砂地层中长大桩基承载特性及荷载传递机理,依托实际工程,结合室内土工试验、现场原位测试和数值模拟手段开展了系统性研究。采用自制的大型直剪仪开展了不同含水率条件下粉土-混凝土界面直剪试验,设计拉压锚法加载反力装置实现了桥梁钻孔灌注桩36000 kN大吨位加载,基于直剪试验和静载试验结果,运用ABAQUS试算拟合土体与界面参数,进一步研究了基桩水平承载能力。结果表明:粉土-混凝土界面剪切强度随粉土含水量的增大而减小,粉土含水量的增加会显著减弱土体与混凝土结构界面的剪切作用。粉土-混凝土界面剪切强度包络线基本符合摩尔库仑强度理论,土体含水量与界面的黏聚力和摩擦角呈负相关变化规律。在建立的桩土竖向静载试验模型与原位测试数据吻合性良好的前提下,开展桩基水平承载力数值模拟,发现所得结果与设计方案基本相当,满足规范要求,文中相关结论可为相关工程设计提供借鉴。

Soil Plug Effect Prediction and Pile Driveability Analysis for Large-Diameter Steel Piles in Ocean Engineering

Long steel piles with large diameters have been more widely used in the field of ocean engineering. Owing to the pile with a large diameter, soil plug development during pile driving has great influences on pile driveability and bearing capacity. The response of soil plug developed inside the open-ended pipe pile during the dynamic condition of pile-driving is different from the response under the static condition of loading during service. This paper addresses the former aspect. A numerical procedure for soil plug effect prediction and pile driveabihty analysis is proposed and described. By taking into consideration of the pile dimension effect on side and tip resistance, this approach introduces a dimensional coefficient to the conventional static eqnihbrium equations for the plug differential unit and proposes an improved static equity method for the plug effect prediction. At the same time, this approach introduces a simplified model by use of one-dimensional stress wave equation to simulate the interaction between soil plug and pile inner wall. The proposed approach has been applied in practical engineering analyses. Results show that the calculated plug effect and pile driveabihty based on the proposed approach agree well with the observed data.

Lateral response of pile foundations in liquefiable soils

Liquefaction has b e e n a m ain cause o f dam ag e to civil en g in eerin g stru ctu res in seism ically active areas.The effects o f dam ag e o f liquefaction o n d eep foundations are v ery d estructive. Seism ic beh av io r o f pilefoundations is w idely discussed by m any researchers for safer an d m ore econom ic design purposes. Thisp a p e r p resen ts a p se u d o -static m eth o d for analysis o f piles in liquefiable soil u n d e r seism ic loads. A freefieldsite resp o n se analysis using th ree-d im en sio n al （3D） num erical m odeling w as p erfo rm ed to d e te rmine kin em atic loads from lateral g ro u n d disp lacem en ts an d inertial loads from vib ratio n o f th e supe rstru ctu re . The effects o f various p aram eters, such as soil layering, k in em atic and inertial forces,b o u n d ary con d itio n o f pile h ead an d gro u n d slope, o n pile resp o n se w e re studied. By com paring th enum erical results w ith th e centrifuge te s t results, it can be concluded th a t th e use o f th e p-y curves w ithvarious d eg rad atio n factors in liquefiable sand gives reasonable results.

Bearing capacity and mechanical behavior of CFG pile composite foundation

CFG pile (i.e., pile constructed by granular materials of cement, fly-ash and gravel) composite foundation is applied in subsoil treatment widely and successfully. In order to have a further study of this kind of subsoil treatment technology, the influencing factors and calculation methods of the vertical bearing capacity of single CFG pile and the CFG pile composite foundation were discussed respectively. And based on the obtained solutions, effects by the cushion and measurements to reduce negative friction area were analyzed. Moreover, the developing law of settlement and bearing capacity eigenvalue controlled by the material strength with the increase of load were given for the CFG composite foundation. The in-situ static load test was tested for CFG pile. The results of test show that the maximum test load or half of the ultimate load is used from all the points of test, the average bearing capacity eigenvalue of single pile is 390 kN, and slightly greater than the design value of bearing capacity. The bearing capacity eigenvalues of composite foundation for 3 piles are greater than 300 kPa, and the mechanical properties of CFG pile composite foundation are almost identical in the case of the same load and cushion thickness. The pile-soil stress ratio and the load-sharing ratio can be adjusted through setting up cushion thickness.

Pit Bearing Capacity Effect on Status of Soil Plug During Pile Driving in Ocean Engineering

Foundation piles of the offshore oil platforms in the Bohai Bay are usually longer than 100 m with a diameter larger than 2 m. Driving such long and large-sized piles into the ground is a difficult task. It needs a comprehensive consider ation of the pile dimensions, soil properties and the hammer energy. Thoughtful drivability analysis has to be performed in the design stage. It has been shown that judging whether the soil column inside the pile is fully plugged, which makes the pile behave as close-ended, strongly influences the accuracy of drivability analysis. Engineering practice repeatedly indicates that the current methods widely used for soil plug judgment often give incorrect results, leading the designers to make a wrong decision. It has been found that this problem is caused by the ignorance of the bearing capacity provided by the soil surrounding the pile. Based on the Terzaghi＇s bearing capacity calculation method for deep foundation, a new approach for judging soil plug status is put forward, in which the surcharge effect has been considered and the dynamic effect coefficient is included. This approach has been applied to some practical engineering projects successfully, which may give more reasonable results than the currently used method does.

不同嵌岩深度下抗拔桩承载特性研究

以广东省江门市某工程为例,通过有限元分析软件ABAQUS,结合地勘报告及现场对桩基进行抗拔静载试验得出的荷载–位移曲线图,建立抗拔桩三维有限元模型进行数值模拟计算分析,研究不同嵌岩深度增量下抗拔桩的承载特性。研究成果表明:增加嵌岩深度可在一定程度上提高桩基抗拔承载力,但二者之间并非呈线性增长关系。当嵌岩深度增量为3D时,相较于原试桩的桩顶位移量减小54.2%,抗拔承载力提高105.2%,对桩基抗拔承载力的提高效果尤为显著。

Evaluation of ultimate bearing capacity of Y-shaped vibro-pile

Based on Mindlin stress solution, a numerical computational method was proposed to calculate the stresses in the ground induced by side friction and the resistance of Y-shaped vibro-pile. The improved Terzaghi's and ЪерезанцевВГ's methods for ultimate bearing capacity evaluation were proposed by considering the stress strength induced by friction resistance at pile head level of Y-pile. A new method to calculate the ultimate bearing capacity of Y-pile was also proposed based on the assumptions of soil failure mode at the tip of Y-pile and the use of Mohr-Coulomb soil yield criterion and Vesic compressive correction coefficient with the induced stresses in the ground. Based on the comparisons with the field static load test results, it is found that the improved Terzaghi's method gives higher ultimate capacity, while the other two methods shows good agreement with the field results.

Application of bi-directional static loading test to deep foundations

Bi-directional static loading test adopting load cells is widely used around the world at present, with increase in diameter and length of deep foundations. In this paper, a new simple conversion method to predict the equivalent pile head load-settlement curve considering elastic shortening of deep foundation was put forward according to the load transfer mechanism. The proposed conversion method was applied to root caisson foundation in a bridge and to large diameter pipe piles in a sea wind power plant. Some new load cells, test procedure, and construction technology were adopted based on the applications to different deep foundations, which could enlarge the application scopes of bi-directional loading test. A new type of bi-directional loading test for pipe pile was conducted, in which the load cell was installed and loaded after the pipe pile with special connector has been set up. Unlike the conventional bi-directional loading test, the load cell can be reused and shows an evident economic benefit.

Experimental study on DX pile performance in frozen soils under lateral loading

Experiments about working mechanism and mechanical characteristics of the DX model pile foundation under lateral dynamic and static loading were conducted by using a model system of the dynamic frozen soil-pile interaction. The horizontal displacement-force relationship of the pile head and bending moment distribution along the body in frozen soils of different temperatures were discussed. According to test results, both the horizontal disp!acement-force relationship of the DX pile head and bending moment distribution of the DX pile body are smaller than that of equal-diameter piles under same lateral loads. The piles with different plate positions show different displacements and bending moments. This phenomenon is mainly related to the soil temperature and bearing plates locations. Thus, dynamic response analysis of the pile foundation should be taken into account.

嵌岩单桩水平静力加载现场试验及 p-y 曲线研究

为研究风化花岗岩地质条件下嵌岩单桩的受荷响应和p-y曲线规律,本文基于现场试验,开展了水平静力荷载作用下嵌岩单桩的荷载-位移关系、弯矩、桩身变形及p-y曲线响应研究。试验表明:在所研究的相对深度范围内,随着z/D的增加,岩土阻力和相应位移都减小,上部荷载很难传递到深部岩层;桩身最大弯矩在3~4倍桩径之间,极限荷载主要取决于桩身强度而不是岩土体。将p-y曲线分别与一般双曲函数和双曲正切函数进行拟合,评估现有p-y曲线模型在风化花岗岩地基中的适用性,修正了模型在风化岩层中的参数取值。结果表明:一般双曲函数在较浅区域拟合良好,相对深度较大的区域数据离散性较强;双曲正切函数在各深度处拟合优度均较好。分析结果简化了现场p-y曲线的预测程序。

海上试桩不同桩型承载力特性研究

天津南港某高桩码头拟建场地有深厚密实砂层,通过试桩测定设计桩型对砂层的穿透及贯入能力,研究不同基桩承载力特性。试验结果表明:混凝土预制桩及钢管桩均有较好的穿透及贯入能力;基桩轴向极限承载力高应变检测结果小于静载试验,误差均在5%以内;混凝土预制桩桩端承载力占总承载力不小于44.6%,钢管桩桩端承载力占总承载力不小于21.9%;相同荷载作用下,混凝土预制方桩静载与动载沉降量之比为1.40,钢管桩为0.90,两者差异明显;基桩承载力达到极值时桩侧摩阻力要明显大于规范极限侧摩阻力,规范取值偏保守。

大直径嵌岩灌注桩竖向承载特性试验研究

为了探讨泥岩地基大直径灌注桩竖向承载性能,依托青岛某机场桩基工程,对嵌入泥岩的9根大直径灌注桩进行了竖向抗压静载试验和桩身应力监测,分析大直径嵌岩灌注桩的竖向抗压性能,明确大直径灌注桩的荷载传递规律。结果表明,试桩桩身完整性较好,桩身质量可靠;试桩荷载沉降(Q-s)曲线均为缓变型,加载初期存在明显的压密段,桩顶沉降量为10.31 mm,最低回弹率大于50%;最大荷载作用下,各试桩的竖向抗压极限承载力特征值均不小于6480 kN,试桩竖向抗压承载能力仍有较大潜力;试桩均表现出端承摩擦桩的特性,轴力自桩顶到桩端逐渐衰减,桩侧摩阻力峰值发生在中风化泥岩段,桩端阻力占桩顶荷载的10.55%~34.48%。

岩溶区PST管桩复合地基的工程应用

经对某场地高层建筑地基素填土厚度大、下伏基岩岩溶发育、以多层串珠状溶洞为主的地层条件研究,提出一种PST管桩刚性复合地基。采用试验和监测等方法来指导复合地基处理设计与施工,根据场地试桩数据来验证设计的合理性。施工完成后,采用静载荷试验对复合地基进行质量验收检测,并连续进行沉降监测。结果表明:岩溶区PST管桩复合地基是一种处理高层建筑地基很可行的方法,处理后可以满足高层建筑物对地基强度、变形及稳定性的要求。

不均匀卵石持力层桩端后注浆效果试验研究

我国东南沿海尤其是温州地区广泛存在上覆深厚软土下覆不均匀卵石的地层。该区域的钻孔灌注桩常采用后注浆技术改善其承载性能。为了评价后注浆技术对这类地层中灌注桩承载力改善效果,开展了相应的模型试验,对比了不同注浆量对桩承载力的影响程度;并结合扫描电镜(scanning electron microscope,简称SEM)试验分析了浆液分布特点,探讨了浆液在卵石层中的扩散范围,研究了浆液扩散范围与桩承载力之间的关系。结果表明:浆液能够有效地填充桩端卵石层,注浆量的增加使得填充范围扩大,填充范围为3~4倍桩径时,桩的承载力改善最显著。在不均匀卵石持力层中存在一个最优注浆量,最优归一化注浆量约为2.8,若超过该最优注浆量归一化值,桩的承载力不再显著提高。单桩模型试验确定的最优注浆量与刘金砺公式[1]的预测结果接近。扫描电镜技术有助于评价桩的后注浆技术在上覆深厚软土下覆不均匀卵石的土层中的效果。

基于BOTDA的砂土地基预应力管桩抗拔静载试验研究

针对砂土地基抗拔桩受力性能与荷载传递机理研究不足问题,将布里渊光时域分析(BOTDA)光纤传感技术应用于长江下游地区厚层砂土地基预应力管桩原位抗拔静载试验研究,采用特殊设计的桩身刻槽钻孔、光纤粘贴保护、接桩过程连续植纤等技术工艺,实现了预应力管桩在拉拔过程中桩身受力变形状态的分布式测量与数据精确定位。研究结果表明:在上拔荷载作用下,试验桩桩身轴力沿桩身方向逐渐减小;桩侧摩阻力在下桩发挥效果较好,上桩侧摩阻力较小,全桩长侧摩阻力最大值在桩底;抗拔桩随上拔荷载的增加,轴力逐渐向下传递,向下传递的轴力主要由预制管桩侧摩阻力承担;分布式光纤应变传感技术能较好地监测预应力管桩桩身贯入施工因素对抗拔承载特性的影响。研究结果可在其他类型抗拔桩受力特性监测项目中推广应用。

基于锚杆静压桩加固的超深基坑邻近建筑沉降控制技术

以某多层砌体结构基础加固施工为背景,阐述了锚杆静压桩在超深基坑邻近建筑沉降控制中的应用,重点介绍了锚杆静压桩分批压桩以配合超深基坑土方分层开挖的施工方法。该法采用PLC自动持荷系统,可对锚杆静压桩的长期持荷动态调整桩端压力。监测数据表明:此方法可有效控制超深基坑土方开挖过程中的邻近建筑物沉降,降低施工风险,可为类似项目提供借鉴。

自平衡法和高应变检测在码头灌注桩中的应用

海南某高桩码头工程地质条件特殊,表面覆盖硬岩层,下部为黏土层,码头基础采用灌注桩结构,以硬黏土层为持力层。施工后分别采用自平衡法静载试验和高应变法检测桩基承载力,将检测结果与规范理论计算结果进行比较。结果表明,通过自平衡检测的荷载-位移关系曲线判断,桩端依旧处于弹性阶段,并根据在加载过程中桩身轴力沿桩身轴向的分布情况,可分别判断各桩侧摩阻力、端承载力的发挥值,从而判断桩阻力并没有全部发挥,桩基的实际极限承载力大于试验值。高应变检测法检测桩侧摩阻力结果大于理论计算结果,桩端承载力小于理论计算结果,总桩基承载力二者比较接近,因此可以作为静载试桩的辅助验证。在港口码头工程中采用自平衡静载测试法,并用高应变检测法进行验证,可以解决水域条件下大质量桩基承载力的检测问题。