基于捷径重试规则晶圆带式搬运系统性能优化

开口管桩由于其承载力高、质量可靠、施工方便等优点得到越来越广泛的应用.土塞的生成使得开口管桩沉桩阻力不同于闭口管桩, 不仅包括桩外侧摩阻力、桩端阻力, 桩内侧摩阻力亦是其重要组成部分.针对开口管桩沉桩受力特性, 采用自主研发的大尺度模型试验装置, 进行不同桩靴形式下开口管桩的贯入试验, 并与闭口管桩进行对比分析.研究表明, 开口管桩随沉桩深度的增加趋于闭塞, 沉桩阻力随沉桩过程基本呈线性增加, 桩内、外侧单位摩阻力均存在“侧阻退化”效应; 桩体贯入时桩周地表隆起量随径向距离增加逐渐减小, 隆起速率随沉桩深度增加逐渐变缓, 桩周土影响范围约为5 ~ 7倍桩径; 桩靴对开口管桩土塞生成、沉桩阻力和挤土效应均有重要影响, 内30°桩靴土塞生成高度、桩内侧摩阻力及其所占总沉桩阻力比例最大, 桩周土地表隆起量最小, 外30°桩靴与内30°桩靴情况相反, 直角桩靴居中; 闭口管桩沉桩阻力、外侧摩阻力与挤土程度均大于开口管桩.      

土塞效应对预应力高强混凝土管桩承载力的影响

为了分析土塞效应对预应力高强混凝土(PHC)管桩单桩竖向承载力的影响程度,利用FLAC3D软件对不同地质条件下的开口桩和闭口桩进行数值模拟,得出预应力高强混凝土管桩的荷载-沉降曲线(Q-S曲线),研究表明:对于端承桩,土塞效应导致单桩竖向承载力降低,而对于摩擦型桩,可不考虑土塞效应的影响,按闭口桩计算PHC管桩的单桩竖向承载力。     

预应力管桩施工中常见质量问题及防治措施

针对预应力管桩在各类建筑工程基础应用中出现的桩体挤土、沉桩困难、斜桩、桩身开裂、桩身上抬等问题进行合理分析,并提出相应的预防措施及解决方案。     

黏土中静压沉桩离心模型

采用西澳大学室内鼓轮式离心机,在预先固结的高岭黏土中开展不同离心力场(50g,125g及250g,g为重力加速度)条件下的模型压桩试验、T-bar试验和静力触探试验,分析了模型桩在贯入过程、静置稳定过程中桩身径向应力(σ_r)的变化规律,并对后期桩体拉伸载荷阶段的径向应力变化值(Δσ_r)及桩侧摩阻力变化情况行了探讨,揭示了在不同超固结比(OCRs)黏土中静压桩侧摩阻力的演变特性.在此基础上,通过两种经验公式方法对桩侧摩承载力进行了预测计算和对比分析.研究结果表明:沉桩过程中桩端相对高度(h/B)对桩身径向应力的发展变化有很大的影响,桩身不同位置(h/B)的总径向应力对同一贯入深度而言,存在桩侧径向应力退化现象;基于静力触探试验提出的经验方法,能有效考虑静力触探锥端阻力(q_t)和桩端相对高度(h/B)因素的影响,将其应用于黏土沉桩时桩侧摩阻力的预测,可取得与试验实测结果较吻合的结果.研究成果对软土地区静压桩施工与承载力设计具有一定的工程指导意义.      

某工程预应力管桩静载荷试验结果分析

通过对某工程预应力管桩单桩竖向抗压静载荷试验结果的分析研究,指出沉桩时的挤土效应、桩的卸压回弹、桩端持力层软化、桩周土体重新固结程度不足等因素,都有可能导致桩在试验时发生异常沉降现象,并总结了设计和施工中应注意的问题及应采取的预防措施.     

板坯连铸结晶器数值模拟

运用Fluent 6.3对板坯连铸结晶器进行数值计算,研究拉速、水口浸入深度及水口开口角度对流场的影响.结果表明:对于断面1400 mm×230 mm结晶器,随拉速增加,液面最大水平和垂直流速均增加,而窄边冲击点的位置基本不变,随距液面距离增加,窄边速度先增加后减小,直至趋向于零;当拉速超过1.2 m.min-1时,液面水平速度增加明显.随水口浸入深度增加,液面最大水平流速减小,浸入深度超过140 mm时,最大水平流速变化不明显;垂直于液面方向的最大速度逐渐增加;对窄边冲击点影响较小.随水口开口向下角度增加,液面最大水平流速减小后增加,水口开口向下12.5°时液面最大水平流速最小,而水口开口向下10°~12.5°时窄边冲击点速度最小.      

新型深基坑支护技术

本文简单介绍一种新型基坑支护结构新技术——锚管桩。它是利用管壁穿孔的钢管，在一定压力下向内注入掺有外加剂的水泥砂浆与纯水泥浆，迫使浆体从壁孔外渗至一定范围内的土体中，形成以钢管为核心（作为锚杆）外裹浆体的粗糙圆柱体，与土体间产生粘结摩阻力，从而使锚入土中的钢管拉住水平围楞（糟钢）与坚向排桩（槽钢），以平衡基坑边壁土产生的主动侧压力，即用注浆锚管拉住槽钢排桩的一种新型支护方法。其深度可达9m。     

饱和软土地基中PHC群桩贯入过程的能量耗散模型

软土地基中群桩稳定性分析是岩土工程的难点之一.通过对饱和软土地基中群桩贯入全过程的力学分析,结合群桩效应与工作性能,根据功能平衡原理,建立了贯入过程中附加应力(含超静孔隙水压力)引起的耗散能量与外力做功、弹性势能三者的平衡关系;同时,针对饱和软土地基中高预应力管桩(PHC)的排土特性,结合现行桩基规范,分别给出了超静孔隙水压力势能、挤土耗散能、重力做功、超静孔隙水压力做功、摩擦耗能、土体弹性势能等的定量表达,构建了PHC群桩贯入过程的能量耗散模型;在此基础上,导出了局部能量安全系数与整体能量安全系数.将上述模型应用于某工程PHC群桩基础的稳定性分析中,并与数值模拟结果对比,验证了该模型的合理可靠性,对饱和软基中PHC群桩稳定性状态的判别具有一定指导意义.     

基于微结构指标主成分分析的沉桩挤土效应研究

前期研究已认识到,土的宏观力学性质及其表现从本质上应取决于土的微观结构.在结构性较强的软土中沉桩,桩周土体内部结构会发生显著变化,土体的强度与变形性质是这种内在变化的宏观表现,研究土体微观结构与宏观力学行为变化之间的关系,对认知土体的力学性质,从微观出发去认识沉桩挤土效应的机理,指导工程实践具有重要地理论和现实意义.本文基于天津滨海地基土实际静压桩工程,在沉桩的不同时刻、沿桩身的不同位置取桩周土体原状土样进行室内三轴固结不排水剪切试验,得到土体强度指标参数,同时进行对应的微观结构试验,得到垂直与水平方向的10个微结构指标.采用主成分分析方法,在微结构指标中提取3个主成分,较好地分析了土体微结构特征.研究表明:3个主成分与黏聚力之间存在较好的相关关系,而与内摩擦角之间的相关性相对较弱;第一主成分对各微结构信息的提取比较充分,第二、第三主成分是对第一主成分未反映信息的进一步补充.同时主成分分析表明,土体微结构性质对强度性质起控制作用,在沉桩过程中,近地表和下部土层宏观力学指标表现出了相反的变化规律.主成分分析方法较好地表述了土体的微结构性质,为进一步从微观入手解释沉桩挤土效应机理提供了有力依据.     

黏粒含量对粉土地震液化影响及机理的探讨

针对鲜少研究黏粒含量对粉土地震液化的影响机制,首先抽象得出了粉土概化模型:砂粒、粉粒等刚性颗粒组成了粉土的骨架结构,黏土矿物为片状颗粒填充于骨架孔隙之间,通过微元受力分析得出:粉土中的粒状颗粒受到支撑力、接触摩阻力、胶结力及孔隙水压力等作用,土体的抗剪强度来源于接触摩阻力、胶结力。分析了粉土液化性能、动孔隙水压随黏粒含量变化趋势,结果表明:随黏粒含量增加,粉土的抗液化性能增强;动孔隙水压初期受黏粒含量影响较小,中期随黏粒含量增加,增速变大。黏粒增加对粉土抗液化效应(表现为黏聚力增大)大于其促进液化的效应(表现为动孔隙水压增大)。     

Behavior of Open- and Closed-Ended Piles Driven Into Sands

Both the driving response and static bearing capacity of open-ended piles are affected by the soil plug that forms inside the pile during pile driving. In order to investigate the effect of the soil plug on the static and dynamic response of an open-ended pile and the load capacity of pipe piles in general, field pile load tests were performed on instrumented open- and closed-ended piles driven into sand. For the open-ended pile, the soil plug length was continuously measured during pile driving, allowing calculation of the incremental filling ratio for the pile. The cumulative hammer blow count for the open-ended pile was 16% lower than for the closed-ended pile. The limit unit shaft resistance and the limit unit base resistance of the open-ended pile were 51 and 32% lower than the corresponding values for the closed-ended pile. It was also observed, for the open-ended pile, that the unit soil plug resistance was only about 28% of the unit annulus resistance, and that the average unit frictional resistance between the soil plug and the inner surface of the open-ended pile was 36% higher than its unit outside shaft resistance.     

Effect of Compressive Load on Uplift Capacity of Model Piles

Thirty six tests on model tubular steel piles embedded in sand were carried out in the laboratory to assess the effects of compressive load on uplift capacity of piles considering various parameters. The model piles were of 25 mm outside diameter and 2 mm wall thickness. The soil–pile friction angles were 21 and 29° in loose and dense conditions of sand. The piles were embedded in sand for embedment length/diameter ratios of 8,16, and 24 inside a model tank. They were subjected to a static compressive load of 0, 25, 50, 75, and 100% of their ultimate capacity in compression and subjected to pull out loading tests. The experimental results indicated that the presence of the compressive load on the pile decreases the net uplift capacity of a pile and the decrease depends on the magnitude of the compressive load. A logical approach, based on the experimental results, has been suggested to predict the net uplift capacity of a pile considering the presence of compressive load.     

Ultimate Lateral Resistance of Pile Groups in Sand

Experimental investigations on model pile groups of configuration 1 × 1, 2 × 1, 3 × 1, 2 × 2, and 3 × 2 for embedment length-to-diameter ratios L∕d = 12 and 38, spacing from 3 to 6 pile diameter, and pile friction angles δ = 20° and 31°, subjected to lateral loads, were conducted in dry Ennore sand obtained from Chennai, India. The load-displacement response, ultimate resistance, and group efficiency with spacing and number of piles in a group have been qualitatively and quantitatively investigated. Analytical methods have been proposed to predict the ultimate lateral capacity of single pile and pile groups. The proposed methods account for pile friction angle, embedment length-to-diameter ratio, the spacing of piles in a group, pile group configuration, and soil properties. These methods are capable of predicting the lateral capacity of piles and pile groups reasonably well as noted and substantiated by the comparison with the experimental results of the writers and other researchers.     

Experimental Testing of Pile-to-Cap Connections for Embedded Pipe Piles

For bridges supported by piles, acceptable system performance under seismic loading depends on effective pile-to-cap connections. A fixed pile-to-cap connection is often desirable to help control deflections during lateral loading when soft soils are present. While reinforcement bar cages that extend from the pile into the cap are effective in providing a fixed pile-to-cap connection, it is more economical to rely on pile embedment to provide fixity and moment resistance. This study investigated embedded pile-to-cap connections for concrete-filled pipe piles. Four full-scale specimens, each consisting of a cap with two piles, were investigated in the field under cyclic loading. The specimens had minimal reinforcement and varying amounts of pile embedment. Results show that the moment resistance of pile-to-cap connections can be significantly greater than what is typically calculated based on the flexural reinforcement and embedment bearing. Excess moment capacity may be explained by friction between the pile and the cap at the connection. This friction mechanism is described and discussed in the context of experimental results from other studies.     

Interface Characteristics and Laboratory Constructability Tests of Novel Fiber-Reinforced Polymer/Concrete Piles

Conventional pile materials such as steel, concrete, and timber are prone to deterioration for many reasons. Fiber-reinforced polymer (FRP) concrete composites represent an alternative construction material for deep foundations that can eliminate many of the performance disadvantages of traditional piling materials. However, FRP composites present several difficulties related to constructability, and the lack of design tools for their implementation as a foundation element. This paper describes the results of an experimental study on frictional FRP/dense sand interface characteristics and the constructability of FRP–concrete composite piles. An innovative toe driving technique is developed to install the empty FRP shells in the soil and self-consolidating concrete is subsequently cast in them. The experimental program involves interface shear tests on small FRP samples and uplift load tests on large-scale model piles. Two different FRP pile materials with different roughness and a reference steel pile are examined. Static uplift load tests are conducted on different piles installed in soil samples subjected to different confining pressures in the pressure chamber. The results showed that the interface friction for FRP materials compared favorably with conventional steel material. It was shown that toe driving is suitable for installation of FRP piles in dense soils.     

Lateral Resistance of Full-Scale Pile Cap with Gravel Backfill

A static lateral load test was performed on a full-scale 3×3 pile group driven in saturated low-plasticity silts and clays. The steel pipe piles were attached to a concrete pile cap which created a “fixed-head” end constraint. A gravel backfill was compacted in place on the backside of the cap. Lateral resistance was therefore provided by pile–soil–pile interaction, as well as base friction and passive pressure on the cap. In this case, passive resistance contributed about 40% of the total resistance. The log–spiral method provided the best agreement with measured resistance. Estimates of passive pressure computed using the Rankine method significantly underestimated the resistance while the Coulomb method overestimated resistance. The cap movement required to fully mobilize passive resistance in the gravel backfill was about 6% of the cap height. This is somewhat larger than reported in other studies likely due to the underlying clay layer. The p-multipliers developed for the free-head pile group provided reasonable estimates of the pile–soil–pile resistance for the fixed-head pile group once gaps adjacent to the pile were considered.     

Evaluation of a Minimum Base Resistance for Driven Pipe Piles in Siliceous Sand

This paper provides a rational method for evaluating a realistic lower bound for the base resistance of pipe piles in siliceous sand. Separate expressions are developed to represent the response to load of the pile plug, the sand below the pile base, and the sand below the pile annulus. These expressions are combined to give the overall base response of a pipe pile. Predicted responses are compared with databases compiled on the ultimate capacities of pipe piles and with base pressure-displacement characteristics observed in static load tests. The estimations are shown to match observed base resistances of large diameter piles for which the coring mode of penetration during driving dominates.     

Analysis of Load Tests on Piles Driven through Calcareous Desert Sands

The ultimate bearing capacity of short, precast concrete piles driven into calcareous sands was examined by pile-load tests carried out at two sites in Kuwait. The piles had a 0.3 m × 0.3 m square cross section and extended to a maximum depth of 12 m. They were driven through a loose-to-compact calcareous surface sand layer underlain by a competent dense-to-very-dense siliceous cemented sand deposit. The pile tips and part of the pile shafts were embedded in the lower layer. The base resistance and shaft friction were calculated using the Meyerhof method for a layered soil profile. The method employs the standard penetration test N values. The results indicate that a great portion of the pile capacity is due to base resistance. The skin friction mobilized is small and consists of two components corresponding to the two layers penetrated along the pile shafts. The calculated pile capacities were very close to the measured values. The unit skin friction is not constant along the pile shafts.     

Cyclic Lateral Load Behavior of a Pile Cap and Backfill

A series of static cyclic lateral load tests were performed on a full-scale 4×3 pile group driven into a cohesive soil profile. Twelve 324-mm steel pipe piles were attached to a concrete pile cap 5.18×3.05?m in plan and 1.12?m in height. Pile–soil–pile interaction and passive earth pressure provided lateral resistance. Seven lateral load tests were conducted in total; four tests with backfill compacted in front of the pile cap; two tests without backfill; and one test with a narrow trench between the pile cap and backfill soil. The formation of gaps around the piles at larger deflections reduced the pile–soil–pile interaction resulting in a degraded linear load versus deflection response that was very similar for the two tests without backfill and the trenched test. A typical nonlinear backbone curve was observed for the backfill tests. However, for deflections greater than 5 mm, the load-deflection behavior significantly changed from a concave down shape for the first cycle to a concave up shape for the second and subsequent cycles. The concave up shape continued to degrade with additional cycles past the second and typically became relatively constant after five to seven cycles. A gap formed between the backfill soil and the pile cap, which contributed to the load-deflection degradation. Crack patterns and sliding surfaces were consistent with that predicted by the log spiral theory. The results from this study indicate that passive resistance contributes considerably to the lateral resistance. However, with cyclic loading the passive force degrades significantly for deflections greater than 0.5% of the pile cap height.     

Assessment of the Axial Load Response of an H Pile Driven in Multilayered Soil

Most of the current design methods for driven piles were developed for closed-ended pipe piles driven in either pure clay or clean sand. These methods are sometimes used for H piles as well, even though the axial load response of H piles is different from that of pipe piles. Furthermore, in reality, soil profiles often consist of multiple layers of soils that may contain sand, clay, silt or a mixture of these three particle sizes. Therefore, accurate prediction of the ultimate bearing capacity of H piles driven in a mixed soil is very challenging. In addition, although results of well documented load tests on pipe piles are available, the literature contains limited information on the design of H piles. Most of the current design methods for driven piles do not provide specific recommendations for H piles. In order to evaluate the static load response of an H pile, fully instrumented axial load tests were performed on an H pile (HP?310×110) driven into a multilayered soil profile consisting of soils composed of various amounts of clay, silt and sand. The base of the H pile was embedded in a very dense nonplastic silt layer overlying a clay layer. This paper presents the results of the laboratory tests performed to characterize the soil profile and of the pile load tests. It also compares the measured pile resistances with those predicted with soil property- and in situ test-based methods.