水泥搅拌桩施工的质量控制要点

水泥搅拌桩作为常用的软土地基处理方法,近年来在深圳地区得到广泛应用,并取得良好效果,但同时也出现了许多质量问题。本文基于多年工程管理经验,论述了水泥搅拌桩施工中常出现的质量问题,并提出从施工准备到工后检测全过程的质量控制方法及控制要点,为施工管理人员加强水泥搅拌桩质量控制提供宝贵经验。     

Distribution of void fraction in bubbly flow through a horizontal channel: Bubbly boundary layer flow, 2nd report

A method of enveloping the hull with a sheet of microbubbles is discussed. It forms part of a study on means of reducing the skin friction acting on a ship's hull. In this report, a bubble traveling through a horizontal channel is regarded as a diffusive particle. Based on this assumption, an equation based on flow flux balance is derived for determining the void fraction in approximation. The equation thus derived is used for calculation, and the calculation results are compared with reported experimental data. The equation is further manipulated to make it compatible with a mixing length model that takes into account the presence of bubbles in the liquid stream. Among the factors contained in the equation thus derived, those affected by the presence of bubbles are the change of mixing length and the difference in the ratio of skin friction between cases with and without bubbles. These factors can be calculated using the mean void fraction in the boundary layer determined by the rate of air supply into the flow field. It is suggested that the ratio between boundary layer thickness and bubble diameter could constitute a significant parameter to replace the scale effect in estimating values applicable to actual ships from corresponding data obtained in model experiments.List of symbols a ₁ proportionality constant indicating directionality of turbulence - B law-of-the-wall constant - C _f local skin-friction coefficient in the presence of bubbles - C _f0 local skin-friction coefficient in the absence of bubbles - d _b bubble diameter (m) - g acceleration of gravity (m/s²) - j _g flow flux of gas phase accountable to buoyancy (m/s) - j _t flow flux of gas phase accountable to turbulence (m/s) - k ₄ constant relating reduction of liquid shear stress by bubble presence to decrease of force imparted to bubble by its displacement due to turbulence - l _b mixing length of gas phase (m) - l _m mixing length of liquid phase (m) - l _mb diminution of liquid phase mixing length by bubble presence (m) - Q _G rate of air supply to liquid stream (l/min) - q _/g velocity of bubble rise (m/s) - 2R height of horizontal channel (m) - T _* integral time scale (s) - U _m mean stream velocity in channel (m/s) - U friction velocity in channel (m/s) - V volume of a bubble (m³) - u, ¯ v time-averaged stream velocities inx- andy-directions, respectively (m/s) - u, v turbulent velocity components inx- andy-directions, respectively (m/s) - v root mean square of turbulence component in they-direction (m/s) - root mean square of bubble displacement iny-direction with reference to turbulent liquid phase velocity (m) - y displacement from ceiling (m) - local void fraction - _m mean void fraction in boundary layer - _m constant relating local void fraction to law-of-the-wall constant - _t reduction of turbulent stress (N/m²) - law-of-the-wall constant in turbulent liquid region in absence of bubbles - ₁ law-of-the-wall constant in turbulent liquid region in presence of bubbles - ₂ law-of-the-wall constant in gas phase - _m constant indicating representative turbulence scale (m) - viscosity (Pa × s) - v kinematic viscosity (m²/s) - density (kg/m³) Suffixes G gas - L liquid - 0 absence of bubbles     

平板喷气粘性流场数值计算方法研究

针对平板底部直接喷气形成气液混合流的复杂情况,采用Mixture模型与RANS方程相结合的方法建立了气液混合流粘性流场数值计算模型.通过对4种湍流模型、4种网格、3种壁面处理方法进行组合,形成了8种不同的数值计算方法,分析了壁面函数、壁面第1层网格、湍流模型等对数值计算结果的影响,并与试验结果进行对比,获得了可有效模拟气液混合流的数值模型.研究结果表明:采用RNG k-ε湍流模型、标准壁面函数、第1层网格1mm、y+为31～35的计算方案,所得结果可用于平底船底部气液混合流分析.     

海相软土地区铁路深长双向搅拌桩复合地基加固效果分析

针对18 m以上深长双向搅拌桩复合地基加固海相软土地区铁路路基的长期加固效果问题,依托新建青连铁路连盐试验段进行了现场试验研究。通过施工期的工艺优化和成桩质量控制,填筑期的荷载传递规律分析,以及贯穿施工期到运营期的长期沉降观测,验证了深长双向搅拌桩复合地基加固的长期可靠性。结果表明:干法和湿法双向搅拌桩加固苏北地区含水量在37%~55%之间的海相深厚软土地层具有可行性,试验桩长20 m范围内成桩质量良好;从施工期到运营期的路基沉降控制效果良好,满足规范对沉降的要求。试验研究成果拓展了双向搅拌桩的适用范围,在加固深度方面突破了现行规范规定的干法桩不宜大于15 m、湿法桩不宜大于18 m的限制,并且具有较好的经济效益和社会效益。     

基于规划求解的矿质混合料级配调试方法及其应用

介绍了运用Excel的线性规划功能快速进行矿质混合料级配调试的方法和过程以及此方法在生产配合比设计阶段的应用。指出此方法可以直接计算出适合于目标级配的矿质混合料的最优配合比,在施工级配控制中有很强的实用性。     

深层水泥搅拌桩处理软基施工摔制与质量检测

深层水泥搅拌桩进行软基处理已得到广泛应用。结合工程实例，介绍了深层水泥搅拌桩施工中施工准备、试桩、施工工艺流程、施工注意事项、安全技术措施等内容，以及常用质量检测方法。     

碎石过渡层沥青路面在广西玉林的应用综述

玉林地区自20世纪80年代开始在半刚性基层上铺设碎石过渡层,多年的施工实践表明,碎石过渡层沥青路面在保证路面质量的同时,可提高路面的使用耐久性和稳定性、减少半刚性基层裂缝向面层的反射、避免水对承重基层的冲刷,因此推荐该结构作为今后路网改造工程中优先考虑的路面结构.     

热拌沥青混合料拌和质量的控制与检测

热拌沥青混合料的质量直接影响到所铺筑路面的质量，因此必须加强对热拌沥青混合料质量的控制与检测。     

农村公路级配砂砾基层厂拌法施工介绍

路面级配砂砾基层路拌法施工与级配料厂拌法施工相比,厂拌法砂砾级配料拌和均匀,可减少级配料离析现象,节约施工机械和人员的投入,保证路面的平整度,节省面层沥青混合料的数量,缩短施工工期,进一步提高农村公路的施工质量.     

废弃尾矿料在路面(底)基层中的应用

分析了废弃尾矿料的化学和物理性质及环境影响情况，结果表明其用作（底）基层材料和路基填料是安全可行的。利用正交试验方法，提出石灰粉煤灰（简称“二灰”）、掺加外剂和水泥的二灰（综合）稳定废弃尾矿料优选配合比，分析混合料强度增长机理和影响因素，并确定优选配合比混合料的路用技术参数。优选配合比将在连云港市旧路改造中作为1km长的试验路基层材料，以便进行现场试验验证和应用机理分析，为其推广应用于路面（底）基层提供技术上可行、经济上合理的优选配合比，并提供工程施工可操作性和质量保证体系。