地下室外墙后浇带封闭施工法

地下室外墙后浇带施工的传统方法以砖砌挡土墙作为回填土与后浇带的隔离,待到符合设计要求时间后,安装模板浇注混凝土,拆模后进行防水层施工,拆除挡土墙后再回填此处土方。这样施工,后工序是前工序的必要条件,施工周期长。为保证地下室结构施工后及时进行外墙防水,更早进行回填土施工,保证基坑安全稳定,地下室外墙后浇带拟采用预制细石混凝土板作为其外侧的模板,提前封闭外墙后浇带。采用此种方法施工,既工序安排合理,节约工期,又使外墙防水和回填土施工保持连续性,并能保护后浇带钢筋不被破坏。     

地下室外墙后浇带提前封闭施工

在地下室外墙施工操作中,传统的施工方法是采用砌砖挡土墙的方式作为后浇带的隔离,在各项设计符合实际要求后,安装模板浇筑混凝土。拆模后进行防水层施工,拆除挡土墙后再回填。实际上按照这样的施工程序,前工序是后工序施工的前提要件,施工周期相对较长。在地下室结构施工操作完成后,为保证地下室结构施工后及时进行外墙防水,更早进行回填土施工,保证基坑安全稳定,地下室外墙后浇带拟采用预制细石混凝土板作为其外侧的模板,提前封闭外墙后浇带。对地下室外墙后浇带提前封闭施工进行简单分析。     

地下室外墙后浇带提前封闭施工

目前在地下室建设中,一般在进行地下室外墙后浇带施工的过程中,采用砖砌挡土墙的方式,隔离回填土以及后浇带,在一定时间过后进行浇筑,最后将挡土墙拆除,将拆除后的材料回填处理。在完成基础准备条件之后,可以对地下室外墙后浇带提前进行封闭施工,加快地下室的施工进程,为工程建设提供便利条件。文章结合工程案例,介绍了后浇带超前处理的目的,讨论了地下室外墙后浇带超前封闭施工措施、质量控制、效益分析等,以期为提高地下室的施工质量提供有益的参考。     

基土下沉致某实验楼梁、板下挠的检测与鉴定

新浇混凝土梁、板构件,若遇雨水天气,雨水未及时排除而流向边跨、变形缝、后浇带附近的支架处,支架持力层为回填土层,回填土层会下沉而引起部分梁、板下挠,下挠严重还伴随梁、板有裂缝产生。下挠并有裂缝出现的梁、板构件安全性可参照《民用建筑可靠性鉴定标准》(GB50292)进行检测与鉴定。     

地下室顶板沉降后浇带提前封闭施工技术

目前地下室外墙后浇带普遍采用防水回填前砌筑或用混凝土板封闭的方式.根据施工现场实际情况,借鉴地下室外墙后浇带提前封闭施工的成功经验,北京雪莲大厦二期工程采取加强后浇带两侧支撑、混凝土盖板覆盖、防水回填土、支模、压力灌注自密实混凝土等措施,达到方便现场平面布置、形成安全消防通道等目的.重点介绍了后浇带封闭、防水施工、顶升配件制作拆除、混凝土浇注等施工工艺.     

开敞式车库楼后浇带贯通裂缝分析及处理方案

从设计、施工、沉降观测报告及实体检测报告不同的角度,对开敞式车库楼后浇带位置出现的贯通裂缝进行分析,未能合理设置伸缩缝、后浇带以及在施工过程中主体施工时间短、后浇带混凝土浇筑时间过早、施工不规范、混凝土后期徐变是裂缝产生的主要因素。根据车库楼不同部位出现的不同宽度的裂缝,相应地采取表面封闭法、压力注胶法和填充密实法对贯通裂缝进行修补加固。     

浅析地下室顶板后浇带中防水施工技术

目前地下室外墙后浇带普遍采用防水回填前砌筑或用混凝土板封闭的方式。根据施工现场实际情况,借鉴地下室外墙后浇带提前封闭施工的成功经验,采取加强后浇带两侧支撑、混凝土盖板覆盖、防水回填土、支模、压力灌注自密实混凝土等措施,达到方便现场平面布置、形成安全消防通道等目的。本文重点介绍了后浇带封闭、防水施工、顶升配件制作拆除、混凝土浇注等施工工艺。     

地下室顶板后浇带超前封闭施工技术分析

地下室顶板后浇带超前封闭施工技术利用定制钢板、膨胀螺栓固定的形式封闭地下室顶板后浇带,采用竖向立管作为预留浇筑口,从而实现地下室顶板提前回填土作业,使得室外管网、道路、景观绿化等室外工序实现提前穿插。待后浇带达到浇筑条件后,通过竖向立管进行灌注自密实混凝土,利用自密实混凝土流动性强、无需外力振捣、能够在自重作用下流动并充满空间的特点,实现后浇带的最终浇筑。     

某工程竖向墙体后浇带挂板侧模施工技术

对于大面积整体地下结构工程(如地下车库),通常后浇带要在结构施工完成1个月以后才允许浇筑混凝土.但为了保护地下室外墙的防水效果,外墙防水卷材应连续1次完成.传统的后浇带外侧独立挡水板做法有铺设钢板和砌筑挡土墙的方法,但这2种方法都存在材料消耗及费用较大,工人操作不方便等缺点.结合具体现场工程实例,以实际住宅楼地下车库工程竖向墙体后浇带挂板侧模施工为基础,对地下回填土竖向墙体后浇带挂板侧模的施工技术及施工过程进行了全面系统的阐述.     

浅谈地下车库钢筋混凝土后浇带逆作法施工工艺

本文主要着眼解决土方回填和地下车库钢筋混凝土后浇带之间的施工矛盾,研究地下车库钢筋混凝土后浇带逆作法施工工艺,在不影响建筑结构主体施工的前提下,采用特殊的逆作业方法,及时将地下车库的防水连成整体并具有一定的刚度和强度,使土方回填和地下车库钢筋混凝土后浇带之间的施工矛盾得到彻底解决。     

Seismic analysis of geosynthetic-reinforced retaining wall in cohesive soils

Although a cohesionless backfill is recommended for geosynthetic reinforced earth retaining walls, cohesive soil have been widely used in many regions across the globe for economic reasons. This type of backfill exposes the soil to the crack formation that leads to reduce the stability of the system. In this paper, to investigate the internal seismic stability of reinforced earth retaining walls with cracks, the discretization method combined with the upper bound theorem of limit analysis are used. The potential failure mechanism is generated using the point-to-point method. Two types of cracks are considered, a pre-existing crack and a crack formation as a part of the failure mechanism. The use of the discretization method allows the consideration of the vertical spatial variability of the soil properties. A pseudo-dynamic approach is implemented which allows the account of the dynamic characteristics of the ground shaking. The presented method is validated using the conventional limit analysis results of an existing study conducted under static conditions. Once the proposed technique to consider the cracks is validated, a parametric study is conducted to highlight the key parameters effects on the lower bound of the required reinforcement strength.     

谈石砌重力挡土墙质量事故的原因及预防措施

介绍了地区丘陵地带及山区的城镇往往形成了若干个建筑平台，随之也出现了高、低不等的挡土墙，为了便于就地取材，减少工程造价，绝大部分采用石砌重力式挡土墙，通过对石砌挡土墙建成后出现的裂缝，变形，位移甚至倒塌事故的分析，提出了造成质量事故的原因及预防措施。     

Case history on failure of geosynthetics-reinforced soil bridge approach retaining walls

Six geosynthetic-reinforced soil (GRS) retaining walls supporting bridge approach roads of an overpass bridge in China exhibited a series of structural problems after 18 years of service. Field investigations demonstrated that the major structural problems consist of excessive lateral facing displacement, settlement and damage of facing panels, and pavement cracks above the GRS retaining walls. The structural problems were mainly caused by inadequate backfill compaction behind the facing, rain water infiltration, the settlement of foundation soil, and reinforcement ageing. Among the six GRS walls, a 22-m-long section collapsed after mild rain in July 2016, and the failure surface in the collapsed zone was mainly located 0.5–0.9 m away from the back of facing panels along the wall height. The field investigation found that external water filtration into the backfill behind the facing panels, and the breakage of connection between reinforcement and facing panels were the main causes of the failure. The connection breakage resulted from the ageing of PP reinforcement strips, and the critical issue of PP reinforcement ageing in complex backfill environment was pinpointed. Remedial measures of the failed section and reinforcing techniques of the remaining GRS walls were briefly presented in the end.     

地下车库上浮事故原因分析与破坏鉴定

对某在建地下车库上浮事故导致的结构破坏情况进行了现场检测,运用PKPM模型验算对地库结构上浮的机理进行了分析,建议采用环氧树脂对裂缝进行封闭;对开裂顶板、底板采用高压灌浆进行堵漏;并采用柔性材料对开裂处进行防水等处理措施。     

复杂条件下挡土墙主动土压力解析解

基于库仑理论的平面滑裂面假设,综合考虑填土具有黏聚力和内摩擦角、挡土墙墙背和填土面均倾斜、填土与墙背间具有摩擦和黏着力、填土浅表具有张拉裂缝和表面有连续均布超载的复杂情况,采用薄层单元法,导出了作用于挡土墙上的主动土压力的解析解,可适用于黏性和无黏性填土的复杂条件;且证明现行经典朗肯理论和库仑理论主动土压力是解析解相应简化假设下的特例。多个工程实例计算均表明,公式计算结果与实测主动土压力非线性分布曲线吻合良好,因而解析解对实际工程中主动土压力的计算精度是可靠的,具有推广应用价值。     

Seismic analysis of semi-gravity RC cantilever retaining wall with TDA backfill

The seismic behavior of Tire Derived Aggregate (TDA) used as backfill material of 6.10 m high retaining walls was investigated based on nonlinear time-history Finite Element Analysis (FEA). The retaining walls were semi-gravity reinforced concrete cantilever type. In the backfill, a 2.74 m thick conventional soil layer was placed over a 3.06 m thick TDA layer. For comparison purpose, a conventional all soil-backfill model was also developed, and the analysis results from the two models under the Northridge and Takatori earthquakes were compared. The FEA results showed that both models did not experience major damage in the backfill under the Northridge earthquake. However, under the Takatori earthquake, the TDA-backfill model developed substantially large displacement in the retaining walls and in the backfill compared with the soil-backfill model. Regions of large plastic strain were mainly formed in the TDA layer, and the soil over the TDA layer did not experience such large plastic strain, suggesting less damage than the soil-backfill model. In addition, the acceleration on the backfill surface of the TDA-backfill model decreased substantially compared with the soil-backfill model. If an acceleration sensitive structure is placed on the surface of the backfill, the TDA backfill may induce less damage to it.     

Reexamination of Mononobe-Okabe Theory of Gravity Retaining Walls Using Centrifuge Model Tests

Gravity retaining walls are widely used in Japan because of their simplicity of structure and ease of construction. In design procedure, the seismic coefficient method is widely employed, in which the earth pressure and inertia force are calculated by converting the seismic force into a static load. Earth pressure is usually calculated by the Mononobe-Okabe formula, which applies Coulomb's earth pressure computed from the equilibrium of forces in the static state. However, the Hyogoken-Nambu Earthquake of 1995 prompted the need to reexamine seismic design methods for various civil engineering structures. Gravity retaining wall is one of such structures whose seismic design has to be reexamined and rationalized. At this moment there is no clear empirical basis for converting the seismic force into a static load. The design method has to take into account the behavior of gravity retaining walls during earthquakes. At the Public Works Research Institute, model tests were conducted on gravity retaining walls using a centrifuge. The acceleration and displacement of a retaining wall and its backfill as well as the earth pressure acting on the wall were measured simultaneously together with the deformation behavior of the wall and its backfill, using a high-precision high-speed camera. The data show that the hypothetical conditions of the Mononobe-Okabe formula do not appropriately express the real behavior of backfill and gravity retaining walls during earthquakes.     

Short- and long-term behavior of EPS geofoam in reduction of lateral earth pressure on rigid retaining wall subjected to surcharge loading

Retaining walls are subjected to dead loads from backfill and adjacent structures, live loads and other loads from the vicinity of the structure. Retaining walls need to withstand earth pressure generated from above mentioned loads satisfactorily throughout their service life. Lateral earth thrust on retaining walls can be minimized by placing a compressible inclusion, such as, EPS geofoam, between the backfill and retaining wall. The present study is aimed at understanding both short- and long-term influence of EPS geofoam on surcharge induced lateral earth pressures on retaining walls through 1-g model studies. Four densities of geofoam in the range of 10–25 kg/m³ and three thicknesses of geofoam in the range of 25–75 mm were used in the present study. Lateral earth pressure at several locations along the height of the wall were monitored using earth pressure cells. Geofoam compression and backfill settlements under the surcharge load were also quantified using image analysis. From the series of model tests, it was observed that with the use of geofoam, lateral earth pressure on retaining wall was reduced under both short- and long-term loading conditions. However, higher reduction was observed under long-term loading.     

Examination of earth pressure reduction mechanism using tire-chip inclusion in sandy backfill via numerical simulation

Tire chips have special features as geomaterials, as they are lighter than soil particles, highly compressible, and softer than sand. In this study, the effect of tire chips used as a compressible inclusion in backfill on the load reduction against retaining walls is numerically investigated. It is known that a reduction in earth pressure in backfill is realized by achieving a quasi-active or intermediate active state; and thus, a field test of this behavior is herein numerically simulated. The influence of the Poisson’s ratio and elastic modulus of tire chips on the reduction in earth pressure against retaining walls is examined by assuming that tire chips can be modeled as an elastic body. The numerical simulation reveals that the attainment of the active state in sandy backfill is primarily due to the light-weight nature of tire chips, along with their low Young’s modulus and Poisson’s ratio. Furthermore, the influence of friction at the bottom of the backfill mass is also considered, and the earth pressure reduction mechanism incorporating this factor is also numerically investigated.     

Solution to active earth pressure of narrow cohesionless backfill against rigid retaining walls under translation mode

In urban construction, retaining walls are usually constructed adjacent to existing structures, and the width of the backfill is limited. In such cases, classical earth pressure theories, such as those by Coulomb or Rankine, are unsuitable. The active earth pressure acting on the retaining wall of a narrow backfill under the translation mode was explored in this study using a finite element limit analysis. The results show that due to the boundary conditions, reflective shear bands occur in the backfill when it is failing. The number of reflective shear bands is determined. Moreover, a theoretical method is proposed using the limit equilibrium method to estimate the active earth pressure acting on the retaining wall of the narrow backfill. The influence of the parameters on the failure mechanisms and the active earth pressure is also discussed.