Experimental evaluation of the effect of compaction near facing on the behavior of GRS walls

Experimental studies have been carried out to evaluate the effect of the compaction condition at the back of block facing on the behavior of geosynthetic reinforced soil (GRS) walls. Three GRS walls with 1.2?m high were constructed at the COPPE/UFRJ Geotechnical Laboratory. The walls were well-instrumented in order to monitor the values of the reinforcement load, toe horizontal load, horizontal facing displacement, horizontal stress at the back of the block facing, and vertical displacement on the top of the walls. The behavior of the walls has been investigated at the end of construction and during the surcharge application (post-construction). At the end of the loading, the toes of the walls were gradually released to also verify the influence of the different toe restraints. The results clearly show the effect and call attention to the importance of the compaction conditions near the facing on the behavior of GRS walls.     

Effects of facing,reinforcement stiffness,toe resistance,and height on reinforced walls

This study numerically investigated the combined effect of reinforcement and facing stiffness, wall height, and toe resistance on the behavior of reinforced soil (RS) walls under working stress conditions. For RS walls with vertical segmental block facing, parametric analyses showed that the combined effect of the facing stiffness, wall height, and toe resistance on the distribution of the maximum reinforcement load with depth may be limited to approximately 4 m above the base of the wall. Furthermore, the shape of the distribution of the reinforcement load may be a function of the combined effect of the wall height, reinforcement stiffness, toe resistance, and facing stiffness. For a given facing stiffness and fixed-base conditions, increasing the height of the wall and reinforcement stiffness may change the distribution shape of the reinforcement load from trapezoidal to the triangular. Additionally, the maximum reinforcement loads calculated using finite element analyses were compared to the values predicted by design methods found in the literature. Some limitations of those design procedures are presented and discussed.     

Numerical evaluation of the effect of foundation on the behaviour of reinforced soil walls

This study numerically investigates the influence of foundation conditions, in combination with other factors such as wall height and reinforcement and facing stiffness, on the behaviour of reinforced soil walls (RSWs) under working stress conditions. The foundation was simulated using different stiffnesses and geometries (with and without slope). The results highlight the importance of the combined effect of foundation conditions and the abovementioned factors on the performance of RSWs. The results of these analyses indicate that the shape of the distribution of the maximum reinforcement loads (T_max) with respect to wall height depends on the combined effect of the foundation condition, facing and reinforcement stiffness, and wall height, and varies from trapezoidal to triangular. Additionally, the results indicate that the effect of variations in foundation stiffness on reinforcement tension mobilisation decreases with wall height. Furthermore, the T_max prediction accuracy of three design methods were evaluated and some limitations of each method are presented and discussed.     

Load-bearing performance of model GRS bridge abutments with different facing and reinforcement spacing configurations

The paper reports the construction and surcharge load-testing of three (3) large-scale (~2.50 m-tall) GRS bridge abutment models in an outdoor test station to investigate the influences that the facing type and reinforcement spacing could have on their load-bearing performance. The facing types examined included cored Concrete Masonry Units (CMU) in Model #1 and much larger solid concrete blocks in Models #2 and #3. Reinforcement spacing in the first two models was 0.20 m, whereas it was increased to 0.30 m in the third model. Results show that using large facing blocks in GRS abutments could lead to significant improvements in their load-deformation performance relative to those with the CMU facing alternative. This improvement was observed even in the case of model with increased reinforcement spacing. Therefore, use of larger facing blocks could also help reduce the cost of GRS abutments by reducing the need for tighter reinforcement.     

Numerical- simulation of compaction-induced stress for the analysis of RS walls under surcharge loading

This study numerically investigates the behaviour of a geosynthetic-reinforced soil (GRS) wall under surcharge loading. Data from a full-scale GRS physical model wall was used to verify the numerical analysis. The modelling was carried out using the two-dimensional finite difference computer program FLAC to verify the post-construction performance of a full-scale GRS segmental wall under surcharge loading. The real value of compaction induced stress (CIS) specified for the vibrating plate compactor used in the physical model wall was employed in the analyses. Two procedures for modelling the CIS found in the literature were used in the analyses: uniform vertical stress applied to the surface of each layer (type I) and uniform vertical stress applied at the top and bottom of each layer (type II). The results clearly showed that the numerical analyses using compaction procedure type II accurately represent the measured values obtained from the full-scale wall under surcharge loading as well as during construction. The numerical analyses considering type I compaction modelling overestimated the measurements during both construction and surcharge application.     

Effect of vacuum removal on consolidation settlement under a combined vacuum and surcharge preloading

The combined vacuum and surcharge preloading technique is extensively used to accelerate the consolidation process of subsoils. The effect of vacuum pressure is often considered as a loading/unloading cycle of mean effective stress, such that elastic rebound occurs after vacuum removal, which cannot explain the observed postconstruction settlement in the field. In this study, the stress state of subsoils subject to vacuum and surcharge preloading is analyzed and decomposed into two components: (a) geostatic consolidation at a different depth, and (b) loading/unloading in the minor principal stress direction. A series of consolidated drained triaxial tests is conducted to simulate the soil behaviour after vacuum removal. Results show that the contribution of unloading in the minor principal stress direction outweighs the magnitude of elastic rebound after vacuum removal, and hence continued settlement dominates. A field case for highways is provided to further demonstrate the proposed mechanism.     

Analyzing the influence of facing batter on reinforcement loads of reinforced soil walls under working stress conditions

The level of reinforcement loads in a reinforced soil retaining wall is important to its satisfactory operation under working stress conditions since it basically determines the wall deformation. Consequently, proper estimation of the reinforcement load is a necessary step in the service limit-state design of this type of earth retaining structures. In this study, a force equilibrium approach is proposed to quantify the influence of facing batter on the reinforcement loads of reinforced soil walls under working stress conditions. The approach is then combined with a nonlinear elastic approach for GRS walls without batter to estimate the reinforcement loads neglecting toe restraint. The approximate average mobilized soil strength in the retaining wall is employed in the force equilibrium analysis. The predictions of reinforcement loads by the proposed method were compared to the experimental results from four large-scale tests. It is shown that the proposed semianalytical approach has the capacity to reproduce the reinforcement loads with acceptable accuracy. Some remaining issues are also pinpointed.     

真空联合堆载预压法的边界效应及其影响因素

介绍了真空联合堆载预压法的边界效应,并通过真空联合堆载预压法加固机理、应力路径及强度增长,阐述了产生边界效应的原因,讨论了造成加固区边界效应的影响因素,最后提出了对加固区边界效应的防治措施。     

Numerical evaluation of secondary reinforcement effect on geosynthetic-reinforced retaining walls

A finite difference method was employed to evaluate the effect of secondary reinforcement on the performance of Geosynthetic-Reinforced Retaining (GRR) walls. The two-dimensional numerical models used a Cap-Yield soil constitutive model to represent the behavior of backfill. The numerical model was first calibrated and verified by the measured results from a full-scale field test. A parametric study was then performed to investigate the effects of secondary reinforcement length, secondary reinforcement stiffness, secondary reinforcement connection, and secondary reinforcement layout. The numerical results show that an increase in secondary reinforcement length and stiffness can reduce the deflection of the GRR wall and the maximum tensile stress of primary reinforcement. The mechanical connection of secondary reinforcement can also reduce the wall facing deflection and result in relatively small maximum tensile stress and connection stress in the primary reinforcement as compared with no connection to the secondary reinforcement. In addition, a wall with fewer but longer secondary reinforcement layers at certain elevations had relatively smaller wall facing deflections than the baseline case. This comparison demonstrates that more optimal layout of secondary reinforcement exists that could further reduce the maximum wall facing deflections and create a better performing wall while the same or less amount of geosynthetic reinforcement material is used.     

Numerical simulation of compaction-induced stress for the analysis of RS walls under working conditions

This paper aimed to verify numerical modelling of compaction-induced stress (CIS) for the analysis of geosynthetic-reinforced soil (GRS) walls under working stress conditions. Data from a full-scale well-instrumented GRS wall was used for a numerical analysis. The results from the wall used in this study have already been used for validation in several other numerical modelling studies. Nevertheless, in none of these studies was the real value of CIS specified for the vibrating plate compactor used in the wall employed. In the present study, the real value of CIS is employed. The CIS is modelled using a new procedure presented in this paper in addition to two other procedures found in the literature. The results indicate that when the real value of CIS was simulated using a strip load applied to the top of each backfill layer, the numerical model accurately represented the measurements. The accuracy of the results, however, depends on the width of the strip load used to model the CIS. Nevertheless, as this type of compaction modelling procedure is time consuming, modelling of CIS by applying a distribution load at the top and bottom of each soil layer is suggested as an alternative procedure.     

真空联合堆载预压法在市政工程建设中的应用

分析了万环西路的工程地质概况,探讨了真空联合堆载预压法在万环西路工程建设中的应用,对该工程处理过程出现的各种情况及处理效果进行了详细论证,得出了具体的结论,积累了市政工程路基处理经验。     

某软基路段真空堆载联合预压监测研究

为促进滨海地区县域公路的建设,提高工程质量,调查连江通港大道工程概况,通过分析软基路段的地质勘察资料,研究采用真空堆载联合预压＋塑料排水板法对软基路段的加固过程,同时对地面沉降、孔隙水压力、深层土体水平位移进行监测。结合理论分析,将收集到的实测数据进行处理。结果表明,软基加固效果显著,能够达到设计要求,可为类似工程建设提供参考。     

真空堆载联合预压处理桥头软基桩体变形控制研究

采用真空堆载联合预压法处理已完成钻孔桩施工的桥头软基,对桥头桩体变形的控制是真空预压实施过程中的关键问题。研究分析及实践表明,将已施工桥桩包含在真空预压作业区内和动态调整真空度及路堤填筑荷载,可有效控制桩体位移。相同荷载强度情况下,真空荷载对于桥桩的影响要明显小于路堤填土荷载和上部水平力的影响,并可采用m法近似对桩体受力进行分析。在条件允许的情况下应先进行真空预压而后再进行桥桩的施工,以减小桩体位移同时降低施工难度。     

超载预压法的超载比及卸载时间控制研究

介绍了超载预压的一般原理,在此基础上通过室内模拟实验,对超载预压法的超载比和荷载作用时间进行了研究,得出了软黏土的卸载控制曲线,并建议超载比应控制在0.4~0.5范围内。     

谈举折与起翘的起源

通过考证举折和起翘起源相关的文献与文物,对举折和起翘的起源进行了对比和分析,提出了举折和起翘在发展过程中存在互相影响的现象,为进一步研究中国古代建筑体系屋顶造型提供了依据。     

太仓煤堆场软黏土地基堆载预压处理效果分析

采用塑料排水板堆载预压法对太仓煤堆场吹填土地基进行了加固处理,根据现场监测数据,分析了软土地基在堆载预压条件下的沉降和超静孔隙水压力的变化规律。研究结果表明:实测沉降—时间曲线与采用Logistic模型拟合得到的沉降—时间曲线较为吻合;塑料排水板插板深度范围内的各层地基土均发生了排水固结,而且地面以下占排水板总长度四分之三深度范围内的加固效果最佳。通过反演实测沉降曲线,得到了场地地基土径向固结系数平均值;最后对地基固结性状进行了分析,分析表明,本场地采用塑料排水板堆载预压法加固地基是有效的,研究成果可为后续工程地基处理设计提供可靠的设计依据。     

Experimental study on the L-shaped anchorage capacity of the geogrid by the pullout test

The soil reinforcement by geosynthetics has been extensively applied in covers and liners of landfills. The stability of this structure is especially dependent on the effectiveness of the anchorages holding the geosynthetic sheets. The simple run-out and L-shaped anchorages are the two most commonly used approaches. For increasing the available knowledge of the anchorage system behavior, experimental studies have been conducted. This paper shows the results of the experimental analysis that are based on the results of large-scale pullout apparatus on geogrid embedded in simple run-out and L-shaped anchorage in two modes (fixed length and fixed space). The influence of different geometric parameters of the trench on the behavior of the geogrid is also examined. Based on the results, the values of pullout force were approximately 69% and 196% higher in the case of the fixed length mode and the fixed space mode, in the respective order, compared to the simple run-out anchorage. In the L-shaped anchorage, it is observed that for the initial length (L) constant, the mode is optimized with a small value of the geogrid rear heel length (B) and a greater value of the depth of the buried geogrid (D) when D+B is constant.     

The effect of geotextile reinforcement and prefabricated vertical drains on the stability and settlement of embankments

The construction of four dikes on deep strata of very soft clay has required the application of several measures to improve the performance of the foundation, such as very wide berms, basal geotextile reinforcement and prefabricated vertical drains (PVDs). In order to control the rate of construction, the foundation and the dikes have been monitored with settlement plates, topographic stakes, inclinometers and piezometers. The use of back-analysis has allowed finding the adequate material model, the smearing of drains and the coefficient of secondary compression necessary to attain a good agreement between the measurements supplied by the instrumentation and the calculated values obtained with an elastic-viscoplastic (EVP) finite element (FE) program. Both the geotextile reinforcement and the PVDs produce an important increase in the safety factor (SF). The PVDs produce a significant acceleration in settlements, but the influence of the geotextile in the settlements is negligible. The combined use of the geosynthetic reinforcement and PVDs enhances embankment performance substantially more than the use of either method of soil improvement alone. The importance of flow in the results has been established.     

外墙外保温系统仿清水墙陶土面砖空鼓预防

胶粉EPS颗粒保温浆料外墙外保温系统仿清水墙陶土面砖空鼓问题较普遍,其主要原因有材料、工艺两方面。针对这些原因,提出了从材料配制使用、基层处理、保温浆料施工、抗裂防水层施工以及饰面砖粘贴等五个方面采取具体的预防措施,可有效防止这类问题的再次发生,并在实际工程应用中取得了成功。     

西方现代景观设计的主要倾向及对中国的启示

通过分析西方现代景观设计的主要倾向,并针对中国当前景观建设中存在的形式主义对西方或中国古典景观元素照抄照搬而缺乏设计内涵等问题,探讨了在我国园林设计中如何互融与借鉴西方现代景观设计的手法。