刚性基础下复合地基褥垫层加筋影响研究

为了提高桩土荷载分担比,一些建筑工程桩筏基础下的复合地基采用了加筋垫层,然而加筋垫层复合地基的变形协调与荷载传递的影响还缺乏深入研究。采用自制的二维多活动门试验装置与椭圆钢棒相似土填料,开展了无筋褥垫层随桩间土下沉过程的模型试验,获得了不同垫层厚度下无筋垫层的变形与应力协调特性。在模型试验基础上,采用颗粒离散元DEM数值模拟建立了无筋与加筋垫层数值模型,揭示了有、无加筋条件下的褥垫层工作特性区别,并探讨了褥垫层厚度、桩间净距以及加筋位置等对褥垫层工作特性的影响。结果表明:当加筋高度距桩顶超过100 mm时,桩土应力比曲线和褥垫层变形均接近未加筋的情况; 加筋体设置高度小于100 mm时,下方颗粒垫层的变形协调会受到影响,格栅与下部垫层之间产生脱空现象,从而导致桩土应力比随着桩间土下沉量的增加而出现陡升; 陡升段起点对应的桩间土下沉量随着加筋位置的提高而增加,工程中可能会导致复合地基桩体超过承载力而引起复合地基发生破坏。     

Effect of random inclusion of sisal fibre on strength behaviour of soil

Construction of building and other civil engineering structures on weak or soft soil is highly risky on geo-technical grounds because such soil is susceptible to differential settlements, poor shear strength and high compressibility. Improvement of load bearing capacity of the soil may be undertaken by a variety of ground improvement techniques like stabilisation of soil, adoption of reinforced earth technique etc. Reinforced earth technique is considered as an effective ground improvement method because of its cost effectiveness, easy adaptability and reproducibility. Therefore, in the present investigation, sisal fibre has been chosen as the reinforcement material and it was randomly included in to the soil at four different percentages of fibre content, i.e. 0.25, 0.5, 0.75 and 1% by weight of raw soil. Four different lengths of fibre, i.e. 10, 15, 20 and 25 mm are also considered as one of the parameters of this study. The main objective of this investigation had been focused on the strength behaviour of the soil reinforced with randomly included sisal fibre. The reinforced soil samples were subjected to compaction and triaxial compression tests. The results of these tests have clearly shown a significant improvement in the failure deviator stress, Shear strength parameters (C and φ) of the studied soil. It can be concluded that sisal fibre can be considered as a good earth reinforcement material.     

单层立体加筋砂土性状的三轴试验研究

针对加筋土中传统的筋材布置特点,提出了立体加筋土的概念,并设计了采用轴对称布置的单层立体加筋砂土的试验方案,进行了48组镀锌铁皮和橡胶板两种筋材的单层立体加筋砂土的室内三轴试验,探讨了不同立体加筋方式、不同围压作用下应力–应变及强度变化规律。通过试验结果对比,分析了立体加筋砂土同传统水平加筋砂土之间应力–应变关系和强度指标的差异规律,竖向筋高度对立体加筋砂土的强度影响,单侧和双侧布置竖向筋材等两种布筋方式对立体加筋砂土强度的影响,以及不同变形模量的加筋材料对立体加筋土强度的影响。试验结果表明:立体加筋砂土的强度随竖向筋的高度增加而增大;立体加筋不仅能提高砂土的粘聚力,同时也能增加砂土的内摩擦角,尤其是双侧立体加筋砂土;在竖向筋总高度相同时,双侧立体加筋形式比单侧立体加筋能更有效提高砂土的强度。     

Centrifuge model tests on the behavior of strip footing on geotextile-reinforced slopes

This paper examines the stability of geotextile-reinforced slopes when subjected to a vertical load applied to a strip footing positioned close to the slope crest. Vertical spacing between geotextile reinforcement was varied while maintaining a constant slope angle, load position, soil density and geotextile type. Small-scale physical tests were conducted using a large beam centrifuge to simulate field prototype conditions. After the model was accelerated to 40g, a load was applied to the strip footing until slope failure occurred. Digital image analysis was performed, using photographs taken in-flight, to obtain slope displacements and strain distribution along the reinforcement layers at different loading pressures during the test and at failure. Stability analysis was also conducted and compared with centrifuge model test results. The vertical spacing between reinforcement layers has a significant impact on the stability of a reinforced slope when subjected to a vertical load. Less vertical distance between reinforcement layers allows the slope to tolerate much greater loads than layers spaced further apart. Distributions of peak strains in reinforcement layers due to the strip footing placed on the surface of the reinforced slope were found to extend up to mid-height of the slope and thereafter they were found to be negligible. Stability analysis of the centrifuge models was found to be consistent with the observed performance of geotextile-reinforced slopes subjected to loading applied to a strip footing near the crest.     

Experimental study on the progressive failure and its anchoring effect of weak-broken rock vertical slope

To improve the understanding on the failure behavior and its anchoring effect of weak-broken rock slope, the rock of grade IV according to China is taken as reference prototype, and a series of model tests were carried out in laboratory. These tests can be divided into two categories, that is, with bolt reinforcement and without bolt reinforcement. In which, the stability of slope reinforced with different bolt diameter, different anchor length and different space are studied. The test results show that the collapse of slope is the combination of tension failure at the top and the compression-shearing failure at the bottom of the slope, and its failure process presents progressive characteristics. The contributions of bolt reinforcement are mainly reflected by the aspects of shear resistance, crack resistance and anti-extension. The reinforcement of blot not only can improve the vertical bearing capacity before failure, but also can reduce the vertical settlement and allow greater lateral rock wall deformation; what is more, the stress concentration degree in rock mass can be dispersed, which do help to improve the stability of slope rock mass.     

Centrifuge model study on low permeable slope reinforced by hybrid geosynthetics

The objective of this paper is to study the performance of hybrid geosynthetic reinforced slopes, with permeable geosynthetic as one of its components, for low permeable backfill slopes subjected to seepage. Four centrifuge tests have been performed to study the behavior of hybrid geosynthetic reinforced slopes subjected to seepage, keeping the model slope height and vertical spacing of geosynthetic reinforcement layers constant. Centrifuge model tests were performed on 2V:1H slopes at 30 gravities. One unreinforced, one model geogrid reinforced and two hybrid geosynthetic reinforced slope models with varying number of hybrid geosynthetic layers were tested. The effect of raising ground water table was simulated by using a seepage flow simulator during the flight. Surface movements and pore water pressure profiles for the slope models were monitored using displacement transducers and pore pressure transducers during centrifuge tests. Markers glued on to geosynthetic layers were digitized to arrive at displacement vectors at the onset of raising ground water table. Further, strain distribution along the geosynthetic reinforcement layers and reinforcement peak strain distribution have been determined using digital image analysis technique. The discharge for the performed model tests is determined by performing seepage analysis. It was confirmed by the centrifuge tests that the hybrid geosynthetics increases the stability of low permeable slope subjected to water table rise. The hybrid geosynthetic layers in the bottom half of the slope height play a major role in the dissipation of pore water pressure.     

In-plane retrofitting of masonry panels with fibre reinforced composite materials

Research activities carried out during the past years concerning the use of fibre reinforced polymers (FRP) as external reinforcement of masonry walls have shown that this system considerably improves structural stability and ductility with minimum increase in the load transmitted to foundations. However, different aspects of this retrofitting system should still be analyzed.The mechanical behaviour under in-plane compression and diagonal compression of clay masonry panels reinforced or repaired with carbon fibre reinforced polymer laminates is experimentally assessed in this paper. The results show that if correct retrofitting schemes are chosen, reinforcement and repairing with fibre reinforced polymers improves masonry behaviour, increasing ductility and, in some cases, ultimate strength and even stiffness. In this way, brittle behaviour and sudden failure of unreinforced masonry can be avoided.     

土工格栅加筋土地基载荷试验的数值模拟

采用FALC^3D对土工格栅加筋土地基载荷试验进行了进一步的数值模拟分析。根据计算结果,针对原型试验中难以量测的试坑变形及筋土界面摩阻力分布特征进行了讨论。利用数值模拟技术的优势,求解加筋地基的应变场,研究了加筋地基的破坏模式。结果表明:在竖向荷载作用下,试坑会发生侧向位移,通过加筋能有效减小试坑的侧向位移;筋土界面摩阻力的分布与筋土之间的相对位移直接相关;加筋地基的破坏机构因筋材的存在而发生改变,“深基础”效应以及“扩散层”效应都是加筋地基的增强机理,但地基的破坏模式随筋材的布置形式改变而有所不同。     

Zeitabhängiges Verhalten von Makrokunststofffaserbeton und dessen Einfluss auf die Bemessung von Industriefußböden

Time Dependent Behaviour of Macro Synthetic Fibre. Reinforced Concrete and its Influence on the Design of Industrial Slabs on Ground Material tests and tests on structural elements with synthetic macro fibre reinforced concrete are presented. The experimental program included the investigation of the load carrying capacity and the deformation behaviour under short‐term as well as under long‐term loading conditions. Long‐term load tests were carried out on pre‐cracked fibrereinforced concrete beams to measure the load level above which creep failure can occur. At service load level creep coefficients for a time period of up to three years were determined. Centre point load tests were carried out on concrete slabson‐ground. Two slabs were reinforced with steel mesh and two with synthetic macro fibres only. The tests were performed under short‐term and long‐term loading conditions over a period of 18 month. The current main application of synthetic macro fibre reinforced concrete is slab‐on‐ground. Slabs‐on‐ground can be designed under the assumption of elastic subgrade reaction. The concrete slab itself can be calculated either by elastic theory for uncracked concrete or by yield line theory taking fibre reinforcement into account. Based on the test results of the experimental programme, design recommendations for permanently loaded slabs‐on‐ground are presented.     

Failure mechanisms governing reinforcement length of geogrid reinforced soil retaining walls

Current design practice of reinforced soil retaining walls is based on the limit equilibrium approach. The walls are designed for both external and internal stability criteria. Design reinforcement length should be such that minimum required safety factors are fulfilled for all failure modes. Most agencies require minimum reinforcement length equal to 70 percent of wall height. However, it is not always possible to have enough space behind a wall to accommodate these required reinforcement lengths due to an existing natural rock formation, man-made shoring system, or the presence of another reinforced soil retaining wall. This study was performed to investigate governing failure mode in determining the required minimum reinforcement length and also to investigate the possibility of shortening the specified minimum reinforcement lengths. Effect of different parameters involved in the design of reinforced soil retaining walls on the required minimum reinforcement length and the governing failure mode were studied. Parameters considered included wall height, surcharge, reinforcement vertical spacing, reinforced soil properties, backfill/retained soil properties, and foundation soil properties. Results indicated that both external and internal failure modes can be governing criteria in determining the required minimum reinforcement length depending on the parameters involved for a specific wall. In addition, it may be possible to use reinforcement lengths as low as almost 50 percent of the wall height, instead of 70 percent as required by many agencies around the world. This paper presents the results of parametric studies conducted, including the effect of different parameters on the required minimum reinforcement length and the governing failure criteria.     

加筋无黏性土斜坡地基承载力模型试验研究

 采用缩尺模型试验研究加筋斜坡地基坡高范围内,不同加筋层数、不同筋带埋深对其极限承载力及破坏形态的影响。通过对比分析试验成果可获得不同加筋层数下最优筋带埋深组合及各试验地基的变形破坏资料。研究表明,在最优筋带埋深组合下,加筋斜坡地基的首层加筋间距随加筋层数的增加有减小趋势,而极限承载力随加筋层数的增加有增加趋势。根据各试验地基的p-s曲线、筋材破坏情况及变形破坏特征,可将不同加筋条件下斜坡地基的破坏形态分为加筋带之上土体破坏、加筋带层间土体破坏、加筋带之下土体破坏3类,并由此获得对应破坏类型的破坏形态图。研究成果对加筋斜坡地基极限承载力变化特性、变形特征及破坏形态的探究具有一定理论参考价值。     

加筋地基承载力特性及破坏模式的试验研究

利用自制的模型试验设备,做了一系列加筋地基的模型试验,应用数字照相变形量测技术,结合地基土压力和基础的沉降的量测来研究加筋地基的加筋机理和变形破坏模式。基础荷载作用下的地基变形场用连续的数码相片记录,然后用数字照相变形量测技术分析得到地基的增量变形场和地基的破坏面。试验结果表明,无加筋地基的破坏模式和经典的地基破坏模式吻合较好,加筋地基的破坏模式会因为加筋体的存在而发生一定程度的改变。文中模型试验所揭示的加筋地基的变形破坏机理可作为加筋地基的极限分析的基础。     

土工袋加固砂性土质边坡模型试验与上限解

 通过模型试验比较有土工袋加固和无土工袋加固时边坡的破坏形态及承载力,验证土工袋对边坡的加固效果,并基于试验结果建立边坡的许可破坏模式及其速度场,利用极限分析上限法求解了边坡的极限高度上限解,利用模型试验结果对边坡极限高度进行验证。试验及计算结果均表明：边坡越陡,有土工袋加固较无土工袋加固时边坡的极限高度和承载力提高越大,表明土工袋加固效果越好。试验结果与计算结果基本吻合,表明该计算方法的可信性,可为边坡的稳定性设计问题提供理论依据。     

Shear strengthening of reinforced concrete beams by means of vertical prestressed reinforcement

Strengthening reinforced concrete (RC) elements critical to shear with prestressed transversal reinforcement can be an efficient method to increase the shear resistance of structures, allowing the development of the full flexural capacity. However, research on the performance of this technique is very limited, and methods for designing the optimum amount of prestressed transversal reinforcement and assessing the retrofitted structure have not been produced yet. Nonlinear finite element models are an important tool regarding predicting the efficiency of these interventions. In this paper, a shear-sensitive fibre beam formulation is extended in order to account for the effects of unbonded vertical external prestressed reinforcement in the structural response of RC beams. The model is validated with experimental tests available in literature, succeeding in capturing the gain of shear strength brought by different strengthening solutions. A parametric study is performed to find the optimal quantity of transversal reinforcement that ensures flexural failure mechanism in a beam with insufficient internal shear reinforcement. The relative simplicity of the numerical model makes it suitable for engineering practice.     

钢-混凝土组合桥梁中无抗剪配筋的桥面板在轴向拉力作用下的抗剪极限承载力试验研究

完成31根钢筋混凝土梁的剪切破坏试验,对钢-混凝土组合桥梁中无抗剪配筋的桥面板在轴向拉力作用下的抗剪极限承载力进行了研究。试验中主要考虑了轴向拉力对抗剪极限承载力的影响,同时对配筋率、最小抗剪配筋、混凝土强度等级等其他因素也进行了研究。试验结果表明,欧洲规范2第1部分中用来计算无抗剪配筋的钢筋混凝土构件的抗剪极限承载力的公式过于保守,建议进行修正。     

FRP筋混凝土梁正截面极限抗弯承载力的性能研究

利用FRP筋混凝土粱截面的平衡条件和变形协调条件．给出梁的平衡配筋率;分析FRP筋混凝土梁三种破坏模式,即受压破坏、受拉破坏和平衡破坏的特性;研究FRP筋混凝土梁配筋率对其正截面极限抗弯承载力的影响,并给出其影响系数。研究表明：配筋率在一定范围内,抗弯承载力随着配筋率的增大而增大;根据配筋率的不同,探讨FRP筋混凝土梁正截面极限抗弯承栽力的计算方法,建立与之相应的计算公式,并将计算结果与国内外文献中的部分试验结果相比较,且两者吻合较好。     

Performance of geosynthetic-reinforced soil foundations across a normal fault

This paper presents a series of model tests on geosynthetic-reinforced soil (GRS) foundations across a normal fault. The aim was to evaluate the performance of reinforced foundations as a mitigation measure for surface faulting hazards. Experimental tests modeled a 3-m thick foundation in prototype subjected to a fault displacement up to 90 cm. Test variables included the number of reinforcement layers, reinforcement stiffness and location, and foundation height. Digital image analysis techniques were applied to determine the ground settlement profile, angular distortion, shear rupture propagation, and mobilized reinforcement tensile strain at various magnitudes of fault offset. Test results revealed that compared with the unreinforced foundation, reinforcement inclusion could effectively prevent the shear rupture propagating from the bedrock fault to the ground surface. It also spread the differential settlement to a wider influential zone, resulting in an average reduction of 60% in the fault-induced angular distortion at the ground surface. The maximum angular distortion decreased as the foundation height, number of reinforcement layers, and reinforcement stiffness increased. Relationships between the maximum angular distortion and maximum mobilized reinforcement tensile strain with fault displacement were therefore established. Based on the findings from this study, design suggestions and implications are discussed.     

Finite element analysis of thin GFRC panels reinforced with FRP

Glass fibre reinforced concrete (GFRC) incorporating fibre reinforced polymer (FRP) bar reinforcement is potentially an ideal composite material for the manufacture of thin structural elements due to its superior durability over GFRC containing conventional steel reinforcement. GFRC without any bar reinforcement has only been used for small units and short spans due to its relatively low flexural strength. Until now, no work has been reported on the use of FRP bars in GFRC. The first part of the paper deals with the stress–strain characteristics of GFRC. In the second part the bond strength of GFRC with both steel and FRP reinforcing bars is determined from a series of 24 pullout tests from which the characteristics of the local bond stress–slip response was established. The results show that the bond of FRP bars in GFRC is, in general, better than the bond in normal concrete, and that conventional numerical models can be used to model the behaviour. The last part of the paper investigates the performance of a 3 m span thin GFRC permanent formwork panel, reinforced with FRP, both experimentally and analytically with finite element (FE) analysis. It is concluded that the behaviour of thin GFRC elements incorporating FRP reinforcement can be predicted by FE analysis in which the GFRC stress–strain characteristics and bond characteristics are modelled with robust spring elements.     

600 MPa高强钢筋与混凝土的粘结锚固性能试验研究

为研究600MPa高强钢筋与混凝土粘结锚固性能,设计了72个棱柱体试件进行拉拔试验,对600MPa高强钢筋粘结锚固的破坏形态及粘结应力分布进行分析,通过建立基本粘结滑移关系及位置函数,确定600MPa高强钢筋在混凝土结构中的粘结滑移本构关系。采用一次二阶矩法进行可靠度分析,提出锚固长度设计建议。研究表明:600 MPa高强钢筋粘结锚固的破坏形态及粘结应力分布与普通钢筋类似且粘结锚固性能良好,《混凝土结构设计规范》(GB 50010—2010)基本锚固长度计算公式依然适用于600 MPa高强钢筋。     

Centrifuge modeling of geotextile-reinforced slopes subjected to differential settlements

Today, geosynthetic-reinforced soil structures are widely used to support bridge abutments and approach roads in place of traditional pile supports and techniques. In such situations, foundation conditions have been shown to adversely affect the stability and deformation behaviour of overlying geosynthetic-reinforced slopes and walls. This paper addresses the response of geotextile-reinforced slopes subjected to differential settlements in a geotechnical centrifuge. Centrifuge model tests were carried out on model geotextile-reinforced sand slopes with two different types of reinforcement. A wrap-around technique was used to represent a flexible facing. In order to initiate failure in the reinforcement layers, the ratio of length of reinforcement to height of the slope was maintained as 0.85. One of the objectives of this paper is to present about a special device developed for inducing differential settlements during centrifuge test at 40g for a reinforced soil structure. A digital image analysis technique was employed to arrive at displacement vectors of markers glued to the reinforcement layers. The displacements were used to compute and analyze the strain distribution along the reinforcement layers during different settlement stages. Results of the centrifuge test indicate that even after inducing a differential settlement equivalent to 1.0 m in prototype dimensions, the geotextile-reinforced soil structure with a flexible facing was not found to experience a collapse failure. Analysis of geotextile strain results shows that the location of the maximum peak reinforcement strain occurs along the bottom-most reinforcement layer at the onset of differential settlements, at the point directly below the crest of the slope.