干、湿喷混凝土和湿喷仿钢纤维混凝土强度性能比较分析

针对干、湿喷混凝土支护强度低、黏结强度低与韧性差等问题,对干、湿喷混凝土与湿喷仿钢纤维进行强度试验及柔韧性分析,并将其与干、湿喷混凝土强度与柔韧性进行对比。采用试验的方法,利用RMT力学试验机对干喷、湿喷混凝土及湿喷仿钢纤维混凝土从抗压强度、抗拉强度及抗折强度三方面力学性能进行试验,通过对试验数据的分析,可以得出湿喷仿钢纤维混凝土力学性能优于湿喷混凝土、湿喷混凝土优于干喷混凝土;其中仿钢纤维的掺入使得混凝土的力学性能大幅增强,相较于干喷混凝土抗压强度提升86.3%、抗拉强度提升85.9%、抗折强度提升132.9%;相较于湿喷混凝土抗压强度提升25.8%、抗拉强度提升24.5%、抗折强度提升45.8%;其柔韧性与抗裂性经折压比比较可知有所提高。     

粉煤灰对喷射混凝土强度和渗透性的影响

试验采用扫描电子显微镜(SEM)对喷射混凝土微观结构进行分析,并采用RCM氯离子渗透法研究了粉煤灰对喷射混凝土抗氯离子渗透性能的影响,并对其抗压强度、劈裂抗拉强度进行研究。试验结果表明:随着粉煤灰掺量增大,喷射混凝土微观结构变得致密,强度和抗渗性显著提高。粉煤灰的最佳掺量为20%左右,超过此掺量喷射混凝土抗压强度降低,喷射混凝土强度和渗透性有较好的相关性。     

In situ testing of young shotcrete subjected to vibrations from blasting

A criterion for how close, in time and distance, to young shotcrete blasting can take place will be an important tool in planning for safe and economical tunnelling projects. As a first step, in situ tests with young, plain un-reinforced shotcrete have been conducted in a Swedish mine. Shotcrete panels were projected on tunnel walls and exposed to vibrations from explosive charges detonated inside the rock at shotcrete ages between 1 and 25 h. The shotcrete was tested to investigate growth of compressive strength and also to determine final compressive and adhesive strengths. The response of the rock was measured with accelerometers, giving signals that were later numerically integrated to particle vibration velocities. An average scaling relation of distance between explosive charges and the point of observation and weight of explosives was also derived. The recorded vibration levels showed that the shotcrete had withstood high particle velocity vibrations without being seriously damaged, even when the rock material was fragmented and ejected. Drumminess of shotcrete appeared, indicating that the major failure mechanism was sudden loss of adhesion at the shotcrete–rock interface. No differences in performance between shotcrete of different ages were observed. It was, thus, confirmed that young shotcrete without reinforcement can also survive high vibration levels without being seriously damaged.     

Laboratory testing of early age bond strength of shotcrete on hard rock

This study investigates early age bond strength of shotcrete (sprayed concrete), in the case of shotcrete sprayed on hard rock. Shotcrete differs from ordinary, cast concrete through the application technique and the addition of set accelerators which give immediate stiffening. The bond between shotcrete and rock is one of the most important properties. During the very first time after spraying the physical properties and the bond to the rock depend on the set accelerator and the micro structure that is formed. In this work a laboratory test method for measuring early bond strength for very young or early age shotcrete is presented. The newly developed method was tested and evaluated and proved that it can be used for bond strength testing already from a couple of hours after shotcreting.     

Experimental evaluation of geosynthetics as reinforcement for shotcrete

One of the commonly used stabilization systems for rock tunnels is shotcrete. This fine aggregate mortar is usually reinforced for improving its tensile and shear strength. In deep tunnels, its capacity to absorb energy has been recently considered for design purposes, as large displacements of the wall are expected. Two of the most used materials of reinforcement are steel welded-wire mesh and fibers (steel or polypropylene) in the shotcrete mix. This study presents the results and discussion of an experimental test program conducted to obtain the load-deformation curves of reinforced shotcrete, according to ASTM C 1550, using geosynthetics grids and geotextiles as alternative reinforcement materials. In addition, plain shotcrete and steel welded-wire mesh reinforced shotcrete specimens are also considered in the experimental program as benchmark cases. The experimental results are analyzed in terms of maximum strength and toughness. Results show that the use of geosynthetics as a reinforcement material is a promising alternative to obtain shotcrete with energy absorption capacity comparable with the most common reinforcement materials used.     

喷射混凝土加固工程中检测与试验应注意事项

为了确保喷射混凝土加固工程的质量,从检测与试验的角度在原材料、配合比设计、强度检验与判定等方面加以分析介绍,提出了应注意的问题,从而使喷射混凝土结构设计满足技术要求。     

Effects of steel fiber reinforced high-strength shotcrete in a squeezing tunnel

In order to quantitatively clarify the effects of steel fiber reinforced high-strength shotcrete (SFRS) applied to a squeezing tunnel, a non-linear numerical analysis is carried out, in which the stress–strain–time constitutive relationships of SFRS and the time-dependent movement of the ground surrounding the tunnel are taken into account. Through a comparison of field measurement and analytical results, it is recognized that SFRS can be applied as a reasonable primary lining for tunnels excavated in grounds with severe geological conditions. In particular, high strength during the early stages of the execution and ductility after its peak strength both contribute to the safe construction of squeezing tunnels.     

Early-age load resistance of fibre reinforced shotcrete linings

Widespread interest has developed into early-age strength development for fibre reinforced shotcrete (FRS) and its influence on the time to safe re-entry immediately after spraying. Cycle times for drive development within mines, and in civil tunnel construction, can strongly depend on the time to safe re-entry and this, in turn, affects excavation progress rates and overall project economy. The majority of research into safe re-entry times has focused on strength development in hardening shotcrete under the assumption that toughness, adhesion to the rock surface, and the ability of the FRS lining to support unstable ground are all related to the strength of the concrete matrix. Although anecdotal evidence supporting this assumption has been gathered through observations of satisfactory ground control at mines utilizing FRS for ground support, ad hoc evidence alone cannot be used as a basis for rational estimation of safe re-entry times. Instead, the present investigation has sought to quantify the parameters that influence early-age FRS lining capacity and develop an engineered approach to shotcrete lining design and estimation of safe early-age re-entry times through a rational assessment of load resistance.     

承载喷射混凝土碳化试验研究

通过对承载喷射混凝土进行快速碳化试验,分析了施工方式、钢纤维、应力水平对混凝土碳化深度的影响规律,同时对其碳化后的力学性能进行了探讨。试验结果表明,承载喷射混凝土的碳化深度与碳化时间的平方根成正比;其抗碳化能力优于同条件下的浇筑混凝土,但是劣于喷射钢纤维混凝土;弯拉应力水平越高,混凝土碳化深度也越大;建立了应力加速因子与应力水平的关系。碳化使喷射混凝土的抗折强度降低,但掺入钢纤维后,其抗折强度相对有所改善。     

Experimental study of shotcrete and concrete strength development in a hot spring environment

To determine the influence of hot spring water on mechanical characteristics of tunnel supports made from Portland cement, this study investigates strength development and associated temporal variations of shotcrete and concrete specimens cast in situ and cured in water from a hot spring. Experimental results reveal that weakly-base hot spring water with a curing temperature of 40 °C does not adversely affect strength development for shotcrete and concrete; however, the hot spring curing environment may benefit early stage strength development and subsequent integrity. Chloride and sulfate ions in hot spring water do not enhance the alkali–aggregate or alkali–carbonate reaction significantly. Concrete specimens with high uniaxial compressive strength have high surface hardness, high electrical resistance and low permeability, implying excellent short-term durability.     

JL-1型低碱液体速凝剂的研制

通过采用无机,有机物质复合的研制路线,使用硫铝酸盐和中性钠盐作为主要促凝物质,并利用高分子物质聚丙烯酰胺对速凝剂进行优化,改善凝聚性,降低喷射过程中的回弹损失量;使用六偏磷酸钠提高速凝剂中有效成分的溶解度,从而进一步提高砂浆强度.结果显示:新型低碱液体速凝剂完全满足JC 477-2005<喷射混凝土用速凝剂>标准中一等品要求,与空白砂浆试块相比28 d抗压强度强度基本无损失,性能优于国内外同类品牌.     

玄武岩纤维喷射混凝土在热害环境下的性能试验研究

以隧道热害问题为背景,通过模型试验、近似模拟湿喷技术、定量分析及微观测试相结合的方法研究不同掺量玄武岩纤维喷射混凝土劈裂强度和粘结强度等力学性能的影响,横向对比标准养护和干热养护下的不同体积掺量的玄武岩纤维混凝土的力学性能,同时也加入硅灰以及钢钎维作为参照,以便从机理程度上提出更有效的解决热害措施。试验研究表明:在混凝土中加入玄武岩纤维,对混凝土起到了增强和阻裂的作用,改善了混凝土的脆性易裂的破坏状况。干热环境下,加入少量的玄武岩纤维能够提高混凝土的力学性能。当玄武岩掺量为0.1%玄+5%硅灰时,喷射混凝土的力学性能最好,加入0.2%玄武岩纤维掺量,也有一定程度的改善。实际隧道施工中,可通过加入适量的玄武岩纤维和适量的硅灰,可降低混凝土在热害环境下的危害。     

C50补偿收缩喷射混凝土的配合比设计及耐久性研究

常规C25喷射混凝土抗压强度低、耐久性差,难以满足高地应力条件下地下洞室的快速支护需求。为解决上述问题,通过降低水胶比、掺入活性掺合料、引入2%~6%氧化钙类膨胀剂对C50喷射混凝土进行配合比设计,并考察其力学、变形、抗渗和抗冻等性能。结果表明:采用10%硅灰、2%~4%氧化钙类膨胀剂、0.35水胶比、抗压强度比120%以上的无碱速凝剂可制备C50补偿收缩喷射混凝土。该混凝土的密实度和耐久性较高,孔隙率仅为常规C25喷射混凝土的44%~50%,80%左右孔隙的直径均在50 nm以内,抗渗等级和抗冻等级也已分别超过W25和F300。     

Enhancement of the tensile strengths of rock and shotcrete by thin spray-on liners

Thin spray-on liners (TSLs) have been available for application in mining and civil engineering situations for about 20 years. They were initially used as sealants, but have subsequently been developed as surface support liners. Although they are used in substantial quantities in mines in South Africa and Canada, widespread application for support purposes has been met with some scepticism. Observations from users, however, have indicated that, contrary to this scepticism, TSL support performance was almost always better than expected. A reason for the scepticism is probably a lack of quantification of the benefits. This paper aims to address this lack of data to some extent. It provides quantification of the enhancement of tensile strengths of rock and shotcrete due to the application of TSLs. The quantification was achieved using Brazilian indirect tensile testing, and several commercially available TSL products. Some tests were also carried out on small rock beams using three-point bending. The results show that, depending on the TSL product used, the tensile strength of a strong, brittle rock can be increased by approximately 30%, and that of shotcrete by more than 40%. TSL application on a weak porous sandstone resulted in an early tensile strength reduction, probably due to absorption of moisture. This was not the case with TSL application on shotcrete.Many of the rock support mechanisms provided by sprayed liners depend substantially or completely on the tensile strength contribution of the liner. Hence the data provided in this paper makes a contribution to knowledge, of value in the design of support for excavations in rock.     

水下系梁高压旋喷桩配合锚网喷支护施工

结合高压旋喷桩配合锚网喷支护施工水下系梁的工程实践，阐述了高压旋喷桩的工作原理、设计方案及施工工艺，实践证明，该技术施工简便、无污染、进度快，能取得较好的经济效益。     

浅谈公路隧道喷射混凝土施工技术

建设高速公路需要大量开凿山洞（隧道）、搭建桥梁。山洞开凿后要进行多项工程,其中隧道喷射混凝土是重要工程之一。本文针对喷射混凝土工程展开浅析。     

喷射混凝土应用实例

结合具体的工程实践，介绍了喷射混凝土作为地下室柔性防水层基面的应用情况及过程分析，探讨如何改善喷射混凝土的配合比以减小施工回弹率，并总结出一些体会。     

如何保证隧道喷射混凝土的质量

对隧道喷射混凝土的四种施工工艺作了介绍,结合工程实例,从工艺选择、配合比设计、混凝土拌制、喷射作业要求等方面阐述了隧道喷射混凝土的质量控制措施,以确保隧道喷射混凝土的整体质量。     

用锚喷混凝土方法加固双曲拱桥

介绍了锚喷混凝土加固双曲拱桥的基本要点,进行了桥梁荷载试验,通过建立有限元模型,计算得出了主拱圈锚喷厚度的一个最优值,使得结构加固后结构既满足受力要求,又达到最优的经济效果。     

喷射混凝土钢纤维分布特性分析

通过钢纤维在喷射混凝土中的受力特性分析 ,说明在以单位球为研究对象时 ,钢纤维在混凝土中服从球面上的Fisher分布 ,其长轴指向与受喷射面基本平行 ,这样的分布特性 ,有利于抵抗巷道由于变形而产生的破坏