基于挣值法的隧道工程喷射混凝土成本控制研究

介绍了挣值法和隧道工程喷射混凝土工艺,对喷射混凝土成本控制关键指标进行了深入分析.以成昆铁路特克隧道为例,基于挣值法对喷射混凝土成本与施工进度进行研究,分析了喷射混凝土绩效影响因素,并结合当前实际状况,提出隧道工程喷射混凝土成本控制策略.     

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。     

喷射混凝土施工技术在隧道工程中的应用

通过对隧道工程喷射混凝土施工过程中的回弹量、厚度、检测等问题的探讨,并结合施工实际对隧道工程喷射混凝土施工提出建议。     

地铁隧道工程中喷射混凝土的超耗分析及控制措施

喷射混凝土在地铁隧道工程中用量很大,因此喷射混凝土的超耗是成本控制的关键。结合工程实例,通过分析施工过程中各环节超耗的原因,制定了相应的控制措施,有效地控制了隧道喷射混凝土施工时的超耗现象,可为类似工程参考。     

喷射混凝土常见质量问题分析及其预防措施

结合喷射混凝土在隧道工程中的应用,对喷射混凝土施工过程中常见的质量问题产生的原因进行了分析,并提出了相应的预防措施,以更好地提高喷射混凝土的质量,确保隧道的施工安全和成本受控。     

隧道工程喷射混凝土质量控制与检测

结合工程实际和实践经验,论述复杂条件下影响隧道工程喷射混凝土质量的原材料、配合比设计、施工控制、以及质量措施与检测技术等主要因素,使隧道喷射混凝土达到最佳支护效果,并为隧道工程建设提供参考.     

客运专线隧道工程喷射混凝土施工质量控制的研究

喷射混凝土是隧道工程复合支护普遍采用的结构材料,具有施工速度快、支护及时、施工安全,以及支护质量好、强度高、密实、防水性能好等特点;为了更好地满足客运专线隧道工程的技术要求,该文对喷射混凝土的原材料、配合比设计及施工的质量控制进行了深入探讨,为今后客运专线隧道工程喷射混凝土的施工提供了较完善的技术支撑。     

论无碱速凝剂喷射混凝土施工

结合工程实例,分析无碱速凝剂喷射混凝土施工。隧道初期支护掺无碱速凝剂喷射混凝土工艺试验主要根据机具配套、工人操作及原材料配合比等,进行喷射混凝土施工及混凝土质量检测。给相关工程提供参考。     

浅析隧洞喷射混凝土施工技术

喷射混凝土作为隧道工程的永久性或临时性支护,也可以与各种形式的锚杆、钢纤维、钢拱架、钢筋网等构成组合支护结构,灵活性很大,在围岩开挖后的主要支护结构中起着相当大的作用,因此,对喷射混凝土施工技术的研究,确保喷射混凝土的质量有着重要的意义。本文结合秦岭某新建隧洞工程实践,分析了隧道喷射混凝土施工中的施工技术及关键问题。     

聚乙烯醇短切纤维喷射混凝土的研究应用

喷射混凝土具有凝结时间短、黏结强度高、支护效果好等优点,但目前喷射混凝土施工过程中普遍存在回弹率过大、喷射质量不达标等不足。以重庆红岩村隧道项目初支喷射混凝土为工程背景,采用现场试验和数值模拟方法研究了聚乙烯醇短切纤维喷射混凝土中纤维的最优掺量,以及对喷射混凝土回弹率和隧道洞室的稳定性、围岩变形等方面的影响。研究结果表明:一定量的聚乙烯醇短切纤维会降低隧道喷射混凝土的回弹率,其最优掺量为0. 132%;相比于普通喷射混凝土,采用聚乙烯醇短切纤维喷射混凝土可使隧道洞室失稳时的竖向位移和水平位移减小,最大减小幅度分别可达2. 0%和4. 3%;喷射混凝土层最大应力较普通混凝土可增大14. 3%。     

锚喷技术在深基坑支护中的应用

简述了锚喷支护技术的工作机理与设计方法,通过一工程实例介绍了该项技术在基坑工程中的应用,最后对锚喷支护的设计与施工提出了几点建议。     

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.     

Adhesion strength and shrinkage of shotcrete

Shotcrete is widely used as rock support in mines and in civil engineering projects. In many cases the adhesion between the shotcrete and the rock is one of the most important properties.The objective of this study was to: (i) identify typical failures of shotcrete in a mining environment, (ii) measure the growth of the adhesion strength of shotcrete with respect to age, (iii) investigate the influence of surface treatment (scaling and cleaning) on the adhesion strength of shotcrete and (iv) investigate the occurrence of shrinkage cracks in the shotcrete and failures in the interface between the shotcrete and the rock.The failure mapping showed that most of the observed failures of shotcrete are in areas with a thin shotcrete layer (<20 mm) together with a low adhesion strength. Furthermore, the measured average thickness of shotcrete (40 mm) was almost the same as the ordered thickness, the problem is the wide scatter. In 18% of the thickness measurements, the shotcrete thickness was less than or equal to 20 mm. If the shotcrete lining in the mine has the same thickness distribution as during the tests, the supporting ability of as much as 18% of the shotcrete lining can be considered as more or less negligible.No differences in free shrinkage were observed between plain and steel fibre reinforced shotcrete. Relatively large areas with lack of contact between shotcrete and wall were observed in the shrinkage tests. This indicates that restrained shrinkage can destroy the bond between the shotcrete and rock. The results from the restrained shrinkage tests show the importance of the bond at the interface. If bond failure occurs, the ability to distribute and control the crack width ceases.The growth of the adhesion strength on a sandblasted concrete wall and the growth of the compressive strength showed a correlation. However, the scatter in the results indicates that further investigations have to be done in order to establish a reliable relation between the growth in adhesion and compressive strength with age. The results from the field tests showed that the adhesion strength was significantly higher on rock surfaces that had been water jet-scaled (with 22 MPa water pressure) than those treated by mechanical scaling followed by cleaning of the rock surface (water pressure 0.7 MPa).     

Interaction of shotcrete with rock and rock bolts—A numerical study

The shotcrete–rock interaction is very complex and is influenced by a number of factors. The influence of the following factors was investigated by a series of numerical analyses: the surface roughness of the opening, the rock strength and Young's modulus, the discontinuities, the extent and properties of the excavated disturbed zone, the mechanical properties of the interface between shotcrete and rock, and the thickness of the shotcrete lining and the rock bolts. The study was carried out as a sensitivity analysis. The results showed that the rock strength and the surface roughness had significant impact on the number of failures at the rock–shotcrete interface and in the shotcrete lining. Furthermore, the behaviour of the lining is sensitive to small amplitudes of the surface roughness. In all the cases investigated, a high interface strength was favourable. The results indicate that if a thick shotcrete lining is dependent on the bond strength. The benefit of using a thicker lining can be doubtful. The analyses showed that for an uneven surface the extent of the EDZ had a minor effect on the behaviour of the shotcrete lining. Furthermore, if rock bolts were installed at the apex of the protrusion instead of at the depression, the number of failures decreased both at the interface and in the lining.     

Fully Automated Shotcrete Robot for Rock Support

Optimized shotcrete application techniques are required in particular tunneling projects. Today, any spraying can be done by hand or by manipulator. With the development in the material technologies, the range of possible operation was enlarged. With automation of the application, an important contribution to improve performance and quality and to reduce rebound may be achieved. At the Swiss Federal Institute of Technology, Zurich, systematic research is done to develop the fully automated process control, focusing on the wet shotcrete method. With the development of the fully automated shotcrete robot, the user will have a very effective tool at his or her disposal to spray concrete shells (fully automated). With the new robot, the user may choose from three different modes: manual, semiautomated, and fully automated spraying. Especially the fully automated mode facilitates higher performance with less danger to the worker's health. Quality control is inherent in the application process in regard to layer thickness, compaction, and homogeneity.     

弯曲应力作用下喷射混凝土氯离子扩散研究

采用弹簧四点弯曲加载法,对弯曲应力作用下喷射混凝土受拉区和受压区氯离子扩散性能进行了研究。以Fick第二定律为基准,对氯离子含量分布进行了拟合,分析弯曲应力作用下喷射混凝土氯离子扩散系数的变化规律。通过对比分析同配合比模筑混凝土、喷射混凝土和钢纤维喷射混凝土中氯离子含量分布规律,研究钢纤维和混凝土的成型方式对氯离子扩散性能的影响。结果表明：弯曲应力对喷射混凝土氯离子扩散影响大。应力改变喷射混凝土孔结构分布和微裂缝的数量及深度,对氯离子扩散速率产生影响。受拉区侧,氯离子含量随弯曲应力比增大而增大;受压区侧,氯离子含量随弯曲应力比增大而减小。氯离子扩散系数变化规律与氯离子含量变化规律相同。同应力比时,喷射混凝土氯离子扩散系数最大,钢纤维喷射混凝土和模筑混凝土氯离子扩散系数关系与受力方式、应力比大小、钢纤维和成型方式等有关。     

不良地质条件下隧道施工技术

结合具体工程实例,介绍了不良地质条件下隧道施工技术,重点对超前小导管施工和锚喷初期支护进行了阐述,总结了工程施工经验,以保证隧道工程质量和隧道施工的顺利进行。     

冻融损伤喷射混凝土本构关系及微观结构

采用棱柱体试件,通过快速冻融试验方法,对冻融损伤后同配合比普通混凝土、喷射混凝土及钢纤维喷射混凝土单轴受压应力应变全曲线进行研究。对应力应变关系中相关参数进行回归分析,得出冻融循环后试件应力应变全曲线方程。结果表明:随着冻融循环次数增加,受压应力应变曲线趋于扁平;峰值应力降低,峰值应变增大,分别与冻融循环次数呈线性和指数变化。与普通混凝土相比,喷射混凝土峰值应力下降速率小,而钢纤维喷射混凝土的下降速率进一步减小。而后,采用扫描电子显微镜及压汞法,对损伤后试件微观结构和孔结构进行观察分析,发现随着冻融循环次数增加,在渗透压和冻胀压力综合作用下,试件内部微裂纹及气孔增多,孔径增大,试件密实度显著降低;而钢纤维喷射混凝土中仅出现少量连通毛细孔,这与宏观力学性能变化呈现一致性。     

Roughness evaluation in shotcrete-lined water tunnels with invert concrete based on cases from Nepal

Most of the existing roughness estimation methods for water tunnels are related to either unlined or concrete/steel-lined tunnels. With the improvement in shotcrete technology, advancement in tunneling equipment and cost and time effectiveness, future water tunnels built for hydropower projects will consist of rock support with the extensive use of shotcrete lining in combination with systematic bolting and concrete lining in the tunnel invert. However, very little research has been performed to find out tunnel surface roughness for shotcrete-lined tunnels with invert concrete, which is important in calculating overall head loss along the waterway system to achieve an optimum and economic hydropower plant design. Hence, the main aim of this article is to review prevailing methods available to calculate tunnel wall roughness, and to use existing methods of head loss calculation to back-calculate roughness of the shotcrete-lined tunnels with invert concrete by exploiting measured head loss and actual cross-sectional profiles of two headrace tunnels from Nepal. Furthermore, the article aims to establish a link between the Manning coefficient and the physical roughness of the shotcrete-lined tunnel with invert concrete and to establish a link between over-break thickness and physical roughness. Attempts are also made to find a correlation between over-break thickness and rock mass quality described by Q-system and discussions are conducted on the potential cost savings that can be made if concrete lining is replaced by shotcrete lining with invert concrete.