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.     

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。     

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.     

实验室喷射混凝土强度计算研究

本文通过采用实验室试验的方法研究喷射混凝土的强度,通过大量试验的基础上,对试验数据进行线性回归分析,分析研究喷射混凝土芯样的点荷载仪读数值与喷射混凝土抗压强度值的相关关系,得出实验室喷射混凝土强度计算公式。为评定喷射混凝土施工质量提供了一种直观、可靠和方便的方法。     

考虑混凝土早期性能的隧道施工进度确定方法

本文建立了按喷射混凝土早期性能确定隧道合理施工进度的研究方法,依托高原铁路通麦隧道,研究了微台阶开挖的V级围岩大断面隧道中不同施工进度安排的合理性,施工进度为2.5 m/d时初期支护不安全;施工进度为0.5 m/d时,初期支护安全但进度太慢会影响工期;施工进度为1.0 m/d时,需要通过适当提高喷射混凝土8 h龄期的抗压强度,或适当增加上台阶的喷射混凝土厚度,以及在上下台阶的分界处采取局部加强措施,在此前提下通麦隧道微台阶开挖在V级围岩段施工进度定为1.0 m/d是可行的。研究还发现:在V级围岩中,控制施工进度的是8 h龄期的喷射混凝土抗压强度,因此,只要通过调整混凝土配比以增加其8 h龄期早期性能,就可以加快施工进度。     

混凝土抗侵蚀抑制剂在高温条件下对喷射混凝土性能的影响

研究了不同材料在高温下对喷射混凝土保水性能和力学性能的影响.试验结果表明:在相同掺量条件下,掺入羟丙基甲基纤维素醚、抗侵蚀抑制剂以及纳米二氧化硅后混凝土的保水率相对于空白组分别增加了5.8％、10.5％和15.8％.使用抗侵蚀抑制剂后,混凝土热养护下抗压强度为32.4 MPa,相对于基准组增加了19.9％,同时对混凝土...     

地下工程中喷层支护机理研究进展

喷射混凝土在岩土和采矿工程中的隧道、巷道及洞室支护中已经有很长时间的应用,它一般与锚杆一起使用,作为主动支护技术取得了突出的支护效果。对于喷层,其支护机理在不同的地质和工作条件下不尽相同,传统的支护理论将喷层作为一种受力承载结构,并强调喷层厚度的重要性。随着科技的进步,新型喷涂材料的出现,一些潜藏的支护作用逐渐凸显出来,例如喷层与岩面的粘结强度,渗入裂隙部分等。本文在总结喷层传统支护机理的基础上,结合新喷层材料的特殊性能,将其支护机理重新归纳总结为承载壳作用,胶结作用,及楔子作用。根据喷层材料及支护作用的不同,对喷层材料的性能测定要求也不一样。     

隧道围岩喷护速凝增强效应试验研究及工程应用

 在隧道工程施工中,喷射混凝土作为一种必要的初期支护手段,对隧道围岩稳定性控制起着重要的作用,而速凝剂的品质及掺量又直接影响着喷射混凝土的强度与施工环境。基于铝酸盐速凝剂促凝机制,研制出一种高性能低掺量液态速凝剂。该液态速凝剂苛性比小于1.2,pH值为9～11,含固量为65%,溶液稳定不析出。通过XRD和SEM图谱分析及相关性能试验,该液态速凝剂能有效提高水泥水化程度,短时间内形成大量硅酸钙凝胶,相互搭接形成晶体结构,减少凝结时间;其适宜掺量为水泥质量的1.5%～3%,喷射混凝土后期强度损失在10%以内。在现场应用中,研制出一种高精度小流量液态速凝剂定量添加装置,确保精确控制液态速凝剂掺量;并完善相应的配套喷射工艺,有效提高喷射混凝土强度,降低施工中粉尘和回弹,具有良好的推广和应用价值。     

钢纤维对喷射混凝土方板早龄期弯曲性能的影响

为了研究隧道支护层钢纤维喷射混凝土在早龄期的力学性能,参照欧洲喷射混凝土标准(EFNARC),对不同掺量的钢纤维喷射混凝土方板进行试验研究,并与传统钢筋挂网喷射混凝土方板进行了对比.通过对10,30,48h龄期钢纤维喷射混凝土方板的荷载-位移曲线及能量吸收能力的比较,分析了不同钢纤维掺量喷射混凝土方板与钢筋挂网喷射混凝土方板的弯曲性能.结果表明:钢纤维可以显著提高早龄期混凝土的抗冲切能力;当钢纤维掺量超过20kg/m~3时,钢纤维喷射混凝土方板由脆性冲切破坏变为弯曲破坏.     

改性脱硫石膏基混凝土力学性能研究

将工业副产石膏,经过改性处理,用改性脱硫石膏做为水泥的替代物。通过试验得出改性脱硫石膏基混凝土的抗压、抗折强度,并与普通混凝土进行对比。从而可知改性脱硫石膏基混凝土具有很高的承载力,用改性脱硫石膏基复合材料部分替代传统的水泥基喷射混凝土应用于矿区的岩巷喷层支护结构中是可行的。     

新型玻璃纤维增强塑料砂浆锚杆的黏结性能试验研究

锚杆广泛应用于隧道、边坡、地下硐室开挖及支护工程中。通过锚杆的支护加固，岩土体的强度和稳定性能够得到显著的改善和提高。传统的钢锚杆在不良地质条件下存在锈蚀严重的缺点，给支护结构的安全性和耐久性带来严重威胁。玻璃纤维增强塑料具有轻质、高强、耐腐蚀等优良特性，是代替钢筋制作锚杆的理想材料之一。在经典拉伸试验模型的基础上，结合锚杆本身的受力特性，建立一种改进的拉伸试验模型，并且根据此试验模型，对直径分别为10，13，16mm的表面经过喷砂和缠绕纤维束处理的玻璃纤维增强塑料锚杆，以及直径为25mm的螺纹钢进行拉伸试验，试样的总数量为24组。试验采用强度等级为C60的混凝土模拟岩体，并采用强度等级分别为41．5，55．5MPa的砂浆作为锚固剂。在试验结果基础上，对玻璃纤维增强塑料锚杆的拉拔破坏模式、临界黏结长度、拉拔承载力、平均黏结强度以及与钢锚杆拉拔性能的比较进行研究讨论，对砂浆锚固玻璃纤维增强塑料锚杆的黏结性能进行系统全面的分析评价，为推广玻璃纤维增强塑料锚杆的工程应用、相关规范的制定，以及进一步研究工作提供一定数据储备和理论支持。     

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.     

砖墙结构加固喷射C30细石混凝土强度配制与配合比设计

参照普通混凝土配合比设计的方法,选择适宜的保证率与之对应的概率度系确定试配强度,推求水灰比,使其水灰比在喷射混凝土规范规定的水灰比的范围之内,进行配合比设计,求出每立方米混凝土的水泥用量,再通过试喷找出适宜的配合比用水量,反算水灰比与之符合,确定喷射混凝土的最佳水灰比,进行合理的配合比设计.再直接用调整后的水灰比和适宜...     

砂浆与岩石黏结性能的试验研究

砂浆与岩石的黏结性能,对岩土工程中的山体支护效果、结构工程中抗浮锚杆的极限抗拔力及混凝土材料基本力学性能起着至关重要的作用。通过灌注于岩石块体内的砂浆圆柱体压出试验得到了砂浆与岩石界面的黏结滑移本构关系,进而研究了砂浆等级、砂浆柱体直径及黏结长度对界面的黏结强度和残余摩擦应力的影响。结果表明:砂浆与岩石界面的黏结滑移曲线由弹性上升段、软化下降段和水平摩擦段3部分组成。而且界面的黏结强度与残余摩擦应力随砂浆等级的提高而增大。但对相同等级的砂浆而言,界面黏结强度与残余摩擦应力随砂浆柱体直径的增大而减小。此外,界面的平均黏结应力随黏结长度的增加而减小。     

早龄期普通混凝土直剪性能及损伤耗能分析

为了研究早龄期普通混凝土直剪作用下的力学性能,完成了12个普通混凝土试件的直剪试验,获取了试件的破坏形态及直剪荷载-位移全过程曲线,分析了直剪作用下龄期对普通混凝土直剪强度、峰值变形、变形模量、损伤演变、能量耗散等力学特征参数的影响规律.结果表明:龄期越长,受剪荷载-变形曲线上升段越陡峭;当龄期≤3d时,混凝土断面剪切...     

超声回弹综合法在隧道衬砌强度检测中的应用

在分析了超声回弹综合法测试公路隧道衬砌强度的局限性后,文章提出了应按围岩等级划分隧道衬砌类别,对不同类别的衬砌分别进行强度推定的原则.并提出了应对衬砌声速进行应力修正、考虑龄期和养护环境等因素的新的超声回弹综合测强公式,按该公式推定的抗压强度与芯样试验结果吻合较好.     

地下油库锚喷支护拱顶圆筒罐室的设计与计算

随着地下工程锚喷支护的广泛应用,以及当前地下支护结构计算方法的提升,考虑到油罐罐室岩质条件好、拱顶圆筒结构受力好,为此提出采用拱顶圆筒锚喷支护结构形式取代当前钢筋混凝土结构,可有效提高工程的安全性、经济性和施工简便性。考虑到拱顶圆筒结构主要承受剪切应力与环向拉应力,为此对抗剪强度与抗拉强度同时进行了折减,并提出了剪切破坏和拉破坏两种安全系数。应用有限元强度折减法除计算剪切破坏安全系数外,还提出了计算拉破坏安全系数的方法。计算得到Ⅱ级围岩稳定安全系数远高于设计要求,Ⅲ级围岩也满足设计要求。在这一基础上提出了实用的锚喷支护结构形式与设计参数。研究表明,锚喷支护拱顶圆筒罐室结构是一种很有前景的结构形式,建议在工程上进一步试验与推广。     

采用微波加热养护法的混凝土强度早期预测

采用微波加热的方法对混凝土试件进行养护,促进混凝土的凝结硬化在短时间内即可形成一定的强度,并建立了以此方式测定的混凝土早期强度与标准养护条件下混凝土后期强度的关系,实现了在混凝土浇筑后6 h内测定混凝土强度,为混凝土强度的快速测量提供了一种有效手段。     

高温后喷水冷却圆钢管再生混凝土界面黏结性能试验研究

为了研究高温喷水冷却后圆钢管再生混凝土的界面黏结性能变化规律,以历经最高恒温温度、再生粗骨料取代率、界面锚固长度为3个变化参数,进行了27个高温喷水冷却后圆钢管再生混凝土试件和2个自然冷却试件（对照组）的静力推出试验,以位移控制的加载方式为主,使自由端的钢管单独受力（核心混凝土不受力）,圆钢管内的混凝土从下向上推出。通过试验观察了圆钢管再生混凝土试件破坏的全过程和形态,获取了加载端和自由端的荷载-滑移曲线,分析了各个变化参数对黏结性能的影响规律。试验结果表明：经过高温喷水冷却后,圆钢管再生混凝土试件加载端和自由端的荷载-滑移曲线形态相似,且和自然冷却试件的曲线相似,同时也和前期做的钢管普通混凝土的曲线具有相似性;加载端和自由端的荷载-滑移曲线大致分为上升段、缓慢下降段和平缓段;并且自由端的初始滑移晚于加载端。定义了极限黏结强度τu和残余黏结强度τr。圆钢管再生混凝土试件表面上应变沿试件高度方向大致呈指数分布。经历消防喷水冷却后,随历经最高温度的升高,黏结强度先增大后减小,在400 ℃时,黏结强度达到最大值,当大于400 ℃时,黏结强度降低。历经高温后试件的平均残余黏结强度分别是常温下试件的1.25倍、1.75倍、1.38倍和1.50倍。再生粗骨料取代率的变化对黏结强度的影响不明显,常温下γ=50%时,黏结强度达到最大值;温度为200 ℃且γ=75%时,黏结强度也为最大。这和自然冷却下钢管再生混凝土的结论类似。锚固长度的增大也使圆钢管再生混凝土试件平均极限黏结强度和残余黏结强度均有不同程度增大。提出了高温喷水冷却后圆钢管再生混凝土极限黏结强度和残余黏结强度的计算公式,用此公式所得计算结果均比较理想。今后对界面黏结性能的研究,可以从增加钢管内壁的粗糙度、钢管内部加入加劲肋和钢管内增设不同长度的螺栓角度进行探讨,进而进一步丰富界面黏结性能的理论研究,以期为消防喷水后建筑结构构件的其他力学性能提供理论基础,同时为现实生活中火灾后钢-混凝土组合结构的灾后评估和加固提供参考。