斜溝煤礦5.0 Mta新井設(shè)計(jì)含5張CAD圖,斜溝煤礦5.0,Mta新井設(shè)計(jì)含5張CAD圖,煤礦,5.0,Mta,設(shè)計(jì),CAD Effect of grout properties on the pull-out load capacity of fully grouted rock bolt A. K?l?c, E. Yasar*, A.G. Celik Abstract This paper represents the result of a project conducted with developing a safe, practical and economical support system for engineering workings. In rock engineering, untensioned, fully cement-grouted rock bolts have been used for many years. However, there is only limited information about the action and the pull-out load capacity of rock bolts, and the relationship between bolt–grout or grout–rock and the influence of the grout properties on the pull-out load capacity of a rock bolt. The effect of grout properties on the ultimate bolt load capacity in a pull-out test has been investigated in order to evaluate the support effect of rock bolts. Approximately 80 laboratory rock bolt pull-out tests in basalt blocks have been carried out in order to explain and develop the relations between the grouting materials and untensioned, fully grouted rock bolts. The effects of the mechanical properties of grouting materials on the pull-out load capacity of a fully grouted bolt have been qualified and a number of empirical formulae have been developed for the calculating of the pull-out load capacity of the fully cement-grouted bolts on the basis of the shear strength, the uniaxial compressive strength of the grouting material, the bolt length, the bolt diameter, the bonding area and the curing time of the grouting material. Keywords: Rock bolt; Grouting materials; Bolt pull-out load capacity; Bolt geometry; Mortar 1. Introduction In rock engineering, rock bolts have been used to stabilise openings for many years. The rock bolting system may improve the competence of disturbed rock masses by preventing joint movements, forcing the rock mass to support itself (Kaiser et al., 1992). The support effect of rock bolt has been discussed by many researchers(e.g. Hyett et al., 1992; Ito et al., 2001; Reichert et al., 1991 and Stillborg, 1984). Rock bolt binds together a laminated, discontinued, fractured and jointed rock mass. Rock bolting not only strengthens or stabilizes a jointed rock mass, but also has a marked effect on the rock mass stiffness (Chappell, 1989). Rock bolts perform their task by one or a combination of several mechanisms. Bolts often act to increase the stress and the frictional strength across joints, encouraging loose blocks or thinly stratified beds to bind together and act as a composite beam (Franklin and Dusseault, 1989). Rock bolts reinforce rock through a friction effect, through a suspension effect, or a combination of two. For this reason, rock bolt technique is acceptable for strengthening of mine roadway and tunnelling in all type of rock ( Panek and McCormick, 1973). Generally rock bolts can be used to increase the support of low forces due to the diameter and the strength of the bolt materials. They enable high anchoring velocity to be used at closer spacing between bolts.Their design provides either mechanical clamping or cement grouting against the rock (Aldorfand Exner,1986). Anchorage system of rock bolt is normally made of solid or tube formed steel installed untensioned or tensioned in the rock mass (Stillborg, 1986). Rock bolts can be divided into three main groups according to their anchorage systems (Franklin and Dusseault, 1989;Aldorfand Exner, 1986; Hoek and Wood, 1989; Cybulski and Mazzoni, 1989). First group is the mechanically anchored rock bolts that can be divided into two groups: slit and wedge type rock bolt, expansion shell anchor. They can be fixed in the anchoring part either by a wedge-shaped clamping part or by a threaded clamping part. Second group is the friction-anchored rock bolts that can be simply divided into two groups: split-set and swellex. Friction-anchored rock bolts stabilise the rock mass by friction of the outer covering of bolt against the drill hole side. The last group is the fully grouted rock bolts that can also be divided into two groups: cement-grouted rock bolts, resin grouted rock bolts. A grouted rock bolt (dowel) is a fully grouted rock bolt without mechanical anchor, usually consisting of a ribbed reinforcing bar, installed in a drill hole and bonded to the rock over its full length (Franklin and Dusseault, 1989). Special attention should be paid to cement-grouted bolts and bolts bonded (glued, resined) by synthetics resins for bolt adjustment. Grouted bolts fix the using of the coherence of the sealing cement with the bolt rod and the rock for fastening the bolts. Synthetic resin (resined bolt) and cement mortar (reinforced-concrete bolt) can be used for this type rock bolt. These bolts may be anchored in all type of rock. Anchoring rods may be manufactured of several materials such as ribbed steel rods, smooth steel bars, cable bolts and other special finish (Aldorfand Exner, 1986). Grouted bolts are widely used in mining for the stabilisation of tunnelling, mining roadway, drifts and shafts for the reinforcing of its peripheries. Simplicity of installation, versatility and relatively low cost of rebars are further benefits of grouted bolts is comparison to their alternative counterparts (Indraratna and Kaiser,1990). Bolts are self-tensioning when the rock starts to move and dilate. They should therefore be installed as soon as possible after excavation, before the rock has started to deform, and before it has lost its interlocking and shear strength. Although several grout types are available, in many applications where the rock has a measure of short term stability, simple Portland cement-grouted reinforcing dowels are sufficient. They can be installed by filling the drill hole with lean, quickly set mortar into which the bar is driven. The dowel is retained in up holes either by a cheap form of end anchor, or by packing the drill hole collar with cotton waste, steel wool, or wooden wedges (Franklin and Dusseault, 1989). Concrete grouted bolts use cement mortar as a bonding medium. In drill holes at minimum of15 8 below the horizontal plane, the mortar can simply poured in, whereas in raising drill holes various design of bolts or other equipment is used to prevent the pumped mortar from flowing out (Aldorfand Exner,1986). The load bearing capacity off ully cement-grouted rock bolts depends on the bolt shape, the bolt diameter, the bolt length, rock and grout strength. The bond strength off ully cement-grouted rock bolts is primarily frictional and depends on the shear strength at the bolt–grout or grout–rock interface. Thus any changes in this interfaces shear strength must affect the bolt bond strength and bolt load capacity. This laboratory testing program was executed to evaluate the shear strength effect on the bond strength of the bolt–grout interface of a threaded bar and the laboratory test results confirm the theory. 2. Previous solutions The effectiveness of a grouted bolt depends on its length relative to the extent of the zone of overstressed rock or yield zone. The shear and axial stress distributions of a grouted bolt are also related to the bolt length because equilibrium must be achieved between the bolt and the surrounding ground (Indraratna and Kaiser,1990). Bearing capacities of cement-grouted rock bolts (Pb) and their anchoring forces are a function of the cohesion of the bonding agent and surrounding rock, and the bolting bar. The ultimate bearing capacity of the bolt (Pm) is expressed as follows (Aldorf and Exner, 1986): (1) where kb, safety coefficient (usually kb =1.5); C1, cohesion of the bonding material on bolting bar, ld, anchored length of the bolt, ds, bolt diameter. (2) where dv, drill hole diameter；C2,cohesion of the bonding material with surrounding rock(carboniferousrocks and polyester resins C2 =3 MPa). (3) where C3, shearing strength of the bonding material. The maximum (ultimate) bearing capacity of the bolt (Pm ) will be the lowest value from P1to P111. Bearing capacities of all type bolts must also be evaluated from the view point of the tensile strength of the bolt material (Pms), which must not be lower than the ultimate bearing capacity resulting from the anchoring forces of bolts in drill holes (Pm). It holds that (4) where Pms, the ultimate bearing capacity of the bolt with respect of the tensile strength of the bolt material;Pm, the ultimate bearing capacity of the bolt. 3. Laboratory study 3.1. Experiments The pull-out tests were conducted on rebars, grouted into basalt blocks with cement mortar in laboratory. The relations between bolt diameter (db) and pull-out load of bolt (Pb) (Fig. 2), bolt area (Ab) and pull-out load of bolt (Pb) (Fig. 3), bolt length (Lb) and pull-out load of bolt (Pb) (Fig. 5), water to cement ratio (w/c) and bolt bond strength (τb) (Fig. 7), mechanical properties of grout material and bolt bond strength (τb) (Fig. 9,Figs. 10 and 11), and curing time (days) and bolt strength (Figs. 12 and 13) were evaluated by simple pull-out test programme. The samples consisted of rebars (ranging 10–18 mm diameters two by two) bonded into the basalt blocks. These basalt blocks used have a Young’s modulus of 27.6 GPa and a uniaxial compressive strength (UCSg) of 133 MPa. Drilling holes which were 10 mm larger than the bolt diameter, having a diameter of 20 –28 mm for installation of bolts, were drilled up to 15–32 cm in depth. The bolt was grouted with cement mortar. The grout was a mixture of Portland cement with a water to cement ratio of 0.34, 0.36, 0.38 and 0.40 cured for 28 days. In order to obtain different grout types that have different mechanical properties, siliceous sand <100μm; 500 μm> and fly ash <10μm; 200μm> were added in a proportion of 10% of cement weight and white cement with a water to cement ratio of 0.40. The sand should be well graded, with a maximum grain size of v2 mm (Schack et al., 1979). The Young’s modulus of the grouts was measured during unconfined compression tests and shear strength was calculated by means of ring shear tests. The test set-up is illustrated schematically in Fig. 1 and the procedure is explained below: 1. After filling prepared grout mortar into the hole, bolt is inserted to the centre of drilling hole. 2. After curing time, the rebars in the rock were axially loaded and the load was gradually increased until the bolt failed. 3. The bond strength (τb) was then calculated by dividing the load (Pb) by surface area (Ab) of the bolt bar in contact with the grout. 4. Pull-out tests were repeated for various grout types, bolt dimensions and curing times. The influence of the bolt diameter and the bond area on the bond strength of a rock bolt can be formulated as follows (Littlejohn and Bruce, 1975): (5) where τb, ultimate bolt bond strength (MPa); Pb, maximum pull-out load of bolt (kN); db, bolt diameter (mm); lb , bolt length (cm); πdblb , bonded area (cm2). 3.2. Analysis of laboratory test results 3.2.1. Infl uence of the bolt material Bolt diameters of 10, 12, 14, 16 and 18 mm were used in pull-out tests. Typical results are represented in Table 1, Figs. 2 and 3. The most important observations were: (1)The maximum pull-out load (Pb) increases linearly with the section of the bolt while embedment length was constant. (2) Bolt section depends upon bolt diameter. The relation between bolt diameter and bolt bearing capacity can be explained as follow empiric formulae (Fig. 2). (6) (3) The values of bolt bond strength were calculated between 5.68 and 5.96 MPa (Table 1). Bolt lengths of 15.0, 24.7, 27.0, 30.0 and 32.0 cm were used in pull-out tests as seen in Fig. 4. Typical results are represented in Table 2, and Figs. 5 and 6.The most important observations were: (1) The pull-out force of a bolt increases linearly with the embedded length of the bolt. (7) (2) Maximum pull-out strength of a bolt is limited to the ultimate strength of the bolt shank. 3.2.2. Influence of grouting material The water to cement ratio should be no greater than 0.40 by weight; too much water greatly reduces the long-term strength. Because, part of the mixing water is consumed by the hydration of cement used. Rest of the mixing water evaporates and then capillary porosities exist which results in unhomogenities internal structure of mortar. Thus, this structure reduces the long-term strength by irregular stress distribution (Neville, 1963;Atis, 1997). To obtain a plastic grout, bentonit clay can be added in a proportion of up to 2% of the cement weight. Other additives can accelerate the setting-time, improve the grout fluidity allowing injection at lower water to cement ratios, and make the grout expand and pressurize the drill hole. Additives, if used at all, should be used with caution and in the correct quantities to avoid harmful side effect such as weakening and corrosion (Franklin and Dusseault, 1989). The water to cement ratio (w/c) in grouting materials considerably affects pull-out strength of bolt. As seen in Table 3, UCSg and shear strength (tg) of grout in high w/c ratio show lower values whereas in low w/c ratio higher values. The ratio between 0.34 and 0.40 presents quite good results. Although the w/c ratio of 0.34 gives the best bond strength, groutibility (pumpability) decreases and a number of difficulties in application appear. In high w/c ratio, the pumpability of grouting materials into the drilling hole is easy but the bond strength of bolt decreases (Figs. 7 and 8). The bond strength off ully cement-grouted rock bolts is primarily frictional and depends on the shear strength at the bolt–grout or grout–rock interface. Thus any change in this shear strength of interfaces affects the bolt bond strength and load capacity. The influences of mechanical properties of grouting materials on the bearing capacity of bolt can be described as follows: (1) The uniaxial compressive and shear strength of the grouting materials has an important role on the behaviour of rock bolts. It was observed that increasing shear strength of the grouting material logarithmically increases bolt bond strength as shown in Table 4 and Fig. 9. The relation between grout shear strength and bolt bond strength was formulated as follows: (8) (2) Table 4 and Fig. 10 show that increasing grout compressive strength considerable increases the bond strength of the grouted bolts. (9) (3) In Fig. 11 and Table 4 show that there is another relationship between Young’s modulus of grout and bolt bond strength. Increasing the Young’s modulus increases bolt bond strength. (10) 3.2.3. Influence of the curing time An important problem in the application of cementgrouted bolts is the setting time of the mortar, which strongly affects the stabilizing ability of bolt. Cementgrouted dowels cannot be used for immediate support because of the time needed for the cement to set and harden (Franklin and Dusseault, 1989). In the pull-out tests, eight group ofbolts having same length and mortar with a water to cement ratio of0.4 were used for determining the effects of curing time on the bolt bond strength. Each group ofr ock bolt testing was performed after different setting times (Table 5). As can be seen in Figs. 12 and 13, the strength of bolt bond increases rapidly in 7 days due to curing time. However, the bond strength of bolt continues to increase rather slowly after 7 days. Rock bolts may lose their supporting ability because of yielding of bolt material, failure at the bolt–grout or grout–rock interface, and unravelling of rock between bolts. However, laboratory tests and field observations suggest that the most dominant failure mode is shear at the bolt–grout interface (Hoek and Wood, 1989). So, this laboratory study focussed on the interface between rock bolt and rock and the mechanical properties of grouting materials. 4. Conclusions The laboratory investigation showed that the bolt capacity depends basically on the mechanical properties of grouting materials which can be changed by water to cement ratio, mixing time, additives, and curing time. Increasing the bolt diameter and length increases the bolt bearing capacity. However, this increase is limited to the ultimate tensile strength of the bolt materials. Mechanical properties of grouting materials have an important role on the bolt bearing capacity. It is offered that the optimum water to cement ratio must be 0.34~0.4 and the mortar have to be well mixed before poured into drill hole. Improving the mechanical properties of the grouting material increases the bolt bearing capacity logarithmically. The best relationship was observed between grout shear strength and bolt bond strength. Increasing the curing time increases the bolt bond strength. Bolt bond strength of 19 kg/cm2 in first day,77 kg/cm2in 7 days and 86 kg/cm2in 35 days was determined respectively. The results show that bolt bond strength increases quickly in first 7 days and then the increase goes up slowly. Bond failure in the pull-out test occurred between the bolt and cement grout, of which the mechanical behaviour is observed by shear spring. This explains the development of bolt bond strength and the failure at the bolt–grout interface considering that the bond strength is created as a result of shear strength between bolt and grout. This means that any change at the grout strength causes to the changing of bolt capacity. The failure mechanism in a pull-out test was studied in order to clarify the bond effect of rock bolt. Thus one main bond effect was explained from bond strength of rock bolts. 中文翻譯 水泥漿性能對(duì)充分注漿錨桿拉拔承載力的影響 A. K?l?c, E. Yasar*, A.G. Celik 摘要：本文代表了一項(xiàng)在安全、實(shí)用、經(jīng)濟(jì)的支持系統(tǒng)指導(dǎo)下的工程結(jié)果。在巖石工程中，沒有被拉緊的且被水泥充分注漿的錨桿已使用多年。然而，對(duì)錨桿的作用過程和其拉拔載荷的能力，以及錨桿注漿或注漿的關(guān)系，水泥性能對(duì)充分注漿錨桿拉拔承載力的影響研究卻很少。為了評(píng)估錨桿支護(hù)效果，我們開始對(duì)水泥性能對(duì)最終錨桿在拉拔試驗(yàn)載荷能力的影響進(jìn)行了研究。大約80個(gè)針對(duì)玄武巖塊的錨桿拉拔試驗(yàn)實(shí)驗(yàn)室已開始進(jìn)行研究以用來解釋和發(fā)展注漿材料和松弛的充分注漿錨桿之間的聯(lián)系。這種注漿材料的力學(xué)性能對(duì)一個(gè)完全錨桿拉拔承載力的力學(xué)性能的影響已被數(shù)量化，而且，為了計(jì)算充分注漿錨桿的承載能力，在考慮剪切強(qiáng)度，注漿材料的單軸抗壓強(qiáng)度，錨桿長度，錨桿直徑，粘結(jié)面積及注漿材料固化時(shí)間的基礎(chǔ)上，一些經(jīng)驗(yàn)公式已被提出和不斷的發(fā)展。 關(guān)鍵詞：錨桿；注漿材料；錨桿拉拔承載能力；錨桿幾何形狀；砂漿 1引言 在巖土工程中，錨桿已多年被用來穩(wěn)定開口。該錨桿支護(hù)系統(tǒng)可通過阻止接縫處移動(dòng)，迫使巖塊支持其本身來提高巖體抗擾動(dòng)能力(Kaiser et al., 1992)。對(duì)這樣的巖錨支護(hù)效果已被許多研究者討論過(e.g. Hyett et al., 1992; Ito et al., 2001; Reichert et al., 1991 and Stillborg, 1984)。巖錨和承受層壓的，不連續(xù)的，有裂隙和節(jié)理的巖體結(jié)合在一起。錨桿支護(hù)不僅加強(qiáng)或穩(wěn)定節(jié)理巖體，同時(shí)也對(duì)巖體剛度有著顯著的影響(Chappell, 1989)。錨桿的支護(hù)效果一個(gè)或幾個(gè)機(jī)制相結(jié)合來實(shí)現(xiàn)的。錨桿通常作為一個(gè)組合梁來增加應(yīng)力和節(jié)理處的摩擦強(qiáng)度，固定松散巖塊或分層巖床(Franklin and Dusseault, 1989)。錨桿加固巖石是通過巖石間的摩擦作用，懸吊形態(tài)，或摩擦作用和懸吊兩者兼有而實(shí)現(xiàn)的?；谶@個(gè)原因，錨桿技術(shù)在支護(hù)巷道方面的應(yīng)用可以適用所有巖石類型的(Panek and McCormick, 1973)。 一般來說錨桿可用于增加由于直徑低勢力的支持和錨桿材料的強(qiáng)度。它們使高速貼壁將在更緊密的錨桿間距使用。他們的設(shè)計(jì)可以用來機(jī)械夾緊或?qū)r石進(jìn)行水泥注漿(Aldorfand Exner,1986)。 錨桿錨固系統(tǒng)通常是指固體或管狀型鋼安裝在松散或堅(jiān)實(shí)巖體中(Stillborg，1986年)。按照其錨固系統(tǒng)，錨桿可分為三個(gè)主要類型(Franklin and Dusseault, 1989;Aldorfand Exner, 1986; Hoek and Wood, 1989; Cybulski and Mazzoni, 1989)。第一類是機(jī)械巖錨，它可以分為兩類：楔縫式錨桿，外殼膨脹錨桿。它們被安裝在錨桿上的一部分，具體是在楔形夾緊的錨桿螺紋部分或者是夾緊部分。第二類是摩擦巖錨，它可以簡單地分為兩類：分節(jié)錨桿和膨脹錨桿分為錨桿。摩擦錨桿錨固巖體是由外露錨桿和鉆孔的摩擦力完成的。最后一類是充分注漿錨桿，它也可分為兩小類：水泥注漿錨桿，樹脂錨桿。 注漿錨桿(樁)是一種無機(jī)械錨定，通常包括一個(gè)帶肋鋼筋，該鋼筋被安裝在一個(gè)鉆孔里面并和超過其全長的巖體結(jié)合(Franklin and Dusseault, 1989)。特別要注意的是水泥注漿錨桿和螺栓(膠合，樹脂)是根據(jù)合成樹脂錨桿適當(dāng)調(diào)整固定的。錨固螺栓要與連桿螺栓和水泥的密封粘結(jié)以及用來拴緊螺栓的巖體相適應(yīng)。合成樹脂(樹脂錨桿)和水泥砂漿(鋼筋混凝土錨桿)可以為這種類型的錨桿使用。這些錨定錨桿可以被固定在所有類型巖石中。錨定桿體可以用多種材料制造，如帶肋鋼筋，光面鋼筋，錨索和其他特殊處理的材料(Aldorfand Exner, 1986)。 注漿錨桿廣泛應(yīng)用于礦井中的掘進(jìn)，巷道，平巷和井筒的支護(hù)和加強(qiáng)其外圍的穩(wěn)定性。與其它替代品相比較，注漿錨桿安裝的簡單性，多功能性和相對(duì)低成本性則會(huì)取得更多的效益(Indraratna and Kaiser,1990)。 當(dāng)巖石開始移動(dòng)和擴(kuò)張時(shí)，錨桿會(huì)自動(dòng)拉緊。因此，在開鑿巷道后，巖體開始變形和已經(jīng)失去聯(lián)動(dòng)性和剪切強(qiáng)度之前要盡快安裝這些錨桿。 雖然只有幾種水泥漿類型可以適用，但是在現(xiàn)場許多應(yīng)用中這些類型水泥漿已經(jīng)足夠，例如在被測得有短暫穩(wěn)定期，用簡單的波特蘭水泥注漿加固銷釘措施的巖體中應(yīng)用。通過傾斜著向鉆孔里面快速注滿灰泥漿，它們可以被安裝在已經(jīng)拉緊的桿體中。保留的銷子最終以簡單的形式形成了錨孔，或用棉花包裝廢棄物，鋼絲絨，或木楔子(Franklin and Dusseault, 1989)。 混凝土錨桿是用水泥砂漿作為粘結(jié)介質(zhì)。在最低低于水平面158的鉆孔里面，砂漿很容易注入，然而在逐漸升高鉆洞中，各種錨桿或其他設(shè)