A Laboratory Study on use of Screw-Type Friction Bolts as New Soft Rock Stabilizers

GeoScience Enginee ing Vol. 70 (2024), No. 2 geoscience.cz pp. 40–50, ISSN 1802-5420 DOI 10.35180/gse-2024-0111 A LABORATORY STUDY ON USE OF SCREW-TYPE FRICTION BOLTS AS NEW SOFT ROCK STABILIZERS E en KOMURLU 1 1 Gi esun Uni e si y, Facul y o Enginee ing, Depa men o Ci il Enginee ing, Gi esun, Tu key E-mail: ekomu lu@gi esun.edu. , ABSTRACT In his s udy, load bea ing capaci ies o sc ew bol s as a new ic ion bol ype was in es iga ed ca ying ou a se ies o labo a o y s udies. New sc ew- ype ic ion bol s wi h sha p h eads we e inse ed in o holes d illed in a ious so ocks by applying o a ion. Sc ew bol s and spli se s inse ed in di e en so ock ypes we e in es iga ed o compa a i ely e alua e hei load bea ing capaci y alues. Acco ding o he esul s ob ained om his s udy, new sc ew bol s we e ound o supply be e load bea ing capaci y alues han hose o he spli se s. Al hough he spli se s a e qui e popula ic ion bol s used in ock enginee ing, hey ha e signi ican disad an ages esul ing om hei poo ancho age pe o mances in so ocks. By making g oo es on d ill hole con ac su aces, inc eased coe icien o ic ion and load bea ing capaci y alues can be supplied by new sc ew bol s which we e ound o be ad an ageous o using in so ocks. Keywo ds: F ic ion bol s; Openings in so ocks; Rein o cing so ocks; Rock bol s; Sc ew bol s. 1 INTRODUCTION Rock bol s which a e widely used o ein o ce mining and ci il enginee ing exca a ions can be classi ied in acco dance wi h di e en pa ame e s such as g ou usage (g ou ed o ic ion bol s), g ou ype (cemen , esin, e c.), shank body ma e ial (s eel, polyme ic composi es, e c.), p e- ensioning p ope ies (ac i e, passi e), ene gy abso p ion capaci ies (ene gy-abso bing bol s and o he s) and e c. [1-6]. G ou ed ock bol s ha e g ou bonds be ween he ock and bol su aces. On he o he hand, ic ion bol s ha e he abili y o bea ing load wi hou using g ou ma e ials. The ic ion ype ock bol s supply suppo p essu e by he ic ion o ces a he con ac o he bol shanks and ock su aces o he d ill holes. The mos popula and economical ic ion bol s, spli se s a e qui e simple and only consis o a ube body and a ma ching pla e pa . Load bea ing capaci ies o ock bol s depend on a ious pa ame e s. No ma e how s ong he bol is, he load bea ing capaci y is limi ed by he ock s eng h in poo ock masses. Gene ally, ock bol s can no supply a good bea ing capaci y o he s abiliza ion o exca a ions in so ocks because o he low ancho age pe o mances in he low s eng h ock masses. E en i a s ong s eel shank body is used in so ock masses, a good bea ing capaci y can no be gene ally supplied by bol ing as a esul o he absence o an enough ancho age capaci y [7-9]. Addi ionally, he wa e y d illing p ocess can make signi ican dec eases in s eng h alues o he so ock masses like hose wi h he poo slake du abili y p ope y. Because he ock s eng h is a de e mina i e pa ame e o he ic ion coe icien o he d ill hole and bol con ac , ic ion bol s like spli se s some imes exhibi undesi ed load bea ing pe o mances in so ocks [10, 11]. Simila ly, g ou ed ock bol pe o mances also depend on he ock s eng h pa ame e [12, 13]. The main mo i a ion o his s udy is o design and in es iga e a new ic ion bol o supply imp o ed bea ing capaci y alues in so ocks. The newly designed ock bol s ha e sc ew-like shanks wi h sha p h eads o imp o e adhe ence in d ill holes. The sc ew-like new bol s a e inse ed in o he d ill holes by o a ing. The sc ew ancho s a e also used in soil masses by using no d ill hole [14-16]. Conside ing hei usabili y in ock masses, i is es ima ed ha i is no possible o ins all sc ew ype new ock bol s wi hou d ill holes excep o ex emely so ocks. The e o e, he holes mus be d illed o inse he sc ew ype new ock bol s in o he ock masses. The e a e wo di e en diame e s o sc ew 41 GeoScience Enginee ing Vol. 70 (2024), No. X geoscience.cz pp. 40–50, ISSN 1802-5420 DOI 10.35180/gse-2024-0111 ype bol s, which a e ou e (do) and inne diame e s (di). To make a good coupling, he ou e diame e (do) o he new ock bol s should be selec ed highe han he d ill hole diame e . Howe e , he inne diame e (di) should be selec ed o be lowe han he d ill hole diame e o he ease o he inse ion. Because o hei sc a chabili y, so ock su aces can be ad an ageous in e ms o inc easing he con ac oughness and hus he ancho ing pe o mance o he sc ew h eads. Some physical p ope ies o he new bol s a e gi en in Figu e 1. I was aimed o use sc ew bol s o u n he so ness o he ock su aces in o an ad an age. Fo he ans e o ock c umbs occu ed du ing ins alla ion, he pi ch and he h ead dep h (do-di) a e impo an physical pa ame e s o be selec ed enough high in e ms o inse ion p ac icali y o he new bol designs. On he o he hand, i should be conside ed o an op imal design ha big pi ches cause a dec ease in he h ead numbe and he adhe ence pe o mance. As ano he impo an equi emen , h ead c es s o he new ock bol s mus be sha p o easily make sc a ches on he so ock su ace and supply an imp o ed adhe ence in d ill holes. Since he sc ew bol s a e inse ed by o a ion, hey can ha e co ne ed ends like iangle, squa e o hexagonal shaped ones o be p ope ly g ipped. The e a e a ious design pa ame e s o he sc ew bol s o selec a p ope ein o cemen o a ele an so ock mass. I should be eminded he ein ha he sc ew bol s a e in es iga ed only o so ocks wi hin his s udy. Use o no g ou ma e ial can be assessed o be an impo an ad an age especially because o he abili y o s a load bea ing immedia ely a e he inse ion wi hou a need o wai g ou cu ing eac ions [17-19]. Sc ew bol s can ha e pipe ype hollow bodies o solid c oss-sec ions. Since o he ic ion bol s ha e no solid bodies, sc ew bol s a e es ima ed o supply signi ican ly highe body s eng hs han hose o he popula hollow body bol s like spli se s and swellex ypes. Wi hin his s udy, i was in es iga ed o assess whe he he sc ew ype new ock bol s a e ad an ageous in e ms o p o iding highe load bea ing capaci y alues in compa ison wi h o he ic ion bol ypes. The new sc ew bol design de ails a e gi en in he ollowing sec ion. Figu e 1. Some physical p ope ies o sc ew bol s 2 MATERIALS AND METHODS Load bea ing pe o mances o he new sc ew bol s in a ious so ock ma e ials we e in es iga ed wi hin he labo a o y s udy. In he labo a o y es s, u , daci ic u , sands one and clayey limes one ype ou di e en ocks we e used o de e mine he new bol pe o mances. Tu , daci ic u , sands one and clayey limes one samples a e so ocks which ha e he uniaxial comp essi e s eng h (UCS) alues o 13 MPa, 18 MPa, 16 MPa and 21 MPa, espec i ely. The UCS es s we e ca ied ou by using ock co e specimens wi h he NX size diame e . The UCS es s we e ca ied ou o ge an idea abou he ock ma e ials used in he bol ancho age es s. Acco ding o he ISRM (2007), all he UCS es specimens we e cu o ha e he heigh o diame e a io o 2.5 and we e loaded unde a comp essi e s eng h es p ess (Figu e 2) [20]. The ock ma e ials we e also examined by using he geological hamme . All he used ock ma e ials had inden a ions made by a i m blow wi h he poin o he geological hamme . Addi ionally, su aces o all he ock ma e ials es ed in his s udy can be sc a ched by he pocke kni e. Acco ding o bo h UCS es and he geological hamme in es iga ions, ock ma e ials used in his s udy can be classi ied as weak ock ma e ials [21-23]. Acco ding o he examina ion wi h he geologis hamme , he so es one wi hin he es ed ocks was p ac ically assessed o be he u samples, and he ela i ely ha de one was de e mined o be he clayey limes one. To 42 GeoScience Enginee ing Vol. 70 (2024), No. X geoscience.cz pp. 40–50, ISSN 1802-5420 DOI 10.35180/gse-2024-0111 illus a e i s so ness p ope y, Figu e 3 shows ha i was ound able o inse a s eel sc ew wi h he ou e diame e o 8 mm in o a u block by hand powe wi hou making a d ill hole. Figu e 2. a) Rock specimen co ing, b) co e cu ing, c) uniaxial comp essi e s eng h es ing Figu e 3. A small diame e sc ew inse ion by hand The clayey limes one, sands one and u blocks we e egula ly cu blocks om he No h-Eas e n and Eas e n egions o Tu key. On he o he hand, daci ic u samples had no sawed su aces and we e b ough om an unde g ound coppe mine in he Black Sea Region o Tu key. Among he daci ic u blocks in he mine, ela i ely egula shape ones we e selec ed and b ough o he labo a o y o be d illed o he bol inse ion. Wi hin his expe imen al s udy, ock blocks we e d illed by using a s and d ille machine (Figu e 4). Fo he p epa a ion o sc ew bol inse ed holes, a d ill bi wi h a diame e o 24 mm was used. In he labo a o y es s, leng h o d ill holes was 25 cm. The ock bol s used in he labo a o y es s ha e a leng h o 60 cm. The 25 cm pa s we e inse ed in o he d ill holes by he o a ion o sc ew bol s. The con ac leng h in he hole was 25 cm o all ock blocks. The inse ion o a ion was supplied by an elec ic machine. To e ec i ely g ip he bol , head pa s o he sc ew bol specimens we e manu ac u ed o ha e a squa e-shaped c oss sec ion (Figu es 5 and 6). To compa e hei load bea ing capaci y alues wi h hose ob ained om he sc ew bol specimens, con en ional s eel spli se specimens we e also used in he expe imen al s udy. Spli se ubes wi h he ou side diame e o 39 mm we e cu o make an angula on end wi h 45° cu angle o hei inse ion in o he holes d illed by using a 36 mm diame e bi . Sli s we e on he longe sides o he ubes wi h he angula on end. Using an elec omechanical loading sys em, spli se s we e pushed in o d ill holes wi h he leng h o 25 cm as seen in Figu e 7. 43 GeoScience Enginee ing Vol. 70 (2024), No. X geoscience.cz pp. 40–50, ISSN 1802-5420 DOI 10.35180/gse-2024-0111 To de e mine he bea ing capaci ies o he bol s, he pull-ou es which is a amous ancho age es was ca ied ou . The aim o he pull-ou es is o de e mine he bea ing capaci ies o ock bol s unde he axial loading condi ion [24-26]. In he pull-ou es , sc ew bol s we e held om he double nu s moun ed a he specially ea ed back ends o he shanks and pulled by he hyd aulic jack o he es equipmen (Figu e 8). In addi ion o he nu holding mechanism, he pull-ou es equipmen jaws s ongly g ipped he shanks. The ou e (do) and inne diame e s (di) o he lab scale sc ew bol s we e 28 mm and 20 mm, espec i ely. The pi ch size o he lab specimens was 4 mm. In he pull-ou es o spli se samples, immed ings we e assembled o hold he cu ubes. As seen in Figu e 9, s eel ods we e d i en in d illed holes o he ubes o ix he ings. The ings a he spli se ends we e con ac ed on he d illed pla e du ing he loading (Figu e 9). D ill hole diame e in ock blocks o spli se ubes' diame e a io was abou 0.92, which alls wi hin he ypical ange o spli se applica ions [27-29]. Figu e 4. Rock block d illing 3 RESULTS AND DISCUSSIONS The pull-ou es esul s ob ained om he labo a o y s udy a e gi en in Table 1. Acco ding o esul s, sc ew bol s we e ound o ha e no ably highe load bea ing capaci ies in compa ison wi h he spli se samples. Sc ew bol s we e e alua ed o supply app oxima ely 2.5 imes highe bea ing capaci y han hose o he spli se s o he same con ac leng h in d ill holes. I was de e mined ha sc ew bol s a e much mo e ad an ageous o supply a p ope load bea ing capaci y pe o mance compa ed o he spli se s. 44 GeoScience Enginee ing Vol. 70 (2024), No. X geoscience.cz pp. 40–50, ISSN 1802-5420 DOI 10.35180/gse-2024-0111 Figu e 5. a) and b) h ead designs o labo a o y specimens, c) a shown o he squa e-shaped end o he sc ew bol s, d) a pho o o sc ew bol inse ion in he labo a o y s udy Figu e 6. Squa e-shaped ends and h eaded pa s o be i ed wi h nu s 45 GeoScience Enginee ing Vol. 70 (2024), No. X geoscience.cz pp. 40–50, ISSN 1802-5420 DOI 10.35180/gse-2024-0111 Table 1. Pull-ou es esul s ob ained om he labo a o y s udy (Fmax: Maximum load, SN: Numbe o specimens, SD: S anda d de ia ion) Rock ype Sc ew bol samples Spli se samples Mean Fmax (kN) SN SD (kN) Mean Fmax (kN) SN SD (kN) Sands one 29 5 3 11 5 2 Tu 35 4 2 13 4 1 Daci ic u 32 5 4 14 5 3 Clayey limes one 40 5 4 16 5 2 Figu e 7. Inse ion o spli se s in he labo a o y s udy Figu e 8. Some pho os om pull-ou es s o sc ew bol specimens used in he labo a o y s udy 46 GeoScience Enginee ing Vol. 70 (2024), No. X geoscience.cz pp. 40–50, ISSN 1802-5420 DOI 10.35180/gse-2024-0111 Figu e 9. Some pho os om pull-ou es s o spli se s (a, b), spli se ubes' holding ing mechanism (c) This s udy does no include a ield-sized bol design in es iga ion. I is a p elimina y one ca ied ou by using an ea ly labo a o y-scale sc ew bol design. Fo an imp o emen o i s suppo pe o mance, new h ead and d ill designs can be in es iga ed wi hin u he s udies. The sc ew bol s we e in es iga ed o so ocks in his s udy. Wi hin he u u e s udies, special sc ew designs can be also in es iga ed o a po en ial use o he new bol s o mid s eng h ocks. In all he load bea ing capaci y es s, bol s slid in he ock blocks as he maximum load le el is achie ed. I can be aimed o design he sc ew h eads o he pu pose o inc ease in he bea ing capaci y o a le el which makes he ailu e o he body s eel. Use o a long bol can be an upcoming s udy opic o make a ious h ead designs in sc ew bol applica ions. The designs o sc ew h eads should be examined in de ail o he ins alla ion o long-dimensional ock sc ews. I is es ima ed ha he sc ew ype ic ion bol leng hs can be limi ed because o possible high ic ions du ing he ins alla ion. In his ega d, di e en pi ches, h ead angles, h ead dep hs and some o he de ails like c es sha pness and ab asion p ope ies can be in es iga ed in u he analyses on he inse ion p ac icali y. One o he signi ican a ge s in he upcoming designs is hough o be dec easing inse ion ic ions while imp o ing he load bea ing capaci y alues o he new sc ew bol s. In case o low adhe ence pe o mances in so ocks, spli se s each hei bea ing capaci y alues which a e a om he load le els o make he body ailu e [30-32]. E en i a good adhesion is supplied, he ailu e o he s eel spli se ube body occu s a ypical load le els o 60 kN - 70 kN [33-36]. Because o he qui e limi ed body bea ing capaci y alues o he ube ailu e, spli se s can no supply he load bea ing capaci ies and suppo p essu es ob ained om he sc ew bol s wi h he solid c oss-sec ion. As a esul o hei ela i ely low suppo p essu es, he spli se s a e disad an ageous o wo k well in he poo so ock masses [37-39]. In his s udy, he bea ing capaci y alues o sc ew bol s in a ious so ocks we e ema kably highe han hose o he spli se s. Due o he s ess elaxa ion, spli se s can ha e dec eases in he no mal s ess alues ac ing on he ic ion su ace. I is a well-known ac ha ic ion capaci ies o he spli se s wo sen depending on ime [40-43]. The s ess elaxa ion can be b ie ly de ined as he dec ease in he s ess alues o a ma e ial kep unde a cons an s ain. The s ess elaxa ion is a cause o bea ing capaci y losses o he spli se ubes which a e comp essed and kep a a cons an diame ic s ain in d ill holes. Spli se s ha e sho se ice li e imes which a e usually limi ed o a ew mon hs. On he o he hand, he sc ew bol is a new candida e o make be e ed se ice li e imes in compa ison wi h hose o o he ic ion bol s. I is hough ha sc ew bol s may ha e ela i ely longe se ice imes due o hei ela i ely hick body s uc u e. In u u e s udies, e ec i e se ice li e imes o he sc ew bol s can be examined as ano he impo an opic o unde s and he long e m suppo p ope ies o he new ock bol . The use o ha d and co osion esis an su ace coa ings o sc ew bol s can also be ano he opic o u he in es iga ions. Va ious ypes o ock bol s ha e been imp o ed a e hey we e i s ly p oposed, in consequence o di e en s udies. Simila ly, sc ew bol s a e belie ed o be made mo e e ec i e wi h new s udies on i s use. 47 GeoScience Enginee ing Vol. 70 (2024), No. X geoscience.cz pp. 40–50, ISSN 1802-5420 DOI 10.35180/gse-2024-0111 D ill bi diame e is an impo an opic o ock bol ing pe o mances. Weak ock masses can be damaged du ing he we d illing p ocess. Especially, he p e e ence o la ge hole diame e s inc eases his damage and can cause so ock masses o be dis u bed [44-46]. I should be eminded he ein ha his s udy was pa icula ly ca ied ou o so ock masses which can ha e no able s eng h losses due o he d illing p ocesses. As seen in Figu e 10 which is a pho o aken om he mine whe e he daci ic u blocks we e b ough om, he ock mass a ound d ill holes becomes agmen al by hand a e he wa e y d illing p ocess because o poo slake du abili y and so su ace p ope ies o he daci ic u ma e ial. Use o he sc ew bol s is also ad an ageous because o using ela i ely low d ill diame e s. Fo ins ance, i was de e mined ha a no ably highe load bea ing capaci y can be supplied by he sc ew bol s inse ed in o he holes wi h 24 mm d ill diame e in compa ison wi h he 36 mm d ill diame e use in he spli se applica ions. Use o ela i ely small diame e d ill holes makes an ad an age o dec ease s eng h losses o so ock masses. Figu e 10. A shown o he daci ic u o ma ion: a d ill hole (a) and i s agmen a ion by hand (b) To deal abou cos s, i can be no ed ha he p ice o shanks o he sc ew bol s wi h he ou side diame e o 28 mm is 7 USD pe one me e leng h. Adding he p ice o he pla e pa , he o al cos o a 1 me e leng h bol is abou 10.5 USD. The cos is app oxima ely 17.5 USD pe a bol wi h he leng h o 2 m. I should be no ed he ein ha he p ices gi en abo e a e calcula ed in conside a ion o he cos s paid in 2023 wi hin his s udy. I is o eseen ha he cos s can be signi ican ly educed o he sys ema ic p oduc ion o a la ge numbe o sc ew bol s in u u e. The ypical p ice in e al o a comme cial spli se wi h he leng h o 2 m is 8 USD-10 USD pe a bol . Al hough sc ew bol s may seem expensi e a he i s glance, hey can be conside ed a o dable due o he ad an age o hei high bea ing capaci y. Sc ew bol s wi h he solid c oss-sec ion we e in es iga ed wi hin his s udy. To dec ease he ma e ial consump ion and he o e all bol ing cos s, hollow body sc ew bol s can be also in es iga ed wi hin u he s udies. Sc ew ype new ic ion bol s a e open o e y di e en and no el in es iga ions o be e unde s and hei ancho age p ope ies and imp o e hei suppo pe o mances. 4 CONCLUSION Sc ew bol s we e in es iga ed as a new ic ion ype ock bol specimens wi hin his labo a o y scale s udy. Sha p h eads o sc ew bol s p o ide ough ic ion su aces and good adhe ence p ope ies by sc a ching he d ill hole walls and c ea ing g oo es on he so ock su ace. Acco ding o he indings, i was ound ha sc ew bol s can be used o ha e an imp o ed load bea ing capaci y and suppo pe o mance in so ocks compa ed o ypical ic ion bol s like spli se s. Because his s udy is an ea ly one, u he in es iga ions and si e scale es s will be highly bene icial o be e unde s and he suppo p ope ies o he no el sc ew bol s o making new and highly 48 GeoScience Enginee ing Vol. 70 (2024), No. X geoscience.cz pp. 40–50, ISSN 1802-5420 DOI 10.35180/gse-2024-0111 e ec i e designs. The new sc ew bol s we e ound o be ad an ageous o ein o ce so ocks and ha e a good po en ial o become a popula ic ion bol ype in ock enginee ing. ACKNOWLEDGEMENT This s udy has been suppo ed by FEN-BAP-A-250221-16 coded scien i ic esea ch p ojec o Gi esun Uni e si y. The au ho exp esses his since e hanks o he suppo by he Gi esun Uni e si y Scien i ic Resea ch P ojec s Coo dina ion Uni . REFERENCES [1] LI, C.C.; STJERN, G. and MYRVANG, A. 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