INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING This paper was downloaded from the Online Library of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). The library is available here: https://www.issmge.org/publications/online-library This is an open-access database that archives thousands of papers published under the Auspices of the ISSMGE and maintained by the Innovation and Development Committee of ISSMGE. 4/63 Friction between Sand and Metal Surface Friction entre Sable et Surface Metallique Y. YOSHIMI Tokyo Institute of Technology, Tokyo, Japan T. KISHIDA Toa Harbor Works Co. Ltd., Yokohama, Japan SYNOPS I S Large frictio n a l resistance is desirable for fric ti o n piles and reinforced earth, whereas low fric tio n is desirable fo r negative skin fric tio n and selfboring pressurem eters. To cope w ith the problems one needs quantitative inform atio n of fric tio n a l resistance as w ell as deform ation of so il near the contact surface because the normal stress may be sta tica lly indeterm inate. This paper presents the results of laboratory tests on f ric tio n between dry sand and m etal surface under constant normal stress conditions over a wide range of surface roughness and sand density. A ring torsion apparatus was used to achieve uniform stres s d istrib u tio n over the contact surface and w ithin the sand specimen. The deform ation in sand n ear the m etal surface was observed by means of X-ray radiography. In addition to the effects of su rface roughness on the ultim ate co e fficie n t of fric tio n , the relationship among m obilized fric tio n , shear strain and slip are discussed. I NTR O DUCTI ON A PPARA TU S A ND TEST PROCEDURE F rictio n between so il and structures often plays A ring torsion apparatus as shown in Fig. 1 was an im portant role in geotechnical engineering. used. Dry sand was rained into the annular Large fric tio n a l resistance is desirable for container lined w ith 0.3 -mm th ick rubber mem­ fric tio n piles, reinforced earth, or base of branes, and the top surface of the sand was retaining w alls; whereas one wants to m inim ize leveled w ith a suction device. A ring shaped fric tio n along the surface of so il samplers or m etal specimen was then placed on the sand, and selfboring pressurem eters, or point bearing sta tic torque was applied thereupon w hile a piles where negative skin fric tio n poses a prob­ constant ve rtica l load was applied w ith w eights. lem. Because frictio n is not sta tica lly deter­ The ve rtica l stress covered a range from 25 to m inate in many o f those problem s, one needs to 15 8 kPa (0.26't'1.61 kgf/cm 2) w ith 105 kPa used know not only maximum fric tio n a l resistance but for most tests. The torque was applied in such also friction-displacem ent relationship. The a way that the m etal surface mo ved at a rate o f need fo r re lia b le estim ates of fric tio n between about 0. 6 mm per m in. in circum ferential direc­ so il and solid surface has increased in recent tion. In addition to measurements of circum fer­ years w ith the development of analytical tech­ e n tia l and ve rtica l di splacem ents of the m etal niques and w ith the recognition of the negative ring, the deform ation of the sand and slippage skin fric tio n problem in which underestim ation at the soil -m etal contact were measured in some of fric tio n causes an error on the unsafe side. tests using X-ray radiography. Based on d ire ct shear tests on skin fric tio n The ring torsion apparatus is essentially the between various so ils and three construction same as th a t reported by Yoshim i and Oh-oka m aterials (steel, wood, and concrete), Potyondy ( 1973). Compared w ith a d ire ct shear de vice the ( 1 961) identified four m ajor factors that de­ ring t orsion apparatus has the follow ing ad van­ term ined skin fric tio n , i.e ., "the m oisture tage s: ( 1 ) the stresses and strains w ithin the content of so ils, the roughness of surface, the specimen are nearly uniform , ( 2 ) because the com position of soils, and the intensity of nor­ specimen is endless it is free from progressi ve mal load." Esashi et al (1966) showed that skin fa ilu re that w ould in itia te at the ends of a fric tio n between sand and three construction d ire ct shear de vice, and (3) unlim ited circum ­ m aterials (steel, wood, and concrete) could be fe re n tia l di splacem ent can be applied. Three correlated w ith quantified surface roughness sands as shown in Table I and three m etals, i.e . regardless of the type of m aterial. In both re­ stru ctu ra l steel, brass, and aluminum, were ferences, the d ire ct shear apparatus was used in tested. Eighty tests were carried out for va ri­ which stresses and strains could not be uniform ly ous com binations of the density of the sands and distributed and the physical significance of the the roughness of the m etal surface. The surface displacem ents could not be cle a rly established. roughness was expressed in term s of a maximum height, Rmax, that is the re la ti ve height be­ The object of the present paper is to quantify tween the highe st peak and the low est v a lle y the effects of the roughness of m etal surface along a surface p ro file o ver a gage length o f and the density of sand on the skin fric tio n 2.5 mm. The contact surfaces of the m etal rings between dry sand (three sands) and m etal sur­ were finished so that Rmax co vered a range fr om face (three m etals), using an apparatus in which 3 to 510 ym, which included w ith ample m argins stresses and strains are nearly uniform ly dis­ the range between 10 and 150 pm fo r ordinary trib u te d . construction m aterials. D etailed descriptions 831 4/63 AB I T LE Pr oper t i es of Sands Test ed PLAN Hydr aul i c j ack Sand Toyour a Tonegawa Ni i gat a Met al 5 i men Mini mum voi d r at i o 0. 628 0. 717 0. 611 Wir e r ope Maxi mum voi d r at i o 1. 019 1. 157 0. 947 10 % si ze ( mm) 0. 16 0. 18 0. 18 Uni f or mit y coef f i ci ent 1. 31 1. 83 1. 64 0. 105 0. 105 0. 105 Grai n si ze r ange (urn) ^ 0. 25 ~ 0. 71 -v-0.71 fr Speci fi c gravi ty of sol i ds 2. 64 2. 76 2. 66 X- r ay sour ce Wat er cont ent (%) 0. 09 0. 51 0. 24 Sand speci Grai n shape Rounded Angul ar Subr ounded Grai n sur f ace Med i um Rough Smoot h SECTION o f the te s t pr o cedure are given b y K ishida (1979). FRI CTI ON-DIS PLACEMENT RELATI ONSHIP Fig. 2 shows a typical set of te st results for Wei ght s the Tonegawa sand ha ving an in itia l relative den s it y of 60 %. The circum ferential displace­ ment is expressed in a dim ensionless form by d i viding it b y the in itia l height of the sand (22 mm). As one would expect, the maximum coef­ Met al speci fic ie n t of fric tio n increases w ith the surface roughness. Note a w ell defined "stick -s lip " phenomenon fo r Rmax<.5 pm (F ig. 2(a)), and marked dilatancy fo r Rmax>.220 ym (Fig. 2(b)). Rubber On the other hand, the in itia l portion of the Sand speci men friction-displacem ent curves is p ra ctica lly un­ Acryl i c ri (9 ^ 42 mm hi gh) affected by the surface roughness as shown in Load cel l F ig. 2 (a'). This is attributed to the fact that For r adi ogr aphy —► For st andar d t est s w ithin a certain lim it (in th is case, x/h< 1.5% o r T S / Ov < 0 .4 ), n o s lip devel o p s at the c o n ta ct F ig. 1 T e s t Apparatu s s u rface even f o r the s m o o th e s t s u rface; there­ f o re the di s placem ent s are w h o ll y accounted fo r EFFECTS OF SANDS AND SURFACE MATERIALS ON THE by the deform ation of the sand its e lf (Fig. 6 ). FRICTI ONAL RESISTANCE The data of Fig. 2 contradicts the pre v i ous a ssu m pti o n that the in itia l tangent m o dulu s i s A s s h ow n in Fig.