ALTERATION OF GEOTECHNICAL PROPERTIES OF PORTLAND LIMESTONE AND MONK'S PARK LIMESTONE UNDER SIMULATED WEATHERING

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1 739 ALTERATION OF GEOTECHNICAL PROPERTIES OF PORTLAND LIMESTONE AND MONK'S PARK LIMESTONE UNDER SIMULATED WEATHERING MURPHY,W. Deprtment of Geology, University of Portsmouth, Burnby Building, Burnby Rod, Portsmouth. P1 3QL. United Kingdom. INKPEN,R.J. Deprtment of Geogrphy, University of Portsmouth, Bukinghm Building, Lion Terre, Portsmouth. P1 3QL. United Kingdom. SUMMARY Using weight hnge nd ousti veloity mesurements to ssess lertion of smples distintions n be mde between different forms of wethering, pre-stress onditions nd the response of eh stone type. Under simulted slt wethering by N 2 S 4 weight hnge suggests tht Monk's Prk Limestone is more suspetible to mteril loss thn Portlnd Stone Limestone smples. Only t the extremes of pre-stress onditions, does indued wethering history pper to mke substntil differene ot the wethering behviour of the smples. Aousti veloity mesurements suggest some ylil trend in the mnner of slt wethering nd indite some ltertion of the jnternl struture of the smples. Under simulted id rinfll onditions weight hnge does do differ gretly from tht experiened under rinfll of distilled wter. Similrly, ousti veolity mesurements indite very little internl struturl tlertion of the stone smples. 1. INTRODUCTION Rok wethering usully produes degrdtion in the qulity of the mteril exposed to whtever ggressive wethering environment. One of the priniple effets of wethering is generl wekening of the mehnil properties of the rok suh s strength nd elstiity. Subsequently, the bility of the rok, or building stone to resist deformtion when subjet to pplied lod is redued. Normlly, roks re strong when subjet to ompressive fores, nd the filure of building stones is seldom seen, even when suh roks re struturl, or lod bering members. However, suh ses n be seen resulting from the wethering of the stone. In one se Bth Stone buttresses hve been seen to fil s result of wethering on St. Judes Churh, Southse (Murphy et l. 1996), nd Portlnd limestone hs filed under low stresses due to wethering. Therefore, the performne of stone in servie n be seriously ltered by wethering. Within engineering geology, it hs been shown tht wethering n result in the development of mirorks (Foookes et l, 1988, lrfn nd Dermn, 1977, Fookes, Gourley nd Ohikere, 1988). Therefore, when investigting the effets of prior wethering history on the response of mterils to wethering gents it ws possible to give the smple pseudo-wethering history by pling the smple under ompressive fore nd using mirorks to develop. The smples of stone, in this se Portlnd limestone nd Monk's Prk limestone were exposed to ggressive slt solutions nd simulted id rin. In ddition, it ws possible to ssess whether these wethering proesses ould use internl hnges in the body of the stone by the ingress of slts whih my use subsequent dmge by rystllistion or hydrtion, nd whether id rinfll would use similr dmge through dissolution of the fbri of the limestone.

2 74 2. EXPERIMENTAL DESIGN Wethering Histories Two different types of building stone, 'Whit Bed' Portlnd Limestone nd Monk's Prk Limestone (Bth Stone) were used in this experiment. Both stone types re medium grined Jurssi limestones. The PorUnd Limestone is white, medium grined, storng ololithi limestone. Monk's Prk Limestone is buff, medium grined modertely strong ooliti limestone with high elsti input of 1-1%. Before testing smples from eh stone type were given rnge of wethering histories. These 'wethering histories' were indued by subjeting smples to different levels of pplied ompressive stress. These predetermined stress levels were, 1,2 nd 3MP. For the Portlnd Limestone smples these stress levels were well below its yield, i.e. the point t whih the rok undergoes non-reoverble strin. For Monk's Prk Limestone smples, hwoever, the 2 nd 3MP stress levels were within the yield stge of rok behviour. Monk's Prk Limestone smples whih hd rehed yield were not inluded in the experiment. In order to be stressed, in Hoek ell, nd internl struturl ltertions ssessed ylinderil smples were required. eh ylinder ws mm in dimeter d mm long. For eh stone type ll smples were ored from the sme blok to redue intrsmple vribility. Slt Tretment Slt wethering ws simulted using O.SM solution of sodium sulphte (N 2 SOJ. A set of ontrol smples were wethered t the sme time in distilled wter. Six smples of eh stone type were ompletely immersed in eh solution for one hour. All smples, from both the slt solution nd ontrol, were then heted t 6 C for five hours, then t 3 C for further eighteen hours, similr yle to tht used by Goudie (1974). This wethering sequene ws repeted for twenty yles. Aid Rinfll Aid rinfll ws simulted using 1 :1 solution of sulphuri nd nitri id with ph of 4.. A ontrol set of smples were 'rined' on by distilled wter. Six smples of eh stone type were wethered by single rinfll dripper (delivery rte of.7ml per minute). Eh smple ws 'rined' on for two hours ontinuously nd then left to ir dry for twenty-two hours. Eh smple ws pled bk into the dripper in the sme position for eh wethering yle. This wethering sequene ws repeted for twenty yles. Assessment of Altertion For eh smple ltertion ws ssessed using two indies, weight hnge nd hnges in ousti veloity. Weight hnge indited the gross hnge in the mss of the smples. Internl ltertion of the stone struture would not neessrily be refleted in this wethering index. Weight hnge ws mesured before immersion t the end of every yle. In order to ssess sturutrl ltertion within the stone ousti veloity mesurments were tken. The veloities of two types of ousti wves, p (Vp) nd S (Vs) wves were used to ssess ltertion. These veloities were mesured every four yles. p wves re ompressive wves nd trvel through the frmework of the pores nd ny fluid there my be within it.

3 741 Their veloity n be slowed if low density mteril, suh s slt or ir, reples the pore struture. S wves re trnsverse wves whih trvel through the solid pore struture nd n not be trnsmitted through fluid. Full detils of these tests nd their nlysis is present in Murphy et l (1996). Control Smples Weight hnges for the ontrol smples for both the slt immersion nd id rinfll tests show very little hnge in weight over the ourse of the experiment (Figures 1-4). Similrly, ousti veloity mesurements for these ontrol smples vried little throughout the experiment (Figures -12). Some smples, prtiulrly Monk's Prk Limestone smples with 2 or 3MP pre-stress, did experiene lrge initil drop in veloity. This ws probbly the result of mirorking indued by the pre-stressing. After this initil drop ousti veloity hnges very little for the rest of the experiment. Sodium Sulphte Smples wethered by the sodium sulphte solution initilly experiened weight gins s the slt migrted into the stone (Figures 13 nd 14). After five to six yles, however, the Monk's Prk Limestone smples strted to lose weight. The Portlnd Limestone smples did strt to lose weight, but only towrds the end of the experiment. Losses from Portlnd Limestone smples were of smller mgnitude nd lost t lower rte thn the Monk's Prk Limestone smples. This implies tht Monk's Prk Limestone is more suspetible to degrdtion in this slt solution thn Portlnd Limestone smples. Aousti veloity mesurements for both stone types show similr pttern, lthough it is probbly esier to see in the Monk's Prk Limestone dt (Figures 1-18). For Portlnd Limestone smples the vrition in Vp over the experimentl run is smll. There is, however, slight yling in Vp. The presene of yle is lerer in the Vs dt. In ddition, there ppers to be differene between smples with different pre-stresses. Smples with low pre-stresses ( nd 1 OMP) hve higher initil derese in veolity reltive to smples with higher pre-stresses (2 nd 3MP). For the Monk's Prk Limestone smples the presene of yles in hnges in ousti veloities is visible for both Vp nd Vs. For smples with pre-stress of 3Mp hve drmti initil derese in Vp nd do not follow the sme ylil trend s the smples with other pre-stresses. After initil differenes in Vs, ll smples, no mtter wht their prestress onditions, follow similr ylil pttern. Smples with pre-stress of 3MP hve lrger mplitude to the yles thn the other smples. Cyling in ousti veloities ould be relted to the lternte uptke of slt nd its loss upon wethering. On uptke the pores beome filled with reltively low density slts through whih the ousti wves trvel. On wethering mteril is lost from the smple, prtiulrly the surfe, nd ousti wves trvel through the stone rther thn the slts, inresing their veloity. Chnges of this mgnitude in ousti veloities imply tht the internl struture of the stone is hnging trhoughout the experiment. In ddition, there is some evidene of slight derese in ousti veloity over the experimentl run. This would suggest tht s well s yling there is some degrdtion in the internl properties of the stone s well.

4 ACID RAINFALL Smples wethered by id rin lost little more weight thn those wethered by distilled wter (Figures 19 nd 2). This implies tht during this experiment the loss of mteril by id dissolution ws reltively minor ompred to tht lost by flowing wter lone. This observtion is supported by the ousti veloity dt (Figures 21-24). For both Vp nd Vs there is little hnge over the experimentl run. There is some evidene of slight yling in veloities, but of very low mplitude. This suggests tht there is little internl ltertion of the stone whtever the pre-stress onditions. 4. CONCLUSION Weight hnge dt suggests tht slt wethering uses ltertion of both Monk's Prk Limestone nd Portlnd Limestone smples beyond tht indued by the wethering proedure lone. Monk's Prk Limestone smples tended to loss more weight thn the Portlnd Limestone smples. This suggests tht Monk's Prk Limestone is more suspetible to degrdtion by sodium sulphte thn Portlnd Limestone. Smples wethered by id rin do not hve signifintly different weight loss from ontrol smples. This suggests tht within this experimentl design id dissolution does not pper to hve n effet on the wethering index of weight loss. Aousti veloity mesurements for smples wethered by sodium sulphte show yling of wve veloities for both stone types. These yles re most pronouned for Monk's Prk Limestone smples. In ddition, there is some distintion in the nture nd mgnitude of these yles for Monk's Prk Limestone smples with high pre-stresses (2 nd 3MP). The yles my be due to yles in the uptke nd loss of slt from the smples. Suh hnges in ousti veloity reflet hnges in the internl sturutre of the stone, nd possibly in the degrdtion of the stone properties. There ppers to be no similr hnge in the internl struture of the stone for smples treted with id rinfll. ACKNOWLEDGEMENTS This reserh ws rried with the finnil support of Her Mjesty's Inspetorte of Pollution, now prt of the Environment Ageny (Reserh Contrt: HMIP/CPR2/41/1/134). The uthors would like to thnk Dr Irwin of the bove orgnistion for his dvie nd the dvie of n unknown set of reviewers of the finl report. The uthors would lso like to thnk John Smith for ll his help in running the experiments. REFERENCES Foookes, P.G., Gourley, C. nd Ohikere, C Rok wethering in engineering time. Qurterly Journl of Engineering Geology, 21, 337. Goudie, A.S Further experimentl investigtion of rok wethering by slt nd other mehnil proesses. Zeitshrift fr Geomorphologie, Supplement Bnd 21, lrfn, T.Y. nd Dermn, W.R The engineering petrogrphy of wethered grnite in Cornwll, Englnd. Qurterly Journl of Engineering Geology, 11, Murphy, W., lnkpen, R.J. nd Smith, J.D Stone wethering- the ltertion of geotehnil properties nd the memory effet. Deprtment of the Environment reserh Report DoE/HMIP/RR/9/17.

5 743 Figure 1. Perentge hnges In weight In Monk's Prk limestone with slt ryslolllstion ontrol testing l different pre-experimentl stresses I wethering yle MPo MPo MPo MP Figure 2. Perentge hnges In weight In Portlnd limestone with slt rystllistion ontrol testing l different pre-experimentl stresses wethering yle MP MPo MPo MPo Figure 3. Weight hnge In Monks Prk limestone smples subjet lo id rinfll ontrol experiments. 3 ) O. u :;:.21 ) ) g -1 )!:! ) wethering yle - - MPo MPo MPo --<-- 3 MPo --=:-=::::"":-=-:::=--t=====-, J

6 wetherlno vle 744 Figure 4. Weight hnge in Portlnd limestone smples subjet to id rlnfli ontrol experiments. e &. :E ; ;i: 3 e -1 e <D wethering yle I - - O MPo MPo MPo --o-- 3 MPo I Figure. Chnges in ousti veloity In Monk's Prk limestone with slt rystlllsllon ontrol testing l different pre-experimentl stresses T e &..?' ; :J wethering yle - - P wove (3 MPo) P wove (2 MPo) -- P wove (1 MPo) p wove ( MPo) Figure 6. Chnges in ousti veloity In Monk's Prk limestone with slt rystlilstlon ontrol testing l different pre-experimentl stresses e.t:.?' ; :J

7 74 Figure 7. Chnges In ousti veloity In Portlnd limestone with slt rystlllstlon ontrol testing t dltterent pre-experimentl stresses QI :.s::: 8 Gi 'iii ;;J I C-6--i wethering yle - - P wve (3 MP) --o- P wve (2 MP) - - P wve (l O MP) -----o-- P wve ( MP) Figure 8. Chnges In ousti veloity In Portlnd limestone with slt rystlllstlon ontrol testing t different pre-experimentl stresses -3-3 wethering yle -11- s wve (3 MP) --o- S wve (2 MP) - - S wve (1 MP) -----o-- S wve ( MP) Figure 9. Chnges In p wve veloity for Monk's Prk limestone subjet lo id rlnfu ontrol experiments. g QI :.s::: Gi 'iii 8-4 wethering yle - - P wve ( MP) -o-- p wve (1 o MP) - - P wve (2 MP) P wve (3 MP)

8 746 Figure 1 o. Chnges In s wve veloity for Monk's Prk limestone subjet to id rlnfh ontrol experiments. 3 <» C.t::;.?: g :; S wo ve ( MPo) S wove (1 MPo) -+- S wove (2 MPo) S wove (3 MPo) Figure 11. Chnges In P wove veloity for Portlnd limestone subjet to rinfll slmulollon ontrol experlmets 1 g <» C.t::;.?: 'iii ::J u wethering yle - - P wove ( MPo) P wove (1 O MPo) - - P wove (2 MPo) P wove (3 MPo) Figure 12. Chnges In S wve veloity of Portlnd limestone with rinfll simultion ontrol experiments. -4 wethering yle S wove ( MPo) ---- S wove (1 MPo) - S wove (2 MPo) ---<- S wove (3 MPo)

9 747 Figure 13. hnge In weight In Monk's Prk limestone with sodium sulphte rystlllsllon testing t different preexperlmentl stresses (l). t -1 "' wethering yle \ MPo --D- 2 MPo MPo --<--- MPo Figure 14. hnges in weight In Portlnd limestone with sodium sulphte testing t different pre-experimentl stresses 2. g (l) _g -2. ;:: (l) ii= wethering yle MPo -o-- 2 MPo MPo --<--- MPo g 1 (l) s ::J -3-4 Figure 1. Chnges In ousti veloity In Monk's Prk limestone with sodium sulphte rystlllstlon testing t different pre-experimentl stresses i wethering yle - - P wove (3 MPo) ---- p wove (2 MPo) - - P wove (1 MPo) --<--- P wove ( MPo)

10 748 g G _g -1 : -1 'i.y Figure 16. Chnges In ousti veloity In Monk's Prk limestone with sodium sulphte rysllllstlon testing l different pre-experimentl stresses wethering yle - - S wve (3 MP) ---o-- S wve (2 MP) -+- S wve (1 MP) ---<--- S wve ( MP) Figure 17. Chnges In ousti veloity In Portlnd limestone with sodium sulphte rystlllstlon testing t different pre-experimentl stresses G. 'i,g :; wethering yle - - P wve (3 MP) ---o-- P wve (2 MP) - - P wve (1 O MP) ---<--- p wve ( MP) Figure 18. Chnges In ousti veloity In Portlnd limestone with sodium sulphte rystlllstlon testing l different pre-experimentl stresses g G. 9.,g :; === -=-----=:::::::::::::.,,_ wethering yle S wve (3 MP) ---o-- S wve (2 MP) - - s wve (1 o MP) ---o- S wve ( MP)

11 749 Figure 19. Chonge In weight during id rinfll simultion experiments for Monk's Prk limestone :E "i ;r:.e -1-2!:! wethering yle - - MPo ---o-- 1 MPo MPo -<-- 3 MPo Figure 2. Chnge in weight during id rinfll simultion experiments for Portlnd limestone.. 3 :E ; ;r: g -1 i» wethering yle - - O MPo ---o-- 1 MPo MPo -<-- 3 MPo I Figure 21. Chnges In ousti veloity for Monk's Prk limestone subfet to id rin slmuttlon experiments. u "i ti :J -3-4 wethering yle - - p wove ( MPo) ---o-- P wove (1 MPo) - - P wove (2 MPo) -<-- P wove (3 MPo)

12 7. veloity In Monk's Prk limestone subjet to id rinfll simultion experiments. Figure 22. Chnge I n ous t 1 1. Ol..?: ; ::;; " wethering yle - - S wove ( MPo) --- s wove (lo MPo) --S wove (2 MPo) ---<--- S wove (3 MPo) Figure 23. Chnges In ousti veloity of Portlnd limestone subjet to id rinfll simultion experiments. 1. Ol..?: ; " wethering yle - - P wove ( MPo) --- P wove (1 MPo) --P wove (2 MPo) --<-- P wove (3 MPo) Figure 24. Chnges In ousti veloity of Portlnd limestone subjet to id rinfll simultion experiments. Ol..?: ;,g :; wethering yle - - S wove ( MPo) --o- S wove (1 MPo) - - S wove (2 MPo) --<-- s wove (3 MPo)