To develop an alternative ground improvement technique in coastal areas based on bio-stimulation, we investigated sand cementation using bacteria that have been shown to enhance beachrock formation. We conducted cementation tests using Pararhodobacter sp. strain SO1, a local ureolytic bacteria originating from the sand near beachrock in Okinawa, Japan. Specifically, we attempted to cement sand specimens to unconfined compressive strength (UCS) of several MPa and establish the influence of several test conditions (curing temperature, injection interval of cementation solution, Ca 2+ concentration and sodium malate concentration in the cementation solution, and test period) on the UCS. Column specimens were cemented up to UCS of 10 MPa after 28 days under the conditions (curing temperature; 30°C, injection interval; 1 day, Ca 2+ concentrations in cementation solution; 0.3 M). Multiple regression analysis showed that the relevant conditions for UCS were test period, D (days), and Ca 2+ concentration of the cementation solution, C ca (M). The prediction formula for UCS, q ud (MPa), was experimentally determined to be q ud = 48.3C ca + 0.456D ¹ 19.51. Overall, the results of this study will contribute to the application of a new technique for coastal sand improvement and bio-stimulation.

Beachrock is coastal sediment that has been cemented mainly by calcium carbonate within the intertidal zone in tropical and subtropical regions. Man-made beachrock has the potential to inhibit coastal erosion. Considering this important application, we performed field investigations and laboratory tests to understand the formation mechanism of beachrock in Nago, Okinawa, Japan. We performed a needle penetration test, microbial population count and urease activity test, and conducted elemental and mineral analyses of the beachrock and sand. Some microorganisms at the site showed urease activity and the beachrock cement comprised high Mg calcite (HMC). Our investigation showed that evaporation of seawater and/or urease activity of bacteria may have resulted in precipitation of HMC, leading to formation of the beachrock, with partial solidification of some sandy specimens.

Beachrock is a type of sedimentary deposit held together mainly by calcium carbonate cement in the tidal zone of sandy beaches in tropical and subtropical regions. Man-made beachrock has the potential to inhibit coastal erosion; considering this important application, we performed field investigations and laboratory tests to understand the formation mechanisms of beachrocks in Okinawa and Ishikawa, Japan. We performed a needle penetration test, microbial population count and urease activity test, and conducted elemental and mineral analyses. Our investigation showed that in Okinawa the evaporation of seawater and/or urease activity of the microorganisms may have resulted in precipitation of high Mg calcite, leading to the formation of beachrock. In Ishikawa, beachrock and sand were present near a spring with a relatively high concentration of Al 3+ . The mixing of spring water (pH 4.7) with seawater could have led to the precipitation of the Al-and Si-bearing cement that is consolidating the sand particles, leading to development of beachrock.

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Gr e a tBa r r i e rRe e f （Ar e aC ） ， We s tI n d i e s （Ar e aD） ， E a s t e r nB r a z i l （Ar e aE ） の各地域である．また，最北部 はS c o t l a n d （北緯5 7 度4 0 分） ，最南部はS o u t hAf r i c a （南緯 o n s h i p b e t we e n l a t i t u d e s a n d f o r ma t i v e p e r i o d s o f d i s t r i b u t i o n o f b e a c h r o c k si （F o r ma t i v ep e r i o do fb e a c h r o c k （F o r ma t i v ep e r i o do fb e a c h r o c k si nJ a p a n（F o r ma t i v ep e r i o do fb e a c h r o c k si nJ a p a n （c o n t . ） ） 図 4 国内ビーチロック分布域の緯度と形成年代の関 表 5 および図 6 は，Ar e aBのI n d i a のGu l fo fMa n n a r B e a c h r o c k sf r o m t h ei s l a n do fL aP a l ma （C a n a r yI s l a n d s , S p a i n ） , Ma r i n eGe o l o g y , Vo l . 1 9 7 ，p p . 7 5 9 3 .6 ） Re y , D. , Ru b i o , B . , B e r n a b e u , A.M.a n dVi l a s , F . （2 0 0 4 ） : F o r ma t i o n ,e x p o s u r e ,a n d e v o l u t i o n o fa h i g h l a t i t u d e b e a c h r o c k i n t h e i n t e r t i d a l z o n e o f t h e C o r r u b e d o c o mp l e x （Ri ad eAr o u s a ,Ga l i c i a ,NW S p a i n ） , S e d i me n t a r yGe o l o g y , Vo l . 1 6 9 , p p . 9 3 1 0 5 .7 ） F e l t o n , A. , J e we l l , P . W. , C h a n , M. a n dC u r r e y , D. （2 0 0 6 ） :C o n t r o l s o f t u f a d e v e l o p me n t i n P l e i s t o c e n e l a k e B o n n e v i l l e , Ut a h , Th eJ o u r n a l o fGe o l o g y , Vo l . 1 1 4 , p p . 3 7 7 3 8 9 .8 ） Kn e a l e , D. a n dVi l e s , H. A. （2 0 0 0 ） : B e a c hc e me n t : i n c i p i e n t C a C O3 c e me n t e d b e a c h r o c k d e v e l o p me n ti n t h eu p p e r i n t e r t i d a l z o n e , No r t h Ui s t , S c o t l a n d， S e d i me n t a r yGe o l o g y , Vo l . 1 3 2 , p p . 1 6 5 1 7 0 .9 ） E r g i n l , A. E . , Ki y a k , N. G. , B o z c u , M. , E r t e k , A. , G n g n e s , H. ,S u n g u r ,A.a n dT r k e r . G. （2 0 0 8 ） :On t h eOr i g i n a n dAg e o ft h e Ar i b u r n u B e a c h r o c k ,Ge l i b o l u P e n i n s u l a , Tu r k e y , Tu r k i s hJ o u r n a lo fEa r t hS c i e n c e , Vo l . 1 7 , p p . 8 0 3 8 1 9 .1 0 ）V t t ,A. ,B r c k n e r ,H. ,Ma y ,M. ,L a n g ,F . ,He r d ,R.a n d B r o c k m l l e r , S . （2 0 0 8 ） : S t r o n gt u n a mi i mp a c to nt h eBa y o fAg h i o sNi k o l a o sa n di t se n v i r o n s （NW Gr e e c e ）d u r i n g C l a s s i c a l He l l e n i s t i c t i me s , Qu a t e r n a r y I n t e r n a t i o n a l , Me d i t e r r a n e a n , C o n t i n e n t a l S h e l fRe s e a r c h , Vo l . 2 9 , p p . 1 9 3 7 1 9 4 7 . 1 2 ）Da v i d ,P . ,P a n a g i o t i s ,T.a n d Ko n s t a n t i n o s ,A. （2 0 0 9 ） :E l e c t r i c a l r e s i s t i v i t yt o mo g r a p h yma p p i n go f b e a c h r o c k s : a p p l i c a t i o nt ot h ei s l a n do fTh a s s o s （N. Gr e e c e ） , E n v i r o n E a r t hS c i . , Vo l . 5 9 , n o . 1 , p p . 2 3 3 2 4 0 . 1 3 ）De s r u e l l e s , S . , F o u a c h e , . , C i n e r , A. Da l o n g e v i l l e , R. , P a v l o p o u l o s , K. , Ko s u n , E . , C o q u i n o t , Y. a n dP o t d e v i n , J . （2 0 0 9 ） : B e a c h r o c...

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