Prac­ti­cal Test: Cat 311 ex­ca­va­tor un­der­takes dam re­pairs

After suf­fer­ing for so long from drought, the flood­ing rains fi­nally came. Hav­ing prepped the dams, stor­age ca­pac­ity was in place but an un­for­tu­nate blow out re­quired Ron Horner to un­der­take ur­gent re­pair works with his trusty Cat 311 ex­ca­va­tor

Earthmovers & Excavators - - Contents -

Aus­tralia has just en­dured one of the worst drought pe­ri­ods in liv­ing mem­ory. This past 18-month pe­riod of well be­low av­er­age rain­fall and ex­tremely hot con­di­tions has cer­tainly made most of us aware of the im­por­tance of sav­ing the pre­cious liq­uid that most of us take for granted.

City dwellers are used to turn­ing on the tap and in an in­stant hav­ing as much clean hot or cold wa­ter as they want, but for those in the bush

(who are just ex­tremely grate­ful to have just enough wa­ter for the ba­sics), life has been more than dif­fi­cult for ev­ery­one.

Ru­ral folk are to­tally de­pen­dent upon the heav­ens open­ing and some di­vine in­ter­ven­tion to make life eas­ier, to en­able stock to feed and drink and to en­able crop­ping to pro­ceed with­out bank man­agers in­ter­ven­ing with threats of mort­gage clo­sure be­cause Mother Na­ture has, al­beit tem­po­rar­ily, called “time out”.

Earth­mov­ing con­trac­tors have en­joyed a long pe­riod of con­tin­ued work in ei­ther clean­ing out dams or cre­at­ing new ones (for those landown­ers whom could still af­ford to do so). Mil­lions of dol­lars have been in­vested in both large and small land hold­ings to stave off the fu­ture ef­fects of ex­tended dry pe­ri­ods. Some projects have been hugely suc­cess­ful and oth­ers have been doomed to fail­ure for a myr­iad of rea­sons.

Such was the case when I was en­gaged to sort out a prob­lem on a newly con­structed dam built in a steep and rocky lo­ca­tion.

This dam was built more than a year ago dur­ing the dri­est pe­riod the dis­trict had seen in over 80 years. They weren’t the best con­di­tions to be con­struct­ing a new dam in as the ma­te­ri­als se­lected had not seen any mois­ture for about a year and even at a depth of five me­tres were still quite dry – risky to say the least but worth­while, tak­ing into con­sid­er­a­tion the ex­ten­u­at­ing drought con­di­tions.


Ev­ery drought has ended with a flood. When the heav­ens even­tu­ally opened up the client waited with baited breath for those ex­pen­sive holes in the ground to even­tu­ally fill to the brim and ease his mind and bank bal­ance. The ex­cite­ment was short lived how­ever, as he watched his pre­cious wa­ter run through the cracks of the walls of his dams and over the edge of the moun­tain, leav­ing him with a big­ger prob­lem than he had be­fore the big wet hit.

This is not un­usual in many dam con­struc­tion projects un­der­taken in ex­tremely dry con­di­tions where on-site wa­ter is just not avail­able to as­sist in con­di­tion­ing the clay used to build the dam. Long pe­ri­ods of ex­treme heat cause the ma­te­rial to ex­pand, leav­ing cracks in the walls and base.

It is only when the rains come that one can assess whether the con­struc­tion has been suc­cess­ful – how­ever, the longer they stay dry the more likely the dams will de­velop cracks.

After the rains had eased enough to make a de­tailed in­spec­tion of the dam walls it was found that, although the dam wall base was about 40m wide, wa­ter had found its way through some de­vel­op­ing cracks and punched a hole some 1.5m in di­am­e­ter through the bot­tom of the wall some 1.2 me­tres above the ex­ist­ing wa­ter level.


How do you fix such a hole in the wall whilst the gul­lies are still run­ning a good flow of wa­ter and how can you save the in-flow­ing wa­ter?

This par­tic­u­lar dam was an ‘L-shaped’ dam, with a wall some 150m in length and be­tween 20 and 40m wide at the base.

The af­fected area was lo­cated some 50m from one end and in the gully from where the wa­ter was flow­ing in.

I de­cided that to save the wa­ter we would con­struct a new wall and split the dam into two sec­tions and pump the wa­ter from the flow­ing gully into the new dam, thus sav­ing about five me­gal­itres a week, drain the ex­ist­ing wet area and con­struct a rock base on the in­side of the failed dam wall to cre­ate a work­ing base.

Do­ing this en­abled us to work from the in­side of the dam wall so we could chase the ‘wom­bat hole’, as I felt that it would vary in di­rec­tion and depth as we opened it up.


In the bush one does not al­ways have the op­por­tu­nity to ac­cess the most suit­able equip­ment nec­es­sary to un­der­take some jobs, but what we lack in choice we make up with in­no­va­tion.

This dam was built over a year ago dur­ing the dri­est pe­riod the dis­trict had seen in over 80 years.

It just hap­pened that I could source the gear best suited for this par­tic­u­lar un­der­tak­ing, that be­ing a Cat 311 with a slightly longer dip­per arm and blade, com­plete with most of the at­tach­ments I re­quired, but I was in dire need of a hy­draulic plate com­pactor for the ex­ca­va­tor.

The 11/12 ton Cat ex­ca­va­tor just hap­pens to be one of my favourites and plate com­pactors have been around for over 40 years now but, be­lieve it or not, there is not that many avail­able when you want one.

This ma­chine came sup­plied with an In­deco hy­draulic vi­brat­ing plate, a used pur­chase from Aus­tralian Ham­mer Sup­plies fit­ted with a 600 x 800mm wide base plate and also fit­ted with a ro­tat­ing head.

This item was piv­otal in the suc­cess­ful, speedy and safe ex­e­cu­tion of the dam wall re­pairs.


By work­ing from the in­side bot­tom of the dam wall and keep­ing the in-flow to a min­i­mum by pump­ing the wa­ter into the new dam we were able to ex­ca­vate some 10m in­side the dam wall by fol­low­ing the hole to a depth of two me­tres be­low the ex­ist­ing wa­ter level.

Our clay and rock-bunded work­ing base proved to suc­cess­fully with­hold any wa­ter from en­ter­ing our work­ings and with 57 ar­tic­u­lated dump truck loads of clay bought in from the on-site clay pit, we were able to not only build the dam wall but back­fill and com­pact the rather large ex­ca­va­tion we had cre­ated by open­ing up and then back­fill­ing/com­pact­ing the af­fected area.

Work­ing two me­tres be­low wa­ter level, 10 me­tres in­side the dam wall and in an ex­ca­va­tion five me­tres wide, we had to work at full ex­ten­sion

Work­ing 2m be­low wa­ter level, 10m in­side the dam wall we had to work at full ex­ten­sion.

of the little Cat to suc­cess­fully plug the gap.

The con­fined space meant that it was a huge un­der­tak­ing to cre­ate a safe work­ing area for any con­ven­tional com­pact­ing gear to work in, but with the In­deco vi­brat­ing plate at­tached to the little Cat ex­ca­va­tor we were able to ex­e­cute the re­pair works within a three-day pe­riod.

The ma­te­rial now in use had plenty of mois­ture in it after the weeks of rain­fall and by key­ing the new false wall into the ex­ist­ing dam­aged wall we were able to cre­ate a new 50m-long wall some three-me­tre wide from the bot­tom to the top mark of high-wa­ter level. The suc­cess­ful pro­ject would not have been achieved with­out the small equip­ment all per­fectly suited to such a job. The In­deco vi­brat­ing plate played a vi­tal ma­jor role along­side the ver­sa­til­ity of the bladed Cat 311cu ex­ca­va­tor.


In­deco/IHC com­pactors are a very ef­fi­cient re­place­ment both for tra­di­tional risky and tir­ing man­ual equip­ment and for self-pro­pelled rollers, es­pe­cially if there is a risk of rollover dur­ing slope

ap­pli­ca­tions or cave-in of trench walls in deep ex­ca­va­tions.

Per­fect for work­ing on grainy, co­he­sive and semi­co­he­sive soils, op­tional adapters on the vi­bra­tory plate turn them into highly-ef­fi­cient pile-driv­ing tools. In­deco’s ro­tat­ing com­paction plate, the IHC R, makes it much eas­ier to po­si­tion the ex­ca­va­tor at the right an­gle to the work­ing sur­face, es­pe­cially for jobs in nar­row pipe trenches and con­fined ar­eas, where the com­paction plate needs to reach into dif­fi­cult cor­ners or skirt round man­holes and other ob­sta­cles.

With a great range of com­paction plates avail­able, sizes vary to suit the size of the ex­ca­va­tor and of course the ap­pli­ca­tion for the tool.

This one weighed in at about 650kg, re­quired about 120 litres per minute at 138 bar, achieves a com­paction fre­quency of 2,100 litres per minute and was fit­ted with a 360-de­gree ro­tat­ing head.

With its sim­plis­tic op­er­a­tion and sim­plis­tic de­sign, along with be­ing in­ex­pen­sive to pur­chase and main­tain, made this the per­fect tool for this par­tic­u­lar ap­pli­ca­tion. I love it!

Op­po­site: Dam wall blowout, caused by ex­pan­sion of the clay Above: Rec­ti­fi­ca­tion works un­der­taken with Cat 311cu ex­ca­va­tor

Above: The key to a suc­cess­ful out­come – the In­deco com­paction plate – not only min­imises risk when com­pact­ing in deep ex­ca­va­tions but achieves bet­ter con­sol­i­da­tion In­set: The In­deco is sim­plis­tic in de­sign, cost ef­fec­tive, af­ford­able and re­quires little main­te­nance

Op­po­site: A safe, neat, speedy and tidy ex­e­cu­tion of the re­pairs Above: Job done, with five me­gal­itres of wa­ter saved – and the gul­lies keep run­ning and fill­ing – great out­come

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