Information regarding two rather extensive grouting operations is here abstracted from published accounts.
The first work was at the Estacada dam near Portland, Oregon, and the second at Lahontan dam. Undoubtedly, experience on the first suggested or influenced somewhat the procedure on the second. While the formation at the two places is quite different and doubtless accounts very largely if not entirely for the difference in results, it is interesting to observe that on the latter work grouting was done at 100 lb. pressure, whereas 200 lb. was used on the first.
The Estacada hydro-electric power development of the Portland (Oregon) Railway, Light & Power Company includes an Ambursen dam 90 ft. high which was completed early in 1912. The foundation was extensively treated by drilling and grouting. The following notes regarding the work are abstracted from an admirable paper entitled "Grouted Cut-off for the Estacada Dam," as contributed to the January, 1914, Proceedings of the American Society of Civil Engineers by Harold A. Rands.
The entire region is covered by a lava flow, some 200,000 square miles in extent, to an average depth of 2000 ft. This volcanic debris is found in every degree of solidity and hardness, varying from the hardest basalt rock to material as loose and friable as garden soil. At the immediate site of the dam the material is a lava conglomerate or breccia, composed of irregular hard fragments embedded in a softer matrix which varies from friable sandy material to a fairly compact clay. The material was such that a Sullivan diamond drill with a single tube core barrel obtained slightly less than 5 per cent, of core; a double tube core barrel used on part of the work produced nearly 80 per cent, of core.
Holes were put down in two rows 6 ft. apart, with 6 ft. spacing of holes in the row. These were known as primary holes, and after being grouted the treatment was tested by one (or in cases) two or three proving holes between the rows. The total number of holes was 555, aggregating 34,038 lin. ft. At first both steam-operated Sullivan diamond drills, and electrically operated Davis-Calyx shot drills were used. After using the diamond drills for 1119 ft. of hole they were moved to other work and the remainder of the drilling was done by the shot drills, using the G-0 class machine of the Ingersoll-Rand Company. The drills were each driven by a 5-h.p. motor at 187 r.p.m. The bit had an outside diameter of 2 3/8 in. and the core of 1 1/2 in. The average progress was 13 ft. per ten-hour shift. The grouting was done by a Caniff machine, using air at 250 lb. per sq. in., usually starting the process at 25 lb. pressure, or whatever was required to start the discharge, and ending up at 200 lb. as the hole tightened to refusal. Though thicker and thinner mixtures were used at times, the best results were obtained with one part of cement and three to five parts of water, by volume.
Twenty-five primary holes in the left section, grouted during September 1910 showed results as follows: Average pressure 19.4 lb.; average leakage 85.7 gal. per min.; total cement 167.25 barrels; average per hole 6.69 barrels; most cement in any one hole 40 barrels. The water for the foregoing leakage tests was supplied from a pump and the pressure was observed from a pressure gage. In the spring of 1911 holes in the right channel were tested and grouted as recorded in the following table:
Leakage gal. per min.
Barrels of cement used in grouting
First primary holes, set in river bed, tested from tank 182 ft. above bottom of hole.
Second primary holes, casings set through a capping of several feet of concrete, tested from tank 146 ft. above bottom of hole.
Proving holes, conditions same as for the 18 above.
In order to show how much tightening between the foregoing primary and proving holes may have been due to the concrete capping, and how much to the grouting, compare with the following holes in an adjoining but somewhat tighter section in which all drilling and testing followed the placing of the concrete.
Leakage gal. per min.
Barrels of cement used in grouting
Primary holes, 146 ft. head............
Island section, May and June, 1911
Casings through concrete, 146 ft. head.
After the dam was completed and with water standing at the crest, two holes were drilled underneath the dam for the purpose of observing leakage through or under the grouted zone. The first was 35 ft. downstream from the cut-off, was drilled 2.5 ft. lower than the grouted cut-off, and with the top of the casing 59 ft. below the water level in the reservoir the leakage was 7.5 gal. per min. The casing was extended upward and the water came to rest at elevation 24.2 ft. below reservoir level. The second hole was 30 ft. downstream from the most pervious part of the grouted cut-off and was drilled 1 ft. below it; with the top of the casing 72 ft. below reservoir level the flow was 53.8 gal. per min., with the casing carried up to 13 ft. below the reservoir level the flow ceased.
Return to left channel, September and October, 1911 conditions as in island section above
Average leakage of holes in gal. per min., at depths of
Cement used barrels, average
Total drilled 555 holes.............
............................34,038 lin. ft.........
Average per drill per ten-hour shift..........
.............................13.2 lin. ft.
Average shot per drill per shift.............
Primary or outside holes grouted............
375 taking 1,526.5 bbl. cement
Proving or middle holes grouted...............
160 taking 275.25 bbl. cement
Tight holes filled..........................
12 taking 15.00 bbl. cement
Setting casings, etc.................
125.25 bbl. cement
555 taking 1,942.00 bbl. cement
Most cement in any one hole..........................
Average for 535 holes taking grout..........
............. 3.37 bbl.
$0.59 per lin. ft.
0.18 per lin. ft.
Cement at $2.20 per bbl. at cut-off.....
0.12 per lin. ft.
Repairs, oil, waste, shot, etc.....
0.17 per lin. ft.
Depreciation on grouting plant, 50 per cent...
0.15 per lin. ft.
1.21 per lin. ft.
Other charges were prorated as follows:
General plant, camp, etc....
0.45 per lin. ft.
Cofferdams and pumping....
0.15 per lin. ft.
Engineering and superintendence....
0.19 per lin. ft.
2.00 per lin. ft.
The following conclusions were drawn from the experience at Estacada. The first four are undoubtedly sound; the last one though probably justified in that particular formation might not apply to a different one.
Do all drilling, testing and grouting through casings set in the concrete cut-off.
Do all testing from elevated tanks, and not by pump.
Test and grout each hole as soon as drilled, and for a few days thereafter keep the drills away from the probable zone of diffusion.
In grouting, especially at high pressures, it is best to close the valve before the tank is entirely empty, because the air which follows the grout into the hole is apt to make trouble.
Begin with a comparatively thin grouting mixture and, if taken freely, thicken until each succeeding batch requires either an increased time for discharging or an increased pressure. To force charge after charge of thin grout into a hole probably means in a great measure the wasting of cement.
For further interesting information, and for results expressed in much greater detail reference should be made to the paper.
In Engineering News of April 3, 1913, is a very good description of the grouting of a zone below the cut-off trench of the Lahontan dam. The operation appears to have been very skilfully conducted and successful in accomplishing the desired result. The following is an abstract of the descriptive article: