International Concrete Abstracts Portal

The Helms Pumped Storage Project is a new hydroelectric facility located in the Sierra Nevada mountains O f California. During excavation of the underground powerhouse complex, a previously unidentified shear zone was encountered in the granitic rock. The shear zone was a near vertical plane, up to 35 ft. in stratigraphic thickness, and was intersected by several tunnels near the powerhouse. During initial water filling of the power tunnel, the shear zone became a conduit for high pressure tunnel water (818 psi), allowing it to leave the power tunnel and seep into adjoining dry access tunnels. An innovative grouting program utilizing ultrafine cement (Blaine fineness of 8,880 cm /g) and pump pressures which were increased progressively with depth (up to 700 psi) was used to create a barrier between the pressure tunnel and the shear zone. The grouting program successfully reduced ground water pressures and seepage downstream of the barrier to acceptable levels. The program demonstrated the superior penetrating capability of grout made with ultrafine cement compared to type II and type III portland cement, and indicates that ultrafine cement grout can be an effective substitute for chemical grout when the properties of a cement grout are required.

Hauser Lake Dam, a concrete gravity structure originally constructed in 1911, is located on the Missouri River fourteen miles north of Helena, Montana. Based on stability analyses performed in 1978, remedial post tensioning was recommended in order to increase the dam's better withstand forces associated with se in 1979, fifteen vertical holes were drill the dam into the quartzite bedrock to a ma in order to install 55 strand tendons. Le gravel-sand mixture indurated with silt, a and inflowing water were encountered benea Cement grouting was performed to stabilize reduce the permeability of the tendon hole factor of safety to ismic events. Beginn ed through the body o ximum depth of 180 fe nses consisting of a s well as weathered r th the dam foundation these lenses and to ing f et, ock s. Because construct ion continued through the winter, special techniques were used for drilling, tendon installation, grouting and post tensioning, in ambient temperatures ranging to minus 30 degrees Fahrenheit.

Prediciting production pumping rates is an important part of estimating the required time and resultant cost of completing a particular grouting project. Due to the very stiff nature of low-slump grouts, pumping at economical flow rates can require the use of very high pressures. In practice, numerous admixtures are used to increase the "pumpability" of these stiff grouts, as definged by the lowering of the pressure required ot achieve a given flow rate. In this experimental study, the influence of the admixture bentonite, in amounts up to 15 percent of the pozzalan content, on the flow rate versus pumping pressure relationship, was investigated in field tests using production scale equipment. Constant diplascement piston pumps were used to achieve flow rates of up to 5cu. Ft./min. resulting in pumping pressures of up to 700psi. Over the range of flow rates and resultant pressures investigated an optimum bentonite content of 5 to 10 percent was achieve a given flow rate. The optimum bentonite content was observed ot increase from approximately 5 to 10 percent as the flow rate increased from slightly less than 1 cu. Ft./min. to about 4 cu. Ft./min.

Tail void filling of soft ground shield driven tunnels has historically been conducted through the use of pea gravel and neat cement grout. This method has normally resulted in some settlement, infiltration of grout into utilities and divided the Engineer and Contractor on the question of how close to the tunnel heading grouting should be conducted. On the recently completed Red Hook Interceptor Sewer, a soft ground shield driven compressed air tunnel in New York City, a contract modification was made to use a low slump, 5-7 inches (12-18 cm), low shrink grout mixture of cement, limeflour, benton-ite and admixtures in lieu of pea gravel and neat cement grout. Placement was made at two to five times overburden pressures in close proximity to subsurface utilities and into the tail of the shield. Settlement monitoring indicated negligible settlement along the tunnel route. This paper describes the use and advantages of this method.

The detection and monitoring of subsurface flow phenomena, such as, seepage, grouting and hydrofracturing, are significant and largely unsolved problem areas. As a nondestructive testing technique, the acoustic emission (AE) method seems to be a likely candidate technique for application to these problems. This paper describes the AE method, in general, and a parti-cular AE system which holds significant promise in this regard. It is a multichannel AE system which will eventually source locate the emissions in three dimensions and in real time on a CRT screen. A series of laboratory tests, where equipment selection and proper system tuning were made, are described. Two field tests where chemical and cement grouts were being injected were also monitored with positive results, indicating the technical feasibility of the method. Computer software is presently being developed and, when complete, further field tests will be forthcoming.