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.

Results from load testing of one-meter-diameter drilled concrete piers showed that the majority of the piers designed as foundation support for the 37-story Jakarta Mandarin Hotel failed to meet load test criteria. The potential causes for load test failure and the load deflection characteristics of the piers were investigated. A layer of unconsolidated sediment of varying thickness was encountered between the pier tips and the bearing strata. Extensive coring through the pier shafts was undertaken to develop data to statistically characterize the thickness and spatial distribution of the unconsolidated sedi-ments. A rehabilitation technique was developed which con-sisted of flushing the sediments from the pier tips utilizing high pressure water jets followed by subsequent cement grouting of the resulting voids. The technique was developed so that production rehabilitation could be practically and reliably achieved. The rehabilitation mechanism filled the void space created in the unconsolidated sediments with grout. The grout intruded and compacted the coarser sediments which remained in the voids. Load testing of the rehabilitated piers showed compli-ance with load testing criteria.

Changes in length and volume of cementitious grouts for use in nuclear waste isolation have been investigated, and com-pared with the behavior of other mixtures, neat cement pastes, fly-ash containing mixtures, and mixtures with high-range water reducers (‘superplasticizers’). Expansive and non-expansive for-mulations are compared with respect to their changes in length and volume, both at atmospheric pressure and elevated curing condi-t ions, including those simulating placement under pressures of up to 1600 psi hydrostatic.

Innovative aspects of the design and construction of the concrete-lined high pressure tunnels of the Drakensberg Pumped Storage Project are described. These tunnels located in weak argillaceous rocks are prestressed and designed to remain crack-free at internal pressures up to 6.2 MPa. The extension of an innovative grouting technique developed in Europe provided an economical and technically acceptable alternative to steel liners. Design criteria for structural deformability, prestressing and creep behavior were developed using a prototype-scale test chamber. The design models and practical technology developed for interface grouting will allow the use of concrete linings in pressure tunnels with greater internal pressures and with poorer rock conditions than previously considered feasible.

Condensed silica fume is a by-product of the fabrication of silicon or ferrosilicon alloys. It is composed of very fine glassy spheres of quite pure silica having an average diameter of 0.1 pm. It is a very reactive pozzolan that has been found to increase drastically the compressive strength of concrete and to reduce significantly its permeability. The unique properties of condensed silica fume can also be used advantageously in grouts if condensed silica fume is used in combina-tion with a superplasticizer. The very fine silica particles give stability to the grout, there is no sedimentation of the cement particles and no bleeding. By adjusting the respective proportions of portland cement, of condensed silica fume,and of the superplasticizer a thixotropic grout can be made. The hardened grout is stronger and less porous when it contains condensed silica fume because the lime liberated during the hydration of portland cement reacts with the very fine silica particles to form a compact secondary CSH. By this way the possibility of leaching out of the lime is practically suppressed and the resistance of the grout to chemical attack should be improved.

A study and report on the application and use of cement grouting techniques. Includes chapters on: the use of condensed silica fume in grouts; design and grouting of a concrete lined high pressure tunnel; changes in length and volume of cementitious grouts; drilled pier foundation rehabilitation; acoustic emissions as a nondestructive testing method; low slump compactive tail shield grouting in soft ground; bentonite effect on pumpability of compaction grouts; ultrafine cement pressure grouting; and cold weather cement grouting and post tensioning. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP83