Determining the Appropriate Sealing Conditions through a Permeability and Groutability Evaluation: A Case Study of Sivaki Dam, Iran

The Sivaki Dam is an earth dam that is located near Yasuj city, 5.3 km northwest of Sepidar village. During excavations at the dam construction site, the high potential of water seepage from the foundation and its abutments has been proven. Some cavities and dissolution have been observed on both sides of the dam, suggesting the possibility of Karstification at greater depths. Most of the outcropping rocks in the study area comprise Asmari Limestone. These rock masses, despite their medium to high strength, have provided unfavorable conditions in terms of permeability and weathering. In this study, the foundation and both abutments of the dam were evaluated and analyzed to determine the permeability and groutability characteristics. To achieve this goal, the engineering characteristics of the rock mass of the construction site were examined by performing rock mass rating (RMR) and geological strength index (GSI) classifications. Moreover, the Lugeon test, secondary permeability index (SPI), rock quality designation (RQD), and monitoring hydraulic flows were used for this purpose. According to the results of this study, for abutments of the dam and in the case of alluvial substrates, grout curtain and the cutoff wall are respectively the best and most compatible methods available.

Case Study: In Situ Experimental Investigation on Overburden Consolidation Grouting for Columnar Jointed Basalt Dam Foundation

The dam foundation rock mass, at the Baihetan hydropower station on the Jinsha River, is mainly columnar jointed basalt, with faults and fissures developed. Considering adverse factors such as the unloading relaxation or the opening of the fissures due to excavation blasting, consolidation grouting is needed to improve the integrity of the dam foundation rock mass. According to the physical and mechanical properties of columnar jointed basalt and the continuity of construction, the effectiveness of overburden consolidation grouting is experimentally studied. The results show that this grouting technology can obviously improve the integrity and uniformity of a dam foundation rock mass and reduce the permeability of the rock mass. After grouting, the average increase in the wave velocity of the rock mass is 7.3%. The average improvement in the deformation modulus after grouting is 13.5%. After grouting, the permeability of 99% of the inspection holes in the Lugeon test section had Lugeon values of no more than 3 LU. This improvement is considerable and provides a case to engineering application.

Water in Site Investigation

It is water that makes the difference between a dried-out clay as hard as a brick, and mud. The dry fields of summer can become a quagmire for construction work.Examples are given of rapid deterioration of chalk when allowance had not been made for the effect of a known high water table when excavation went below it and the effect of water on loose backfill at an opencast site. Houses had been built before the water level rose in the old pit and were damaged by the resulting settlements.Soil fabric can make the overall field permeability much greater than that obtained from tests on small samples and completely upset predictions of quantities of water and number of wells required for ground water lowering.Out of balance water pressures caused by allowing the water level in a borehole to be much below the ground water level can lead to low SPT N values and disturbed samples. The result could be unnecessary expense on the new works.False results may be obtained if excessive pressures are used in making field permeability tests such as the Lugeon test. On the other hand, hydraulic fracture tests can be used to obtain an assessment of total stress conditions in the ground.