Important Database For Dam and Tunnel Safety

A systematic recoding and registration of geo-data following international standards does not appear to have not been conducted, which is a very critical task in order to allow a systematic analysis of rock mass/soil and joint characteristic data. It is suggested that a proper data base of the following parameters is maintained during construction activities. This will serve for updating design during construction activities and will also be database for future dam safety assessment.1. Classification and description of rocks and soils

ROCK NAME Supplementary petrographic properties Rock material properties Colour Texture Grain size Other textural features and fabric State of weathering State of alteration StrengthRock mass properties Structure Discontinuities Weathering profileand for soils:SOIL NAME Including minor constituents Genetic type Soil material properties Colour Texture Particle shape and composition State of weathering Strength Consistency Undrained shear strength Moisture condition Relative density CompactnessSoil mass properties Structure Discontinuities Weathering profileFull descriptions of rocks and soils are reserved for the legend of small-scale maps, whereas large-scale plans may show the same rock type subdivided into separate map units on the basis of one or more attributes, for example, degree of weathering or jointing, or both.2. Hydrological conditions

Hydrological conditions, including surface hydrology, affected land-use etc. does not appear to have been presented. It is strongly advised to prepare a hydrogeological map of the area of interest of the project under construction.Groundwater and surface water play an important part in present-day weathering, slope movements, active development of karst, volume changes by shrinking and swelling of susceptible soils, and the tunnel erosion and general collapse of loess. Rock and soil properties are largely dependent on their moisture content. Groundwater may influence methods of excavation and construction by flowing into excavations, and by producing seepage forces and uplift pressures. Both surface and underground waste disposal may be influenced by hydrogeological conditions. Provision of hydrological information on maps facilitates prediction of undesirable changes in the hydrological regime and the recommendation of methods to avoid them. Therefore, on engineering geological maps it is necessary to assess and represent the following: the distribution of surface and subsurface water; infiltration conditions; water content; direction and velocity of groundwater flow; springs and seepages from water-bearing horizons; depth to watertable and its fluctuation range; regions of confined water and piezometric levels; hydrochemical properties such as pH, salinity, corrosiveness;

3. Geomorphological conditions

Geomorphological mapping is an essential part of engineering geological mapping, which is missing in the report, which can be carried out cheaply and quickly by suitably trained people. Evaluation of geomorphological conditions is more than a simple description of surface topography. It should provide the basis for an explanation of:

the relation between surface conditions and geology; the origin, age and development of individual geomorphological elements; the influence of geomorphological conditions on hydrology and geodynamic processes; the impending development of geomorphological features such as the erosion of river banks,

On medium- and large-scale maps and plans of the actual boundaries and morphology of geomorphological features needs to be mapped of the reservoir and project area. On small-scale maps, point symbols are used to show significant geomorphological elements. The base maps are contoured to show the surface topography.

4. Active geomorphological processes

Surface geological processes that may be active at the present time in the reservoir and project area, or the legacy of formerly active processes, include:

those due to erosion and deposition; aeolian processes; slope movements; permafrost; formation of karstic conditions suffusion; volume changes in soils.

All these present and paleo-geologic features, important in planning and engineering construction, can be shown on special-purpose or general-purpose comprehensive maps, and on topical maps. The amount of detail depends on the scale of the map.

5. Geodynamic conditions

Geodynamic phenomena result from so-called endogenetic processes operating in the Earth's crust at the present time that have a surface expression. Chief among these are seismic and volcanic activity, which may be associated, and neo-tectonic movements resulting in uplift or depression of the surface.

Seismic activity may be mapped in terms of the intensity of the event, using isoseismal lines, or surfaceexpression of present-day and historical events. Mappable features include: offset streams, terraces and manmade structures; sag ponds; lines of springs; linear trenches and fault scarps.

The frequency and intensity of volcanic activity, together with the nature, location and extent of the volcanic products, are of importance in engineering geology. But in the project area we think it may not be important but still need to say something about this in the report.

6. Discontinuities

The report does not appear to have appreciated proper recording or description of discontinuities. It is of paramount importance to have an accurate and systematic recording of all parameters of all geological discontinuities. This record/data of present condition is not only important now during construction phase but will also be of immense value in the future for interpretation when periodic assessment of the dam safety is carried out.

A discontinuity is a surface within the rock mass that is open or potentially openable under the stress level applicable in engineering because the tensile strength across the surface is lower than that of the rock material. Thus a discontinuity is not necessarily a plane of actual physical separation within the rock mass, for example slaty cleavage.

Discontinuities have many modes of origin, but two main types may be recognized: those that occur in sets, for example bedding planes, joints, cleavages, foliations, and those that are unique, for example individual joints or faults. Of these, bedding planes, cleavages and foliations are discontinuities only where there is a parting or substantial weakening of the rock across them. Similarly joints and fault planes may be healed by introduced minerals or by alteration along them.

Description of discontinuities is aimed at determining their nature, orientation, spacing, persistence, roughness, wall strength, aperture, infilling, seepage, number of sets, and block size and shape. It has to be carried out following ISRM or BSEN Standard which is not mentioned in the report.

Orientation: A compass with clinometer is used to measure the dip - the maximum inclination from the horizontal - of the planar feature being measured with reference to magnetic or true north. Alternatively, the dip and dip direction of the plane may be determined, and this is commonly preferred.

The joint rosette or a contoured spherical projection needs to be presented, which is missing.

Spacing: The mean or modal spacing of a set of joints that is the perpendicular distance between adjacent discontinuities.

Persistence: This is a measure of the areal extent of a discontinuity from its inception to its termination in solid rock or against another discontinuity. For major joints, the plane may extend beyond the limits of the exposure and then the maximum trace length or area should be recorded.

Roughness: A discontinuity surface may be planar, undulating or stepped, and descriptive terms are based on two scales of observation: small scale (several centimetres); large scale (several metres).

Wall strength: The shear strength of a discontinuity may be significantly affected by the condition or strength of the rock material forming the walls of the discontinuity, especially where infilling is small or absent and wall roughness is significant. Wall strength may be measured in terms of compressive strength, which may be lower than the strength of the fresh rock material due to weathering or alteration of the walls.

Infilling: The infilling between discontinuity surfaces may be soil introduced into the opening, minerals such as calcite or, in the case of faults, clay gouge or breccia. The width of an infilled discontinuity - the perpendicular distance from wall to wall - is important in conjunction with the roughness in determining the resistance to shear along the discontinuity. The infilling material should be identified and described. Strength of the infill may be assessed visually and manually, or should be measured.

7. Permeability of Dam Foundation by Lugeon Test

The extents of grouting and cut-off depths required in a dam foundation are directly related to the hydraulic conductivity (permeability) of the rock masses involved. In contrast to other geotechnical parameters for which variations can usually be measured in percentage terms (e.g., shear strength, density, compressibility, etc.), variations in hydraulic conductivity are usually measured in terms of magnitudes. Selecting a representative value of hydraulic conductivity becomes of the outmost importance during design; especially, since under such a wide variation range, averaging the measured values will not suffice.

Unlike soils, where seepage takes place through a series of small, closely spaced, interconnected pore spaces, seepage through rock masses occurs mostly along discrete planar discontinuities (e.g., joints, foliations, shears, etc.). Thereby, whereas in soils hydraulic conductivity is mostly controlled by the size, shape and arrangement of its voids, in rock masses the conductivity depends on the aperture, spacing and infilling characteristics of its discontinuities.

Discontinuity aperture plays a particularly important role in the hydraulic conductivity of a rock mass. Consequently changes in the stress condition of the rock mass can produce significant changes on its hydraulic conductivity. The existence of an interrelation between stress and hydraulic conductivity ultimately means that accurate estimates of the hydraulic conductivity of a rock mass can only be obtained using in-situ tests.

For this purpose - the most commonly used in-situ test Lugeon Test (also called Packer Test) to estimate hydraulic conductivity of rock masses must be in place and data has to be recorded and presented systematically, which is not found in the Report.

8. Soil and Rock testing

The report does not say anything about proper recoding of soil and rock testing and results in a systematic way. For future data baseline and dam safety assessment it is advised that recoding of the following information is maintained for the soil, in-situ rock, rock used for the construction material and water used for mixing with concrete.

Recommended for soil:

Compressibility, permeability, durability

One-dimensional consolidation test in an Oedometer as BS1377: 1990 pt 5 method 3

Swelling pressure test in an Oedometer

Permeability by constant head permeability test as BS1377: 1990 pt 5 method 5

Falling Head Test (Head 1982)

Dispersivity test by dispersion method BS1377 pt 5 method 6.4

Shear strength (total stress)

Undrained Shear strength of a set of three 60mm x 60mm square specimens by direct shear, test duration not exceeding 1 day per specimen as BS1377: 1990 pt 7 method 4

Undrained shear strength of a set of three 38mm diameter specimens in triaxial compression without the measurement of pore pressure as BS1377: 1990 pt 7 method 8

Undrained strength of a single 100mm diameter specimen in triaxial compression without the measurement of pore pressure as BS1377: 1990 pt 7 method 8

Undrained shear strength of single 100mm diameter specimen in triaxial compression with multistage loading and without measurement of pore pressure as BS1377: 1990 pt 7 method 9

Shear strength (effective stress)

Consolidated undrained triaxial compression test with measurement of pore pressure (set of three 38mm specimens) as BS1377: 1990 pt 8 method 7

Consolidated undrained triaxial compression test with measurement of pore pressure (multi-stage test using single 100 mm specimen) as BS1377:1990 pt 8

Consolidated drained shearbox test; peak and residual shear strength of a set of three 60mmx60mm square specimens as BS1377: 1990 pt 8

Mineralogical Testing

Petrographic Analysis ASTM C 295-03

X-ray diffraction analysis of finely ground sample

Recommended for rock:

Natural water content of rock sample BS EN 1097-5:1999

Porosity/density using saturation and buoyancy BS EN 1097-6:2000

Slake durability Index; ASTM D4644

Flakiness Index BS EN 933-3:1997

Elongation Index; BS 812-105.2:1990

Los Angeles Abrasion Value; ASTM C535

Aggregate crushing value; BS 812-110:1990

Ten percent fines value; BS 812-111:1990

Aggregate impact value; BS 812-112:1990

Aggregate Abrasion value: BS 812-113:1990

Water Absorption Index; BS EN 1097 pt 6

Specific Gravity; BS EN 1097 pt 6

Specific Heat; CRD-C 124

Linear Thermal Expansion; CRD-C 125 / 126

Schmidt Rebound Hardness

Particle Size Determination; BS EN 933-1:1997

Organic Content (natural sand) BS EN 1744-1:1998

Alkali Reactivity; Quick Chemical Test; ASTM C 289

Alkali Reactivity; Accelerated Mortar Bar Test

Determination of point load strength of rock specimen

Uniaxial compressive strength

E.O item 7B803 for deformability in uniaxial compression

Indirect tensile strength by Brazilian Method

Undrained triaxial compression without measurements of porewater pressure

Undrained triaxial compression with measurement of porewater pressure

Direct shear strength on orientated joint plane

Direct shear strength on grout / joint interface

Direct shear strength extended test to determine residual shear strength

Pulse Velocity Test; ASTM C 2848

Creep in Compression

Swelling Test in triaxial cell

Free Swell Test

Determination of Cerchar Abrasiveness Index (CAI)

Water Chemistry Testing:

General Water Chemistry

Mixing Water for Concrete test in accordance with BS EN 1008:2002

9. Rock Mass Classification Using RMR and Q Systems for Tunnel Support

RMR parameters of Bieniawski 1989

It is mentioned in the Report that RMR is being used for rock mass classification in one of the tunnels.

But the parameters used to classify a rock mass using the RMR system have not been presented. There are no geotechnical logs of the tunnels for side walls, crown or blasted face. It is suggested to record RMR data for dam and tunnels in a systematic fashion.

Uniaxial compressive strength of rock material.

Rock Quality Designation (RQD).

Spacing of discontinuities.

Condition of discontinuities.

Groundwater conditions.

Orientation of discontinuities.

Rock Tunneling Quality Index, Q of Barton et al (1974)

There is no record of Q for tunnel condition. It is strongly suggested that Q system, along with RMR, muse be in place for rock mass classification, which is widely used nowadays worldwide and useful for arbitration in case something goes wrong in the tunnels after construction.

Specific parameters to calculate Q are given below and must be recorded by experienced rock mass classification geologist(s).

RQD is the Rock Quality Designation

Jn, the joint set number

Jr, the joint roughness number

Ja, the joint alteration number

Jw, the joint water reduction factor

SRF, the stress reduction factor

10. Numerical Modeling of Underground Excavations

It is strongly suggested that numerical models, especially for tunnels, be set up in order to understand the adequacy of used support. Simple software such as RS2(Phase29.0), which is a powerful 2D finite element program for soil and rock applications, can be used for a wide range of engineering projects and includes excavation design, slope stability, groundwater seepage, probabilistic analysis, consolidation, and dynamic analysis capabilities etc.Complex, multi-stage models can be easily created and quickly analyzed for tunnels in weak or jointed rock. The models will also allow checking performance of rock/soil support during events of earthquake of various magnitudes.This is not found to be studied in the report.