自然资源部岩岩溶动力学重点实验室

KARST ENGINEERING GEOLOGY

2002-07-10KDL 12698

KARST ENGINEERING GEOLOGY

16

Kartification below Dam Sites: A Mode of Increasing Leaksge from Reservoirs

W. Dreybrodt, D. Romanov,
Karst Processes Research Group, Institute of Experimental Physics, University of Bremen,
D-28334 Bremen Germany, dreybrod@physik.uni-bremen.de
F.Gabrovsek, Karst Research Institute, Postojna, Slovennia, gabrovsek@zrc-sazu.si

Abstract

Unnaturally steep hydraulic gradients below foundations or across abutments of dams may cause solutional widening of fractures in karstifiable rocks of carbonates or gypsum. This could cause increasing leakage, which may endanger the performance of the construction. To investigate this problem recent models on natural karstification have been applied. We have performed numerical simulations of leakage below a model dam with a grouting curtain reaching down to 100m below its impermeable foundation of 100m width. Water is impounded to a depth of 100m. The dam is located on a terrane of fractured rock dissected by two perpendicular sets of fractures with spacing of 5m, and with a log-normal distribution of their initial aperture widths of about 0.02cm. In the first state of karstification these fractures widen slowly, until a pathway of widened fractures below the grouting has reached the downstream side with exit widths of about about 1mm. This causes a dramatic increase of leakage and turbulent flow sets in. After this breakthrough at time T, in the second state of karstification, dissolution rates become even along these fractures and cause widening of about 0.1cm/year for limestone, and at least of 1cm/year for gypsum. This leads to an increase in leakage to unbearable rates within further 25 years for limestone, but only 5 years for gypsum. We have performed a sensitivity analysis of breakthrough time T for the various parameters, which determine the problem. The result shows breakthrough times in the order of several ten years for both limestone and gypsum. We have also modeled leakage to caves or karst channels 200m below the bottom of the reservoir, which could induce the formation of sinkholes. The model can be extended to more realistic settings. In conclusion our results support the suspicion that increasing leakage at dam sites can be caused by recent kasrtification which is activated after filling the reservoir and can lead to serious problems within its lifetime.

17

The Relationship between Karstification and Morphotectonic Characteristics of Gachsaran Evaporitic Formation, Jarreh Dam, Sw Iran

Arash Barjasteh, Geology & Geotechnics Group,
Technical Bureau, Khuzestan Water& Power Authority,
P.O.Box 61335-137  Ahvaz-Iran
E-mail: barjasteh@hotmail.com

Abstract

JARREH DAM with a nearly 12km long reservoir and total volume of 242 million cubic meters is constructed over Rud Zard (yellow) River, on the northeast of Ramhormoz City, in Khuzestan Province, southwest of Iran. The dam site is located on Pleistocene Bakhtiyari Conglomerates but over than two-third of reservoir area is in contact with Miocene Gachsaran Evaporites composed locally of the anhydrite, red and grey marls, salt and sandy limestone. The study area is a part of Zagros active fold belt and three main thrusts pass through it. The fault planes dip northeast and trend due NW-SE, general trend of Zagros Mountains. Being parallel, two of them are located about 3.5km upstream the dam site, creating a tectonic depression. Their trend is normal to the reservoir extension. Tectonic condition of the reservoir area and unique lithologic sequence of Gachsaran Formaton increased its erodability so that various erosional features have occurred specially at the fault junctions. Investigation of frature trends on satellite image and field surveys together with determination of some morpho-tectonic indices, say, mountain front sinuosity(Smf), valley floor width-depth ratio( Vf) and stream-length gradient index(SL), indicate high activity of the region. The general trend of Rud Zard river course coincide with a regional N30E trending lineament. Furthermore, straight parts of the river follow the existing NE-SW, and N-S fractures. The effect of morphotectonic characteristics on the karst development and spring appearance is considerable particularly along fault strikes and intersections. Although Gachsaran Formation is primarily considered impervious, its highly tectonized nature may produce unexpectable problems after impounding.

Key words   Jarreh, Gachsaran Evaporites, Zagros, Karstification, Morphotectonic, lineament

18

Special Speleothems in Cement –grouting Tunnels 
and Theirimplications of the Atmospheric CO2 Sink

Zaihua Liu, Dianbin He
(Institute of Karst Geology, Guilin, Guangxi, 541004)

Abstract

Based on the analyses and comparisons of water chemistry, stable carbon isotopes and deposition rates of speleothems, the authors found that there are two kinds of speleothems in the tunnels at the Wujiangdu dam site, Guizhou, China, namely the CO2-outgassing type and the CO2-absorbing type. The former is natural, as observed in general karst caves, and the product of karst processes under natural conditions. The latter, however, is special, resulting from the carbonation of a cement-grouting curtain and concrete. Due to the quick absorption of CO2 from the surrounding atmosphere, evidenced by the low CO2 content in the air and the high deposition rate of speleothems (as high as 10cm/a) in the tunnels, the contribution of the carbonation process to sink of CO2 in the atmosphere is important (in the order of magnitude of 108 tons c/a) and should be taken into consideration in the study of global carbon cycle because of the use of cement on a world wide scale.

Key words  Speleothem , Cement grouting ,  Atmospheric CO2 sink

19

The Role of Tectonic Environment on the Karstification of Two Dam Sites, West and South of Iran

Arash Barjasteh
Dez Ab Consulting Engineers Co., Golestan Road, Ahvaz-Iran

Abstract

Two dam sites namely Baneh and Kavar in the western and southern Iran respectively are discussed. Both sites are located in mountaineous regions, and have nearly similar annual precipitations. In the geological point of view, kavar dam site is located in Zagros Folded Belt whereas Baneh dam site lies in Sananda j-Sirjan Zone. While the former is composed mainly of sedimentary rocks, the latter is a complex metamorphic assemblage. The study shows that karstification is basically fault-controlled in the Kavar area so that big springs are observed along the fault trends. In Baneh area, however more karstic features are limited to the interfaces between schistosity and joint surfaces. The depth of faulting affected karstification extent in Kavar area, causing it to increase deep to approximately 160m. This depth is limited to about 80m in Baneh area. According to geotechnical investigations, permeability values in the Baneh and Kavar dam sites are up to 15.6 and greater than 25 Lugeons, respectively. It is concluded that the karstification extent and its geotechnical impacts on the discussed dam sites are governed by their tectonic environments.

Key word: tectonic environment, karstification, Zagros Folded Belt, Sananda j-Sirjan Belt,

faulting, permeability

20

Evaluation of Solubility Behavior of Carbonaceous Rocks at Kavar Damsite  (Fars Province –Iran)

Ajalloeian R.* & Ghobadi M.H.** & Karami R.***
*PhD of engineering geology (Isfahan University-Iran)
**PhD of engineering geology (Shahid Chamran University-Ahvaz)
***MSc of engineering geology (Isfahan University-Iran)

Abstract

Natural solution of soluble rock such as limestone is usually not problem within our timeframe since solution is very slow, However, instability within existing dissolution enlarged joint sets or caves are of interest since collapse may be triggered by different factors such as variations in the watertable, excessive rainfall, and enlargement of underground voids either naturally or by man. However, it is important to assess the main causes of subsidence and sinkhole collapse in selection of damsite. Present paper is dealing to investigate the solubility rate of rocks in Kavar damsite.

The Kavar damsite is about 10km far from Kavar city in Fars Province, in south of Iran. Regarding to karst investigation and assessment of carbonaceous rocks solubility rate, several tests on Asmari limestone cores which obtained from different depths has been carried out. Solubility behavior of carbonaceous rocks samples in the water with different acidity has been evaluated. The water samples were taken in special split time and sent to laboratory to analyzed the water quality.

In this paper, besides the approaching of chemical analysis of samples, variation of calcium ion concentration in different times,(dc/dt)-(Cs-C), and variation of water acidity versus concentration and verifying of calcium ion concentration(dc/dt) in various times are investigated.

The results of these analyses show the general view of carbonaceous rocks solubility behavior of damsite. Also, regarding to the changing of calcium concentration versus time in each cycle (with different acidity ), the average constant solubility rate obtained as equal to 3.06×10-7cm/s. It can be concluded that the solubility of damsite carbonaceous rocks is low.

21

Engineering Geology of Karst Areas in South Africa and Legislation

Nicole Trollip
Council for Geoscience, Private Bag×112, Pretoria 0001, South Africa

Abstract

Significant portions (approximately 20 percent) of densely populated areas in Gauteng Province, some parts of the North West Province, and most of the gold-mining distracts in the Far West Rand are underlain by dolomitic limestone formations (colloquially known as dolomite). During the past 40 years, 38 people have died as a result of sinkhole formation, in excess of one billion rands worth of property damage has occurred and property values in certain areas have fallen below market trends.

Sites for urban development were investigated on an ad hoc basis until 1965 when legislation was passed to regulate land development. It required that each portion of land (in the former Transvaal) earmarked for urbanization had to be investigated prior to actual development.

In recent times the Housing Consumers Protection Measures Act was introduced in essence to protect housing consumers and to facilitate the establishment and functions of the National Home Builders Registration Council (NHBRC)

This Council regulates the home building industry and publishes a home building manual containing requirement and guidelines (including specifications for dolomitic land ) with which registered home builders/developers must comply.

In terms of this Act the following is required:

1. Sites must be classified appropriately

2. Appropiate precautionary and remedial measures must be recommended

3. A risk management system must be designed

4. Ongoing involvement in the project (i.e. inspection of trenches, changes, confirmation documented in a Construction report and signing of layout plans)

This is indeed a unique and valuable piece of legislation. For development on dolomite this has an immense impact. Although different dolomite regions in the world do not experience the same problems, the sharing of information assists scientist to be open minded and receptive to new ideas. For us as an organization, involved in the setting of standards, spread of knowledge is certainly essential.

22

Review of Karst Collapses in China During 1999-2000

Mingtang Lei  Jiang Xiaozhen  and  Liyu
(Institute of Karst Geology, Guilin, Guangxi 541004, China)
E-mail: mingtang@mailbox.gxnu.edu.cn

Abstract

As a main geohazard in karst region, more than 13 sinkhole collapse events happened from 1999 to 2000, directly economic losses are more than 50 million yuan. All of the sinkholes are distributed in south of China (table1, figure1), most of them are induced by human activities including mining, pumpage, waste storage etc.

The newest critical sinkhole event happened in Hongshan District, Wuhan, Hubei Province, in April 6th, 2000. There are 21 sinkholes formed, and the influence area is more than 0.1km2(figure2). Two buildings were swallowed, and sixteen cracked (figure3-6). About 150 families are suffered from the accident, more than 900 residents are homelees. Organized by government, these people are diverted on time without casualties. The major inducing factor is the fluctuation of water level in Changjiang River.

23

Engineering Geology of Limestone in Malaysia

By  TAN Boon Kong