Journal of Materials Processing Technology 65 (1997) 22 -25

A note on the stresses of the middle gate bay of Three Gorge Lock

Wang Feng a,*, Ma Wen a, Xie Huimin b, Li Laishou a a Deparmtent of Machinery. Yantai Uniaersity, Qhtgyttanzltai, Sltandong Prorkw 264005, People’s Republic of Chu

b Department of‘ Machinery, Tsingittta Utticersity. Beijing, Proplr ‘s Rrprthlic c!f Cltinu

Received 3 February 1995; revised 17 October 1995

Industrial summary

On the basis of geological measurement data and criteria, this paper studies the stress distribution in a horizontal section of the middle gate bay of Three Gorge Lock by the photoelastic experimental method, with the middle gate bay and the rock foundation jointly subjected to load under the action of the thrust of the gate. The results obtained are compared with those calculated using the finite-element method. This article also estimates the three-dimensional stress distribution in the lock and identifies the danger region, which is of reference value for the design of the Three Gorge Lock. 0 1997 Eisevier Science S.A.

Keywork Stresses; Photoelastic method: Three Gorge Lock; People’s Republic of China

1. Introduction

Three Gorge Lock in China is composed of two groups of parallel, si4ti-stepped, permanent, navigable structures. The head of the gate, the chamber, the water-carriage system, the valve well, etc., are all pro- tected by concrete lining walls. The bedrock consists mainly of black granite and fine epidiorite. In accor- dance with the preliminarily suggested value of the rock mechanical index application of the San Douping Dam of the Three Gorge key water-control project, the de- formation moduli of the bedrock vary within the range of 19.6-39.2 GPa.

Plane photoelastic experiments have been conducted using models of the same modulus of elasticity, of combined materials, and of variable thickness. Under situations of various bedrock moduli of elasticity, a study is made on the strese distribution on the middle gate bay, when the structure is under the lock-sill gate push, on a horizontal section of 100.00 m typical elevation, at the 136.00 m chamber water level. An evaluation is also given of the disadvantageous factors in operating with a single lock group.

* Corresponding author.

OPX-Ot36/P7/$17.00 Q 1997 Elsevier Science S.A. All rights reserved SSDI 0924-0136(95)02237-6

2. Model design and exerting load

The scale of modelled simulation involves each half of the two groups of locks, with a 205.00 m length of bedrock in between, including 16 valve wells. The geo- metric scale is LJL, = 500, the model being 41 cm in length and 0.87 cm in thickness. In consideration that the lining between the gate bay and the chamber is separated by an expansion joint, no effect will be made to the lining wall of the chamber when the gate bay is under thrust. In addition, because this lining is fairly thin, the concrete lining wall can be omitted in the experiment. For simplification of the model, the lining for the valve wells is also omitted.

The concrete modulus of deformation, provided by the design department, is: E, = 25.5 GPa. The bedrock moduli of deformation are illustrated in Table 1.

In order to simulate bedrock with variable moduli of deformation, three different models are devised, their deformation moduli all being replaced by their elasticity moduli. A model of the same elasticity modulus is made of an identical plate material and used to simulate a situation where the deformation moduli of the bedrock

If’. F@/fC 1’1 UI. JOIE)71U/ Of .WOiH lUl.5 PloW.C.$:/ig TwhtZcJ/f~gj~ 65 f1997) 22 _‘5

Table 1 Bedrock moduli of deformation

__- Classilication of bedrock

_~____ Black granite Fine epidiorite

--_____ Mechanical Fresh Slight CYcaC Brcsh Siighi Vc’c‘ik properties ef%loresccnce CiflQlTSCCIW effiorescence enlorescence

Deformation (39.2-49.0) x 601 29.4 - 39.2 IY.h-29.4 -79.4 - 39.2 19.6-29.4 9.8- 19.6 modulus E, (GPa)

.-_-._____ ---

23

is equal to the elasticity moduii of the concrete. The combined model is made by sticking together materials of different moduli of elasticity, whereas the model of

ickness is made by ~acbi~~n~ a single mate- rial into varying t icknesses. These latter two models simulate the ~ornb~~ator~a~ conditions when the moduli of the bedrock differ from that of the concrete.

2.2. Experimenml condiitiorzs und the applied-loud experiment for the combined model

After the annealing treatment of the machined com- ponents, the combined model is stuck together using a room-temperature adhesive agent. Then it is placed into a double plastic bag containing drying material, the experiment being conducted after the adhesive agent solidifies. The laboratory is provided with an air condi- tioner and a moisture separator, in order to maintain constant room temperature and a dry state.

The model is put into a load-applying fixture of ring shape, and fastened at both the top and bottom ends. in order to resist the push of the door. A sectional dis- tributive force is applied to the combined model

Fig. 1. The isochromatic lines.

the Boading of a backing plate. The sectional atic lines are illustrated in Fig. 1.

The elastic modulus of the bedrock is 29.4 GPa and the elastic modulus of the concrete is 25.5 GPa when the combined model is used to determine the boundary stress. The results are illustrated in Fig. 2.

The rock modulus is simulated with three goups of different plane models. Under the action of the same load, the stress at the orifice, the stress on the border, and the stress distribution pattern of section I -I which is near to the load area, are extracted, shown in Table 1.

The state of stress at the corner points of the valves is listed in Tabie 2.

Fig. 2. The boundary stress distribution of the lock loaded on a single side (unit: MPa; compressive stress: - ; tensile stress: + 1.

24 I#‘, Fettg er al. /Jottwal of Materials Processing Technology 65 (1997) 22-25

Table 2 Stress (MPa) at the corner points of the valves (N is the ratio of Young’s modulus for rock, I&, to that for concrete. EJ’

Models

N= 1 (model of identical modulus) N = 1.22 (combined model) N = li .42 (model of varying thickness) -- .--~-

Point

Valve number A

#1 - 1.28 t2 -0.63 #3 -0.09 #4 -0.09 #5 #6 #7 -0.52 #8 -0.40 #9 -0.34 #lO -0.28

B C D A B C D A B c D

0.09 - 1.0 0.34 - 1.39 0.21 -1.64 0.43 - 1.29 0.34 -1.01 0.37 0.23 -0.86 0.18 - 1.36 0.52 -1.39 0.49 -1.01 0.49 - 1.29 0.49 0.37 -0.31 0.37 -0.49 0.52 - 0.34 0.64 -0.58 0.52 -0.15 0.60 0.31 -0.40 0.40 -0.09 0.49 -0.29 0.64 -0.09 0.49 -0.21 0.64

0.37 -0.20 0.40 -0.20 0.40 -0.21 0.43 -0.21 0.43 -0.24 0.37 -0.18 0.40 -0.24 0.40 -0.26

0.43 -0.72 0.49 -0.58 0.40 -0.64 0.40 -0.58 0.37 - 0.46 0.46 0.20 -0.34 0.09 -0.61 0.34 -0.46 0.34 - 0.46 0.40 - 0.46 0.37 0.37 -0.28 0.37 -0.34 0.37 -0.37 0.40 -0.37 0.40 -0.43 0.37 0.22 -0.37 0.37 -0.37 0.34 -0.29 -0.46 -0.43 0.21 -0.21 0.46

a Compresive stress: -; tensile stress: +.

4. Stress analysis of the three-dimensional lock conversely, the further from the loading area, the structure smaller the stress.

The united action of the lock gate bay and the bedrock is a complicated space problem. It is quite a different approximate method to simplify the external forces and structure into a plane problem, as the action of the push of the gate at different elevations is, indeed, not the same. The magnitude of the push of the gate is related to the water level elevation. The entire loaded structure can be simplified as the action of two ‘beams’ which a&t and act on each other, with one of them as a horizontal beam supported on both sides (the experi- mental state), with the other as a vertical cantilever beam. It can be assumed that, under the action of the gate push, a reverse bending movement is produced on the vertical cantilever beam. A tensile stress C, is pro- duced on the contact surfaces, and a compressive stress 6, is produced on the unloaded border, thus enlarging the structural stress on the supporting area for the lock-sill under the load of the gate push; furthermore, because of the resistant shear effect between the ?evel surfaces, the further it is from the loading area, the more reduced the stress becomes. Hence, under the sole load of the push of the gate, the concrete near to the loading area may be in a bi-axial tensile state; this is the most dangerous area under load. In order to retain the safety of the structure, an adequate amount of concrete reinforcing bars must be deployed when the construc- tion is actually carried out. Areas further away from the loading area are under smaller tensile streses, hence there is no need to worry about the strength of the bedrock.

Since the structure’s own gravitational force, and the upstream water pressure on the gate bay, etc., are not considerea in the experiment, there may exist a large difference between the calculated results and the stress that the structure actually bears. When the effect of the structure’s gravitational force is taken into consider- ation, the tensile stress 6, produced by the gate push is counter-balanced by the compressive stress produced by the gravitational load, and the residual tensile stress will be greatly reduced. However, under the effect of the gravitational load, there may appear tensile stresses iongitudinally in the water-carriage system: this is an area that requires adequate attention.

5. Conclusions

From the experiment and through further analysis, the following conclusions may be drawn:

1. The areas where tensile stresses appear when the gate head and bedrock are jointly under tension by the effect of the gate push are: (i) the concrete lock-sill supporting area at the boundary of the upstream sur- face of the loading side; (ii) near to the angular points of the valve well, normal to the load. In these areas, engineering measures should be adopted in order to reduce the tensile stress, or a better design should be made for the same effect,

The same is true of the valve well. The nearer it is to the loading area, the greater the tensile stress becomes;

2. When the bedrock’s elastic modulus changes, affected by the load, there are different stress distribu- tions on the concrete and the bedrock. Under the above structural conditions, when the elastic modulus of the bedrock and that of the concrete are roughly similar to each other, the stress distribution is most favourable.