Advance on Unloading Rock Mass Mechanics

Prof. Li Jianlin Dr. Li Xinzhe

China Three Gorges University Dec. 2016 Hong Kong CONTENTS

1、Research Background 2、Methodology 3、Research Contents 4、Engineering Application 5、Research Platform 1. RESEARCH BACKGROUND

1.1 Industry Background Over the past few decades, China has successfully built a number of hydropower stations. According to the National Energy Development Projects (2006-2015), plenty of hydropower based constructions have been built in China.

13 Hydropower Bases 西电东送West Power -to-East 1. RESEARCH BACKGROUND

Hydropower Bases 1. RESEARCH BACKGROUND

1.2 Engineering Background • Three kinds of rock masses Slope Foundation

Tunnel 1. RESEARCH BACKGROUND

Example 1: Slope Engineering

Excavation rock masses

휎1 . 휎1 A 휎3 휎3

Unloading

•For point A

•Before excavating: 휎1, 휎3 → loading condition.

•After excavating: 휎1 →loading condition, 휎3 → unloading condition. 1. RESEARCH BACKGROUND

Example 2: Tunnel Engineering

A A

Distribution of σθ Distribution of σr Enlarged drawing of point A

•For point A

Before excavating: 휎θ，휎r →loading condition.

•After excavating: 휎θ →loading, 휎r → unloading. 1. RESEARCH BACKGROUND

Example 3: Foundation Engineering

휎1 Dam

휎3 Initial ground

Force diagram of point A A •For point A

•Before excavating: 휎1, 휎3 → loading condition.

•After excavating: 휎3 →loading, 휎1 →unloading condition.

•Dam construction: 휎1, 휎3 → loading condition 1. RESEARCH BACKGROUND

Different unloading paths of the unloading rock masses

The stress state 휎1, 휎3 change process unloading

휎1 unloading

휎3 unloading

 In different forms of rock masses engineering, the mechanics action process of the rock masses is different.  The mechanical properties of rock masses are varied during the process of bearing alterative forces.  There are essential distinctions between the mechanical characteristics of rock masses under unloading and loading conditions. 1. RESEARCH BACKGROUND

The discrepancy between the deformations computed by using traditional method (without considering unloading condition) and the actual deformations are shown in this table.

Calculating deformation Engineering Actual deformation by traditional method Lianzi cliff dangerous rock body 2.17m 10cm in the Three Gorges Jinchuan mine slope 1.52m 20cm Ertan hydropower station 17.57cm 3cm The Three Gorges permanent 17.38cm 3.47cm lock slope

Considering the above all, one should study the unloading mechanics to solve those problems as a new approach. 2 Methodology

Multi-crossed Disciplines

Engineering Geology Reconnaissance Engineering Survey Mechanics

Unloading Rock Engineering Computer masses Structure & Science Mechanics Construction

Engineering Engineering Mathematics Economics … … 2 Methodology

Research Procedure

Understanding of Rock Masses

Utilization of Rock Masses

Protection of Rock Masses

Monitoring of Rock Masses 3 Researech Contents

(1) Division of Excavation Damage Zone

The essential of unloading rock masses is that the adjustment of the internal stress state of the rock masses leads to the damage of rock masses quality during the excavation process.

Moreover, the stress adjustment in different rock masses region changes Weak Strong unloading unloading at different levels, corresponding to the different deterioration degree of Excavation rock masses quality. Therefore, how to divide the excavation damage zone becomes one of the key problems in the study of unloading rock masses.

Excavation Damage Zone 3 Researech Contents

(1) Division of Excavation Damage Zone

Method of dividing Excavation Damage Zone  In-situ stress measurement  Acoustic wave test  Numerical simulation

Distribution of horizontal stress Distribution of point safety factor 3 Researech Contents

(2) Quality Evaluation of Unloading Rock Masses

Excavation unloading effect of rock masses is introduced into RMR.

RMR 3 Researech Contents

(3) Anisotropy of unloading rock masses

Anisotropic mechanical characteristics of jointed rock masses is revealed by experimental study.

变形模量Deformation弹性模量 modulus

45.0

GPa 7.0 Young modul 40.0 MPa 35.0

6.0 MPa / 30.0

5.0 GPa

/ 25.0 4.0 20.0 3.0 15.0 2.0

变形参数 10.0 单轴抗压强度 1.0 5.0 0.0 0.0

0° 30° 45° 60° 90° strength/ Compressive Deformation parameters/ Deformation 0 15 30 45 60 75 90 0 15 30 45 60 75 90 节理倾角/° 节理倾角/° Shear failure Angle/° Angle/°

Loading常规加载 Unloading卸荷Load Unloading卸荷 Loading常规加载 卸荷试验线性回归分析 常规加载试验线性回归分析 25.0 50.0 20.0 40.0 15.0

 30.0

/

c/MPa

10.0  sliding failure 20.0 5.0 10.0 0.0 0.0 0 20 40 60 80 100 0 20 40 60 80 100 Angle/α/°° Angle/α/°° 3 Researech Contents

(4)Size Effect

Model of jointed rock masses Four sets of discontinuities in the

Three Gorges Ship Lock

Unloading curves of different geometric similarity scale

3 Researech Contents

(4)Size Effect Relationship between Relationship between compressive tensile strength and strength and size size

Deformation modulus varies with the size

Rock masses size(m) 0.75×0.75 2.25×2.25 6.75×6.75 20.25×20.25

Compressive deformation modulus 50 45 38 35 (GPa) Tensile deformation modulus (GPa) 6 4 2.0 1.5 Initial unloading modulus (GPa) 35 32 28 26 3 Researech Contents

(5) Yield criterion for unloading rock masses

Drucker-Prager criterion is established by considering the shear failure characteristics of unloading rock masses.

Formulation of D-P criterion:

F I1  J 2  J 2  k  0

Material parameters:

2  m c 12cos    2 m c  3sin  3cos   12cos    22  ks c 4cos  3 Researech Contents

(6) Creep behavior

The nonlinear constitutive model of unloading creep for jointed rock masses is established.

b() t t* Damage factor Da1  (  )

EK

损伤因子 D    K  EM M

M K Creep behavior of intact rock Nonlinear constitutive model

E      K t   t 1  eK ( t  t* ) EE   MMK   E  K t   *    (a  )b()* t t t  1  eK ( t  t ) EE    Creep behavior of jointed rock masses  MMK  3 Researech Contents

(7) Fracture behavior

An equivalent analytical model of compression shear and tension shear for unloading rock masses is proposed.

y xy Actual

stress Equivalent Actual stress stress a b a Equivalent stress b d A B 0 l  y`  x y xy a c x y xy x` Compression-shear fracture Tension-shear fracture

a(1/ 1) 2 m   c s m 16Kc / 2lKc (1 Kc / Kc ) 2K Ic a 16K 2  2a(1/ 1)K m  (1/ 1) s 2 2  C C c 2 c s  32Kc /l c (1 Kc / Kc ) 3 Researech Contents

(8) Constitutive model of unloading rock masses

An incremental constitutive model of unloading rock masses and a hyperbolic nonlinear elastic constitutive model of unloading rock masses are established.

Plastic deformation

T FF    b s   b s      d  D T  d  e FF    AC b s    b s   e   Yield function EEEEbs F f  f  0 b sEEEEs b b s b s

Elastic-brittle-plastic constitutive model 3 Researech Contents

(9) Determination of mechanical parameters for jointed rock masses

A method, which suggests starting from the small-size fracture to the large-size fracture to study the size effect of mechanical parameters, has been proposed to obtain mechanical parameters of jointed rock masses.

裂隙-5，宽度10cm,间距15m e 裂隙-1，宽度1cm,间距1m

3 f 裂隙-2，宽度1cm,间距1m

a b Jointed rock masses 1

d 2 c 裂隙-3，宽度4cm,间距4m

裂隙-4，宽度8cm,间距10m

Analytical model 3 Researech Contents

(10) Inversion of mechanical parameters of unloading rock masses

Based on the artificial neural network, the excavation unloading effect has been considered in the inversion of rock mechanics parameters.

Deformation mechanism of unloading rock masses Comparison of calculation and monitoring in slope

Analytical model

In situ stress Monitoring

Geological Monitoring Excavation factor data Support

Impoundment Deformation/mm Inverse analysis Rainfall

Predicting the Earthquake Calculation deformation Creep 4. ENGINEERING APPLICATION

4.1 Applied valley

Jingping I Project 14 valleys Jingping II Project Shenxigou Project Lianghekou Project Pubugou Project 46 projects Yagen Project Daba Project Jinchuan Project Baihetan Project Lenggu Project Cihaxia Project Xiluodu Project GuandiProject Maerdang Project Ahai Project Lawa Project Ludila Project Tingzikou Project

Yellow River

Han River Xiaowan Project Jialing River Dadu River Sanliping Project Rumei Project Qing River Yangtze River Lidi Project Ya-lung River

Jinghong Project The Three Gorges Loushui River Geheyan Project Jinsha River Shuibuya Project Nanpan River Gaobazhou Project Lantsang River Beipan River Sujiahekou Project Binlangjiang Jiangpinghe Project

Dongqing Project Tianshengqiao Project Guangzhao Project Nuozu Project

4. ENGINEERING APPLICATION

4.2 Applied Engineering

Cihaxia Shuibuya Hydropower station Hydropower station Geheyan Hydropower station Jingping II Hydropower station

Rumei Hydropower station

The Three Gorges Project

Xiaowan Hydropower station

Shenxigou Hydropower station

4. ENGINEERING APPLICATION

4.2 Applied Engineering

1 ELEMENTS AUG 13 2009 MAT NUM 06:43:13

Z X Y

a model of slope ! Landslide-Geheyan Slope-Jiangpinghe High slope-Rumei High slope-Jinchuan

Tunnel-Dashankou Tunnel-Danba Slope-Xiaowan Slope-Dongqing 5. RESEARCH PLATFORM

5.1 Introduction of CTGU China Three Gorges University China Three Gorges University

Three Gorges Dam Gezhouba Dam 5. RESEARCH PLATFORM

5.2 Research team Team members

5. RESEARCH PLATFORM

5.3 Research platform  National Field Observation and Research Station of Landslides in Three Gorges Reservoir Area of Yangtze River

5. RESEARCH PLATFORM

5.3 Research platform  Key Laboratory of Geological Hazards on Three Gorges Reservoir Area（China Three Gorges University），Ministry of Education

Monitoring System 5. RESEARCH PLATFORM

5.3 Research platform Equipment（1）

Three dimensional landslide physical model test system (12mx6mx6m)

5. RESEARCH PLATFORM

5.3 Research platform Equipment （2）

ELE rock seepage system PCI-2 acoustic emission detection system ST500 three-dimensional non- contact surface profilometer

RMT-150C rock mechanics test system Adaptive automatic triaxial testing machine RLW-2000 triaxial creep test system 5. RESEARCH PLATFORM

5.3 Research platform Equipment （3）：

quadruple direct shear JSM-7500F scanning Computer controlled electro-hydraulic apparatus for unsaturated soil electron microscope servo soil dynamic triaxial testing machine

轴向加压装置 压力室 UPS 应急 位移传感器 反 电源 压 进气管 压力室 控 进气口 制 加热板 器

进水管 排水口

排水管

平衡手轮 轴压控制器 孔压传感器 差压传感器

DHJ-50 large single shear、 HKUST-GDS unsaturated The soil-water characteristic curve tester direct shear apparatus soil triaxial apparatus THANKS

2016.12