岩体不连续的剪切强度 | Barton-Bandis Model

1 引言

由于岩体是地质体，因此所有的岩体都含有不连续(discontinuities)，诸如层面、节理、剪切带和断层。对于原岩应力较小的浅层岩体，原岩的本身的破坏可能性较小，主要的破坏模式是沿着不连续面发生滑动，例如岩体边坡的破坏以及岩体地基的破坏。为了分析由单个岩块组成的系统的稳定性，需要了解控制分离不连续的剪切强度的因素。对于平面不连续的剪切强度，我们可以使用摩尔-库伦准则来计算；对于带有粗糙面的不连续面，我们使用Barton-Bandis剪切强度模型来计算。

2 Barton-Bandis剪切强度

硬岩中的天然不连续面永远不会是光滑的平面，节理面上总是带有起伏和粗糙度。这种特性对岩体的剪切行为有很大影响。一般来说，节理面的粗糙度会增加其抗剪强度，这种强度增加对岩石开挖的稳定性极为重要。Barton-Bandis（BB）模型用来模拟带有粗糙面的节理的剪切行为。

3 Barton-Bandis主要命令

block config barton-bandis

block contact cmodel assign barton-bandis

block contact property st-normal 40000 ...

st-shear 40000 jrco 8 jcso 30 ...

sigmac 50 lo .1 phir 20

block contact cmodel default barton-bandis

block contact list barton-bandis 

列出Barton-Bandis节理的节理模型接触参数。可以带三个关键字

(1) aperture 

(2) normal

(3) shear

block contanct change model 7

4 关键字描述

(1) phir 残余摩擦角的估计

其它参数的选择可参考文献：

[1] International Society for Rock Mechanics Commission on Standardisation of Laboratory and Field Tests. 1978. Suggested methods for the quantitative description of discontinuities in rock masses. Int. J. Rock Mech. Min. Sci. & Geomech. Abstr. 15, 319-368.

[2] Barton, N.R. and Bandis, S.C. 1990. Review of predictive capabilites of JRC-JCS model in engineering practice. In Rock joints, proc. int. symp. on rock joints, Loen, Norway, (eds N. Barton and O. Stephansson), 603-610. Rotterdam: Balkema.

5 关键bb.fin

bb.fin使用FISH储存Barton-Bandis joint model的参数。

set echo off

fish def $bb_fin

;  Barton-Bandis material model parameters -- FISH Include file

; --------------------------

;  index to Barton-Bandis joint property list is c_jex(zi)

;   (all values are floating-point type unless declared otherwise)

;  Barton-Bandis model parameters (JOINT MODEL BB)

; ------------------------------------------------

$bb_kn     =  1 ; joint normal stiffness (MPA / m)

$bb_ks     =  2 ; joint shear stiffness (MPa / m)

$bb_phir   =  3 ; residual angle of friction (degrees)

$bb_jcso   =  4 ; lab-scale joint wall compressive strength (MPa)

$bb_jrco   =  5 ; lab-scale joint roughness coefficient

$bb_aper   =  6 ; initial aperture of joint (mm)

$bb_ln     =  7 ; field-scale joint length (m)

$bb_lo     =  8 ; lab-scale joint length (m)

$bb_sigmac =  9 ; intact rock uniaxial compressive strength (MPa)

$bb_bbdtab = 10 ; damage table number

$bb_bbdmin = 11 ; minimum value of dilation allowed (mm)

$bb_bbdmax = 12 ; maximum value of dilation allowed (mm)

$bb_bbdam  = 13 ; Barton-Bandis shear damage factors

$bb_nc     = 14 ; joint normal displacement load cycle ( =load,-=unload)

$bb_sc     = 15 ; joint shear cycle

$bb_usmb   = 16 ; max. shear disp. ratio previous load cycle

$bb_usc    = 17 ; current shear disp. (mm)

$bb_usm    = 18 ; max. shear disp. ratio this load cycle

$bb_unc    = 19 ; current normal disp. (mm)

$bb_unm    = 20 ; max. normal disp. this load cycle (mm)

$bb_unpc   = 21 ; sum of previous irrecoverable closures (mm)

$bb_vmi    = 22 ; max. allowable closure this load cycle (mm)

$bb_kni    = 23 ; initial joint normal stiffness (MPa / mm)

$bb_virr   = 24 ; irrecoverable closure (unload cycle only, mm)

$bb_jrcn   = 25 ; full-scale joint roughness coefficient

$bb_jcsn   = 26 ; full-scale joint wall compressive strength (MPa)

$bb_unl    = 27 ; max. normal disp. previous load cycle (mm)

$bb_dil    = 28 ; current cumulative dilation

$bb_empb   = 29 ; empirical multiplier for fluid flow law

$bb_expa   = 30 ; exponent of joint hydraulic multiplier

$bb_grdex  = 31 ; gradient exponent

$bb_jperm  = 32 ; joint permeability

end

@$bb_fin

set echo on

6 结束语

Barton-Bandis (BB) 剪切强度模型用来计算带有粗糙度的节理强度，这个模型比库伦滑动模型更复杂。BB模型可来模拟岩石剪切试验以及岩石边坡稳定性分析。目前除了UDEC内置BB模型外，Rocscience的大部分软件也内置了BB模型。