BÀI TẬP THỰC HÀNH GEOSLOPE PLAXIS

BÀI TẬP THỰC HÀNH PLAXIS

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Trung tâm ĐTTH & Chuyển giao công nghệ Giao Thông Vận Tải

Fax: 08 37360676; Email:ttđtth@gmail.com; Website: www.uct2.edu.vn

TRƯỜNG ĐẠI HỌC GIAO THÔNG VẬN TẢI CƠ SỞ II TRUNG TÂM ĐÀO TẠO THỰC HÀNH VÀ CHUYỂN GIAO CÔNG NGHỆ GIAO THÔNG

- o0o -

BμI TËP THùC HμNH

PHÇN MÒM GEO-SLOPE/W, PLAXIS 2D, PLAXIS 3DF

THÁNG 03-04, NĂM 2011

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Thực hành Geo-Slope/w- ĐHGTVT CS2- trang 1

PHẦN 1: THỰC HÀNH GEO-SLOPE/W

2.1.1 Defining the problem

To open the GeoStudio SLOPE/W Define module:

Set the working area

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Define soil properties

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Draw regions

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Draw piezometric lines

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Draw entry and exit location

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Display soil properties

Create dynamic sketch text

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Verify the problem

2.1.2 Solving the problem

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2.2.2 Lesson 2 – Bishop’s method of analysis

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2.2.9 Lesson 9 – non-circular slip surfaces

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KHAI BAO TAI TRONG NGOAI

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1 SLIDE Verification Problem #1

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Thực hành Plaxis 2D- ĐHGTVT CS2- TRANG 1

PHẦN 2: THỰC HÀNH PLAXIS 2D

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2 TÍNH TOÁN NỀN BẰNG CỌC XI MĂNG ĐẤT

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3 BÀI 1: TÍNH ỔN ĐỊNH HỐ ĐÀO

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KHAI BÁO VẬT LIỆU

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GIAI ĐOẠN 1

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GIAI ĐOẠN 2

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GIAI ĐOẠN 3

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GIAI ĐOẠN 4

GIAI ĐOẠN 5

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4 TÍNH TOÁN NỀN ĐƯỜNG THEO THỜI GIAN

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5 PHÂN TÍCH ĐƯỜNG HẦM TRONG ĐÔ THỊ

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PLAXIS - Finite Element Code for Soil and Rock Analyses

User name : Univ of Transport & Communicatons

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1 2

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Page : 1Output : Soil and Interfaces Info - Linear Elastic Step : 24

γsat[kN/m3]15.8

kx[m/day]

0.0000

ky[m/day]

0.0000

kz[m/day]

0.0000

ν[ - ]0.30

Eref[kN/m2]37750.0

Eincr

[kN/m3] 0.0

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Page : 2Output : Soil and Interfaces Info - Linear Elastic Step : 24

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Page : 1Output : Soil and Interfaces Info - Mohr-Coulomb Step : 24

γsat[kN/m3]15.2

kx[m/day]

2.1500E-3

ky[m/day]

2.1500E-3

kz[m/day]

2.1500E-3

ν[ - ]0.35

Eref[kN/m2]934.6

cref

[kN/m2] 6.9

ϕ

[ ° ] 8.0

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Page : 2Output : Soil and Interfaces Info - Mohr-Coulomb Step : 24

cincr

[kN/m3] 0.0

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280.00

Np[kN/m]

1E10

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http://utc2.edu.vn/trungtamdaotao/

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http://utc2.edu.vn/trungtamdaotao/

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SAFETY ANALYSIS OF AN EMBANKMENT (LESSON 4)

6-1

6 SAFETY ANALYSIS OF AN EMBANKMENT (LESSON 4)

After the construction of an embankment on soft soil with a high ground water level, an

additional load will be applied very fast As a result of the ‘undrained behaviour’ of the

soil the effective stresses remain low resulting in a low shear strength A consolidation

period is necessary to let the excess pore pressures dissipate so that shear strength of the

soil can increase

The undrained behaviour of the soil will be modelled by an undrained effective stress

analysis with effective parameters instead of undrained strength parameters, as used in

Lesson 3 An undrained effective stress analysis with effective parameters will give a

realistic prediction of pore pressures and can be followed by a consolidation analysis

This lesson concerns the safety analysis of the embankment A safety factor by means of

phi/c-reduction will be calculated for three situations, i.e., when no load has been

applied yet, immediately after applying the load and when a consolidation period has

been considered

The proposed geometry is 90 m long and 30 m wide The embankment is 4.0 m high

The slope at the left has an inclination of 1:4 and the slope at the right has an inclination

of 1:3 Figure 6.1 shows the geometry of the embankment

Objectives:

x Undrained effective stress analysis with effective parameters

x Non-horizontal ground surface

x Non-hydrostatic water conditions

x Triangulate (mesh option)

x Mesh refinement of lines

x Gravity loading

x Consolidation

x Phi/c reduction

x Viewing excess pore pressures

x Viewing incremental displacements

Figure 6.1 Geometry and dimensions of the embankment

25 kN/m 2

4 m

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TUTORIAL MANUAL

6.1 GEOMETRY INPUT

The proposed geometry for this exercise is 90 m long and 30 m wide As the ground

surface is non-horizontal, first some geometry lines have to be added to be able to define

this ground surface

x After entering the general settings for this exercise, add a geometry line

between (16.0, 0.0) and (16.0, 30.0), one between (32.0, 0.0) and (32.0, 30.0),

one between (40.0, 0.0) and (40.0, 30.0) and one between (52.0, 0.0) and (52.0,

30.0)

Add a borehole at (32.0, 0.0) and change the y-value of the first layer boundary

to y = 4.0 m and the y-value of the second layer boundary to y = 0.0 m Add two

layer boundaries at y = -0.5 m and y = -10.0 m

x Create both material data sets given in Table 6.1 and assign them to the

appropriate soil layers It is not necessary to enter K0 values as the initial

stresses will be generated by means of gravity loading

Table 6.1 Material properties for the soil layers

Material model Model

Mohr-Coulomb

Coulomb

MohrType of material behaviour Type Drained UnDrained -

-Soil weight above phreatic level Ȗunsat 17 15 kN/m3

Soil weight below phreatic level Ȗsat 20 18 kN/m3

Young’s modulus Eref 1.9·104 2000 kN/m2

Interface reduction factor Rinter Rigid Rigid -

x Uncheck the Hydrostatic box Select the third layer boundary and change the

water pressure to Wpress+ = 0.0 kN/m2 and Wpress- = 0.0 kN/m2 (see Figure

6.2)

x Add a second borehole at position (16.0, 0.0) The borehole will be an exact

copy of the previous one Change the y-value of the first layer boundary to 0.0

m to reduce the thickness of the embankment layer to zero The water

conditions must remain unchanged

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6-3

Figure 6.2 The Borehole window

x Add boreholes to other points and change the values of the first layer boundary

as given in Table 6.2 The water conditions must remain unchanged

Table 6.2 Y-coordinates for the layer boundaries of the boreholes

Open the Work Planes window and change the work plane level to y = 4.0 m

Draw a geometry line from position (36.0, 30.0) to position (36.0, 24.0) and end

at position (40.0, 24.0) to define for the cluster the distributed load

Add a distributed load on a horizontal plane to this cluster

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TUTORIAL MANUAL

Mesh generation

The mesh for this example will be of medium coarseness, with a further refinement of

some clusters and the toe of the embankment To generate this mesh, follow these steps:

x From the Mesh menu, choose the Triangulate option PLAXIS 3D FOUNDATION

will now perform a very coarse triangulation of the geometry in the draw area

before the mesh is generated The purpose of this triangulation is to define

planes between geometry points and the model boundaries, where the ground

surface level and the soil layer boundaries of the generated 3D mesh are linearly

interpolated

x Select Global Coarseness from the Mesh menu and set the horizontal as well as

the vertical element distribution to Medium Select the cluster with the

distributed load as well as the cluster representing the steep slope at the right

hand side Hold down the <Shift> key to select multiple clusters Choose Refine

Cluster from the Mesh menu and the Output program will show the generated

2D mesh

x Return to the main draw area, select the geometry line at x = 52.0 m and choose

Refine Line from the Mesh menu

Hint: In particular, for safety analysis a fine mesh is required A mesh that is too

coarse leads to an over-estimation of the safety factor In this example the

current mesh is accepted to avoid excessive calculation times

x Return to the main draw area and generate the 3D mesh (see Figure 6.3) Click

Close to return to the main draw area

Figure 6.3 Preview of the generated 3D mesh

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6-5

6.2 CALCULATIONS

The calculation consists of 6 phases The construction of the embankment itself is not

considered in this exercise; the embankment will already be present during generation of

the initial stresses As the ground surface is not horizontal the initial stresses will be

generated using Gravity loading.

Open the Phases window and check that the calculation type is set to Gravity

loading Select the Parameters tab sheet and make sure the Ignore undrained

behaviour option is checked

Hint: Since the initial stresses are not affected by undrained behaviour, it is

important that undrained behaviour is disabled during Gravity loading This

can be done by selecting Ignore undrained behaviour in the Parameters tab

sheet of the Phases window

> In contrast to the K0 procedure, the calculation of initial stresses by means of

gravity loading results in displacements These displacements are not

realistic, because the embankment is modelled as it appears in reality and the

calculation of the initial stresses should not influence the displacements

computed later in the analysis These unrealistic displacements can be reset to

zero at the start of the next calculation phase by selecting Reset displacements

to zero in the next phase

x Add a new calculation phase In this phase, additional load will be applied on

the embankment Leave the Calculation type to Plastic In the Parameters tab

sheet, make sure the Reset displacements to zero option is checked

x Close the Phases window by clicking the OK button and activate the distributed

load at y = 4.0 m Change the load to -25.0 kN/m2 in y-direction

x Add a new phase and change the Calculation type to Consolidation to simulate

the consolidation process Keep Ultimate time as the Loading input in the

Parameters tab sheet and change the Time interval to 200 days

Hint: By default, all model boundaries are considered to be permeable These

boundary conditions can be modified by clicking the Advanced button in the

General tab sheet In this exercise the default boundary conditions are

adopted

x Add a new calculation phase Change the Calculation type to Phi/c reduction

and select 0 – Initial phase in the Start from phase combo box to perform a

safety analysis when no load has been applied yet In the Parameters tab sheet

change the Additional steps to 40 and make sure the Reset displacements to zero

as well as Delete intermediate steps options are checked

x Add a new phase and change the Calculation type to Phi/c-reduction and select

1 - <Phase 1> in the Start from phase combo box to perform a safety analysis

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TUTORIAL MANUAL

immediately after application of the load In the Parameters tab sheet change

the Additional steps to 40 and make sure the Delete intermediate steps option is

checked

x Add a new phase and change the Calculation type to Phi/c-reduction Select 2 -

<Phase 2> in the Start from phase combo box to perform a safety analysis after

consolidation Change the Additional steps to 40 and make sure the Delete

intermediate steps option is checked

Hint: The default value of Additional steps in a Phi/c-reduction calculation is 100

In contrast to a Plastic or Consolidation calculation, the number of additional

steps is always fully executed In most Phi/c-reduction calculations, 100 steps

are sufficient to arrive at a state of failure If not, the number of additional

steps can be increased to a maximum of 1000 If necessary, the number of

additional steps can be decreased to 1

x Close the Phases window

Click the Select points for curves button to open the Output program Select the

tab sheet at y = 4.0 m Select the node on the crest of the embankment at (40.0,

4.0, 30.0) by just clicking once (see Figure 6.4 ) It may be necessary to zoom

into the area around the crest to select the correct point

Figure 6.4 Location of selected corner point for curves

x Close the Output program by clicking the Update button and start the

calculation After the calculation save the project

Tiêu đề	Bài Tập Thực Hành Geoslope Plaxis
Trường học	Trường Đại Học Giao Thông Vận Tải
Chuyên ngành	Transportation Engineering
Thể loại	Thực hành
Năm xuất bản	2011
Thành phố	Hồ Chí Minh

Định dạng
Số trang	118
Dung lượng	10,92 MB