54
55
56
57
Revised approach can be used for cohesive soil with c’ and f’ – how?
F M
h
0
at O
'
c1' f1'
0
1sat
For two unk nowns: F ? D?
' c2 f 2'
2 sat
Essential References: (1) Das, Braja M. (2007). Principles of Foundation Engineering (6th edition), Thomson, United States (ISBN 0-534-40752-8)
2
Lecture 6: Sheet Pile Walls (Chapter 6-Das) 板樁墻
深基坑开挖与支护设计
殷建华
The Department of Civil & Structural Engineering The Hong Kong Polytechnic University, Hong Kong, China
1
Outline of Lectures by JH YIN:
Lecture 1: Subsoil Exploration (Chapter 2-Das) Lecture 2: Shallow Foundations (Chapter 3-Das) Lecture 3: Mat Foundations (Chapter 4-Das) Lecture 4: Lateral Earth Pressure and Retaining Walls (Chapter 5-Das) Lecture 5: Sheet Pile Walls (Chapter 6-Das) Lecture 6: Braced Cuts (Chapter 7-Das) Lecture 7: Pile Foundations (Chapter 8-Das) Lecture 8: Soil Improvement and Ground Modification (Chapter 11Das plus others)
3
Lecture 6: Sheet Pile Walls (Chapter 6-Das) 板樁墻
6.10 Anchors 6.11 Ultimate Resistance of Anchor Plates and Beams in Sand（锚板和锚梁的极限承载力） 6.12 Ultimate Resistance of Anchor Plates and Beams in Clay (fu=0 condition) 6.13 Factor Safety for Anchor Plates and Beams
H
sat 19.5kN / m3
K a (3 D) [2 ' ( D 1)]K a ( ' )( D 1) K a (18 9.69)( D 1) K a 8.31( D 1) K a
47
D
Head difference h a 水头差 Total distance 渗流路径 L a b b a 2b Hydraulic gradient 水力梯度 h a L a 2b Total head drop at C : i hC 2b i 2ba a 2b Porewater pressure at C :
58
Free earth method: from Soil Mechanics by Craig (2004)
M
iA
0
59
Two equations (moment at A and horizontal force equilibriums) for two unknowns (d and T)
Total stress parameters:
f 0; c 0
K a K p 1
32
33
L3=D-L4 Two equations for D and L4
34
35
36
37
38
39
40
41
Free earth method (no bending at “O”) (simple and good): from Soil Mechanics by Craig (2004)
42
2.25m
0.225m>0.25m
6.25m 7m
Depth
6.625m
d=2.75m
d (2.75 1) 0.2 0.75m
Water tables in front and back of the sheet pile is the same. There is no seepage. The water pressure is self-balanced. 43
Fixed earth method (bending here)
18
Purpose: To design D （入土深度）for the sheet pile to be safe! See equations below:
No water pressure is considered: self-balanced（自平衡）
4
6.1 Introduction
Purposes: supporting excavation, retaining soil, stopping water inflow, … 支撑开挖，挡土，阻止水渗流
5
Diaphragm walls（地下连续墙）:
• Diaphragm walls are underground structural elements commonly used for retention systems, permanent foundation walls, deep groundwater barriers.地下连续墙普遍用于支撑体系，永久性 的基础外墙，挡水的地下结构体。 • Diaphragm walls are constructed using the slurry trench technique, which was developed in Europe and has been used in Hong Kong since the 1970„s.地下连续墙施工过程中采用了泥浆护壁。 • The technique involves excavating a narrow trench that is kept full of an engineered fluid or slurry. 泥浆护壁技术是开挖窄槽.. • The slurry exerts hydraulic pressure against the trench walls and acts as shoring to prevent collapse.泥浆给窄槽壁施加水压，防止坍塌
12
13
6.2 Construction Methods(后填土支护的施工过程)
14
15
6.3 Cantilever Sheet Pile Walls（悬臂板桩墙，实际
变形、受力图）
Rotation point: How to find it?旋转点？
16
Fixed earth (bending here)
• Slurry trench excavations can be constructed in all types of soil, even below the ground water table.泥浆护壁沟渠开挖适用于各种土层 6
Bentonite Slurry （工程中 配置泥浆 的原理图）
7
3-D View of Diaphragm Wall Construction
8
9
Wooden sheet pile and concrete sheet pile（木板桩，混凝土板桩）:
10
Steel sheet pile (used a lot in Hong Kong):
11
Steel sheet piles from Japan and UK are often used in Hong Kong. Below is from USA.
60
F
ih
0
61
62
2 6 4.5 u D 9.8 32.1 kN / m 2 4.5 2 6
2ቤተ መጻሕፍቲ ባይዱa uC w a 2b
63
Considering effective stress increase due to seepage Considering effective stress decrease due to seepage
6.1 Introduction 6.2 Construction Methods(施工方法) 6.3 Cantilever Sheet Pile Walls（悬臂板桩墙） 6.4 Cantilever Sheet Piling Penetrating Sandy Soils 6.5 Cantilever Sheet Piling Penetrating Clay 6.6 Anchored Sheet Walls 6.7 Free Earth Support Method for Penetration of Sandy Soil 6.8 Moment Reduction for Anchored Sheet Pile Walls 6.9 Free Earth Support Method for Penetration of Clay