1 General provisions
1.0.1 This specification is developed to ensure safety, reliability, advanced technology, economy and rationality and the safe surrounding environment in the investigation, design, construction, monitoring and testing for building foundation excavation.
1.0.2 This specification is applicable to the investigation, design, construction, monitoring and testing for the retaining and protection for temporary building foundation pit under general geological conditions in Guangdong.
1.0.3 For building foundation excavation, the engineering practice shall be combined with the surrounding environmental conditions to achieve reasonable design, careful construction, strict monitoring and testing.
1.0.4 In addition to this specification, the building foundation excavation shall also meet the requirements of the relevant current national and professional standards, as well as the relevant management regulations and technical specifications.
2 Terms and symbols
2.1 Terms
2.1.1
building foundation pit
pit or trench to be excavated underground for the foundation or basement construction of buildings (structures)
2.1.2
retaining and protection for foundation pit
measures of retaining, strengthening, protection and groundwater control adopted for building foundation pit to endure the safety of underground structure construction and surroundings around foundation pit
2.1.3
surroundings around foundation pit
buildings (structures) within the influence range of foundation excavation, including houses, roads, underground facilities and pipelines, rivers, cultural relics and historical sites, etc., as well as rock, soil and adjacent underground waters
2.1.4
ultimate limit states
critical states when the supporting structure reaches the ultimate bearing capacity or before the loss of bearing capacity of the retaining and protection structure due to soil instability
2.1.5
serviceability limit states
critical states before the hindrance of normal construction of underground structure or normal use of surroundings around foundation pit caused by excessive supporting structure or soil deformation or failure of water interception measures
2.1.6
retaining and protection structure
structural system that provides retaining resistance and ensures the safety of the foundation pit
2.1.7
side of foundation pit
vertical structure of retaining and protection structure, including row piles, diaphragm wall, soil nailing wall and gravity cement-soil wall
2.1.8
embedded depth
buried depth of pile and wall retaining and protection structure below the excavation surface of foundation pit
2.1.9
capping beam
concrete structure coupling beam set on the top of the side of foundation pit
2.1.10
waling
concrete beam or steel beam which is arranged on the profile of the side of foundation pit and transfers the pivot point force of retaining and protection structure and support
2.1.11
pivot point
horizontal constraint point of anchor, strut or other elements for retaining and protection structure
2.1.12
pivot horizontal stiffness
ratio of horizontal force of anchor or strut on retaining and protection structure to its displacement
2.1.13
anchor
tensile rod composed of steel bars or steel strands which are arranged in the drill hole, set with free section and anchorage section and extended into the stable rock-soil layer, and grouting body in the drill hole
2.1.14
strut
structural system arranged in the foundation pit to apply horizontal force on the side of foundation pit
2.1.15
(composite) soil nailing wall
soil nailing wall: retaining and protection structure formed by the cooperation of soil nailing, sprayed concrete surface, reinforced in-situ rock (soil) and necessary waterproof and drainage system; composite soil nailing wall: composite retaining and protection structure formed by the combination of soil nailing wall and one or more of pre-stressed anchor, curtain for cutting of water and miniature pile
2.1.16
gravity cement-soil wall
column reinforced cement-soil solid, which is continuously overlapped and formed by curing agent (cement-based material) mixed with or partially replacing in-situ soil through stirring and high-pressure jet grouting
2.1.17
miniature pile
small-diameter pile, including concrete pile, steel pile, reinforced cement-soil pile, which is installed in (composite) soil nailing wall, gravity cement-soil walls or excavated slope soils for forepoling to improve the strength and stability of retaining and protection structure
2.1.18
groundwater control
measures such as open pumping, dewatering, water interception or recharge taken for normal construction and prevention from the adverse impact of groundwater changes on the surroundings around foundation pit
2.1.19
curtain for cutting off drains
vertical diaphragm wall used to prevent or reduce water outside the foundation pit and groundwater under the pit from flowing into it
2.1.20
mildtype well point dewatering
water absorption and dewatering by embedding 40mm to 80mm diameter steel pipe with a filter screen at the head into the ground, and using a vacuum pump (jet pump) or a jet device at the head to make vacuum
2.1.21
tube wells well point dewatering
dewatering by embedding a large diameter steel pipe or plastic pipe wrapped with filter screen underground to make a deep well, equipped with submersible pump
2.2 Symbols
2.2.1 Physical and mechanical indexes of soil
c, ?——the characteristic values of cohesion and internal friction angle of soil;
k——the permeability coefficient of aquifer;
Ka——the coefficient of active soil pressure;
Kp——the coefficient of passive soil pressure;
?——the natural unit weight of soil;
?i——the average natural unit weight of the i-th layer of soil;
?mh——the weighted average natural unit weight of soil;
?w——the unit weight of water;
?ak——the weighted average of equivalent internal friction angle of soil
2.2.2 Physical and mechanical indexes of material
A——the sectional area of material;
As, Ap, Asy——the sectional areas of general steel bars, prestressed steel bars and steel strands;
Es——the elastic modulus of steel;
fc——the design value of axial compressive strength of concrete;
fcs——the design value of axial compressive strength of cement-soil at excavation age;
fy and fpy——the design tensile strength of general steel bar and prestressed steel bar;
K——the stiffness of material;
qsk——the characteristic value of the ultimate bond strength of the interface between the anchor or soil nail and the rock and soil;
W——the section modulus of material;
?——the design value of shear strength of material;
?——the design value of bond strength of concrete.
2.2.3 Actions and effects
eaik——the characteristic value of horizontal load of retaining and protection structure;
epik——the characteristic value of horizontal resistance inside foundation pit;
Ea——the resultant force of characteristic values of horizontal load of retaining and protection structure;
Ep——the resultant force of characteristic values of horizontal resistance of rock and soil inside foundation pit;
G——the self-weight of structure;
M——the design value of bending moment of section;
N——the design value of axial force of section;
Nu——the characteristic value of axial ultimate tension of anchor;
Nt——the calculated value of axial tension of anchor;
p——the characteristic value of additional pressure at the bottom of foundation;
q0——the uniformly distributed load acting on the ground outside the retaining and protection structure;
q——the distributed load on the ground outside the foundation pit or additional distributed load under the adjacent building foundation;
T——the design value of horizontal tension of anchor;
V——the design shear of section;
?aik——the characteristic value of vertical stress acting at depth zi;
?pik——the characteristic value of vertical stress acting at the depth zi below the bottom of foundation pit;
?rk——the vertical stress caused by the self-weight of soil;
?0k——the vertical stress in soil caused by uniformly distributed ground load;
?1k——the vertical stress in soil caused by local ground load.
2.2.4 Geometric parameters
a——the distance between the foundation edge and the retaining and protection structure;
b——the width of structure;
B——the width of foundation pit;
dh——the embedded depth of foundation;
d——the steel diameter;
D——the pile diameter;
hw——the depth of groundwater level;
hi——the thickness of the i-th layer of soil;
hd——the design value of embedding depth;
H——the excavation depth of foundation pit;
l——the length of foundation bottom;
L——the length of foundation pit;
q——the design water yield of single well;
Q——the water inflow of foundation pit;
r0——the equivalent radius of foundation pit;
rw——the radius of single well;
R——the influence radius of dewatering well;
s——the design dewatering depth of groundwater level;
sw——the calculated dewatering depth of pumping well point, sw≥s;
V——the volume of water discharge;
z——the depth from the top of wall to the calculated section;
α——the inclination angle between the soil nailing or prestressed anchor and the horizontal plane;
β——the included angle between slope and horizontal plane of soil nailing wall;
?——the inclination angle between anchor and vertical plane.
2.2.5 Calculation parameters
kr——the horizontal stiffness of elastic pivot point;
K——the safety coefficient;
Ks——the overall stability safety coefficient;
Kt——the safety coefficient of anchor pullout;
Km——the safety coefficient of anchor;
n——the number of well points;
n'——the porosity of filter tube;
α——the internal force coefficient, 1/16 for continuous beam and 1/8 for simply supported beam;
?l——the safety coefficient of stability against uplift;
?0——the importance coefficient of foundation pit;
?k——the partial coefficient of overall stability;
?s——the partial coefficient of axial tensile resistance of anchor;
?t——the pile type adjustment factor of allowable hold-type pile pressing force of pressing precast concrete pile;
?——the reduction factor of axial load on soil nail;
?——the reduction factor of combined action of anti-sliding moments generated by each retaining and protection body;
?——the friction coefficient between structure and soil;
v——the velocity of groundwater entering the filter tube.
Foreword ii
1 General provisions
2 Terms and symbols
2.1 Terms
2.2 Symbols
3 Basic requirements
3.1 Environmental investigation and protection
3.2 Design requirements
3.3 Construction requirements
3.4 Detection and monitoring
4 Geotechnical engineering investigation
4.1 General requirements
4.2 Investigation requirements and environmental investigation
4.3 Investigation report
5 Calculation of horizontal load and resistance of retaining and protection structure for foundation pit
5.1 General requirements
5.2 Determination of the characteristic value of horizontal load
5.3 Determination of the characteristic value of horizontal resistance
5.4 Geotechnical parameter value
5.5 Structural calculation
5.6 Cross section bearing capacity calculation
5.7 Stability calculation of support structure
6 Retaining and protection of slope ratio method
6.1 General requirements
6.2 Design
6.3 Construction
7 Gravity cement-soil wall
7.1 General requirements
7.2 Design
7.3 Construction
8 Retaining and protection of row pile
8.1 General requirements
8.2 Design
8.3 Construction
9 Retaining and protection of diaphragm wall
9.1 General requirements
9.2 Design
9.3 Construction
10 Retaining and protection of soil nailing wall and composite soil nailing wall
10.1 General requirements
10.2 Design
10.3 Construction
11 Retaining and protection of steel sheet pile
11.1 General requirements
11.2 Design
11.3 Construction
12 Retaining and protection of double-row pile
12.1 General requirements
12.2 Design
12.3 Construction
13 Strut
13.1 General requirements
13.2 Design
13.3 Construction
14 Anchor
14.1 General requirements
14.2 General anchor design
14.3 General anchor construction
14.4 Design and construction of reaming anchor
14.5 Design and construction of recoverable anchor
15 Reversed construction method
15.1 General requirements
15.2 Design
15.3 Construction
16 Center island method
16.1 General requirements
16.2 Design
16.3 Construction
17 Excavation and backfilling of foundation pit
17.1 General requirements
17.2 Excavation
17.3 Backfilling
18 Groundwater control
18.1 General requirements
18.2 Open ditches drainage of foundation pit
18.3 Foundation pit dewatering
18.4 Water interception of foundation pit
18.5 Special rock and soil foundation pit basement treatment
19 Foundation pit monitoring and testing
19.1 General requirements
19.2 Monitoring
19.3 Inspection and acceptance
20 Assessment and prevention of environmental impact of foundation pit excavation
20.1 General requirements
20.2 Assessment of environmental impact of foundation pit dewatering
20.3 Assessment of environmental impact of support
20.4 Prevention and control of environmental impact of foundation
Appendix A (Normative) Incremental method for pile-wall retaining structure
Appendix B (Informative) Determination method of deformation modulus of soil
Appendix C (Normative) Circular sliding method
Appendix D (Normative) Calculation of bend bearing capacity of normal section
Appendix E (Normative) Simplified calculation for water discharge in excavation pit
Appendix F (Normative) Kernel of soil nail pullout test
Appendix G (Normative) Anchor test
Explanation of wording in this specification
List of quoted standards
