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For this standard, the project is approved in accordance with the document YUEJIANHAN [1993] No. 265 “Notice on issuing the task of developing Specification for static pressing precasted concrete pile foundation” issued by the former Guangdong Construction Committee. Previously, the static pressing precast concrete piles used in Guangdong were precasted reinforced concrete square-piles with side length less than 400mm; at the end of 1994, the technical difficulties in the construction of prestressed tube-piles by static pressing method were overcome. In the following years, the application of static pressing precast concrete tube-piles has developed rapidly in Guangdong Province and even the whole country, and great progress has also been made in the aspect of manufacturing technology of hold type hydraulic pressing pile machine. In June 1998, the preparation of this Specification was officially started, and the name of the specification was Specification for static pressing precasted concrete pile foundation; the discussion draft was completed in 2001, and the exposure draft was basically completed in 2003. However, in order to coordinate with the revision of the standard of Guangdong DBJ/T 15-22 Specification for driven prestressed concrete tube-pile foundation and the national standard GB 13476 Pretensioned spun concrete piles, the compilation speed was slowed down, during which period modification has been carried out for several times. The edition of this Specification is mainly in charge of the Civil engineering and Architectural Society of Guangdong, participated by 20 units including schools, manufacturers of static pressing precast concrete pile and pressing pile machine, and those for survey, design, construction, supervision, quality inspection, scientific research.
There are 6 clauses and 6 annexes in this Specification, with the main technical contents as follows: general provisions; terms and symbols; geotechnical engineering investigation of static pressing precast concrete pile foundation; design of static pressing precast concrete pile foundation; construction of static pressing precast concrete pile; and engineering quality inspection and acceptance of works.
Specification for static pressing precasted concrete pile foundation
1 General provisions
1.0.1 This specification is developed with a view to implementing the national technical and economic policies, so that the design and construction of static pressing precast concrete pile foundation in Guangdong Province meet the requirements of safety and application, technological advance, economic rationality, quality assurance, and environmental protection.
1.0.2 This Specification is developed in accordance with the current relevant standards of the nation and Guangdong Province, on the basis of summarizing the existing experience in Guangdong and taking into account the particularity of the design and construction of the foundation of static pressing precast concrete pile.
1.0.3 This Specification is applicable to geotechnical engineering investigation, design, construction, quality inspection, testing and project acceptance of static pressing precast concrete pile foundation with low pile caps of buildings (structures) constructed by static pile pressing machine. Other contents not specified in this Specification shall comply with the current relevant standards of the nation and Guangdong Province.
1.0.4 Static pressing precast concrete pile may be pre-tensioned pre-stressed concrete tube-pile (hereinafter referred to as static pressing precast concrete tube-pile) and prefabricated reinforced concrete square-pile (hereinafter referred to as static pressing precast concrete square-pile).
1.0.5 Static pressing precast concrete pile is applicable to non-seismic areas and areas with seismic fortification intensity of 6 and 7 and those with seismic fortification intensity of 8 in which category of building sites is I or II, with the mechanical indexes of the selected pile type meeting the design requirements and relevant standards.
1.0.6 The construction provisions in this Specification are compiled based on the performance and construction technology of the hold type hydraulic pressing pile machine. When using other types of pile pressing machine or pile pressing construction method, attention shall be paid to the particularity of their respective construction technologies.
1.0.7 Static pressing precast concrete pile foundation should be used for rock stratum with covering stratum easy to be pressed through and pile tip bearing stratum intensely or completely weathered; hard plastic~hard cohesive soil layer; medium-dense~dense gravelly (cobbly) soil, sandy soil and silt layers.
Unless effective measures have been taken, the static pressing precast concrete pile foundation should not be adopted for the following geological conditions:
1 Untreated sites with soft topsoil and ground bearing capacity characteristic value ≤120kPa;
2 There are many spherical weathered bodies (boulder) or other obstacles in the covering stratum;
3 The pile tip bearing stratum is medium-dense~dense sand layer and its covering stratum is almost all slightly-dense~medium-dense sand layer.
4 The covering stratum contains a hard included thin layer which is difficult to press through;
5 Karst stratum with large fluctuation of bedrock surface and no suitable bearing stratum on it;
6 Non-karst areas, with covering stratum being soft soil layer such as sludge and moderately weathered or slightly weathered rock layer directly under the covering stratum;
7 The pile tip bearing stratum is weathered rock stratum which is easy to soften after disturbance.
8 Sites with seismic fortification intensity of 8 and construction sites of Category III or IV;
9 Sites with ground water or foundation soil strongly corrosive to pile shaft concrete, steel bars and steel parts.
1.0.8 Static pressing precast concrete pile foundation is a kind of pile foundation project that can be successfully completed only by close cooperation between investigation, design and construction. Especially in the construction stage, investigation, design and construction technicians shall cooperate closely. When the actual pile length is much shorter than the design pile length, they shall study together and make necessary adjustments to the bearing capacity and number of piles in time.
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2 Terms and symbols
2.1 Terms
2.1.1
method of static pressing of pile
construction method of pressing precast pile into the foundation soil (rock) layer with pile pressing machine by certain depth, which is called static pressing method for short
2.1.2
static pressing precast concrete pile
precast reinforced concrete pile constructed by static pressing method
2.1.3
static pressing precast concrete square-pile
precast reinforced concrete square-pile constructed by static pressing method
2.1.4
static pressing precast concrete tube-pile
pretensioned pre-stressed concrete tube-pile constructed by static pressing method
2.1.5
foundation of static pressing precast concrete pile
foundation of building (structure), which is composed of static pressing precast concrete pile and pile cap connected to the top of pile, which is called foundation of static pressing pile for short
2.1.6
slenderness ratio
ratio of pile length to diameter for static pressing precast concrete tube-pile or that of pile length to side length of static pressing precast concrete square-pile
2.1.7
hydraulic pressing pile machine
static pressing precast concrete pile construction machine which applies pressure to the pile shaft through a hydraulic force transmission mechanism
2.1.8
jack type hydraulic pressing pile machine
hydraulic pressing pile machine with pile pressing force acting on the top face of pile
2.1.9
hold type hydraulic pressing pile machine
hydraulic pressing pile machine applying pressure downward with the clamping device holding the pile shaft
2.1.10
clamping device
hydraulic component of a pile pressing machine which uses a plurality of hydraulic clamping blocks to hold the pile shaft from the side and may move up and down along the guide frame
2.1.11
device of pressing border pile
set of special pile-holding and pile-pressing mechanism which is installed on the side of pile pressing machine and is used for pressing border piles
2.1.12
additional weight
detachable weight block attached to the pile frame for adjusting the weight of the pile pressing machine
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2.1.13
minimum distance for border pile
minimum distance from the center of the pile that can be pressed when the pile pressing machine is adjacent to an existing building (structure) to the edge of such building (structure)
2.1.14
pressure intensity of ground contact
average pressure value per unit area of the grounding part during traveling or construction of the pile pressing machine
2.1.15
method of repeated pressing
operation method of applying pressure again after a period of time after the final pressure of static pressing precast concrete pile construction
2.1.16
allowable pressure of clamping pile shaft
maximum pile pressing force allowed by the pile shaft when the pile shaft is held and pressed by hold type pile pressing machine
2.1.17
control standard of final pressing
control measures and conditions for termination of pile pressing construction determined to meet the design requirements of static pressing precast concrete pile
2.1.18
final pressure value
final pile pressing force applied when the control standard of final pressing is reached and thus the pile pressing is terminated
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2.1.19
times of continuously repeated pressing with final pressure
number of times that the static pressing precast concrete pile is continuously pressed with final pressure value in an intermittent way when the static pressing precast concrete pile is finally pressed
2.1.20
time of steady pressure
time of applying pressure continuously with the final pressure value at the time of final pressing
2.1.21
ultimate vertical compression bearing capacity of a single pile
maximum load borne by a single pile under the vertical load before it reaches the failure state or when it is deformed and is no longer suitable for bearing
2.1.22
ratio of ultimate vertical bearing capacity and final pressure value
ratio of ultimate vertical compression bearing capacity of a single pile to final pressure value for construction of static pressing precast concrete pile
2.1.23
method of pressing pile with pre-augering
operation method of pre-hole-forming at the pile location with pilot hole equipment, then placing the precasted pile into the hole and applying pressure with a pile pressing machine
2.1.24
pile loading
construction process of lifting static pressing precast concrete pile into the clamping device of pile pressing machine
2.1.25
characteristic value of the vertical bearing capacity of a single pile
bearing capacity value obtained by dividing the maximum load borne by a single pile under the vertical load (pressure or uplift) before it reaches the failure state or when it is deformed and is no longer suitable for bearing by the safety factor
2.1.26
machine floating
state with part of the chassis of the pile pressing machine lifting off the ground and becoming suspended during the pile pressing process
2.2 Symbols
2.2.1 Resistance and material performance
Ec——the elastic modulus of pile shaft concrete of static pressing precast concrete pile;
fc——the design value of the axial compressive strength of concrete;
fnk——the standard value of bond strength between core concrete and inner wall of tube-pile;
Fptk——the standard value of tensile strength of pre-stressed steel bar of tube-pile;
fy——the design tensile strength of steel bar;
qsia——the characteristic value of lateral resistance of the ith layer soil (rock) of single pile;
qpa——the characteristic value of tip resistance of a single pile;
qc——the cone head resistance of static cone penetration;
Ra——the characteristic value of singe pile vertical compression bearing capacity;
Rha——the characteristic value of singe pile horizontal bearing capacity;
Rta——the characteristic value of singe pile vertical uplift bearing capacity;
Rm——the design value of bending bearing capacity of pile shaft;
Rp——the design value of vertical bearing capacity of pile shaft of static pressing precast concrete pile;
σpc——the effective compressive pre-stress value of pre-stressed tube-pile concrete;
Pjmax——the allowable pressure of clamping pile shaft.
2.2.2 Actions and effects
Fk——the vertical forces acting on the top of pile cap in the standard combination of load effects;
Gk——the standard value of dead weight of pile cap and the soil thereon;
Gp——the dead weight of static pressing precast concrete pile;
Hk——the horizontal force acting on the bottom of pile cap in the standard combination of load effects;
Hik——the horizontal force acting on the top of any pile in the standard combination of load effects;
Mxk——the bending moment acting on the bottom of pile cap through the x axis of pile group centroid in the standard combination of load effects;
Myk——the bending moment acting on the bottom of pile cap through the y axis of pile group centroid in the standard combination of load effects;
M——the design value of bending moment of single pile in the basic combination of load effects;
N——the measured standard penetration number;
N′——the corrected standard penetration number;
Nk——the standard value of measured standard penetration number of layer;
Pze——the final pressure value of construction of static pressing precast concrete pile;
Qk——the vertical force of any pile under the axial vertical force in the standard combination of load effects;
Qik——the vertical force of the ith pile under the eccentric vertical force in the standard combination of load effects;
Qt——the design value of single pile vertical uplift force in the basic combination of load effects;
Qtk——the vertical uplift force acting on the top of a single pile in the standard combination of load effects;
Ymax——the maximum pile pressing force of hydraulic pressing pile machine.
2.2.3 Geometric parameters
A——the sectional area of static pressing precast concrete pile;
Aa——the nominal sectional area of a single pre-stressed steel bar of tube-pile;
Ap——the horizontal projection area of static pressing precast concrete pile tip;
b——the side length of static pressing precast concrete square-pile;
d——the outside diameter of static pressing precast concrete tube-pile;
d1——the inside diameter of static pressing precast concrete tube-pile;
h——the buried depth of static pressing precast concrete pile;
hb——the depth of static pressing precast concrete pile tip into the bearing stratum;
L——the length of single section of pile; the buried depth of static pressing precast concrete pile;
I——the cross sectional inertia moment of static pressing precast concrete pile;
La——the depth of core concrete on the top of pile;
li——the thickness by which the static pressing precast concrete pile passes through the ith layer of soil (rock);
Up——the outer perimeter of pile shaft of static pressing precast concrete pile.
2.2.4 Calculation coefficients
α——the length correction coefficient of penetration rod used in standard penetration test; the recovery coefficient of soil; the horizontal deformation coefficient of static pressing precast concrete pile;
β——the ratio of ultimate vertical bearing capacity and final pressure value;
λi——the reduction coefficient of anti-uplift frictional resistance;
ξp——the correction coefficient of resistance at static pressing precast concrete pile tip;
ψc——the pile formation technological coefficient.
3 Geotechnical engineering investigation of static pressing precast concrete pile foundation
3.0.1 For the geotechnical engineering investigation point of foundation of static pressing pile, the plane layout, depth and sampling and testing requirements of each main soil layer within the exploration depth shall meet those specified in the current national standard GB 50021 Code for investigation of geotechnical engineering and JGJ 72 Specification for geotechnical investigation of tall buildings as well as the following:
1 The spacing of exploration points should be 12m~24m, and there should be no less than 5 exploration holes in each unit project, in which the number of control exploration holes shall not be less than 1/2 of the total number of exploration holes and not less than 2. If the geological conditions are complex, the number of exploration holes shall be properly added.
2 The depth of general exploration hole shall be enough to reach 3 m ~ 5 m below the estimated pile tip bearing stratum; the depth of the control exploration hole shall be enough to reach 5 m ~ 10 m below the estimated pile tip bearing stratum;
3 The topsoil of the construction site shall be investigated in detail. For the investigation, portable dynamic sounding, soil sampling, standard penetration test and other means shall be adopted to accurately find out the bearing capacity of 3m thick soil layer on the surface.
3.0.2 If the static pressing precast concrete pile is selected as the foundation in the design, in-situ tests such as standard penetration test, heavy cone dynamic sounding test and double bridge probe static sounding test shall be appropriately added according to the characteristics of geotechnical layer in the geotechnical engineering investigation.
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3.0.3 The following requirements shall be met if standard penetration test is carried out:
1 Within the depth range of the control exploration hole, each soil layer and completely weathered and strongly weathered rock stratum shall be subject to standard penetration test. The standard penetration test shall be carried out once each layer in sludge and muddy soil layer, once every 2m in thickness in hard plastic~hard clay layer, residual soil layer and completely weathered rock layer, once every 1m in thickness in medium-dense ~ dense sand layer, and once every 1m in thickness in soil (rock) layer to be used as the pile tip bearing stratum;
2 For the general exploration hole in the layer to be used as pile tip bearing stratum, the standard penetration test shall be carried out once every 1m in thickness;
3 If the standard penetration test is conducted in the soil (rock) layer to be used as the pile tip bearing stratum, and the number of blow count has reached 100 and the penetration depth is less than 30cm, the test may be terminated, with the actual penetration depth at 100 blow counts recorded, but the drilling depth shall still meet those specified in 3.0.1.
3.0.4 If double bridge probe static sounding test is adopted, those specified in national standard GB 50021 Code for Investigation of Geotechnical Engineering shall be met, and the hole shall reach the depth about 5m for the rock-soil layer with tip resistance qc≥20MPa or the hole shall be drilled until the static penetration force ≥300kN. 3.0.5 If the empirical values of pile side friction characteristic value and tip resistance characteristic value in completely and strongly weathered rock stratum are selected, the standard penetration number corrected according to the length of drill stem shall be adopted. The corrected standard penetration number N' shall be calculated using the following equation:
N′＝αN (3.0.5)
where,
N′——the corrected standard penetration number;
N——the measured standard penetration number;
α——the correction coefficient of drill stem length, which may be adopted according to Table 3.0.5.
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Table 3.0.5 Correction coefficient of drill stem length
Stem length (m) ≤3 6 9 12 15 18 21
Correction coefficient α 1.00 0.92 0.86 0.81 0.77 0.73 0.70
Stem length (m) 24 27 30 33 36 39 ≥42
Correction coefficient α 0.67 0.64 0.61 0.58 0.55 0.52 0.49
3.0.6 Completely and strongly weathered granite rocks and residual soils may be classified according to the measured standard penetration number N, N≥50 means the rock is strongly weathered, 50>N≥30 means the rock is completely weathered, and N<30 means the rock is weathered into residual soil. Reference may be made to this for the classification of completely weathered and strongly weathered rocks of other types. When estimating the depth of pile pressing, the corrected standard penetration number N′ shall be adopted.
3.0.7 In geotechnical engineering investigation, the corrosivity of water and soil in the project site to precast piles shall be evaluated; when there is enough experience or sufficient data to determine that the water or soil in the project site is not corrosive to building materials, it is not necessary to take samples to test the corrosivity index; otherwise, water samples or soil samples shall be taken for testing. Sampling methods of water samples and soil samples, testing of corrosivity indexes of water and soil, and evaluation of corrosivity shall be carried out in accordance with those specified in the national standard GB 50021 Code for investigation of geotechnical engineering.
3.0.8 The geotechnical engineering investigation report of foundation of static pressing pile shall meet those specified in the national standard GB 50021 Code for investigation of geotechnical engineering, and should list the following contents:
1 Project overview, site location, topography and geomorphology, names and characteristics of various rock and soil layers, as well as geological age of geomorphic units and main rock and soil layers and analysis and demonstration of the causes thereof;
2 There shall be a clear judgment conclusion on the distribution and origin of bad geological phenomena in the construction site, such as boulder, hard interlayer, karst, soil cave, and structural fracture, and on the influence of rock slope on the stability of pile tip;
3 Ground water type, stable water level and its variation range;
4 The conclusion of evaluating the corrosivity of ground water and foundation soil in the site to the precast concrete piles;
5 Liquefiable stratum distribution and judgment data provided according to seismic intensity in seismic fortification area;
6 Test results of standard penetration test and other in-situ tests;
7 The evaluation of the possibility of sinking machine in static pressing precast concrete pile construction made according to the bearing capacity of soil layer within 3m depth of topsoil;
8 Suggestions proposed for selecting pile tip bearing stratum and for pile sinking feasibility;
9 Put forward the side friction characteristic value and tip resistance characteristic value in accordance with the foundation of static pressing pile; estimate the characteristic value of the vertical bearing capacity of a single pile and its deformation characteristics;
10 Assess the weathered rock layers on the site that are easy to soften after disturbance, and put forward countermeasures;
11 Evaluate the impact of pile pressing on the surrounding environment;
12 The plan layout of exploration points, engineering geological histogram, engineering geological profile, and contour map of rock and soil layers such as strongly weathered rock which are capable of being used as pile tip bearing stratum and color photo of rock core.
4 Design of foundation of static pressing pile
4.1 General requirements
4.1.1 According to the building scale, functional characteristics, adaptability to differential deformation, complexity of site foundation and building (structure) shape, and the degree of damage or influence on normal use of building (structure) caused by pile foundation problems, the design of foundation of static pressing pile shall be classified into three design grades listed in Table 4.1.1. When designing the foundation of static pressing pile, the design grade shall be determined according to Table 4.1.1.
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Table 4.1.1 Design grade of foundation of static pressing pile
Design grade Building type
Grade A (1) Important industrial and civil buildings;
(2) High-rise buildings with more than 30 storeys or with height more than 100m;
(3) Buildings with complex shapes formed by high building and low building connected to each other with the high one 10 storeys more than the low one;
(4) Buildings (structures) with special requirements for foundation deformation;
(5) General buildings with more than 7 storeys and complex site and foundation conditions, and buildings located at sloped land and shoreside.
(6) Newly built buildings (structures) which have great influence on the existing works;
(7) Large-span (≥60m) structural buildings;
(8) Large-area multi-storey underground buildings (structures).
Grade B Buildings (structures) other than those of Grades A and C
Grade C General buildings with 7 storeys or less and with simple site and foundation conditions and uniform load distribution, and minor light buildings (structures)
4.1.2 For the design of foundation of static pressing pile, the following basic data shall be made available:
1 Geotechnical engineering investigation report meeting those specified in clause 3 of this Specification;
2 Construction site and environmental conditions, including the distribution of high-voltage overhead lines, underground pipelines and underground structures; the safety level, subgrade and foundation conditions of adjacent buildings (structures) that may be affected by pile pressing; and the entry and exit and field operation conditions of pile pressing machine;
3 Types and forms of superstructure of buildings (structures); load size, distribution and nature; requirements of production technology and equipment on foundation settlement and horizontal displacement;
4 The general plan of the construction site, and the plan of the basement or the first floor structure of the buildings (structures);
5 Relevant data on seismic fortification;
6 Specifications and models, length of single section of pile, joint form and supply conditions of optional static pressing precast concrete pile;
7 Pile pressing equipment performance and its adaptability to geological conditions, as well as capability of pressing border pile.
4.1.3 For foundation of static pressing pile, the following calculations and checking shall be carried out according to specific conditions:
1 The vertical bearing capacity and horizontal bearing capacity of pile foundation shall be calculated respectively according to the use function and stress characteristics of foundation of static pressing pile;
2 The bearing capacity of pile shaft and pile cap structure shall be calculated; and the pile shaft bearing capacity shall also be checked according to the stress conditions during hoisting, transport and pile loading operations;
3 If there is a soft substratum below the pile tip plane, the bearing capacity of the substratum shall be checked;
4 For foundations of static pressing pile located at sloped land and shoreside, the overall stability shall be checked; for foundations of static pressing pile located in area with a large area of silt and muddy soil, when the foundation pit is excavated and there is a pile load around the foundation pit, the overall stability shall be checked, and the relevant prevention measures shall be taken;
5 For foundation of anti-uplift static pressing pile, the anti-uplift bearing capacity of single pile and pile group shall be calculated;
6 For foundations of static pressing pile within seismic fortification area, the seismic bearing capacity shall be checked;
7 For foundations of static pressing pile with design grade of Grade A and with Quaternary soil layer or completely weathered rock layer as the pile tip bearing stratum or those with design grade of Grade B, with complex shape and obviously uneven load distribution or soft soil layer below the pile tip plane, settlement calculation shall be carried out;
8 For foundations of static pressing pile bearing large horizontal load or having strict restrictions on horizontal displacement, the horizontal displacement shall be checked;
9 When the service conditions require to limit the concrete cracks, it is necessary to check the crack resistance or crack width of the foundations of static pressing pile.
Foreword ii
1 General provisions
2 Terms and symbols
2.1 Terms
2.2 Symbols
3 Geotechnical engineering investigation of static pressing precast concrete pile foundation
4 Design of foundation of static pressing pile
4.1 General requirements
4.2 Type, connection and selection of piles
4.3 Pile foundation calculation
5 Construction of static pressing precast concrete pile foundation
5.1 General rules
5.2 Pile pressing equipment
5.3 Lifting and stacking of piles
5.4 Pile pressing
6 Engineering quality inspection and acceptance of works
6.1 Inspection and testing of pile shaft and pile tip before pile pressing
6.2 Engineering quality inspection and testing in the course of pile pressing
6.3 Pile quality inspection and testing after pressing pile
6.4 Acceptance of works
Annex A Requirements for structure and quality of static pressing precast concrete piles
Annex B Structure diagram of commonly-used static pressing precast concrete tube-pile tip
Annex C Schematic diagram for structure of hold type hydraulic pressing pile machine
Annex D Basic parameters table for pile pressing machine
Annex E Reference for static pressing pile machine selection
Annex F Construction record sheet of static pressing pile
Explanation of wording in this specification
