Pile foundation as the most important part of structure bears all static and dynamic loads of structure and transfers them to ground base so as to ensure the regular service of structure under safe conditions and the minimization of loss caused by unexpected disasters (such as earthquake and typhoon etc.).Therefore, construction management of pile foundation works is particularly important. Construction management means construction process management or control. Construction management of pile foundation work normally includes construction organization, planning, technology, quality, safety, equipment, material, finance, cost and civilized construction site etc., among which quality control is the link of the highest importance and must be attached great importance to by constructor, supervision unit, property owner and relevant authorities as it is the key to eliminate hidden quality troubles, reduce accident loss, avoid safety risk and preclude major accident.
2 Quality Control
Pile sinking mode is classified into dynamic sinking (hammering and vibration) and static sinking (i.e. pile jacking).
Before pile sinking, be sure to develop detailed construction organization plan, carry out close investigation on hydrological conditions, meteorological phenomena, geology, land form, existing building material or old buildings (or obstructions) in construction area, analyze construction difficulties and problems that may occur and take corresponding measures on a targeted basis while using appropriate constructional appliance and equipment so as to ensure the efficient and safe progress of construction.
(1) Over-water pile sinking
Special attention shall be paid to quality control of over-water pile sinking that features high difficulty and multiple influencing factors. Its control points are as follows:
① Provide on-board mechanical equipment of which the wind resistance (vessel), water flow resisting capacity, hoisting capacity and pile sinking ability (pile driving barge) meet the requirements. In addition, sufficient quantity of towing ships and tug boats with adequate capacity shall be provided.
② Be sure to attach importance to the analysis on geology and geomorphic information. It should be particularly noted that steep bank slope in pile sinking area may result in pile gliding, and thus bringing about increase in pile sinking plane deviation; on the other hand, land-slip may occur due to vibration and the increase in pore water pressure during pile sinking, so special attention shall be paid to this case.
③ Be sure to attach importance to the effect of wave force and drag force on process of and conditions after pile sinking. Wave force and drag force would not only affect the plane accuracy at pile position, but would also exert adverse impact on pitching of pile. Pile placement should be conducted in advance or in a delayed manner according to flow direction and velocity of water during pile placement. Be sure to prevent the impact of surge, wave, ship wave and heavy wind etc. during pile placement or sinking.
④ Try not to perform pile extension during over-water construction since the two pieces of piles above and below joint point may sway ceaselessly under the effect of water flow, wave and wind.
⑤ Technical personnel for pile foundation construction or survey personnel shall observe the pile sinking process at front section of pile driving barge or in front of pile driver and carry out corresponding treatment according to pre-plan in case of any exception.
⑥ Upon the completion of pile sinking, the pile shall be integrated with finished steel surrounding purlin in a timely manner so as to prevent the damage of single pile due to its repeated swaying under the effect of water flow and waves.
(2) In case of static jacking of pile, the management of the following points and the quality control shall be enhanced besides above noted relevant issues:
① During over-water pile jacking, it is necessary to adjust front and rear ballast water of vessel in a timely manner so as to assure the perpendicularity of pile during pile jacking; in the meantime, be sure to prevent the adverse effect of wave (especially surge), water flow and tidal level etc.
② In case of over-land pile jacking, there is a need to properly treat the foundation under pile jacking bracket so as to prevent the non-uniform settlement of foundation during pile jacking that may result in pile holder inclination. Adjust the equipment properly during pile jacking and ensure the perpendicularity of pile at the connection of upper and lower pieces of piles so as to avoid broken line intersection point at connection.
(3) Jacking equipment is recommended. Once holding equipment is used, it is necessary to check the fixture in order to ensure that the pile would not be damaged due to improper clamping.
3 Safety Management
To take safety measures, it is necessary to have an overall understanding of local hydrologic condition, meteorological phenomena, environment and natural disaster etc. and perform comprehensive analysis, take corresponding safety precautions and make safety pre-plan according to characteristics of this project.
(1) Hydrologic condition
Determine water flow velocity, direction, water element, tidal information, existence of surge, storm tide, slush, water depth, fluctuation of low water level and flood level, and analyze the cause of disasters and their potential impact on this project.
Exploration bore hole, exploration data, land form (including over-land and under-water land forms), ground water level, confined water condition, pressure, distribution and layer height, and the existence of shifting sand, inflammable gases, underground river, erratic boulder, geological fracture zone, karst topography, underground obstruction, existing underground works and the erosion status in neighboring area of submerged structure etc.
(3) Weather condition
Collect meteorological data gathered by local weather station over the years, analyze the impact of wind, rain, snow, thunder, ice and fog etc. on engineering safety, and analyze the frequency and time period of disastrous weather such as typhoon, seasonal strong wind, thunderstorm and rainstorm etc.
(4) Environment conditions
Learn about the conditions, construction year and foundation type of buildings and structures in surrounding area of project and check if the said structures are constructed and reinforced and if there is precision instrument, meters and dangerous premises that are extremely sensitive to vibration; check if there is underground pipelines, dangerous goods storage tank and pool, HV line, under-water pipeline and hospital, school and residential area etc.
If necessary, be sure to supplement above-mentioned data in a timely manner and then make analysis and study on potential safety and quality troubles so as to enact corresponding measures. Develop pre-plan for unexpected accident that may occur and perform supervision from time to time according to relevant rules and regulations.
4 Equipment Management
During the process of construction, different types of construction equipment (including main piling equipment and auxiliary equipment) shall be used depending on pile foundation, specification, construction technology, geology, hydrologic data, meteorological phenomena and other factors. The name, dead weight, volume, energy support and consumption, power, and mechanical and electrical principle of these equipments may differ significantly. The fault of these equipments would have a strong impact on the progress, safety, quality, cost and environmental protection etc. of the whole project. Hence, the type selection, leasing, management, use, maintenance and repair of equipment shall be conducted by persons specially assigned during the overall process of construction.
5 Accident Prevention and Handling
(1) Over-land works
① Pay close attention to foundation and overhead pipelines
All pile foundation works are carried out on soft-soil foundation, so there is a need to check if the bearing capacity of foundation meets the requirements of constructional appliance on ground contact pressure, if there is hidden pitch or loosened soil for landfill of refuse so as to prevent constructional appliance overturn caused by inadequate local foundation strength. In the meantime, pay close attention to the distance between overhead pipelines and construction equipment so as to prevent electric shock or collision damage during equipment operation as a result of insufficient safe distance.
② Pay close attention to meteorological phenomena
During the periods of typhoon or monsoon, reliable draught-proofing measures shall be taken when stopping the service.
③ Pay attention to dangerous and old buildings in surrounding areas
In case there are dangerous and old buildings in the neighborhood, isolation means such as vibration-proof trench and anti-vibration wall etc. shall be provided so as to avoid the damage and collapse of dangerous and old buildings as a result of vibration and earth squeezing.
④ Informationized construction
Informationized construction shall be carried out for important buildings or works with complicated surrounding environment, i.e. to arrange observing points there-around, control the change in its plane and elevation, measure its pore water pressure, mount inclinometry pipe, measure the displacement of deep soil mass, and if necessary, to measure seismic wave or the stress and strain on important structures. Collect the said data in a timely manner so as to take corresponding measures.
⑤ Pay close attention to underground buildings and structures
Be sure to check upon underground buildings or structures before the commencement, and if necessary, work with relevant departments to find original completion data etc. Take particular care of urban water supply and drainage pipes, power cables, communication cables, coal gas and military facilities of which unnecessary loss may be caused due to long-term operation, poor data accuracy or inadequate completion information and great errors etc.
(2) Over-water works
The construction technique and management of over-water pile foundation works is more difficult due to the effects of factors such as water flow, wave, tide, strong wind, rain and fog etc.
① Matters needing attention during pile placement
a. With respect to over-water pile foundation positioning, the upstream-oriented allowance of pile placement should be determined based on the flow velocity and direction during pile placement; more attention is required in case of large water depth and high flow velocity. If the degree of impact of water flow on pile is unclear, pile placement trial could be conducted for fear that excessive pile foundation deviation would occur. Furthermore, the gradient of underwater topography also has great effect on pile placement position; hence, an allowance is reserved, and this allowance is associated with gradient and the hardness of surface soil conditions. Several trials could be conducted before formal pile placement if there is no experience that can be referred to.
b. For over-water pile foundation works, tidal difference is usually used for construction. Pile foundation in areas with low water level at bank side is usually constructed at the time of high water in the sea or tidal estuary so as to solve the problem of insufficient immersion depth of pile driving barge or inadequate height of pile driving frame; piles (especially concrete tubular pile) with cap elevation is usually driven at low water level; in order to protect pile body against the adverse effect of water hammer, pile sinking through hammering is not allowed when pile cap is submerged in water. Pile sinking shall be performed by taking the advantage of low-water season during construction in river or lake so as to create conditions for dry construction of top-side structure.
② Set up clear indications of navigation obstruction lamp etc.
Be sure to set up navigation obstruction lamp and other clear indications at pile cap so as to enable the personnel on ships can see over-water or under-water navigation obstructions both in the daytime and at night. Construction vessels shall be kept away from construction area at night so as to prevent dredging anchor breaking finished piles.
③ Clamp surrounding purlin for linkage in a timely manner
Upon the completion of one group of piles, they should immediately be connected using surrounding purlin which shall be designed and calculated according to operating conditions and have adequate rigidity and strength.
④ Make emergency pre-plan for protection against typhoon and flood
In order to ensure the safety of construction ship and personnel, emergency pre-plan shall be made against typhoon and flood according to data gathered by local weather station and oceanographic station over the years, and there is a need to arrange for shelter anchorage and towing ship on duty. In the meantime, completed works shall also be reinforced before typhoon and flood so as to ensure the safety. Marine operation personnel must receive information from local weather station and oceanographic forecasting station three times a day while collecting and analyzing medium-and-long-term weather and water level conditions so as to develop corresponding construction plan and countermeasures.
⑤ Pay attention to over-water structure, submerged structure and obstruction in construction area
Learn about the navigational clearance and clear width of over-water HV lines, bridges, pipe supports, submerged pipes, lines, fiber-optic cables, underwater obstacles, shipwreck and old structures in construction area; when necessary, exploration or clearing shall be made in advance, while cooperating with maritime affairs authorities and pipeline authorities to handle relevant formalities and setting up proper over-water signs and marks.
⑥ Attach importance to operation on foggy days
Develop measures for operation and safe navigation on foggy days and mark the ships and pile foundations so as to prevent collision with other ships.
⑦ Formulate over-water operation safety system
It is essential that an operation system should be established for over-water operation safety management. Drinking is strictly prohibited during over-water operation. Be sure to wear life jacket. Staircase must be provided with safety net and life buoy, while corresponding medical and rescue facilities and networks shall be established. Relevant personnel shall receive trainings on over-water operation safety and obtain a certificate before going to work.
6 Intermediate Acceptance and Completion Documents
Handover of completed works to subsequent working process or property owner is an essential link of construction and an important part of construction management.
(1) Intermediate acceptance
Intermediate acceptance means the handling of handover procedure toward next process of pile foundation work or the handover to general contractor.
(2) Completion documents
As one of the important engineering documents, completion document shall be prepared according to file management standard and requirements of national or local government.
(3) Preparation of completion document
The essential purpose of preparation of completion document is to factually and comprehensively reflect relevant techniques and quality concerned during construction, and the documents include design document, drawings, design modification notice, construction related contact list, relevant meeting records & minutes, construction organization design document, record files relevant to construction, quality certificate and review report of material and semi-finished product, concrete related test report, qualification of welding procedure, report on handling of accident due to quality, builder's diary, economic contract and final account for completed project etc