Patent Introduction: Method for securing sheet piles

Patent 6664509 Issued on December 16, 2003
Estimated Expiration Date:  September 27, 2022

Abstract

A method for securing sheet pile includes interlocking the two sheet piles by utilizing sheet pile interlocks having an axial groove formed between the sheet pile interlocks. The method further includes introducing a welding electrode into the axial groove and welding the interlocked sheet pile interlocks together.

Sheet Pile Support Construction Points

For construction projects that need sheet pile as support, here are nine main construction points to smooth the whole construction:

1. Inspect and correct sheet piles, including test its length, width and thickness, in addition to visual inspection, other deficiencies must be corrected too.

2. In sheet pile insertion and play,  put line by measurement and try to pile vertically. The pile position deviation should be less than 50mm, the vertical degree of deviation less than 1%. Should start by the river, and finally be closed far from the river, so as to prevent the small toe mouth of sheet pile leaks by the river side.

3. At the lockings of two sheet piles, put on some butter to facilitate the play and pull, while prevent water seepage.

4. In sheet pile cofferdam, excavation needs a long time, there is large soil lateral pressure. In order to ensure sheet pile stability, according to the design , excavation depth should be 50cm lower than that in each purlin support. Timely add purlin bracing for support. Until the reinforcement completed at this layer, start excavation for stability.

5. Make sure level status for inside support to prevent accident from local deformation by the force discontinuity.

6. Inside the cofferdam, components within the support must be welded solid. Non-dense places between sheet piling and purlin need to work closely with the steel packing to avoid local buckling.

7. When excavate to the end of pile cushion, should immediately pour concrete manor to prevent boiling occurs in substrate by the constant term of water soaking, which would affect the overall pit stability.

8. At the four sides of base should set drains, water wells to ensure the water can flow out of the pit timely.

9. Do not remove sheet pile untill main structure construction  and soil’s backfilling completed. But also consider the impact of pile-removing at the surrounding environment, timely adjust the removal rate. Cavity after pile removal should be timely compacted by yellow sands to prevent the surrounding soil subsidence.

Note : the article is excerpted from Sheet Pile Support Construction Points

Sheet Pile Construction Monitoring Methods

Sheet Pile Displacement Monitoring

1) Vertical position monitoring
Surveying use Trimble DINI12 Digital Precision  Levels and WILD NA2 + GPM3 precision optical levels. The vertical deformation point error is more than + 0.5 mm in control. To ensure the monitoring accuracy, according to the specifications in the dock construction impacts outside the security and stability, in the good visual area, they set the two elevation reference points and three point field levels, composed of vertical displacement of the control network,taking1 to 2 months once Regular individual test to  test its stability and ensure the quality of test facilities. The elevation of each monitoring point is composed of a close working standard line level loop, the vertical displacement of the monitoring points is calculated by the twice measured height difference of the monitoring points. The amount of vertical displacement is calculated to mm.

2) Horizontal displacement monitoring 
They use LeicaTC402 Total Station and the United States Ashtech Z-survey dual-frequency GPS receiver. Benchmark test for the monitoring network together once a month. Monitoring point observation use the measured edge intersection, the intersection angle controls between 60 ° ~ 120 °. Monitoring point’s prism used to force the final heart devices to boost the accuracy. Deformation point relative to the operating point of the position error control ≤ ± 2.0 mm.

The horizontal displacement of monitoring points is calculated by the difference between two measured data. The amount of horizontal displacement is to mm.

Sheet Pile Deformation (inclinometer) Monitoring
Steel sheet pile and the soil type inclinometer and domestic use U.S. Geokon603 CN-1-type inclinometer, bottom-up by 1.0 m equidistant measurement, automatic storage records, forward-backward two readings of 180 ° observed.  To ensure the accuracy of observation, each measurement, the test sensor isto be placed in the bottom of the hole to 10 ~ 15 min, to ensure that the temperature balance. Monitoring the value of precision is ± 0.1 mm.

Stresses and Pressure Monitoring
The test of stresses, earth pressure, pore water pressure use the domestic XP05-type vibrating wire frequency (temperature) readout and XP99-type vibrating wire multi-frequency instrument, taking the readings and automatic direct-reading.Thereading accuracy  is ± 0.5Hz, ± 0.5 ℃.. Monitoring accuracy: steel sheet pile stress is ± 0.01 Mpa and earth pressure is± 1 Kpa and pore water pressure value is± 1 Kpa.

Groundwater Monitoring
The underground water level observation use SWJ-8090 type selection of domestic electricity type ruler over the two DaXun and typhoon period. Practice has proved that the water level gauge to monitor selected to take direct readings, the smallest ruler depicts 1 mm. Monitoring methods is appropriate and monitoring points layout is reasonable and the value of the sensor accuracy is ± 2 mm. Scale design and observational accuracy are to meet the requirements of the project, playing a guiding role in the construction.

Underwater Slope Stability Monitoring
Underwater slope stability monitoring uses U.S. AshtechZ-survey, based on the monitoring of large-span steel sheet pile cofferdam works double frequency GPS receivers with choke-type antenna with domestic HY1700 bathymetric features, increasing the lateral earth pressure of steel sheet pile, inside and outside the row of steel sheet pile deformation detection instrument on board operations, automatic continuous record storage measuring with the stress changes of the standards supporting  process  and pore-water pressure outside the cofferdam and the steel rod depth rod method. The former measurement accuracy≤±the stress and guide beam stress. Monitoring, testing is very comprehensive The latter accuracy ≤ ± 5 cm, similar to hydraulic engineering at home and abroad is rare.

How to Do Sheet Pile Finite Element Analysis

In sheet pile construction, by Finite Element Method, we should establish analysis model first.Then calculate and analyze sheet pile security and stability.

The external force is mainly hydrostatic pressure and water pressure, by the force expectations and calculations the combined load in each condition can be drawn. Using ANSYS Finite Element software to build a solid model, define the real constants and material properties, take four-node shell element Shell Elastic 4Node63 to divide unit for the model, respectively calculate the deflection, stress, bending moment in the model under these N kinds of loading conditions.

Combining loading conditions, calculate by finite element to get force map, and then by the post-processing data to get the maximum stress on sheet pile. Taking into account stress reduction factor 0.7 for the old or used sheet pile, the stress’s expansion factor 1.3 for the temporary structure and the sheet pile materials, calculate sheet pile actual allowable stress.

Similarly, from the analysis obtain the sheet pile deflection diagram in the X and Y direction, from the map we can intuitively know the location of maximum deflection under the wost condition. Compare the distance with the actual allowable sheet pile deflection.

If the maximum stress obtained through finite element analysis is less than the actual allowable stress, the maximum deflection less than the actual alloable deflection, it indicates that the strength and stiffness of the selected sheet pile in this condition meet the design requirements.

In the same way, we can also calculate maps of the displacement, deflection, bending moment and the axis of purlin and inside-support, compare the maximum value with the actual allowable one, to determine if the strength,stiffiness and stability of purlin and inside-support meet the design requirements.

How to Select Piling Vibratory Hammer?

To form sheet pile retaining wall, we need vibratory hammer to drive piles into the soil. Then how to select the hammer?

Vibratory hammer selection should meet three basic conditions :

1) Excitation force of vibratory hammer P0 should be equal to or greater than the sinking components being vibrated and soil’s dynamic lateral friction Tv ;

2) The total weight of vibratory hammer system Q0 should be greater than the driven components’ dynamic tip resistance Rv ;

3) Work rate of vibratory hammer system A0 should be greater than the minimum required amplitude A0 when driven components go through soil layers.

Note: For more information, please read Vibratory Hammer in Sheet Pile Driving

Sheet Pile Wall Design

Generally in sheet pile wall design, normally we need to calculate all kinds of loads, scour depth, length of sheet pile (including pile embeded depth, the concrete cover thickness) through test algorithm. According to different construction conditions in process aselect sheet pile sections, supporting layers and structure, at last check the overall stability of sheet pile wall.

1. Data Collection
Collect and analyze geological maps, the highest water level, the highest level of construction and so on.

2. Determine Geometry Size
Plane size is often dermined by upper structure and its foundation size. Sheet pile wall construction should be in accordance with the whole project construction and template installation, so the wall’s size should be at least 1.5m greater than the basic outline. It must also consider the needed size of pumping equipment and wells’ installation.

Dimensional size is usually influenced by water level, scour depth, the depth of excavation inside wall and factors such as stability in the pit end. But the most direct impact is water level.

3. Calculate Sheet Pile Wall Lateral Pressure

Assume sheet pile’s embedment depth first, then calculat lateral pressures hydrostatic pressure, water impact, ice pressure, wind, wave power and earth pressure.

4. Force Checking by Constructin Conditions

5. Stability Checking
Need to analyze wall’s overall stability and soil stability at the end of the foundation such as arch, water well-out and sand-cast.

Article Source:   Sheet Pile Wall Design Steps

Sheet Pile Driving Frequently Problems

Hard to insert Sheet Pile by large resistance force

There are two main reasons : solid and gravel sand layer; corrosion and deformation of connected sheet pile lockings. For the former case, in the pile tip's forwarding direction, cut the side angle to the slope of 1:2 to 1:4, and pile by high-pressure water flush or vibration method instead of hard hit with a hammer only; for the latter one, remove rust, grease and correct lockings to reduce resistance.

Pile tilting in driving direction

When pile larsen sheet pile, the connection resistance is relatively large. And the unbalanced given forces at both sides of cross section make piles easily to incline. To prevent such a tilt, in the piling direction set clip plates at the interlockings of steel sheet pile. At the same time, pre-calculate the position of every plates on purlin for calibration at any time. If the tilt is inevitable, the correction method is to use wire rope and hoist to reversely pull the sheet pile and then hammer, or use a special wedge-shaped sheet pile to correct.

Sinking of both sheet pile and neighborhood inserted piles

The reason is caused by the increasing resistance force of steel sheet pile bending notch. The treatment measure is promptly correct the tilting piles, use angle steel to fix the problem piles temporarily by welding with inserted pile(s).

Using of Corner Pile

For the need of pit structure, often we need corner pile, a special shaped pile to change the piling axis direction. Corner pile is normally made by larsen sheet pile cut along the midline, then combine and weld by actual needs.

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Article Source:

Sheet Pile China Manufacturer, Supplier - Shunli Sheet Piling Industrial Co., Ltd.