How to Drive Steel Sheet Pile?

There are three typical sheet pile driving methods.

1. Single Pile Driving Method

From one of corners of sheet pile walls, drive the pile one by one until the end of the project. This method is convenient, fast and does not require auxiliary support, but pile easily incline during driving, and the error accumulation is not easy to correct.

2. Screen-Piling Method

Put 10~20 sheet piles in rows into the leading guide or frame to shape it like a screen wall, then pile driver play back and forth, first drive both ends to the required depth, then pile the middle sheet pile sequentially. This method prevents the sheet pile’s larger inclination by reducing the tilt error accumulation, and easy to close up after construction. But its drawback is that construction process is a bit slow, and need the erection of a higher pile frame.

3. Piling by Waling Piece Method

At a certain height on the ground some distance from the axis, firstly build single or double layers of circle waling pieces as bracing system, then insert sheet piling one by one inside. When four corners are closed up, gradually drive sheet piles block by block in steps’ way to the designed elevation. This approach ensures flat size of sheet pile wall, squareness and flatness, it is suitable for occasions requiring higher precision, fewer pile amounts. The disadvantage is the complexity and slowness in construction, and it requires shaped sheet pile in wall closure.

( Excerpted From Three Typical Sheet Pile Driving Methods  )

Sheet Pile Pit-Retaining Structure Design

Design of  sheet pile retaining structure in foundation pit can be divided into the following three categories:

1. Cantilever Support Structure – when the excavation is not very deep, the cantilever support structure can be used to block soils behind the wall.

2. Single Support Structure – when the excavation depth is larger, to ensure the retaining structure safety and reduce distortion, often set a support or an anchor near the top of the supporting structure.

3. Multi-support Structure – when the excavation depth is large, we can set multi-layers of support or anchors.

Design Contents of Steel Sheet Pile Retaining Structure

1. Select the sheet pile type and model cross-section;

2. Calculate and check sheet pile insertion depth, cross-section strength and deformation;

3. Consider the corresponding precipitation plan and its impact on the surrounding environment (including the vibration impact in pile recycling or removing)

(Excerpted From Steel Sheet Pile Pit-Retaining Structure Design Classification )

Calculation Points on Sheet Pile Wall Structure in Soft Soil Water

1. Three Types of Calculation

A. The whole sheet pile wall structure must meet construction requirements in strength and stablity. In calculation, we should consider the worst construction condition and flowing water pressure from above riverbed to river surface, water foce when ships passing by and in tide situation. Pressure from below the riverbed to sheet pile end is combined by hydrostatic pressur and positive earth pressure.

B.  Because of three layers steel waling system, the whole weight is on the sheet pile, we must calculate the vertical load of sheet pile wall.

C. Because of soft soil with deep excavation, the base of sheet pile wall must do stability calculation mainly including Pile Sand Welling and  Base Bumping Calculation.

2.   Establish Calculation Model

 

Use Infinite softwarelike Midas Civil, sheet pile is modeled or simulated by pile units, support and waling system is simulated by beam units.

3、Notes on Base Stability Calculation

 

3. 1　Pile Sand Welling in Base End Calculation

In the pumping of base end, it easily brings danger of pipe sand welling, we should calculate in simplized way. The rule of calculation is by the enough sheet pile embeded depth t to increase water flow length and reduce upward water force. The frequently used calculation formula for non-sandwelling is : K·i·γ≤γ

In this formula：

K-Safe Coeffcient (less than 2 is required) ;
I—hydraulic gradient;
i = h′/(h1+ t) ;
γ—Water Weight ;
γb —Soil Effective Weight

3.2  Base Bumping Calculation

After deep excavation in soft soil foundation pit, under the water pressure and unbalanced soil pressure inside and outside, there may be bumping situation at the end of soft base,  we can claculation by slip surface way, the frequently used fomula is :

Slip Moment：Md=γMH（x2/2）
Stable Moment：Mr=x∫π/2+α0 SM(xdθ), α＜π/2

In this formula：
α=atg(b/h);
h – the height of bottom inside support against to concrete casting height
b – Haft length of base end;
SM -shear strength without watering in slip surface

Note: the article is from  Calculation Points on Sheet Pile Wall Structure in Soft Soil Water

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.