A barge on stabilized soil using different techniques
On the use of a barge on stabilized soil with different techniques - a lecture presented at the "Sixth Construction and Infrastructure Conference" of the "Association of Construction and Infrastructure Engineers" in November 2009.
Alternatives to foundation solutions
In this article we will present possible solutions for the foundation using the "barge on piles" method, when instead of using reinforced concrete piles attached to the barge, "concrete pillars" or other material are used, while maintaining a space between them and the bottom of the barge in such a way that the stress applied to the barge, from the structure (vertical and horizontal) acts directly on the concrete columns.
The purpose of the "pillars" is to serve as elements that stabilize and improve the properties of the soil mass in which they are installed, so that the combined mass can be attributed uniform improved mechanical properties when the system as a whole functions similarly to a barge on stilts, at lower costs.
Another significant advantage is that the afore mentioned change allows the barge to be treated as a normal barge, based on land with improved properties, which simplifies the calculation of the barge, as a normal barge, with springs, relying on the new parameters determined by the land consultant.
Barge on stilts
In Israel and in the world it has been known for many years [Burland et al. (1977), Davis & Poulos (1972), Zeevaert (1957) ] (1979 (Hooper)) as the method of establishing high-rise buildings and special buildings with heavy loads such as silos and storage tanks while combining barge and pilings when the pilings are mainly used as elements to reduce the subsidence expected in the barge. In this method the pilings are usually made as an integral part of the barge with a constructive connection between them.
The piles in this method are calculated according to several alternatives:
• A group of piles in a uniform distribution when the barge acts as a common head for the piles.
In this situation the piles carry most of the load and the barge carries a small part of the load and the calculation is like that of a group of piles with a common head when the piles have an acceptable safety factor.
• Piles evenly distributed under the barge, designed as "creeping" piles by calculating them for a tolerance of about 80% of the destruction tolerance and the total load between the piles and the barge is distributed accordingly.
• Piles "creep" in an even distribution, where the piles are calculated for 100% of the load in destruction tolerance.
In such a situation, the treatment of piles is only as subsidence reducers, while increasing the general security factor of the system.
• Making groups of piles only in areas of heavy loads to reduce differential subsidence in the area of the barge, between more loaded and less loaded areas.
With the development of the barge on stilts method and the experience gained, the question of the meaning and necessity of connecting the stilts to the barge was raised. When the piles are connected to the barge, most of the horizontal forces acting on the structure are transferred to the piles, due to their relatively high rigidity, and this can cause shear stresses and moments in the piles to the point of failure.
This can require the addition of pilings beyond what is required to limit subsidence.
In special buildings, where the useful loads are high and change (silos and silos), the connection also causes pullout forces in the piles that previously sank under the load that is removed afterwards.
In light of this, they began making barges on piles without a constructive connection between them and even creating a space between the piles and the barge in such a way that the barge would not be in contact with the pile heads at all.
As soon as there is complete separation between the piles and the barge, the reference to them can be changed and they can be seen as part of a system of stabilized and reinforced soil (1979, Hooper).
One of the problems with the calculation methods of a barge on stilts as detailed above is the complexity and difficulty of the calculation. The calculation is essentially three-dimensional which also requires the use of advanced three-dimensional computer programs. This causes many engineers to shy away from the method, which therefore does not become common knowledge.
Land stabilization and improvement
There are currently several options for soil stabilization that can be used to improve the soil under the barge:
• Stone pillars - with this method it is possible to drill, using modified methods, a borehole and fill it from the top with hard stone aggregate that will be tightened in stages using a vibrator. In cases where the bore is not stable, it is necessary to insert a corrective stepping stone into its lower part and tighten while lifting and tightening in stages which requires the use of special equipment.
• Using the technology of Jet Grout columns - with this method, a drill is inserted to the planned depth and gradually raised while rotating and laterally injecting cement mortar at very high pressure in a way that produces columns of cement mortar that is also mixed with the local soil.
• Drilling and casting of concrete columns using the "dry" method, or in case of stability and groundwater problems, drilling and casting using a CFA machine or bentonite technology.
• Use of other reinforcing materials such as lime columns, thin concrete and CLSM, provided that their tolerance to the various troubles and their effectiveness in curbing subsidence are proven.
calculation methods
• As mentioned, one of the advantages of the application described above is that it allows for the simplification of the calculation method and bringing it to a situation where all that is required of the constructor is to calculate a normal barge on stabilized and improved ground that has the property of a spring coefficient proposed by (1867 Winkler), according to the relationship δ = κ ⋅ σ [where δ - the settlement at a certain point under the barge, κ - stiffness of the Winkler spring, or as it is called the "substrate modulus" and σ - the contact stress at the point].
As part of the development of stone and lime columns, different calculation methods were proposed, of which we have given her
A weighted substrate number modulus was calculated for the methods described above for soil stabilization and improvement, such as by (Prof W. VanImple (1983) and (Dr H. Bredenberg (1983). An article was also published in 2002 (unsigned) by the Technion Institute titled Deep Mixing-Lime Columns in 2002. The mirror is also a calculation method.
• Based on the above it is possible to calculate a weighted κ:
Required data:
1. Determination of intervals x, y between the stiffening columns.
2. Finding the modulus of elasticity of the column and the ground.
3. Determining the cross-section dimensions of the column and its depth in the ground.
Calculations:
* The figure κtotal is used by the constructor for the barge calculations, while the calculation of the settlement in the structure can be performed by the foundation consultant, according to the shortening of the mass of the stabilized soil, plus the settlement in the ground below the stabilized soil.
Summary
The method simplifies the calculation of the foundation for the barge on the Winkler medium on the one hand and determining the properties of the medium on the other hand.