ES2562841B2 - Soft terrain improvement device and method - Google Patents

Abstract

Hollow element (10, 20, 30, 40, 50) configured to enter soft ground (38, 48, 58), and open at least by its lower end, such that when said hollow element (10, 20, 30, 40 , 50) is introduced into the soft ground (38, 48, 58) its interior is filled with said existing soft ground (38, 48, 58), and comprising a geored (11) of cylindrical shape configured to allow the circulation of water through it; a geosynthetic (12) that covers the outer surface of the geored (11) and performs a filter function, allowing water to pass but not the existing soft ground particles (38, 48, 58); and at least one geosynthetic (13) that covers the interior surface of the geored (11) and that performs a double function: on the one hand it lets the water pass but not the soft ground particles (38, 48, 58) -function filter - and on the other hand it provides the hollow element (10, 20, 30, 40, 50) with a radial stiffness - resistance function. A soft ground improvement method (38, 48, 58), using the hollow element (10, 20, 30, 40, 50) defined.

Description

DEVICE AND METHOD OF IMPROVEMENT OF SOFT LAND

FIELD OF THE INVENTION

5 The present invention belongs to the field of Terrain Engineering, Geotechnics and Foundations, and more specifically, to the field improvement techniques.

BACKGROUND OF THE INVENTION

10 Any type of structure (building, civil works, etc.) must be supported or laid on the ground, so that the resistance and defonnability of the land must ensure that the foundation is stable and that the defonnaciones are admissible. When the characteristics of the land are not adequate, a

15 traditional deep foundation or to improve the ground.

Traditional deep foundations are made using piles, and almost always have a considerably higher cost than that of ground improvement techniques (Wissman, KJ, Fax, NS, and Mar / in, JP 2000. Rammed aggregale piers 20 defeat 75 1001 long driven piles Performance confirmation 01 constructed geolechnicallacilities, Geotechnical Special Publication, Vol. 94, ASeE, Res / on, VA, 198-210). In addition, ground improvement techniques are generally more environmentally friendly, because they require less use of construction materials such as steel or honnigón (Rujikiatkamjorn, C. e 25 lndraralna, B. 2014. Environmental sustainability 01 soft soil improvement via vacuum and surcharge preloading GEO-Congress 2014: Geo-Characterization and Modeling for Suslainabiliry (pp. 3658-3665) (Uniled Slales: ASeE or Egan. D. and Slocombe BC 2010. Demonslrating environmental benefils 01ground improvement Proc. ICE -Ground lmprovement 163 (1): 63-69) Thus, these economic and environmental conditions are causing the ground improvement techniques

Be increasingly popular.

These techniques are abundant and diverse. Its objective is to improve the properties (for example, resistance, rigidity and / or pennability) of the land that will be used as the foundation of a structure (embankment, fill, building, bridge ...). Among them, sporadic use techniques are included, such as, for example, freezing of the land, and more common and widely used techniques such as preloading or overloading of the land, the use of vertical drains, gravel colwnnas or dynamic compaction.

The ground freezing technique literally consists of freezing the ground to increase its resistance. This increase in resistance is due to the transfonnación of the water that is between the pores of the ground in ice. The usual technique of freezing the ground consists in circulating liquid nitrogen through it. However, its cost is very high and is only used in very particular circumstances.

Land preload or overload is one of the most common ground improvement techniques. This technique consists in applying a greater load of the load to which the land will finally be subjected, once the structure to be built is built. That is to say, with this technique the terrain is overconsolidated, increasing its resistance and reducing the defonnaciones that will suffer when cementing the future structure. The overconsolidation of the land is quantified through the ratio of overconsolidation (CSR), which is defined as the ratio between the maximum effective tension to which the land has been subjected throughout its history between the actual effective tension it has. Thus, its value is always equal to or greater than l. The overconsolidation of the land can be understood as that the land "gets used" to a higher load value, being therefore positive to increase the value of the CSR.

The fine soils on which this improvement technique is usually applied are not instantaneously defonted when the load is applied, but rather undergoes a deferred defonation process over time, which is called consolidation. This process consists of the defonnación due to the expulsion of part of the water that occupies the hollows between the particles or grains of soil. This expulsion is not instantaneous since it takes some time for the water to circulate along the ground and reach a draining contour. Thus, the consolidation time depends on the drainage path.

The preload or overload technique has the inconvenience of the consolidation time of the land which, in many cases, is not compatible with the structure execution time.

To accelerate the production of seats and reduce the waiting time with overloads

or preloads, vertical drains are usually used. These vertical drains constitute draining contours that reduce the water drainage path, accelerating consolidation. At present, vertical drains are generally prefabricated with flat fonna and consist of a geored wall that has hollow channels through which water can circulate, and are surrounded by a geotextile that performs a filter function, that is, leaves pass the water but not the soil particles.

However, the latter technique, even accelerating the consolidation of the land, does not consider the inclusion of resistant elements that strengthen the terrain to directly improve its stability and bearing capacity. To do this, we usually resort to gravel column or gravel column solutions encapsulated with geotextile.

The technique of improvement by gravel columns, also called vibrosubstitution or vibro-displacement due to the constructive form, consists of making vertical perforations in the ground to be improved that are filled with compacted gravel. An advantage of this technique with respect to prefabricated vertical drains is that it not only acts as a vertical drain accelerating the consolidation of the fine terrain, but also reinforces the terrain because a terrain is introduced

of better characteristics such as gravel. In this way, not only are the seats accelerated, but also their total value is reduced and the ground resistance is directly increased. There are some variants of est3: technique, such as the one presented in patent EP 11571 69 B 1 (Geopiers) where special emphasis is placed on the compaction of gravel by tapping ("tampered or rarnmed columns"). However, there is no experimental evidence to show that this technique of compacting gravel by beating produces a greater improvement than conventional gravel columns constructed by vibrosubstitution or vibro-displacement (Sluedlein A. W and Ha / lz. RD Analysis 01 Foofing Load Test are Aggregate Pier Reinforced e / a and Journal o / Geotechnical and Geoenvironmental Engineering 138 (9): J091-J / 03). Another similar variant is set out in EP 1273713 B 1, which in turn presents another variant (EP 1609914 Al) with the inclusion of reinforcing elements (bars, rings or reinforcing steel plates). The inclusion of reinforcement elements does improve the behavior of the columns but also increases their cost and hinders their execution.

In any case, on very soft terrain, gravel columns do not have enough lateral confinement to function properly. Therefore, there are modifications consisting of adding cement to the gravel (controlled module columns: Keller. Rigid Inclusions CSe ". Catalog 35-02 EN) or confining the columns laterally with a geosynthetic, usually a geotextile (encapsulated columns ° confined laterally with geotextile) For example, the company Huesker uses the geotextile called RingtraC® to confine the columns laterally.The effect of encapsulation or lateral confinement is a "corset" type effect that prevents the column from expanding radially and fails. Specifically, Babu et al. (A Critical Review o / Construction, Analysis and Behavior o / Slone Columns. February 2013, Volume 31, Issue 1, pp 1-22) collects the state of the art on gravel columns, which also explains the bagged columns and new variations such as internally reinforced columns or columns with some binding element, such as cement (controlled module columns, CMS). Jie Han {"Recenl research and development o /

ground column / echnologies') collects the state of the art of gravel columns and vadas techniques.

In some cases geogrids ("plastic lattice") are used instead of

5 geotextiles (pennable and flexible synthetic fiber fabric, usually polypropylene and polyester), the drawback is that in these cases the hollow cylindrical membrane is not usually used directly and it is necessary to glue or weld the geomaJlas. Gniel and Bouazza (2009) propose that it is not necessary to weld but that it is sufficient that there is an overlap ("Construclion o / geogrid encased slone co / umns: A new proposal

10 based on laboratory tesling "). In addition, other new developments are committed to the use of plastic bottle material to encapsulate gravel columns instead of using geotextiles (Dulla S, Mandal JN. 20/3. Feasibility S / udy on Was / e Plas / ic Water BOllles as Case / s of S / one Co / umnsfor Ground improvemen /. in Design and Prac / ice of Geosynthe / ic-Reinforeced Soil Strucfures: (HI Ling, G Gottardi, D.

15 Cazzujfi, J Han, F. Ta / suo / w (eds.)), Des / eeh Publica / ions, 14-16 Oc / ober 2013, Bologna. pp. 379-388).

However, one of the main constructive problems of gravel columns is the need to provide large volumes of gravel. Therefore, currently

20 is about finding alternative solutions or techniques. One of these solutions is to use recycled concrete or other recycled materials to make ("fill") the gravel columns or encapsulated gravel colwnnas.

In this sense, there are several scientific publications on the use of recycled materials for use in gravel columns:

Jefferson 1, Ga / erell M, Thomas AM, Serridge CJ. 2010. Procedings of / he

ICE -Ground lmprovemen /, Volame 163, ¡ssue 1, 71-77.

Serridge CS 2005. Aehieving sus / ainability in vibro s / one column / echniques.

30 Proceedings of the ICE -Engineering Sus / ainability, Volume J58, Issue 4, 211-222.

Serridge CS, Sarsby RW, 2010, Assessment of the use offers / ed aggregates in vibro-slone column ground improvement techniques. in Conslructionfor a Sustainable Environment (Sarsby & Meggyes (eds). Tay / or and Francis Group, London pp 75-89. Joe Persichetti, EIT Hayward Balcer ne. Sustainability Seminar. Hollywood, AC. Oc / Apr 12, 2010. Recycled Concrete as Vibro Slone Column Backjill.

However, the use of recycled materials is not always possible or economically viable, since the cost of these materials may also be high, they may not be available or contain undesirable substances or contaminants that do not pennite their use.

Another alternative to the use of static loads (preload or overload), is to apply dynamic loads, as for example is done in dynamic compaction. Dynamic compaction is used in fundamentally granular soils and heterogeneous landfills. A detailed description of this technique can be found in Lukas RG. 1995. Dynamic Compaction -Geotechnical Engineering Circular No. l. USO Department of Transportation, Federal Highway Administration, Washington D.C, FHWA-SA-95-03 7. It consists of the densification of the land, that is, the reduction of the volume of holes, which improves its mechanical properties (stiffness and resistance). Densification is achieved by striking or impacting the ground from its surface, dropping a club or weight from a certain height. These impacts can be carried out repeatedly and are usually executed in a mesh of points evenly distributed on the surface of the land to be improved. This technique was invented and developed by Louis Menard (US 3898844 A). Some terrain improvement techniques that use similar concepts are: US 1650827 A, US 5244311 A and EP 1375753 A2. Also, there are existing patents on the equipment used to apply these impacts (US 4580765 A, US 3067657 A).

However, dynamic compaction is not effective in fine (clay) soils.

and / or silty) since its low permeability makes it impossible to dissipate interstitial pressures generated by surface impacts. Thus, to improve fine terrain, gravel is usually added to the crater generated by the impacts, forming a gravel column of short length. This technique is called dynamic substitution.

And, similar to gravel columns, it has the disadvantage of the gravel consumption that is necessary and the associated cost. On the other hand, there are some experiences in fine terrain in which dynamic compaction has been used in combination with prefabricated drains or gravel columns (Shenthan T, Nashed R, Thevanayagam S, Martin GR. 2004. Lichen / ac / mitiga ion / ion in silty soils using composite slone columns and dynamic compaclion. J Earthquake Eng 3 (1): 205-220). The combined use with gravel columns continues to present the disadvantage of gravel consumption and consequently increases the cost significantly. Dynamic compaction combined with prefabricated drains slightly improves the results achieved by hitting a fine ground without including any additional element (traditional dynamic compaction), in the sense that it is possible to increase the ratio of overconsolidation of the terrain, since the prefabricated drainage pennite accelerate the expulsion of water from the ground. However, the increase produced is not important.

SUMMARY OF THE INVENTION

The present invention seeks to solve the aforementioned drawbacks by means of a hollow element and a method of ground improvement thanks to said hollow elements and a punctual overload, which encompasses much of the advantages of gravel colwnna techniques described above (accelerates consolidation and reinforces the land), and also avoids the use of gravel.

Specifically, in a first aspect of the present invention, there is provided a hollow element configured to enter soft ground, and open at least by its lower end, such that when said hollow element is introduced into the ground

soft inside is filled with said existing soft ground, and comprising

a cylindrical geored configuration configured to allow the circulation of water through it; a geosynthetic that covers the outer surface of the geored and that performs a

filter function, allowing water to pass but not soft ground particles

existing; and at least one geosynthetic that covers the inner surface of the geored and that performs a double function: on the one hand it lets water through but not the particles of

soft ground - filter function - and on the other hand gives the hollow element a rigidity

radial -function resistance-, In a possible embodiment, the geosynthetic covering the outer surface of the

Geored is a geotextile.

In a possible embodiment, the inner surface of the geored is covered by a single geosynthetic that performs the double function of filter and resistance. Alternatively,

the inner surface of the geored is covered by two geosynthetics such that both

They form a geocomposite, and such that one of the geosynthetics, preferably a geotextile, performs the filter function, and the remaining geosynthetic. preferably a geogrid, performs the resistance function

In a possible embodiment, the at least one geosmetic that covers the inner surface of the geored and that performs the resistance function preventing the hollow element from being radially defendant, has a stiffness in the circumferential direction of at least 1000 kN / m.

In a possible embodiment, the hollow element has a thickness whose order is between approximately 5 millimeters and 10 centimeters, a radius whose order is between approximately 10 centimeters and 5 meters, and a

length whose range is between approximately 2 and 10 meters.

In another aspect of the invention, a soft ground improvement method is provided, utilizing the hollow element defined above. The method comprises the steps of:

5 -introduce at least one hollow element from the surface into the soft ground, such that the longitudinal axis of each hollow element remains substantially vertical, and such that when the element is introduced into the soft ground and being hollow by at least the lower end, its interior is filled with existing soft ground, thus laterally confining the existing soft ground column.

10-make a point overload, such that said overload is only located on the soft ground located inside the hollow element, thus improving the characteristics of said existing soft ground colwnna.

In a possible rea1ization, the introduction of the hollow elements into the soft ground 15 is carried out by driving or displacement, and by means of double-walled hollow cylinders, the method also comprising the steps of:

-

As a preliminary step to introduce the hollow element at least to the soft ground, place the hollow element between the walls of a double-walled hollow cylinder;

20-then, at the bottom of the hollow cylinder, and attached to the hollow element, place a sheet configured to anchor the hollow element to the desired depth; - Insert the hollow elements into the soft ground, by means of the double-walled hollow cylinders, and once the cylinder and hollow element assembly is driven into the soft ground, remove the cylinder, such that the hollow element remains

25 placed on the soft ground, and anchored at the bottom by the sheet.

In a possible reset, said sheet is metallic and ring-shaped.

In the possible way to carry out this punctual overload, it is dropped

30 from a certain height aJ minus a heavy element on each column of existing soft ground surrounded ° encapsulated by each hollow element, such that

W1a applies certain energy to the soft ground that consolidates and overloads it. In W1a possible embodiment, said heavy element is a mallet and a crane is used to lift said mallet and drop it.

5 Alternatively. a plurality of hollow elements are introduced into the soft ground and to perform this localized point overload, modular elements are used with such an arrangement that they rest solely on the surface of the existing soft ground columns surrounded or encapsulated by the hollow elements, and such that they form a surface on which to place a weight that constitutes the

10 preload or overload. In a possible embodiment, said modular elements are made of plastic and said weight is a floor as a filling material. In addition, and in the case of using modular elements, the method comprises the steps of:

-

Wait long enough to consolidate the soft ground: 15 - Remove the overload.

BRIEF DESCRIPTION OF THE FIGURES

In order to help a better understanding of the features of the invention,

20 according to a preferred example of practical realization thereof, and to complement this description, a set of drawings is attached as an integral part thereof, the character of which is illustrative and not limiting. In these drawings:

Figure 1 shows a diagram of a cross-section of the hollow element, according to an embodiment of the invention.

Figure 2 shows a diagram of the introduction of the hollow element into the double-walled cylinder, in accordance with an embodiment of the invention.

Figure 3 shows a diagram of the introduction and removal of the double wall cylinder in the field, according to an embodiment of the invention.

Figure 4 shows a perspective in elevation and in another perspective in plan, of a static point overload of the land, according to an embodiment of the invention.

Figure 5 shows a dynamic point overload of the terrain, according to an embodiment of the invention.

Figure 6 shows the ratio of overconsolidation under the axis of the hit surface, for different land improvement methods considered.

DETAILED DESCRIPTION OF THE INVENTION

In this text, the term "understands" and its variants should not be understood in an exclusive sense, that is, these terms are not intended to exclude other technical characteristics, additives, components or steps.

In addition, the "approximately", "substantially", "around", "ones", etc. they should be understood as indicating values close to which these terms accompany, since due to calculation or measurement errors, it is impossible to achieve with total accuracy.

The lands are classified in rocks or soils, being the latter thick or thin. Fine soils, mainly clayey and / or silty, are classified as hard and soft. In the context of the present invention it is understood as soils or terrains, those soils or fine soils and of low bearing capacity, that is soft.

The following preferred embodiments are provided by way of illustration, and are not

It is intended to be limiting of the present invention. In addition, the present invention covers all possible combinations of particular and preferred embodiments indicated herein. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention,

Next, the hollow element and the method of ground improvement are described by means of said hollow elements and point overload, which encompasses much of the advantages of gravel column techniques described above (accelerates consolidation and reinforces the ground), and It also prevents the consumption of gravel.

First, and optionally, the land surface is prepared. This preparation may imply the need to excavate the land to achieve a horizontal surface, clearing of vegetation, removal of topsoil (topsoil), etc. In some extreme cases, of extremely fine soils, in which an adequate access of the machinery cannot be guaranteed, it may be necessary to perform some surface treatment, such as for example a crust of ground cement.

Next, at least one hollow cylindrical shaped element is introduced into the ground, and opened at least by its lower end, such that the longitudinal axis of each hollow element is positioned substantially vertically in the ground. Therefore, by introducing the element into the ground and being hollow by at least the lower end, its interior is filled with existing ground in such a way that said hollow element laterally confines the existing floor column.

The composition of the hollow element is novel, since said hollow element is not included in the state of the art. Specifically, and as shown in Figure 1, each hollow element 10 comprises: a cylindrical geored 11 configured to penetrate the circulation of water therethrough; a geosynthetic 12, preferably a geotextile, that covers the outer surface of the geored 11 and that performs a filter function, that is to say, lets the water pass but not the particles of existing terrain, thus achieving drainage and consolidation of the terrain; and at least one geosynthetic 13 that covers the inner surface of the geored 11 and that performs a double function: on the one hand it lets the water through but not the particles of

5 fine soil (filter function) and on the other hand it gives the hollow element 10 a radial stiffness (resistance function).

In a possible embodiment, the inner surface of the geored is covered by a single geosynthetic that performs the double function of filter and resistance. In another possible embodiment, the inner surface of the geored is covered by two different geosynthetics such that both form a geocomposite. In this case, one of the geosynthetics, preferably a geotextile, performs the filter function and the remaining geosynthetic, preferably a geogrid, performs the resistance function.

In addition, the geosynthetic that covers the inner surface of the geored and that performs this resistance function preventing the hollow element from being deflated radially. it presents a high rigidity in the circumferential direction (preferably, Jg> 1 000 kN / m) to confine the ground column correctly, minimizing the radial expansion of the membrane, and therefore the ground seats

20 on the surface.

This hollow element 10 has a thickness whose order is between

approximately 5 millimeters and 10 centimeters, a radius whose order is

between approximately 10 centimeters and 5 meters, and a length whose

25 range is between approximately 2 and 10 meters.

The introduction of the hollow element in the ground is carried out from the surface and, preferably, by driving or displacement of the land, without the need to dig it. In a possible embodiment, as shown in Figure 2, a hollow double-walled cylinder 24 is used to perform the driving or displacement of the terrain, between which walls the hollow element 20 described above is located. Also in

the lower part of the cylinder 24 and attached to the hollow element 20 is placed a sheet 25, preferably metallic and with a ring shape, configured to anchor the hollow element 20 to the desired depth. One skilled in the art will understand that once the cylinder assembly 24 and hollow element 20 is driven into the ground, then it is possible to extract ("recover") the cylinder 24, so that the hollow element 20 remains placed in the ground, and anchored at the bottom by the plate 25 cancel. Figure 3 shows a diagram of the introduction of the double-walled cylinder 34 into the soft ground 38, between which walls the hollow element 30 is located, and with the sheet 35 located at the bottom of the cylinder 34 and

10 attached to the hollow element 30. In addition, Figure 3 shows the removal of the cylinder 34 once the desired depth has been reached, such that the hollow element 30 remains in the soft ground 38, and anchored at the bottom by the sheet 35

15 Next, and in order to improve the characteristics of the existing terrain column that hangs inside the hollow element, a point overload is performed, located on the ground located inside the hollow element.

Preferably, and as shown in Figure 5, to reset this point overload

20 located at least one heavy element 59, such as a hub, is dropped from a certain height onto each column 50 of existing soft ground 58 surrounded or encapsulated by each hollow element described above, so that a certain energy is applied to the terrain Soft 58 that consolidates and overloads it. In a possible embodiment, a crane 60 is used to lift the heavy element 59 and leave it

25 fall. One skilled in the art will understand that these impacts of the heavy element 59 on the soft ground 58 can be performed repeatedly, and that the footprint left by the heavy element 59 on the soft ground 58 should approximately coincide with the terrain surrounded by each hollow element. In this embodiment, the overhead is dynamic.

One skilled in the art will understand that in this case, the invention can be considered

as an improvement of the efficiency in the technique of dynamic compaction in fine terrain since a cylindrical element is introduced that laterally confines the ground and allows its rapid consolidation during impact or striking from the surface. In addition, with the method of the invention, costs are reduced with respect to replacement

5 dynamic, since the contribution of gravel is replaced by the hollow element.

In another possible embodiment, to perform this localized point overload, modular elements are used, preferably made of plastic, which allow rapid placement and removal and form a surface, on which to place a weight.

10 which constitutes the overload, preferably a soil as filler material. In this embodiment, the overload is static. One skilled in the art will understand that in this case, and for the use of modular elements, it is necessary to use a plurality of hollow elements.

15 The objective of the modular elements is to transform a uniform overload, such as a landfill of ground driven directly on the surface of the land, into a point overload that acts only on the columns of land to be overloaded. To do this, these modular elements must have an arrangement such that they only rest on the surface of the columns of

20 existing land, surrounded or encapsulated by the hollow elements described above.

For example, in one possible embodiment, and as shown in Figure 4 in an elevation perspective and in another perspective in plan, the hollow elements are arranged in the soft ground 48 by connecting a square mesh, and each modular element 46 comprises four supports, such that each support is placed only on 'l.í of the existing soft terrain column 48. In this way, on each column 40 of existing soft ground 48 four supports are supported belonging to four different modular elements 46. In addition, each modular element 46 has a domed shape on which to place the weight 47 that constitutes the overload. In this possible embodiment, the ends of the vault and / or the supports have some

projections, such that they penniten a fast and continuous connection of the modular elements 46. One skilled in the art will understand that there are as many modular elements 46 as columns of existing soft terrain 48, surrounded and encapsulated by the hollow element. Subsequently a filling material is placed

5 or overload on the modular elements (figure 4, reference 47).

In addition, a person skilled in the art will understand that the modular elements must be designed and have a thickness such that it can withstand the loads applied to them, and that their dimensions are a function of the characteristics of the elements.

10 holes In addition, its height can be variable and is conditioned by an optimal design of the structural element that supports the loads, and can vary between approximately 0.2 meters and 3 meters.

The next step of the method, and in the case of having used a static overload,

15 is to wait long enough until the consolidation of the land occurs. This waiting time can vary between a few hours and a few months, and in general, it should not exceed 3-5 months. Then, once the waiting time is over, the overload is eliminated. At this time, it is possible to recover the modular elements used, which can be reused, even

20 within the same work.

Finally, the structure that is intended to cement is executed.

The method of the invention pennite improve the terrain simply with the inclusion

25 of hollow elements, and the realization of a punctual overload, avoiding the consumption of gravel or other necessary materials in the column-type techniques, described in the state of the art, which means a reduction in the construction process.

30 In addition, the removal of gravel implies that it is not necessary to make a hole in the ground to introduce it, and therefore that the construction process is faster and more comfortable. The double function that the gravel performs (draining element and

ground reinforcement) in column type techniques, it is substituted in the method of the invention by the geosynthetic, preferably a geored, (draining element function) and by the overload and the at least one radial encapsulation geosynthetic

5 (land refurbishment function).

Example

Below are the results of numerical simulations that

10 demonstrate the technical feasibility and the competitive advantage of the proposed land improvement method over other existing methods, taking as an example and without excluding one of the preferred embodiments. In particular, the case has been used in which the application of punctual overload is carried out in a dynamic way by striking. To simplify the numerical simulations, it has been

15 simulated only one hit at one point, although it is usual to hit

repeatedly and in several pwltos.

To simulate the striking, a dynamic load with a circular voltage of 60 cm in diameter and with a harmonic wave time distribution with a frequency of 20 Hz has been assumed. To model a stroke, half of a stroke is considered wave (180 "). The amplitude of the dynamic load has been calibrated so that the footprint it leaves

the hit on the ground is 4 cm in each of the analyzed cases. To simulate the existing soft terrain, usual realistic values have been taken.

For the proposed improvement method, a hollow element of 5 m in length, 60 cm in diameter and a circumferential stiffness of Jg = 5000 kN / m has been considered.

Figure 6 shows the results obtained: the overconsolidation ratio under the axis of the surface hit for different land improvement methods considered. The reason for initial overconsolidation of the land was l in all depth. For prefabricated drains and gravel colwnnas have been considered

usual settings and parameters.

The results reflect that the proposed method is the only one that manages to increase

notably the CSR of the land, especially from 3 m deep. The

5 dynamic compaction by itself or with vertical drains increases fonna

negligible CSR except on the surface. Dynamic compaction with

gravel columns achieves better results but lower than those achieved with the

Proposed method. In the case of gravel columns, it should be mentioned that

It produces an important improvement when introducing gravel, which does not happen with the proposed method 10. The improvement when entering the gravel is not quantified in the graph shown

but it also causes a very significant cost increase.

Claims (14)

l. Hollow element (10, 20, 30, 40, 50) configured to enter soft ground (38, 48, 58), and open at least by its lower end, such that when said 5 hollow element (10, 20, 30, 40, 50) is introduced into the soft ground (38, 48, 58) its Intentor is filled with said existing soft ground (38, 48, 58), and characterized in that it comprises a geored (11) of cylindrical shape configured to penetrate the circulation of water through it; a geosynthetic (12) that covers the outer surface of the geored (11) And that performs a filter function, letting the water pass but not the 10 soft ground particles (38, 48, 58) existing; and at least one geosynthetic (13) which covers the interior surface of the geored (11) and that performs a double function: one side lets the water pass but not the soft ground particles (38, 48, 58) filter function - and on the other hand it gives the hollow element (10, 20, 30, 40, 50) a  radial stiffness -function resistance-o 2. The hollow element of claim 1, wherein the geosynthetic (12) covering the outer surface of the geored (11) is a geotexti \. 3. The hollow element of any of the preceding claims, wherein the The inner surface of the geored (11) is covered by a single geosynthetic (13) that performs the double function of filter and resistance. 4. The hollow element of any one of claims 1 to 2, wherein the inner surface of the geored (11) is covered by two geosynthetics (13) such that both form 25 a geocomposite, and such that one of the geosynthetics performs the filter function, and the remaining geosynthetic performs the resistance function. 5. The hollow element of claim 4, wherein the geosynthetic that performs the Filter function is a geotextile. and the geosynthetic that performs the resistance function 30 is a geogrid. 6. The hollow element of any of the preceding claims, wherein the al minus a geosynthetic (13) that covers the inner surface of the geored (11) and that It performs the function of resistance preventing the hollow element (10, 20, 30, 40, 50) from being radially defonated, presenting a stiffness in the circumferential direction of the 5 minus 1000 kN / m. 7. The hollow element of any of the preceding claims, which has a thickness whose order is between approximately 5 millimeters and 10 centimeters, a radius whose order is between approximately 10 10 centimeters and 5 meters, and a length whose range is between approximately 2 and 10 meters. 8. Soft ground improvement method (38, 48, 58), using the hollow element (10, 20, 3D, 40, 50) according to any of the preceding claims, 15 characterized in that it comprises the steps of:

-

introduce into the soft ground (38, 48, 58) at least one hollow element (1O, 20, 30, 40, 50) from the surface, such that the longitudinal axis of each hollow element (10,

20, 30, 40, 50) remains in a substantially vertical position, and such that when entering 20 the element in the soft ground (38, 48, 58) And being hollow by at least the lower end, its interior is filled with existing soft ground (38, 48, 58), thus laterally confining the existing soft ground column. - make a point overload, such that said overload is only located on the soft ground (38, 48, 58) located inside the hollow element (1O, 20, 25 30, 40, 50), thus improving the characteristics of said existing soft terrain column (38, 48, 58). 9. Method of claim 8, wherein the introduction of the hollow elements (10, 20, 30, 40, 50) in the soft ground (38, 48, 58) is carried out by driving or moving, 30 and by means of hollow cylinders (24, 34) of double wall, comprising the stages of:

-

As a preliminary step to introduce the hollow element (10, 20, 30, 40, 50) into the soft ground (38, 48, 58), place the hollow element (10, 20, 30, 40, 50) between the walls of a hollow cylinder (24, 34) of double wall; - then, at the bottom of the hollow cylinder (24, 34), and attached to the hollow element (10, 20, 30, 40, 50), place a sheet (25, 35) configured to anchor the hollow element (10 , 20, 30,40, 50) at the desired depth; - insert the hollow elements (10, 20, 30, 40, 50) into the soft ground (38, 48, 58), by means of the double-walled hollow cylinders (24, 34), and once the cylinder assembly (24, 34) And hollow element (10, 20, 30, 40, 50) is driven into the soft ground (38, 48, 58), remove the cylinder (24, 34), ta! that the hollow element (10, 20, 30, 40, 50) remains placed in the soft ground (38, 48, 58), and anchored at the bottom by the sheet (25, 35).

10. The method of claim 9, wherein said sheet (25, 35) is metallic and with ring shape 11. The method of any one of claims 8 to 10, wherein to carry out this localized point overload, a heavy element (59) is dropped from a fixed height at least on each column (50) of soft ground (38, 48, 58 ) existing surrounded or encapsulated by each hollow element (10, 20, 30, 40, 50), ta! that a certain energy is applied to! soft ground (38, 48, 58) that consolidates and overloads it. 12. The method of claim 11, wherein said heavy element (59) is a hub and where a crane (60) is used to lift said club and drop it. 13. Method of any of claims 8 to 10, wherein they are introduced into the soft ground (38, 48, 58) a plurality of hollow elements (10, 20, 30, 40, 50) And where to perform this localized punctual overload, modular elements (4ó) are used with an arrangement ta! that rest solely on the surface of the  existing soft terrain columns (38, 48, 58) surrounded or encapsulated by hollow elements (10, 20, 30, 40, 50), and ta! that form a surface on which place a weight (47) that constitutes the overload. 14, Method of claim 13, wherein said modular elements (46) are made of plastic and wherein said weight (47) is a floor as filler material. 5 15. The method of claims 13 to 14, further comprising the steps of:

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wait long enough to consolidate the soft ground (38, 48, 58); -Delete the overload.