Methods for the production of a liquid soil structure and liquid soil structure

Abstract

The present invention relates to a method for producing a liquid soil structure and to said liquid soil structure itself. The liquid soil structure comprises a base slab and at least two lateral retaining walls. Due to the impermeability of the base slab and retaining walls, the water level below the base slab does not vary, or only varies minimally, in response to fluctuating groundwater levels. This prevents settlement and damage to the liquid soil structure. The method and the liquid soil structure are particularly suitable for supporting the road structure of roads built over soils with highly variable and problematic subsurface conditions.

Description

[0001] The present invention relates to a method for constructing a flowable soil structure, preferably a substructure for roads, from a temporarily flowable backfill material - preferably RSS® flowable soil and the corresponding flowable soil structure.

[0002] In road construction, contractors are frequently confronted with highly variable subsurface conditions. Different soil types can alternate over relatively short distances. These soil types are characterized by varying permeabilities, bearing capacities, moduli of elasticity, and other properties. Therefore, expensive deep foundations are often necessary, which also have several technical disadvantages. However, a consistently reliable and load-bearing foundation is essential for the road alignment, one that is not compromised by settlement, slumping, or the formation of so-called sills in rigid deep foundations such as concrete piles.

[0003] The problems are particularly pronounced in soils with low bearing capacity or those that exhibit significant volume changes due to fluctuating water content. Certain soils, such as peat, are also prone to mineralization, meaning that chemical reactions during water removal irreversibly alter their properties, especially their volume. Such soils are therefore considered problematic and can often only be addressed through soil replacement or deep foundations.

[0004] To address the resulting problems for road construction, various engineering solutions have been developed. In extreme cases, the problematic soils are replaced far below ground level with load-bearing soils, or expensive and even more complex deep foundations are constructed, for example, with piles or columns. This is extremely labor-intensive and regularly causes problems, for example, due to insufficient compaction of the replacement material and resulting settlement, or the rigid reactions of some types of deep foundations, such as concrete piles or vibro-compaction columns, which are further reinforced in their rigidity by grout, or insufficiently uniform consolidation of non-rigid deep foundations, such as geotextile-encased sand columns.

[0005] DE 10 2007 056 408 A1 describes a method involving a large-area soil replacement and the creation of trenches for utility lines beneath the road. The entire subgrade of the soil replacement, including the trenches, is filled with a flowable, self-compacting, and hardening construction material. This flowable material is intended to be a soil mortar according to DE 103 32 249 A1. However, it is known that soil mortars, due to their cement content and its typical reaction processes, are prone to failure in humic soils and often also acidic groundwater. Furthermore, they do not allow for elastic reactions in the form of reversible deformations in response to traffic-related dynamic loads, exhibiting a completely different load-deformation behavior. It is precisely such soils and acidic groundwater that make foundation work in road construction problematic and costly.The other load-deformation behavior is that it results in fractures under load and, due to material aging, leads to a relatively early reaching of the limit of tolerance in such rigid materials when the dynamic load inputs cause deformations of the soil body or base slab formed from such materials in the plastic range. Correspondingly over-dimensioned soil bodies as a solution for excessive deformations in the plastic range are, in turn, associated with increased effort, energy consumption, and consequently, additional CO2 emissions and costs.

[0006] Other methods involve stabilizing problematic soils using pile foundations and transferring the actual load-bearing capacity from the soil to the foundation piles, i.e., a typical deep foundation. In addition to rigid piles, US 4,024,719 B1 proposes using piles with buckling properties that bend near the surface towards the road edge, thus providing additional stability. This method is intended to be particularly suitable for road widening. However, this method cannot compensate for the disadvantages of a material lacking elasticity along the length of the pile and is associated with the typical drawbacks of deep foundations, ranging from costs to the effects of the piles on the load-distributing surface layers.

[0007] Other known approaches involve laying concrete slabs on the problematic soils. However, this method suffers from the same disadvantages under traffic-related dynamic loads as those already mentioned for the hydraulically bound soil backfill materials. It can also hardly prevent damage due to differential settlement of the subsoil resulting from mineralization processes and the associated formation of voids beneath the slabs, or excessive edge stress on the slabs. Furthermore, the rigidity of the concrete slabs leads to high stress peaks under traffic-related loads, which in turn cause faster fatigue of the rigid slabs and thus earlier damage due to the prematurely reached limits of the materials, i.e., the concrete and the reinforcement.

[0008] EP 0 968 330 B1 proposes the use of elevated road slabs, each comprising at least one precast slab spanning freely over the ground. Individual support elements are provided at the ends of the precast slab, extending longitudinally or transversely to the roadway. These support elements bear the precast slab and provide downward and lateral bracing. Basins are provided for the support elements, resting on a subgrade or foundation, within which the support elements are received and supported. Such a procedure is disproportionately complex and only practical for a few locations. Furthermore, it is associated with the disadvantages already described for rigid foundation types on subgrades with varying load-bearing capacities.

[0009] The task is therefore to propose a method for producing a liquid soil structure, preferably for a road with the associated road base or road superstructure above this liquid soil structure, that is suitable for all soils, preferably problematic soils (low and varying load-bearing capacity, soft to muddy, highly draining or mineralizing soils, as well as soils under the influence of groundwater and highly fluctuating groundwater levels).

[0010] According to the invention, the problem is solved by a method according to claim 1 or by a fluid soil structure, preferably as a load-bearing structure under the road structure, accommodating the road substructure and the road surface, according to claim 5. Advantageous embodiments are disclosed in the dependent claims.

[0011] The method according to the invention provides at least the following steps: a) Determination of specifications regarding the load-bearing capacity and dimensions of the liquid soil structure to be constructed, b) Preparation of geotechnical reports and determination of the lowest expected groundwater level and the type, soil stratification including layer thickness and composition of the subsoil, c) Development of the planning specifications as a result of the calculations and verifications for the flowable fill structure, generally based on numerical calculation methods, e.g., FEM, which dimension the structure with the relevant parameters of the temporarily flowable backfill material, preferably RSS® flowable fill, as its target properties and are able to specify the geometry of the elements, thickness of a base slab, slot depth and slot width for retaining walls, as well as the material parameters of the temporarily flowable backfill material, preferably RSS® flowable fill, at least the water permeability value (kf value) and the soil mechanical parameters such as cohesion, friction, bearing capacity, flexural strength, uniaxial compressive strength, modulus of elasticity, load-deformation behavior, wherein the slot depth is sufficiently deep, e.g., at least 10% of the total height of the retaining walls, below the expected lowest groundwater level. d) Construction of the lateral retaining walls, wherein the slots are excavated and filled with temporarily flowable backfill material, preferably RSS® Flowable Soil, e) Construction of the base slab across the retaining walls by installing temporarily flowable backfill material, preferably RSS® Flowable Soil, and embedding the base slab in or placing it on the retaining walls.

[0012] The method is suitable for all soils (substrates) requiring effective load distribution and minimized settlement, including problematic soils and situations with high groundwater levels or flood-prone areas.

[0013] The liquid soil structure according to the invention for receiving the road structure comprises at least one base plate and two retaining walls running in the direction of the road and parallel to each other, and at least one base plate that rests laterally on or is integrated into the two retaining walls, wherein - the base plate and the retaining walls are largely watertight and airtight, and are also largely watertight and airtight when connected to each other, - the base slab and retaining walls were constructed from temporarily flowable backfill material, preferably RSS® flowable fill, - enclose the problematic soil with the base slab and the retaining walls or support it in a load-distributing manner, - the retaining walls are located sufficiently, for example, at least 10% of their height below the lowest expected groundwater level.

[0014] According to the invention, the flowable fill structure is designed in an inverted U-shape in cross-section to minimize settlement and, in the case of strongly fluctuating groundwater levels, to prevent the consequences of such fluctuations, such as drying and settling soils, and thus to prevent mineralization processes. The U-shape, more precisely the shape of an inverted U, is created by the base slab and the two lateral retaining walls extending into the ground. For the purposes of the invention, flowable fill (often also referred to as temporarily flowable backfill material – preferably RSS® flowable fill) is understood to be a temporarily flowable, controlled re-solidifying, and self-compacting backfill material. RSS® flowable fill is particularly preferred.Furthermore, the preferred backfill material is a backfill material conforming to the FGSV 563 guideline ZFSV "Guidelines for the production and use of temporarily flowable, self-compacting backfill materials in earthworks," dated 2012, with soil-typical properties and according to the VSS REGnorm Guide Flowable Fill. The flowable fill is therefore highly variable in its soil-mechanical, technologically relevant, and specific performance characteristics and can be permanently adjusted to the target properties required for the respective task from a structural engineering perspective. These properties are selected and validated according to the results of mathematical modeling. This modeling is generally based on numerical calculation methods, such as FEM, and is tailored to the specific application situation and task.RSS® flowable fill is particularly preferred due to the precise adjustability of its desired parameters, largely independent of the properties of the materials used in its production, such as the locally existing soils. This temporarily flowable backfill material, preferably a suitably formulated RSS® flowable fill, can have its properties—such as re-solidification behavior, cohesion, internal friction, elasticity, load-deformation behavior, volume stability, load-bearing capacity, vibration absorption, deformability under load (elasticity to spring action), relaxation capacity, etc.—adapted to the specific installation situation.This allows for adaptation to the specific requirements of the local situation, such as transition zones with varying bearing capacities of the subsoil, the respective hydrogeological conditions, the type of subsoil, and the expected loads of subsequent use in terms of type and magnitude. The backfill material, or flowable fill, is preferably produced from locally excavated soil, flowable fill compound, and water, as well as optional aggregates (e.g., sand as an addition to control the specific density of a lighter material such as peat). The flowable fill compound consists primarily of derivatives of naturally occurring clay minerals (e.g., types of bentonite specifically modified and adapted to the construction requirements, suitable in their genealogy and rheological properties) with non-declarable additives and a suitable reaction behavior.Preferably, a material is used that meets the reaction-specific requirements of the RSS® liquid soil process as a dry mixing process with regard to the temporal and mass-related reaction of the additives with water and / or optionally the required capabilities for the permanently safe binding of contaminated soil constituents.

[0015] The properties are advantageously adjusted by selecting the mixing ratios of excavated soil, liquid soil compound, water, and aggregates, as well as the type of aggregates, the technology required for production and tailored to the RSS® liquid soil process, and the associated reaction kinetic processes, according to a previously developed recipe or, in the case of varying soil types, a recipe matrix. In particular, the reconsolidation behavior can be influenced by the type, quantity, and reaction kinetic conditioning (e.g., mixing duration and intensity, type and form of energy input, temperature, and technology tailored to the process steps and suitable in form and type) of the aggregates (e.g.,...).The type, properties and quantity of the layer minerals and their reaction kinetic behavior under the conditions of energy input into the liquid soil and its components during the manufacturing process can be well controlled by using suitable technology, equipped with the corresponding possibilities for regulating the execution and processes of the procedure and comprehensive documentation of the entire process.

[0016] In the present case, a higher clay content is preferably used if required, also to achieve the required watertightness. Methods for producing suitable flowable fills are described, for example, in DE 10 2004 023 482 A1 or DE 10 2005 056 568 A1. Under certain circumstances, hydraulically setting, temporarily flowable construction materials may also be suitable for the inventive method or the inventive road substructure.

[0017] In its simplest form, the road substructure consists of two lateral retaining walls or slots running in the direction of the road, and a base slab extending flat at their upper ends to serve as the road foundation. The road itself can then be constructed on top of this base slab in the usual manner.

[0018] According to the invention, the lateral retaining walls, with their lower edges, extend securely below the lowest groundwater level. The lateral retaining walls are designed to be watertight. The base slab connects directly and also watertight to the retaining walls. The base slab itself is also watertight. In the context of the present invention, watertight or impermeable means that the water permeability is so low that even during the maximum expected duration of a minimum groundwater level around the structure, the drop in the groundwater level between the retaining walls is only a few percent, preferably less than 15%, particularly preferably less than 10%, and most preferably less than 3%. The retaining walls are to be founded securely, preferably by at least 10% of their total height, below the lowest expected groundwater level.

[0019] Together with the foundation slab, the flowable fill structure largely encloses the soil located between the retaining walls in a pressure-tight (airtight) manner. If the problematic soil is predominant only in certain areas of the building site and is bordered by cohesive soil, the cohesive soil, the retaining walls, and the foundation slab form a watertight and largely airtight seal of the problematic soil to the top and sides. The seal to the bottom is achieved by the groundwater. The same functionality also occurs in pure peat or peat embedded in groundwater, at groundwater levels close to or at groundwater level, and in a flooded state, i.e., when the flowable fill structure, designed as an inverted U, is integrated into this subsoil. This functionality continues even with a falling groundwater level, as long as the lateral slots securely and thus tightly connect to the groundwater (principle of communicating vessels).

[0020] In one embodiment, the retaining walls are arranged completely or at least partially around the lateral boundary of the base slab. This embodiment can be advantageously used for the construction of storage areas, parking lots, or halls.

[0021] The precise calculation of the required thickness of the retaining walls, or the trenches in which the retaining walls are constructed, must be determined in conjunction with the calculation and verification of the functionality and dimensioning of the flowable fill structure and the derivation of the target properties of the flowable fill relevant to its mix design or mix matrix. The respective mix design, among other statically and dynamically relevant properties, results in a specific permeability value. Based on this value, the thickness of the retaining walls can be designed so that, during periods of near-complete drying within the timeframe of the maximum expected dry periods in the respective region, the water permeation on the outside of the retaining walls does not exceed the permissible limit. This prevents, for example, the peat between the retaining walls from losing water, thus preventing settlement under the road.

[0022] The formulations of the mixtures used for flowable fill cannot be specified universally, as there are a number of variable factors that must be considered individually, such as the soil type, which can always originate from a different source soil whose properties must be taken into account in the formulation, or whether different load conditions need to be ensured, different hydrogeological conditions prevail, etc. Therefore, the local, site-specific conditions, the hydrogeology, and the requirements of the structure must always be considered in the calculations and procedural specifications. For example, if watertightness (or near-complete airtightness) is desired, the expert is familiar with this approach, namely modifying the water permeability using standard construction techniques, e.g.,...This involves modifying the particle size distribution to minimize pore spaces or adding swelling materials, such as bentonite. Target values ​​include, for example, a kf value of approximately 10. -9While flow rates in meters per second (m / s) can be specified, they can also be modified if, for example, the layer thicknesses of the flowable fill components (retaining walls and foundation slab) are changed and the maximum expected dry periods for a region are known and considered as a planning step during dimensioning and calculation. As a general rule, the pore spaces in the excavated soil are determined (this is regularly done as part of geotechnical reports, allowing, for example, the determination of the water volumes required to establish temporary flowability). Depending on the requirements of the structure and its interaction with the surrounding soil under typical loads, the necessary structural dimensions and the target properties of the flowable fill are derived. In this application, these properties also include minimizing the pore spaces and thus changing the water permeability.These pores must be at least completely filled with water and form thin slip layers of water so that the excavated soil can be temporarily made flowable. Thus, the minimum amount of water is determined or can be precisely calculated. Based on this, the quantity of suitable clay minerals required to bind the water that fills these pore spaces and also forms the temporary slip layers is determined. This binding of water and the associated formation of cohesion then lead to the re-solidification of the soil.To control the timing of the process, varying amounts of cement and layer minerals can be used, or the grain sizes of the cement and layer minerals in the mixture can be changed, so that a smaller or larger surface area is available on the cement particles as well as on the layer minerals for water absorption, and increasing the reactive surface area available for the respective additives increases the reaction rate of the affected component or components, while reducing this surface area reduces the reaction rate of the affected component or components.Since a portion of the water that previously formed the slip layers is gradually chemically bound by the cement as a consequence of hydration, depending on the hydration process, this reaction terminates the flowability of the temporarily flowable backfill material, preferably the liquid soil produced using the dry-mix method, also known as the RSS® liquid soil method. In the present task, both watertightness (experience has shown that a kf value in the range of 10 is sufficient) and water resistance (kf value in the range of 10 are required) are to be ensured. -9The goal is to achieve both a flow rate (m / s) and a high degree of airtightness. It is known that clays, in particular special layer minerals selected for their reactivity to suit the soil type and the desired reconsolidation time, are suitable for this purpose. Therefore, in the procedure described above, to achieve the objective, the proportion of the clay component is increased beyond the level necessary for water binding to establish temporary flowability and as the basis for subsequent reconsolidation through permanently stable water deposition on the layer minerals until the specified permeability coefficient is reached for an assumed material thickness of the flowable fill.

[0023] Optionally, the integration of pipelines, drainage lines, and / or power or data lines into the flowable fill structure can be included in the planning process according to step c) and the construction phase according to step d). This integration can be achieved along the entire length of the lines / cables / pipes and other installations within the flowable fill. Alternatively, penetrations through the areas filled with flowable fill are also possible, with the flowable fill acting as a cuff-like seal due to its inherent properties, ensuring that the lines penetrate the flowable fill structure in a watertight manner.

[0024] Depending on local requirements, identical formulations for the production of the flowable fill can be used for the foundation slab and the retaining walls, or different formulations adapted to the desired properties of the flowable fill can be used. For example, it may be necessary to achieve a different, possibly higher or lower, modulus of elasticity for the foundation slab than for the retaining walls. This can be achieved by modifying the flowable fill mixture through different ratios and quantities of the aggregates and by altering the reaction times of the aggregates with water. Other additives according to the state of the art are also possible. For instance, water permeability can be reduced by polymer additives, and strength can be increased by adding reinforcing fibers or reinforcements of any kind. Such measures are known from the prior art.During construction, care must be taken to ensure a direct connection between the base plate and the retaining walls in order to achieve the required high degree of water and air tightness.

[0025] In addition to water permeability, other structurally relevant parameters must be considered in the design of the retaining walls and the foundation slab, such as shear parameters, load-deformation behavior, elasticity, flexural-tensile behavior, bearing capacity, etc. During the development of the design specifications, for example, in the form of a mix design specification, and the subsequent calculations and verification, the structure is dimensioned and the relevant parameters of the flowable fill are derived. This includes the geometry of the elements, such as foundation slab thickness, trench depth, trench width, and kf value (water permeability), as well as the flowable fill parameters relevant to the structural engineering task, such as cohesion, friction, bearing capacity, uniaxial compressive strength, modulus of elasticity, compression-pressure (load-deformation behavior), etc.The calculation of these target values ​​is based on a mathematical model that must be precisely calibrated (preferably using numerical calculation methods, e.g., the finite element method). This model incorporates suitable material models for the liquid soil used, representing the soil mechanics principles, such as settlements depending on the subsoil and loads, as well as the geometry of the structure and the properties of the liquid soil. This allows for the dimensioning of the structure and the derivation of the liquid soil properties required to fulfill the construction task. The aim of this approach is to create a pressure-tight, downward-opening, and top-loading body made of liquid soil, whose lateral boundaries, in the form of retaining walls arranged in slots, securely anchor it to the groundwater.

[0026] The depth of the retaining walls determines the magnitude of the counter-pressure exerted on the outside of the structure, in the form of the hydrostatic pressure of the groundwater and the geostatic pressure of the soil. As long as the groundwater level on the outside of the retaining walls does not fall below the depth of the trenches in which the retaining walls are located, the soil beneath the liquid soil slab, and thus the load-bearing problematic soil (e.g., peat), does not dry out and therefore cannot lose volume and load-bearing capacity. The load-bearing capacity of the liquid soil slab, and consequently of the road, increases with the depth of the trenches for the retaining walls. Watertightness is therefore only a means to an end and can certainly have different target values ​​depending on the local conditions and the varying properties and dimensions of the liquid soil elements of the structure.

[0027] Optionally, partition walls extend between the retaining walls and are connected to them and the base slab in a watertight and largely airtight manner. These partition walls preferably reach the same depth as the retaining walls. If simulations show that the partition walls do not need to extend to the same depth as the retaining walls to prevent them from drying out at the lowest groundwater level, they can also be founded at a shallower depth than the retaining walls.

[0028] Partition walls are particularly necessary when problematic soil extends over large sections of the planned road construction or large areas to be developed. Together with the retaining walls and the foundation slab, the partition walls then form individual sections that enclose the problematic soil in a watertight and airtight manner. A series of such sections then forms the overall structure. Partition walls are also necessary when inclines or gradients need to be addressed. The sections formed by the partition walls must then be individually dimensioned so that the retaining walls cannot dry out, even at the lowest groundwater level. The distances between two partition walls in the longitudinal direction are chosen, depending on the road or terrain gradient, to ensure that the permissible difference in the bottom edges of the partition walls, which is relevant for settlement, is not exceeded.

[0029] In one embodiment, the partition walls can be used to create cell-like or honeycomb-like structures, each of which individually exerts the water-retaining effect described above and better stabilizes the flowable fill structure. This embodiment is suitable, for example, for parking lots, storage areas, or as a foundation for the construction of buildings. The same applies to the design and construction of the additional retaining walls as described for the lateral retaining walls.

[0030] In another embodiment, the width of the base slab exceeds the outer width of the retaining walls, resulting in a lateral overhang of the base slab. The width of the permissible lateral overhang can also be determined in advance using calculations (finite element method) depending on the stability of the flowable fill structure. The overhang may depend, for example, on the flow of utilities, the slope areas to be covered, and / or water-bearing ditches.

[0031] To maintain the watertightness and near-airtightness of the foundation slab, care must be taken to ensure that any road drainage systems, pipe penetrations, etc., do not allow any media pathways (water, air) into the interior of the flowable fill structure. It is therefore advisable to integrate the necessary pipes, etc., into the foundation slab or retaining walls in the manner described in DE 103 32 249 A1, such that they run within the flowable fill. For penetrations, a highly adhesive flowable fill is used that does not form annular gaps and whose properties are verified, for example, by push-through tests. Due to the relatively easy mechanical extrusion of the flowable fill, the pipes remain accessible for maintenance and repair work even when running entirely within it.When backfilling after completion of the aforementioned work, it is essential to ensure that flowable fill material with the same properties required for the construction work is used again. If there is a risk of penetrating into the interior of the flowable fill structure during the work, it should be carried out when the groundwater level is as high as possible. This prevents the air supply from causing the groundwater level inside the flowable fill structure to drop. Otherwise, at the moment the flowable fill structure is opened, the groundwater level outside the structure would adjust according to the principle of communicating vessels (with deviations caused by capillary action).

[0032] The road structure is then built on the base plate in a manner known per se. This is preferably done using the known layered structure, which in turn then receives the road surface.

[0033] In summary, the principle of the sealed siphon (attached pipette) plays a central role in the structure according to the invention. As long as the water in the sections of the existing soil bounded by the retaining walls, the base slab and soil, or by partition walls cannot be replaced by air (or another medium), the water is retained in these sections of the locally occurring soil. Even if the groundwater level outside the structure decreases, the water cannot escape. Should the retaining walls dry out, the structure's downward seal would be compromised, allowing air to enter and water to escape. The problematic soil would dry out, and the known problems of drying, including mineralization and shrinkage, could occur. Preventing this negative consequence is the central idea of ​​the present invention in the case of such subsoils and / or groundwater levels.

[0034] The invention is not limited to the embodiments shown and described, but also includes all embodiments that have the same effect in terms of the invention, such as implementation in non-mineralizing soils and areas with high groundwater levels or flood-prone regions. Furthermore, the invention is not limited to the specifically described combinations of features, but can also be defined by any other combination of certain features from all disclosed individual features, provided that the individual features are not mutually exclusive. Figures Fig. Figure 1 schematically shows the liquid soil structure according to the invention as a road base in cross-section (perpendicular to the road direction 5) Fig. Figure 2 schematically shows a section (along the direction of the road 5) through the liquid soil structure according to the invention in the embodiment with partition walls 2. Fig. Figure 3 schematically shows the water level conditions in the liquid soil structure at the lowest groundwater level 44. The water level 45 in the liquid soil structure largely corresponds to the normal groundwater level 44, even when the lowest groundwater level 44 is reached outside the liquid soil structure. This is because the liquid soil structure is largely airtight and watertight. In this way, no air can penetrate the cavity formed by the retaining walls 10, the base slab 11, and the surrounding soil or an intermediate wall (soil not at risk of mineralization and intermediate walls not shown), so that the water cannot escape from this cavity and the problematic soil could dry out. Reference symbol list 10 Retaining wall 11 Base plate 12 Partition wall 2. Existing cohesive soil 21 problematic soil (peat) 31 gravel layer 32 Asphalt layer of the road 41 Ground level 42 Fleet (street drainage) 43 normal groundwater level 44 lowest groundwater level 45 Water level in the flowable fill structure 5. Road direction Example of implementation

[0035] The initial situation consisted of a 3.8 m wide through road with a surface paved with concrete slabs, which were cracked and tilted over large sections. The verges were 1.5 m to 2.2 m wide and, in the section under construction, were overgrown with trees. The verges dropped almost vertically into roadside ditches on both sides, which had depths between 1.2 m and 2.2 m.

[0036] The soil investigations revealed a distinctly heterogeneous subsoil. Several glacial channels were filled with peat 21 down to the level of the roadbed, with peat thicknesses reaching several meters. In other areas, the sands extended down to the level of the roadbed.

[0037] The groundwater level 43 was measured at depths of 1.1 m to 1.3 m below ground level 41. Given the fluctuations in the groundwater level, it was assumed that it could drop so low that the peat 21, or a significant portion thereof, would dry out. The drying out of the peat 21 is regularly associated with settlement, which may only be partially reversible if the groundwater level 43 rises. The planning had to take into account the possibility of cavities forming beneath the floating foundation slab 11, and these had to be avoided in the new construction. A solution for this had to be found in the design.

[0038] In particular, the older buildings were founded on flat mounds of earth, often built over peat 21, without further deep foundations.

[0039] The road was to be widened from 3.8 m to 5.0 m. As a through road, it was also intended to be able to handle heavy traffic loads (SLW 60). Residents demanded that as many of the existing trees as possible be preserved.

[0040] With conventional construction methods, replacing the peat 21 would have been necessary to achieve the required stability, or alternatively, constructing an equally expensive deep foundation. Soil replacement would have necessitated a localized replacement width extending into the trench slope to achieve the required load-bearing angle. Calculations showed that a large proportion of the existing trees would have had to be felled. Furthermore, groundwater lowering would have been required, with unforeseeable consequences for the planned construction. The vibrations caused by the dynamic compaction could have led to additional building damage, a concern shared by local residents.

[0041] As an alternative to conventional construction, a floating base slab 11 made of flowable fill, which meets the requirements of the RSS® flowable fill method and the VSS REGnorm Guide flowable fill, was proposed and tested. This proposal was based on existing experience in road construction using the RSS® flowable fill method, which was also presented by the method developer at a BAST conference.

[0042] The solution determined during the specialist planning for flowable fill is based on a summary and evaluation of the soil conditions, the soil parameters relevant to the construction project, and the project's requirements for the use of the structure. Furthermore, local conditions such as hydrogeology, the foundations of adjacent buildings, berm widths, trench depths, and other framework conditions were recorded and assessed. The necessary structural analyses (settlement, deflection, and impact resistance) and the verification of environmental compatibility and system optimization (e.g., by utilizing the equivalent angle of friction according to DIN 1054:2005) were carried out. Finally, the specifications for the final and serviceability of the road were evaluated and expressed as achievable target properties to demonstrate serviceability, such as permissible settlements, permissible differential settlements, and desired bearing capacities.questioned and specified as target values ​​for the functionality of the structure (road substructure).

[0043] As a result, the systems analysis not only provided a concrete solution for the construction. During the specialist planning for the flowable fill, the dimensioning of the elements of the flowable fill structure, the target values ​​for the flowable fill and thus the specifications for the objectives of the flowable fill mix were determined for the developed solution based on the planning calculations and verifications, specific specifications for the installation technology were developed and specifications for the installation logistics including the necessary technology were worked out.

[0044] The flowable fill mix is ​​identical for the retaining walls 10 and the base slab 11 in this case. The flowable fill used consisted of approximately 3% of its total mass in the form of suitable bentonites, corresponding to the requirements of the parent soil with its humic soil components; approximately 2-3% of its total mass in the form of suitable cement in the form of CEM IR; locally sourced soil; and a quantity of water that depended on the water-cement ratio specified in the mix design – here, 15. With the exception of the water, the components were pre-treated dry using the technology of an RSS® compact plant and then mixed and fed into a truck mixer. After water was added to the truck mixer, this dry mix was then blended with the water for approximately 8-12 minutes to create the previously planned flowable fill matrix.The liquid soil was thus flowable and was poured into the lateral slots and into the area of ​​the base plate 11. In this example, the liquid soil with the specified properties re-solidified after approximately 4-8 hours.

[0045] The basic principle of the solution using flowable fill was that a 0.6 m wide retaining wall 10 filled with flowable fill was to be constructed on both sides of the road, in this case extending to 0.5 m below the existing base of the adjacent, water-bearing ditches, depending on the subsequent load situation. A base slab 11 made of watertight flowable fill was then to be built on top of this wall. The flowable fill was to be installed up to the lower edge of the gravel base course 31. The flowable fill thus took on the shape of an inverted "U" (see Fig. 1).

[0046] The inverted "U" shape clamps the soft soil layers 2. Lateral displacement caused by loads is effectively prevented by integrating the lateral retaining walls into the subsoil. The required hydrostatic and geostatic pressure was generated by the depth and thickness of the lateral slots for the retaining walls and the properties of the flowable fill used to backfill them. This pressure reliably stabilizes the RSS® flowable fill slab 11 against settlement, even under traffic loads, and also reliably prevents the peat 21 from drying out.

[0047] To minimize the required construction width, the effect of increasing the cohesion of the flowable fill on the load distribution angle was first investigated. It was assumed that increasing the cohesion would result in a significantly steeper equivalent friction angle, as described in DIN 1054: 2005. The relationship between the friction angle, cohesion, and equivalent friction angle can be represented in a σ / τ diagram.

[0048] The normal stress (σ) and the shear stress (τ) can be determined from the triaxial test according to DIN 18137-2. The shear stress (τ) provides the measure of cohesion. Since the cohesion in the liquid soil can be precisely controlled by the quantity and type of additives according to the formulation and the type and intensity of reaction kinetic processes (energy inputs into the liquid soil matrix), the friction angle (φ) assumed for sand, approximately 32°, could be adjusted to an equivalent friction angle (φE) greater than 60° via the formulation.

[0049] The result of this optimization was that, for the planned road width of 5.0 m, only a total construction width of 5.6 m was required. This reduction in construction width meant that of the originally planned 25 trees, only 4 had to be felled because they were too close to the new roadway.

[0050] Another advantage of the high cohesion inherent in the RSS® flowable fill used was the increased support it provided to the trench walls. The calculation of the slip circles showed that, particularly in deeper trenches, slope failures could occur under conditions of high dynamic loads from road traffic and very low water levels. The high cohesion of the flowable fill provided the necessary protection against such slope failures.

[0051] The inverted "U" shape prevented the peat 2 beneath the liquid soil slab from drying out, even at very low groundwater levels 44. By embedding the retaining walls 10 to well below the lowest possible groundwater level 44, the water present in the peat 2 was "encapsulated." Even if the water level drops, the soil 2 beneath the roadway (32) does not dry out until the water level falls below the embedment depth of the trenches.

[0052] To minimize the required excavation depth, consideration was given to extending the flowable fill to the lower edge of the gravel base course 31. However, this placed the flowable fill within the frost zone.

[0053] When assessing the feasibility of installing flowable fill up to the frost line, a fundamental principle was followed: frost heave, which can lead to road damage, is only possible if free water is available to rise into the pore spaces filled with it. To prevent the presence of free water, the flowable fill was formulated to be "watertight." "Watertight" flowable fill was defined as having a permeability coefficient of < 10⁻⁹ m / s. Since the water contained in the system is almost entirely "crystalline," meaning permanently and stably bound within the flowable fill matrix, free water is either not present in the flowable fill or is only present in very small quantities, adhesively attached to the surface of the smallest pore spaces.Freezing is not possible in this respect, since the expansion of the remaining free residual water can take place in the existing small pore spaces without filling these pore spaces and thus without causing an increase in the volume of the total matrix of the liquid soil.

[0054] Freeze-thaw cycles, conducted according to the Technical Testing Regulations for Mineral Materials in Road Construction (TP Min-StB) and the Additional Technical Contractual Conditions and Guidelines for the Structural Maintenance of Traffic Areas (ZTV BEB-StB), showed volume changes on 28-day-old test specimens only within the permissible tolerances. All test specimens were found to be non-destructive.

[0055] A layer of gravel 31 with a grain size of 0-32 and a thickness of 46 cm was applied to the base plate 11, on which an asphalt layer 32 of 16 cm was laid as road surfacing. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2007 056 408 A1

[0005] DE 103 32 249 A1 [0005, 0031] US 4,024,719 B1

[0006] EP 0 968 330 B1

[0008] DE 10 2004 023 482 A1

[0016] DE 10 2005 056 568 A1

[0016]

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