System and method for injecting expanding resins into soils to be consolidated

Abstract

A system for injecting expanding resins into soils to be consolidated, includes a pump apparatus which is operationally associated, at a delivery port, with a tubular element which can be inserted into a respective hole defined in the soil to be consolidated and is adapted to send to the tubular element a mixture at a preset supply pressure. The tubular element has a number of holes, at least two of the holes including respective calibrated holes.

Claims

1. A method for injecting expanding resins into soils to be consolidated, the method including the following steps: drilling a soil to be consolidated in order to provide at least one hole, estimating a rupture pressure of the soil at regions affected by said hole, providing a system for injecting expanding resins into said soils to be consolidated, said system comprises: a pump apparatus operationally associated, at a delivery port, with a tubular element having, at a lateral surface thereof, a plurality of holes mutually spaced apart along a direction of longitudinal extension of said tubular element, wherein at least two of said plurality of holes comprise respective holes which have an outlet, said pump apparatus being adapted to supply intermittently said expanding resin toward said delivery port, calculating a rupture pressure of the soil at each one of said plurality holes, inserting, into said at least one hole, said tubular element and supplying intermittently, by way of said pump apparatus at a preset supply pressure, said expanding resin toward said delivery port, providing dimensions of the outlets of said plurality holes and the preset supply pressure of the resin to said tubular element so as to provide an outflow of the mixture through the respective outlets at a pressure that is higher than said rupture pressure, and so as to provide a substantially identical flow-rate of the mixture passing through each one of said at least two holes.

2. The method according to claim 1, wherein said at least two holes have the outlet with a dimension that increases progressively as a distance from said delivery port increases.

3. The method according to claim 1, wherein the dimensions of the outlets of said at least two holes and said preset supply pressure are adapted to ensure a substantially identical flow-rate of the mixture passing through each one of said at least two holes.

4. The method according to claim 1, wherein said pump apparatus comprises an injection gun connected by a flexible hose to said delivery port.

5. The method according to claim 4, wherein said injection gun comprises a mixing chamber connected in input to a first supply duct and to a second supply duct which are heated and are adapted to convey into said chamber, at a predefined pressure, components of said mixture, said mixing chamber being further connected to a third supply duct configured for supplying air under pressure for the activation of said injection gun, a discharge duct being provided which is connected to said mixing chamber and is connected to said tubular element.

6. The method according to claim 1 wherein the dimensions of holes are calculated on the basis of distributed load losses and of localized load losses.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further characteristics and advantages of the disclosure will become better apparent from the detailed description that follows of a preferred, but not exclusive, embodiment of the system for injecting expanding resins into soils to be consolidated according to the disclosure, which is illustrated for the purposes of non-limiting example in the accompanying drawings wherein:

(2) FIG. 1 is a cross-sectional view of a soil to be consolidated with a tubular element inserted into the soil; and

(3) FIG. 2 is an enlarged-scale longitudinal cross-sectional view of a portion of the tubular element of a system according to the disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) With reference to FIGS. 1 and 2, the system for injecting expanding resins into soils to be consolidated, according to the disclosure, generally designated by the reference numeral 1, comprises a pump apparatus 2 which is operationally associated, at a delivery port 4, with a tubular element 3.

(5) In particular, the pump apparatus 2 is adapted to send a mixture at a preset supply pressure to the tubular element 3.

(6) The tubular element 3 can be inserted into a respective hole 11 defined in the soil to be consolidated 10.

(7) The tubular element 3 has, at its lateral surface 3a, a plurality of holes 20 which are mutually spaced apart along the direction of longitudinal extension 100 of the tubular element 3.

(8) According to the present disclosure, at least two of the plurality of holes 20 comprise respective calibrated holes 21a, 21b, 21c, etc. which have a respective outlet.

(9) The system 1 further comprises an estimate of the rupture pressure of the soil (cleavage pressure) at each one of the calibrated holes 21a, 21b, 21c, etc.

(10) The dimensions of the outlets of the calibrated holes 21a, 21b, 21c, etc. and the preset supply pressure of the mixture to the tubular element 3 are, in particular, such as to allow the outflow of the material through the respective outlets at a pressure that is higher than the cleavage pressure.

(11) According to a preferred embodiment, the dimensions of the outlets of the calibrated holes 21a, 21b, 21c, etc. and the preset supply pressure are adapted to make the flow-rate of the material through the outlets substantially equal in each one of the at least two calibrated holes 21a, 21b, 21c, etc.

(12) “Substantially equal” means that between various calibrated holes 21a, 21b, 21c, etc. the variation in flow-rate can be approximately 15%.

(13) In this regard, it is possible for the calibrated holes 21a, 21b, 21c, etc. to present an outlet that increases progressively as the distance from the delivery port 4 increases.

(14) According to a preferred practical embodiment, the pump apparatus 2 comprises an injection gun 2a which is connected, by way of the flexible tubes 2b, to the delivery port 4.

(15) Advantageously, the injection gun comprises a mixing chamber which is connected in input to a first and to a second supply duct which are heated and are adapted to convey into the chamber, at a predefined pressure, the components of the mixture, the mixing chamber being further connected to a third duct for supplying air under pressure for the activation of the injection gun, a discharge duct being provided which is connected to the mixing chamber and is connected to said tubular element.

(16) The switch of the nozzle is actuated manually by the operator by way of a sprung trigger or by way of an electromechanical actuator, and this determines the opening of the flow of the two components toward the mixing chamber and as a consequence generates the outflow of the mixture from the discharge duct toward the tubular element. The release of the trigger by the operator immediately interrupts the flow of the two components toward the nozzle and therefore the injection of mixture into the soil.

(17) Preferably the injection-and-pause intervals can be extremely short, of the order of a few seconds, and more generally, comprised between 1 second and 10 seconds.

(18) Preferably, the calibrated holes 21a, 21b, 21c, etc. are mutually spaced apart along the direction of longitudinal extension 100 of the tubular element 3 for the full extension of the aforementioned tubular element 3.

(19) According to a further aspect, the present disclosure relates to a method for injecting expanding resins into soils to be consolidated 10 that comprises: a step of drilling the soil to be consolidated 10 in order to provide at least one hole 11; a step of estimating the rupture pressure of the soil (cleavage pressure) at the regions affected by the hole; a step of inserting, into the hole 11, a tubular element 3 which has, at its lateral surface 3a, a plurality of holes 20 which are mutually spaced apart along the direction of longitudinal extension 100 of the tubular element 3, at least two of the holes 20 comprising respective calibrated holes 21a, 21b, 21c, etc.; a step of supplying intermittently, by way of the pump apparatus 2, expanding resin toward the delivery port 4, the dimensions of the outlets of the calibrated holes 21a, 21b, 21c, etc. and the preset supply pressure of the resin to the tubular element 3 being such as to allow the outflow of the material through the respective outlets at a pressure that is higher than the cleavage pressure.

(20) Conveniently, the injection is carried out by connecting an injection gun 2a to the delivery port 4 (or head) of the tubular element 3, and dispensing the expanding resin with well-defined parameters so that this exits from each calibrated hole 21a, 21b, 21c, etc. present on the lateral surface 3a of the tubular element 3 with a regulated flow-rate and, once it has reached the soil, spreads into the surrounding volume in a controlled manner. The injection is continued for a time necessary to detect the start of lifting of the overlying built structure or, in the absence of this, the vertical movement of the soil at the surface.

(21) The new method therefore has two principal objectives: to enable the outflow of the expanding injection resin with a preset flow-rate from each calibrated hole 21a, 21b, 21c, etc. present on the lateral surface 3a of the tubular element 3 so that the speed of the expanding resin is sufficient to generate a spread into the soil by simple permeation or, in fine-grained soils, by cleavage; to control the spread of the expanding resin into the soil, i.e. to prevent it from venturing too far from the exit points and so affecting volumes of soil other than those planned.

(22) In order to achieve the above advantages, it is necessary to act on the following parameters: pressure and flow-rate of injection; geometry of the holes present on the lateral surface 3a of the tubular element 3; gelification and hardening times of the mixture; time intervals for dispensing the mixture.

(23) The system and method according to the disclosure is based on different principles to the conventional methods, in that: it does not use inner tubes which are inside the injection duct, plugs, or blockers, but simply entails, on the lateral surface 3a of the tubular element 3, the provision of calibrated holes 21a, 21b, 21c, etc. with appropriate geometry and dimensions; it carries out the injection by way of an injection gun 2a fitted onto the mouth of the tube, which ensures constant flow-rate and pressure; it uses a mixture, usually synthetic and expanding, which has well-defined gelification and hardening times.

(24) To explain the principle at the base of the new system and of the new method according to the disclosure, it is necessary to analyze the behavior of the fluid in the tubular element 3 and subsequently in the soil.

(25) The flow of the mixture through the tubular element 3 is determined by the laws of hydrodynamics.

(26) A fluid moves inside a tube from the point of highest pressure toward the point of lowest pressure. If there are no variations of pressure between the two ends, the fluid remains under static conditions.

(27) Bernoulli's principle, which is valid for perfect fluids (zero friction and viscosity) in a rigid conduit with steady motion (a constant flow-rate), states that for horizontal tubes the static pressure of a fluid in motion varies inversely with its speed. In other words, we can say that as long as the speed of the fluid increases, the static pressure decreases. The overall energy, given by the sum of the pressure energy, the kinetic energy and the potential energy, therefore remains constant.

(28) Furthermore, when motion is stationary, the flow-rate remains constant, i.e. the volume of fluid that transits one cross-section of the tube in a unit of time must also transit a previous or subsequent cross-section, of different dimensions.

(29) Accordingly, in the presence of areas of narrow cross-section, the fluid increases its speed in order to keep the flow-rate constant and as a consequence it decreases its static pressure.

(30) Differently, if the fluid is not perfect, i.e. it presents viscosity and friction on the walls of the tube, the conditions change.

(31) The energy expressed by Bernoulli's principle is not conserved, but decreases along the direction of the flow.

(32) The loss of pressure or loss of “continuous” load is constituted by the amount of energy lost by the fluid in order to overcome the friction it encounters in flowing inside the tube.

(33) In addition to the loss of continuous load, the fluid in motion is subject to further “localized” load losses, which entail sudden dissipations of energy that are due to variations in cross-section of the tube, variations in the direction of flow, outlets to the outside etc.

(34) The distributed load losses are regulated by Darcy's law, and we can extracting the following considerations from its formulation: the continuous load losses increase with the length of the duct; the continuous load losses increase with the narrowing of the cross-section of the tube; the continuous load losses increase with the density of the fluid; the continuous load losses increase with the increase in the flow-rate (and therefore of the speed of the fluid for the same diameter of the duct); the continuous load losses increase with the viscosity of the fluid.

(35) By contrast, the localized load losses increase with the density of the fluid, with the flow-rate (and therefore with the speed of the fluid for the same diameter of the duct) and with the hindrances present on the inner lateral surface of the duct (sudden changes in cross-section or in direction).

(36) The flow of a mixture through a tubular element that has holes on the lateral surface is therefore described in the following manner.

(37) The mixture introduced into the tubular element 3 by injection starts at the height of the mouth of the tube, with a well-defined flow-rate and pressure.

(38) Along the portion that precedes the first calibrated hole 21a, the mixture undergoes continuous load losses, which reduce its energy. The cross-section of the tubular element 3 is the same, so that, to conserve the flow-rate, the flow speed does not change. The decrease in energy is therefore absorbed by the potential energy and pressure energy terms of the Bernoulli equation.

(39) At the first calibrated exit hole 21a, the mixture loses further energy, in this case localized, owing to the exit cross-section, and is divided into two flows: the first flow exits into the soil from the calibrated hole 21a, and the second flow continues downward. In this case all three of the terms that make up the Bernoulli equation decrease. The flow-rate of the first flow is defined as a function of the soil consolidation requirements and of the characteristics of the soil.

(40) Therefore if the change in energy owing to the outlet losses is known, and the injection flow-rate for the first calibrated hole 21a is defined, then by the principle of conservation of flow-rate, it is possible to calculate the diameter of the second calibrated hole 21b to be provided on the lateral surface 3a of the tubular element 3 and the speed of continuation of the flow toward the subsequent calibrated holes.

(41) Therefore if the speed and pressure of the mixture in the portion that follows the first calibrated hole 21a and which precedes the second calibrated hole 21b are known, it is possible to reiterate the same method for the subsequent calibrated holes, until the hole arranged on the bottom of the tubular element 3 is reached.

(42) The method of calculation is easy to implement and makes it possible to determine the diameter of the calibrated holes 21a, 21b, 21c, etc. to be provided on the lateral surface 3a of the tubular element 3.

(43) The diameter of the calibrated holes 21a, 21b, 21c, etc. is therefore strictly linked to the flow-rate that it is desired to provide and is the first condition to be met in order that the described system functions correctly.

(44) A second necessary condition for the correct development of the injection relates to the possibility that the mixture exits from all the holes present on the lateral surface 3a of the tubular element 3 and spreads inside the soil, be it granular or cohesive, without creating obstructions.

(45) This it is possible only if the output speed of the mixture from each calibrated hole 21a, 21b, 21c, etc. corresponds to a static pressure that exceeds the pressure necessary for a correct spread of the mixture.

(46) For coarse-grained soils, by virtue of the granularity that gives them high permeability values, the exit pressure into the soil influences the correct spread of the mixture (and therefore the possible blockage of the holes) only in the long term, i.e. when most of the inter-granular voids have been filled and therefore the permeability has been reduced.

(47) For finely-grained soils, characterized by very low initial permeability values, the value of the exit pressure assumes a key role right from the start of the process. It must always be greater than the hydraulic fracturing pressure, which allows the free spread of the mixture and prevents the blockage of the holes.

(48) The last condition to be met so that the new system and the new method operate correctly is linked to the propagation distance of the mixture into the soil. It happens in fact that the process of hydraulic fracturing of the soil, necessary in order not to clog the calibrated holes 21a, 21b, 21c, etc. arranged on the lateral surface 3a of the tubular element 3, triggers the propagation of fissures within the soil. These fissures, fed by the mixture that flows from the cannula, tend to propagate in the soil in an uncontrolled manner.

(49) For this reason it is necessary to calibrate some parameters, which on the one hand impede the clogging of the holes and on the other hand it make it possible to manage with precision the distance from the exit point into the soil that the mixture can travel, which are: gelification and hardening times of the mixture; injection times.

(50) The gelification and hardening times of the mixture make it possible to obtain a first calibration of the method of injection, in that they must be sufficiently lengthy to not clog the holes but at the same time they must be limited in order to not excessively disperse the mixture into the soil.

(51) Obviously the gelification and hardening times of the mixture alone are not sufficient to best manage the process of spreading the mixture into the soil, since each site has different characteristics from the next and the parameters of the mixture are not continuously modifiable.

(52) Hence it is necessary to avail of an additional parameter that makes it possible to refine the process: the injection time.

(53) As already anticipated, each injection is performed intermittently, i.e. for each process, time intervals in which the mixture is dispensed continuously are alternated with intervals in which the injection is suspended. In this manner it is certain that the injected mixture will exit from the calibrated holes 21a, 21b, 21c, etc. with a greater pressure than the hydraulic fracturing pressure and simultaneously that it will not venture too far from the injection point. The injection suspension intervals are in fact defined so that the mixture injected up to that moment begins the process of gelification before the arrival of the subsequent mixture and therefore the pressure necessary for the same fracture to spread in the soil grows until it exceeds the hydraulic fracturing pressure. In this manner the mixture that is subsequently dispensed, instead of following the same fracture created previously, describes a new fracture, remaining confined adjacent to the outlet of the injection hole.

(54) In practice it has been found that the disclosure fully achieves the intended aim and advantages by providing a system and method that make it possible to control the outflow of the injection mixture with a preset flow-rate from each calibrated hole present on the lateral surface of the tubular element, so that the speed of the mixture is sufficient to generate a spread into the soil by simple permeation or, in fine-grained soils, by cleavage.

(55) Furthermore, the system and method according to the disclosure makes it possible to control the spread of the mixture into the soil, i.e. to prevent it from venturing too far from the exit points and so affecting volumes of soil other than those planned.

(56) The disclosure thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Moreover, all the details may be substituted by other, technically equivalent elements.

(57) In practice the materials employed, provided they are compatible with the specific use, and the contingent dimensions and shapes, may be any according to requirements and to the state of the art.

(58) The disclosures in Italian Patent Application No. 102018000007020 from which this application claims priority are incorporated herein by reference.