JPH0118211B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF INDUSTRIAL APPLICATION The present invention relates to a method for replacing bentonitic slurry in a cavity with a curable mixture. More specifically, the present invention is characterized in that the bentonitic slurry contains lime. [Prior art] When digging the ground, a colloidal water dispersion of bentonite is used to fill the cavity of the hole in order to maintain the outer wall of the hole and prevent the hole from collapsing during the digging operation. It is known to use bentonitic slurries. Similarly, in many cases, the bentonitic slurry is replaced with a hardening mixture such as a grout, cement paste, mortar, or concrete composed of a cement-rich bentonitic slurry. It is also well known that This displacement places the curable mixture into the cavity containing the bentonitic slurry, for example at the bottom of the cavity, such that the volume of the curable mixture inside the cavity gradually increases and the volume of the bentonitic slurry decreases. This is done by introducing For example, this method involves digging a very long hole, placing a component such as a conduit, steel frame, or panel beneath the bentonitic slurry that fills the hole, and then positioning the component in the hole. After securing, a curable mixture can be introduced to partially or completely fill the holes. However, such methods have serious problems in implementation. Especially after curing,
Pockets of bentonitic slurry may remain inside the curable mixture, which may reduce the durability of the entire foundation. Therefore, in order to solve this problem, the present applicant did not excavate at the bottom of the conventional bentonite slurry, but instead excavated from a bentonite slurry containing a cement component so that it could harden after a certain period of time. A method was developed that consisted of excavating the lower part of the grout that was constructed. This method eliminates the problem of replacing pure bentonitic slurry. However, this method has the disadvantage that it is not possible to use excavating means such as milling cutters, which risk being blocked very quickly by coagulating grout. [Problems to be Solved by the Invention] The present invention solves the risk of formation of lumps (pockets) of bentonite slurry inside the hardened curable mixture in a method of replacing bentonite slurry in a cavity with a curable mixture. The purpose is to significantly reduce the SUMMARY OF THE INVENTION The present invention provides that before replacing the bentonitic slurry in a cavity with a curable mixture, an amount equal to the amount required for the lime-containing bentonitic slurry to exhibit maximum stiffness. or 10 in excess of the required amount and expressed as the weight of calcium oxide relative to the weight of bentonite contained in the bentonitic slurry.
% or less of lime to the bentonitic slurry in the cavity, and then replacing the bentonitic slurry containing lime with a curable mixture. the bentonitic slurry in the cavity in an amount equal to or in excess of the amount necessary for the bentonitic slurry containing lime to exhibit a maximum modulus of stiffness and bentonite; lime in an amount that is not more than 10% by weight of calcium oxide relative to the weight of bentonite contained in the slurry;
In addition to the bentonitic slurry in the cavity, a powdered cement or a cement-containing composition is then added to the bentonitic slurry containing lime and mixed to form a hardenable mixture. and a curable mixture. The present invention will be explained below. Colloidal dispersion, e.g. 20-40Kg per ^m3 of water
The stepwise addition of a small amount of lime (CaO) to a conventional bentonitic slurry consisting of bentonite increases the stiffness of the slurry, which goes through a maximum value and then decreases. Rigidity (i.e. shear stress)
For the measurement, a bladed testing machine (consisting of a torque meter and four blades) is used. Measurement is performed as follows. The four blades are immersed in the slurry and then the torque meter is rotated to apply shear stress to the slurry. Increase the rotation speed of the torque meter and measure the maximum shear stress just before the slurry can no longer resist. However, rigidity (shear stress)
can also be calculated from the viscosity using Marcille's cone. a co^ne called MARSH
to determine the time required for a given amount of material to flow through a funnel and to measure the apparent viscosity value, which depends on the true viscosity of the material as well as its modulus of stiffness. It is also well known that this is possible. Marshy's cone, also called Marshy's funnel, is a funnel that is adjusted so that 946 cm ³ of water flows out in 26 seconds ± 0.5 seconds at 21°C ± 3°C. Marshyu's funnel is the aperture part of the funnel (length 305mm, diameter 152mm,
The capacity of the area below the sieve is 1500cm ³ ), orifice (length 50.8mm, inner diameter 4.7mm) and sieve (mesh size 1.6mm,
It is fixed 19.0mm below the top (opening part) of the funnel). To measure viscosity, press the outlet of the orifice provided at the bottom of the funnel with your finger, and introduce the sample into the funnel from the top of the funnel through the sieve until the top surface of the sample touches the sieve. Then, remove your finger, pour the sample into the container marked at 946 cm ³ , and then remove your finger.
Measure the time (in seconds) until it reaches the ^946cm3 mark. It represents the viscosity (apparent viscosity) measured with a Marsh cone at the time. In accordance with the present invention, in order to determine the concentration of lime that must be added to a bentonitic slurry in order for the slurry to have its maximum stiffness, a series of It is sufficient to prepare a sample of and in each case measure the apparent viscosity with a Marsille cone. According to the invention, in order to carry out the method of the invention, the proportion of lime is near or slightly higher than the proportion which gives the maximum time with Marseille's awl. According to the invention, the amount of lime is brought to such a level that the slurry has a maximum stiffness under such conditions that after the supplementary addition of a small amount of lime the runoff time measured by the Marcille device decreases again. is possible. Tests conducted by the applicant have shown that this maximum value generally corresponds to an amount of quicklime (CaO) in the bentonitic slurry, i.e. no more than 10% based on the weight of bentonite introduced into the slurry. It was shown that this can be achieved when a certain amount of lime is introduced. Of course, the value depends on the properties of the bentonite used. In the present invention, it is preferred that the apparent viscosity of the slurry containing bentonite and lime is in the range of 40 to 80 seconds when using a Marsh cone. According to the first mode of the substitution method according to the invention,
The bentonitic slurry is replaced by a hardenable mixture (grout, mortar, or concrete). According to the method of the present invention, even by replacing the bentonitic slurry with a bentonite cement grout whose density is almost the same as that of the slurry, there is a very clear gap between the bentonitic slurry and the grout. Notice that a separation front appears. Moreover, even if some lumps of the bentonitic slurry form inside the grout, this can be agitated by, for example, mechanical means, injection of compressed air, and even circulation of the product by pump means. Alternatively, it can be eliminated very easily by treatment such as mixing. According to a second alternative mode of the invention, the properties of the bentonitic slurry are modified by injecting a composition containing an excess amount of cement or by dosing powdered cement onto the slurry. It can be changed depending on the case. Similarly, when using a lime-rich slurry according to the invention, the sand necessarily mixed into the slurry during excavation has a very low tendency to settle; can remain in a very stable suspension state. Thus,
It is possible to prevent the deposition of large amounts of sand at the bottom of the hole, which can cause serious problems in some cases. In another aspect of the practice of the invention, the method of the invention for replacing bentonitic slurry with concrete can be utilized to obtain reinforced concrete wall members of very long and relatively limited width. In this case, the bentonitic slurry is immiscible with concrete and the large density difference between the slurry and concrete can be utilized in the replacement. After excavation and installation of panels or reinforcing bars with the aid of a bentonitic slurry exhibiting such properties, concrete is poured inside the hole, thereby eliminating the bentonitic properties to be eliminated in the process. The slurry can be pushed upward in stages. It is important to note that the evidence indicates that the bentonitic slurry utilized in accordance with the present invention participates in soil retention with properties very similar to bentonitic slurries that are not rich in lime. That's true. The practical advantage of drilling below the bentonite slurry is the bentonite-rich shell or cake. The marsh-rich shell or cake forms on the walls of the borehole to prevent water contained in the slurry from damaging the underground walls. By using the lime-containing bentonite slurry of the present invention, the water leakage of the bentonite shell formed on the wall by the slurry is further improved. The method of the invention has the advantage of being simple and economical to implement. The slurry of the present invention contains less bentonite than conventional slurries and has a significantly lower cost. The slurry of the present invention has a relatively high rigidity,
This high stiffness prevents separation of surrounding soil particles. Furthermore, there is no risk of acquiring excessive stiffness due to lime components originating from the surrounding soil, which may in turn be calcareous. A further object of the present invention is to provide a bentonitic slurry useful for carrying out the method of the present invention. This slurry is characterized by having a stiffness modulus that is either at its maximum or slightly lower than the maximum by adding an appropriate amount of lime. EXAMPLES For the purpose of understanding the present invention even better, Examples are described below, but the present invention is not limited by these Examples in any way. Example 1 For example, assume that a hole is dug with a depth of 4 or 5 m and a length of several hundred meters. This hole is a conduit for draining used water or other fluids,
Furthermore, it is used to receive reinforced concrete members used to construct one wall of the retaining wall. The drilling of the hole is carried out by conventional equipment operating under a bentonitic slurry having the following structure: Bentonite 35Kg/m ³ Quicklime (CaO) 2Kg/m ³ (i.e. 6% on bentonite basis) The viscosity of the slurry according to the Marsille cone is 45 seconds. The proportion of quicklime was determined such that a maximum viscosity due to Marseille's cone was obtained by gradually adding increasing amounts of lime. Thus, the following apparent viscosities were obtained using Marsille's cone for increasing lime contents for bentonite as follows and for a constant content of bentonite of 35 Kg/ ^m3 .

Table: In this example, a ratio of 6% was chosen, corresponding to an apparent viscosity of 46 seconds, slightly lower than the maximum value of 50 seconds. The replacement mixture consisted of bentonite grout containing 150 Kg/m ³ of cement. The density of the grout is approximately 1.1. The density of the slurry is about 1.05-1.1, depending on the amount of sand produced during excavation that contaminates the slurry. To carry out the method, it is generally of interest to produce a new grout and optionally extract the slurry for reuse. It is clear that, without departing from the spirit of the invention, it is also possible to use a slurry whose composition is pre-subtracted from the additives required to give the grout the desired texture. In carrying out the method of the invention, the grout is injected at a sufficient distance from the bottom of the hole so that it does not come into contact with the slurry-immersed portions of the hole or with the drilling equipment. The grouting can be carried out, for example, at a distance of 50 m from the point of excavation of the hole. Example 2 According to the invention, a depth of several tens of meters and 0.2
Create piles of circular cross-section or barrettes of rectangular cross-section with a cross-sectional area in the range ~7 ^m2 . The piles or bars, which consist of a steel cage surrounded by concrete, serve to transmit the action of the construction structure down to the base layer. A correspondingly shaped hole is made under a bentonitic slurry growing a composition similar to that of Example 1 using conventional equipment, such as a Kelly auger or bucket. Next, the steel stage is installed, and concrete is introduced through a conduit to the bottom of the hole. The concrete used has the following composition (per 1 ^m3 ): Cement 400Kg Sand (0-5mm) 600 Finely ground stone (5-25mm) 600 Water 200 Plasticizer and retarder Introducing the concrete into the hole As it progresses, the concrete pushes up the slurry, surrounds the steel, and eventually completely fills the hole. Upon contact with concrete, the bentonitic slurry of the present invention becomes fluidized so that it can be easily extruded by concrete. Conversely, the bentonitic slurry of conventional methods is converted to a gel that is difficult to remove due to slurry lumps forming inside the concrete or on the walls of the hole. The gel can cause numerous defects to the shaft or rod. Example 3 Similar to Example 1, a hole is dug under a bentonitic slurry according to the invention. During excavation, the bentonitic slurry is filled with sand and the slurry has a density of about 1.2, making it difficult to replace the bentonitic slurry with a lower density grout. The invention proceeds in the following manner: First, a bentonite cement grout containing 300 Kg/m ³ of cement is prepared. 10 m ^{3 of} bentonite cement grout with a cement content of 300 Kg/m ³ is introduced onto ^each cylinder with a volume of 20 mm 3 and a hole depth of 5 m. Mechanical agitation is then carried out by compressed air or other means to ensure homogenization of the grout. Thus, by intimately mixing 10 m ³ of bentonite cement grout containing 300 Kg/m ³ of cement with 10 m ³ of the bentonitic slurry of the present invention, bentonite cement grout can be obtained,
This mixture contains 150 Kg/m ³ of cement as desired. Such implementation is possible thanks to the bentonitic slurry according to the invention. Example 4 A waterproof wall 15 m deep and 0.5 m thick is made according to the invention. A hole corresponding to a length of 3 m is made according to conventional drilling techniques, for example under a bentonitic slurry according to the invention having the composition of Example 1. The slurry occupies a volume of approximately 45 m ³ . Finally, operate as follows to form a solidified bentonite cement grout containing 100 Kg/m ³ of cement. 4.5 t of powdered cement is introduced into the hole filled with slurry, while 1.7 m ³ of slurry corresponding to the volume of introduced cement is taken out. There is then a disturbance movement in the hole, for example by compressed air, pumping and recirculating if necessary, until a sufficient homogenization of the grout is achieved, which can be easily achieved according to the invention. induce. It should be understood that the above embodiments do not limit the invention in any way, and that any desired modifications can be made without departing from the scope of the invention. In particular, it is not restricted to large width or very deep holes; the method of the invention can be used in particular for constructing wells, for example.

Claims (1)

Claims: 1. an amount equal to or as necessary for the lime-containing bentonitic slurry to exhibit maximum stiffness before replacing the bentonitic slurry in the cavity with the curable mixture; and not more than 10% by weight of calcium oxide relative to the weight of bentonite contained in the bentonitic slurry is added to the bentonitic slurry in the cavity, and the bentonitic slurry containing lime is then added to the curable mixture. A method for replacing a bentonitic slurry in a cavity with a curable mixture, the method comprising: replacing a bentonitic slurry in a cavity with a curable mixture; 2 The bentonite slurry containing lime is
2. A method according to claim 1, having a viscosity of 40 to 80 seconds as measured by Marsille's cone. 3. Before replacing the bentonitic slurry in the cavity with the curable mixture, an amount equal to or in excess of the amount necessary for the lime-containing bentonitic slurry to exhibit a maximum modulus of stiffness and the bentonitic slurry Lime is added to the bentonitic slurry in the cavity in an amount that is not more than 10% by weight of calcium oxide relative to the weight of bentonite contained in the cement or cement-containing composition. A method for replacing a bentonitic slurry in a cavity with a curable mixture, the method comprising: adding and mixing to form a curable mixture. 4 Bentonite slurry containing lime is
4. A method according to claim 3 having a viscosity of 40 to 80 seconds as measured by Marsille's cone. 5. The method according to claim 3 or 4, wherein the addition of powdered cement or cement-containing composition is carried out while stirring the lime-containing bentonitic slurry. 6. The method according to claim 5, wherein the stirring is performed by mechanical means. 7. The method according to claim 5, wherein the stirring is performed using compressed air. 8. The method according to claim 5, wherein the stirring is carried out by circulating a bentonitic slurry containing lime and/or cement.