Foaming additive for soil conditioning in the presence of mechanised excavation for tunnel construction

Abstract

Disclosed is a liquid foaming additive for use in mechanised excavation by a tunnel boring machine, containing 5-40% by weight of one or more surfactants, 0.01-5% by weight of one or more biopolymers, and 55-94.99% by weight of water.

Claims

1. Method of conditioning excavated soil with a liquid foaming additive containing 5-40% by weight of one or more surfactants, 0.01-5% by weight of one or more biopolymers and 55-94.99% by weight of water, said method comprising: adding said liquid foaming additive to an excavation chamber of a tunnel boring machine, and conditioning said excavated soil.

2. The method according to claim 1 wherein the additive is added, in percentages ranging from 0.1 to 4.0% by weight, to water pumped into a foam generator.

Description

DESCRIPTION OF THE INVENTION

(1) The present invention relates to a novel foaming additive designed to be added in percentages of 0.1-4% by weight to an aqueous solution, able to generate foam to be injected into the tunnel face. Said foam is used on the face to soften the soil and allow faster extraction, and in the conditioning chamber to maintain the stability of the tunnel face.

(2) The high stability of the foam generated, expressed as half-life, allows the conditioning in the excavation chamber to be maintained for longer.

(3) The additive according to the invention, in the form of an aqueous solution classifiable as readily biodegradable, comprises at least one surfactant in percentages ranging between 5 and 40% by weight, and at least one biopolymer in percentages ranging between 0.01 and 5% by weight. The percentage of water can range from 55% to 94.99% by weight. The surfactant can be anionic, cationic or non-ionic, preferably anionic. The preferred anionic surfactants are alkyl sulphate salts and alkyl heterosulphates, in particular the sodium salts. An alkyl ethoxy sulphate salt having a C.sub.10-C.sub.14 alkyl chain and an ethoxylation number ranging from 1 to 9 is particularly preferred as anionic surfactant.

(4) The term biopolymers refers to polymers degradable due to the effect of micro-organisms such as bacteria, fungi or seaweed. They are mainly water-soluble polysaccharides able to increase the viscosity of an aqueous system in a pH range between 4 and 12. The preferred biopolymers are xanthan gum and guar gum.

(5) The foaming additive according to the invention is classifiable as readily biodegradable according to the OECD 301 guidelines.

(6) The foaming additive according to the invention is characterised by high stability, even in the presence of brine.

(7) The foaming additive can also contain other compounds used to deal with specific problems such as clogging due to clayey soils, to prevent high consumption of the cutters fitted in the cutterhead, or to reduce the quantity of soluble salts in the water present in the excavation soil.

(8) A further object of the invention is the use of the additive to generate foam able to condition excavation soils. The additive is preferably added, in percentages ranging from 0.1 to 4.0% by weight, to the water pumped into a foam generator.

(9) The characteristics and advantages of the additive according to the invention are more particularly described in the examples below. The percentages of the ingredients are expressed by weight.

Example 1

(10) The foaming additives have the following compositions:

(11) TABLE-US-00001 TABLE 1 composition of samples Parts by weight (%) Sample 1 Sample 2 Sample 3 Sample 4 Sodium lauryl 20.0 20.0 20.0 12.0 ether sulphate Xanthan gum 0.0 0.5 2.0 0.3 Biocide 0.2 0.2 0.2 0.2 Water 79.8 79.3 77.8 87.5

(12) The stability of the foam generated by an aqueous solution prepared by adding 2% by weight of foaming additive to 5000 g of water is evaluated. The stability is expressed as the half-life, which indicates the time required for the weight of the foam to halve. The test is conducted by evaluating the time in which water amounting to half the weight/volume of the foam is released in a 250 ml cylinder.

(13) The foam is formed by a generator that conveys the flow of liquid at a constant airflow into a glass ball mixer.

(14) TABLE-US-00002 TABLE 2 half-life Half-life (sec) Sample 1 540 Sample 2 730 Sample 3 1800 Sample 4 690

(15) The figures set out in Table 2 indicate that the stability of the foam increases when the dose of biopolymer is increased. The biological degradation results of sample 4 according to OECD 301 classify the product as readily biodegradable with a value of 84% after 28 days.

Example 2

(16) The foaming additives have the compositions reported in Table 1.

(17) The aggregate used to evaluate the stability of the conditioning is a standard quartz with a well-defined particle-size distribution curve (0.06-0.25 mm).

(18) The foam used to condition the matrix is generated by mechanical mixing at 2000 rpm starting from an aqueous solution prepared with 65 g of water and 0.65 g of foaming additive.

(19) The evaluation involves adding the foams generated with the foaming additives reported in Table 1 to three 1000 g samples of standard quartz, and homogenising the mixture in a Hobart mixer for 3 minutes at standard speed. The matrix conditioning is expressed as the viscosity value, measured with a Brookfield DV-I Prime viscometer, using spindle D and a speed of 5 rpm. The viscosity of the conditioned matrix is evaluated at time 0 and 60 minutes after mixing. A smaller difference in the values obtained after 60 minutes compared with the initial figure suggests better conditioning by the foam used.

(20) The results are set out in Table 3:

(21) TABLE-US-00003 TABLE 3 viscosity of conditioned quartz. Viscosity (Pa*s) 0 minutes 60 minutes Water Not evaluatable Sample 1 145 325 Sample 2 150 240 Sample 3 145 200 Sample 4 155 300

(22) The test conducted with the addition of water alone gave rise to a cohesionless matrix; the viscosity measurement was not significant.

(23) The data set out in Table 3 indicate an improvement in the stability of the soil conditioning when foams with long half-lives are used.

Example 3

(24) The foaming additives have the following compositions:

(25) TABLE-US-00004 TABLE 4 composition of samples Parts by weight (%) Sample 5 Sample 6 Sample 7 Sodium lauryl ether sulphate 15.0 15.0 15.0 Guar gum 0.0 0.1 0.5 Water 85.0 84.9 84.5

(26) The stability of the foam generated by an aqueous solution prepared by adding 2% by weight of foaming additive to 5000 g of water is evaluated. The stability is expressed as the half-life, which indicates the time required for the weight of the foam to halve. The test is conducted by evaluating the time in which water amounting to half the weight/volume of the foam is released in a 250 ml cylinder.

(27) The foam is formed by a generator using a constant airflow.

(28) TABLE-US-00005 TABLE 5 half-life Half-life (sec) Sample 5 480 Sample 6 530 Sample 7 560

(29) The figures set out in Table 5 indicate that the stability of the foam increases when the dose of biopolymer is increased.

Example 4

(30) The foaming additives have the following compositions:

(31) TABLE-US-00006 TABLE 6 composition of samples Parts by weight (%) Sample 8 Sample 9 Sample 10 Sample 11 Sample 12 Sodium 10.0 10.0 0.0 0.0 5.0 lauryl ether sulphate Sodium 0.0 0.0 10.0 10.0 0.0 lauryl sulphate Cocamide 0.0 0.0 0.0 0.0 5.0 MEA Guar gum 0.1 5.0 0.0 0.5 0.5 Water 89.9 85.0 90.0 89.5 89.5

(32) The stability of the foam generated by an aqueous solution prepared by adding 2% by weight of foaming additive to 5000 g of water is evaluated. The stability is expressed as the half-life, which indicates the time required for the weight of the foam to halve. The test is performed by evaluating the time in which water amounting to half the weight/volume of the foam is released in a 250 ml cylinder.

(33) The foam is formed by a generator that conveys the flow of liquid at a constant airflow into a glass ball mixer.

(34) TABLE-US-00007 TABLE 7 half-life Half-life (sec) Sample 8 600 Sample 9 7200 Sample 10 450 Sample 11 860 Sample 12 650

(35) The figures set out in Table 7 indicate that the stability of the foam increases when the dose of biopolymer in the additive is increased.

Example 5

(36) The foaming additives have the following compositions:

(37) TABLE-US-00008 TABLE 8 composition of samples Parts by weight (%) Sample 13 Sample 14 Sample 15 Sodium lauryl ether sulphate 12.0 12.0 12.0 Xanthan gum 0.0 0.3 2.0 Water 88.0 87.7 86.0

(38) The stability of the foam generated by an aqueous solution prepared by adding 2% by weight of foaming additive to 5000 g of brine is evaluated. The brine used is characterised by a sodium chloride concentration of 2%. The stability is expressed as the half-life, which indicates the time required for the weight of the foam to halve. The test is conducted by evaluating the time in which water amounting to half the weight/volume of the foam is released in a 250 ml cylinder.

(39) The foam is formed by a generator that conveys the flow of liquid at a constant airflow into a glass ball mixer.

(40) TABLE-US-00009 TABLE 9 half-life Half-life (sec) Sample 13 510 Sample 14 650 Sample 15 1720

(41) The figures set out in Table 9 indicate that the stability of the foam generated by a brine solution increases when the quantity of biopolymer in the additive is increased.

Example 6

(42) The foaming additives have the following compositions:

(43) TABLE-US-00010 TABLE 10 composition of samples Parts by weight (%) Sample 16 Sample 17 Sodium lauryl ether sulphate 10.0 1.0 (ethoxylation number 2) Sodium alkyl ether sulphate 10.0 (ethoxylation number 7) Xanthan gum 0.3 Water 90 88.7

(44) The stability of the foam generated by an aqueous solution prepared by adding 2% by weight of foaming additive to 5000 g of brine is evaluated. The stability is expressed as the half-life, which indicates the time required for the weight of the foam to halve. The test is conducted by evaluating the time in which water amounting to half the weight/volume of the foam is released in a 250 ml cylinder.

(45) The foam is formed by a generator that conveys the flow of liquid at a constant airflow into a glass ball mixer.

(46) TABLE-US-00011 TABLE 11 Half-life Half-life (sec) Sample 16 450 Sample 17 560

(47) The figures set out in Table 11 show a stable foam when a sodium alkyl ether sulphate characterised by an ethoxylation number of 7 is used as surfactant.