A Study of the Compaction Effect of Expansive Admixture for the Development of an Expansive Compaction Packer

Abstract

Although permeating injection is ideal for grouting reservoir embankments, it is usually combined with fracturing injection for grouting, which can disturb the original soil. Compaction with low expansive pressure followed by grout injection can overcome this problem. An expansive compaction (EC) packer was developed in this work to easily apply sequential injection and compaction at a work site. Furthermore, to achieve compaction around the grouting hole, a mixture of expansive admixtures and grout was injected with the EC packer to trigger an increase in volume of the grout material. This work verifies the compaction effect of the EC packer and the expansive admixture. It reports the concepts of the EC packer, the range of expansive compaction, the effectiveness of injection, and the results of indoor tests performed to verify the effectiveness of the expansive admixtures. The indoor testing comprised a preparatory test and the main test. The preparatory test assessed the admixtures for their compaction effects, while the main test measured and analyzed the admixtures' expansive force, pressure, and compaction effect with a mold to verify the effectiveness of the compaction effect.

Introduction

Recent geo-technology research has sought to develop high-performance materials that provide increased durability and strong injection effects compared with current materials. This has been achieved through micronizing particles that are non-polluting, developing injection devices to mitigate the damage done to adjacent structures by low-pressure compound injection, and increasing the integrity of injection methods via computerized injection management and monitoring. (Kim, J., 1999)

Although permeation injection is considered ideal for reservoir embankment grouting, permeation and fracturing injection are often combined, which can disturb the original soil (Korea Rural Community Corporation, 2001). In this research, an expansive compaction (EC) packer is developed to ameliorate this problem. It performs compaction with low expansive pressure (Korea Rural Community Corporation Embankment Grouting Design and Practice Guidelines, 2010; 0.035-0.043 MPa per meter), and it can perform repeated cycles of injection and compaction. The fundamental study conducted here assesses the effects of compaction caused by expansive admixtures, which are added to induce expansive pressure. This paper reports the concept of the EC packer, the range of expansive compaction, the effectiveness of injection, and the results of indoor tests of the expansive admixtures. The indoor tests comprised a preparatory test that assessed the admixtures for their compaction effects, and a main test that measured and analyzed their expansive force, pressure, and compaction effect through a mold in order to verify the effectiveness of the compaction effect.

 

EC packer

An EC packer provides structural stability through expansive compaction type tip-point equipment, which performs simultaneous injection and compaction to the ground, resulting in reduced permeability, enhanced strength, and a dense ground structure. In general reservoir grouting, an EC packer can be installed as shown in Fig. 1.

Fig. 1.Illustration of EC packer installation.

The injection method can use EC packer grout sat 80%-85% of the maximum water injection pressure used in general grouting. The grouting of expansive admixtures then provides an expansion effect of 15%-20% of the maximum pressure. Expansive compaction injection is done every 3 m, as the injection position in reservoir grouting is generally 3 m per step and the expansion reaches 15%-20% (Fig. 2). An EC packer needs a separate injection device to inject grout and expanding agent simultaneously; thus, a special packer unifying the two processes is required. Fig. 3 outlines the EC packer development.

Fig. 2.Range of effect of an EC packer.

Fig. 3.Schematic of parts of EC packer development.

To illustrate the effect of injection, Fig. 4 shows the ground condition before treatment, during penetrating and fracturing injection, and after thorough compounding of the ground. The figure shows the reduced permeability after injection and overlapping compaction. The main goal of this work is the development of a sleeve-shaped EC packer for low-pressure grouting such as reservoir grouting. The casing is drawn out after penetration, the EC packers are installed, and upward injection is conducted. Maximum injection effect is achieved through the expansive compaction and injection being performed with the EC packer at each step of injection. Fig. 5 shows the workings of the EC packer.

Fig. 4.Injection effect of EC packer.

Fig. 5.Construction using an EC packer.

 

Preparatory test

Test outline

The preparatory test examined the characteristics of the expansive admixtures to identify the most suitable admixture, method of use, and mixing ratio. Two different types of admixture, cement and urethane, were separately examined. The test criteria were the expansion rate and the single-axis compressive strength.

Cement-Type expansive admixtures

Three cement-type expansive admixture samples were compared (Table 1). Two were from Korean companies and one was from a company in the UK. Water per cement (W/C) mixing ratio of 90% was chosen based on the final ratio from reservoir grouting. Each of the three samples of admixture was used at 1% of the total weight of cement (Table 2).

Table 1.Details of the cement-type expansive admixtures.

Table 2.Test mixing ratio.

Cement-Type expansive admixtures: results and analysis

Specimens were 5.0 cm cubes (volume 125 cm3) and were measured after being left for 2 hours at room temperature. The molds that were used in the single-axis compressive strength test after 24 hours of waiting at room temperature were the same. Expansion was assessed by calculating the volume change from the changes in the cubes’ vertical dimensions. Sample C-100 showed almost no bleeding, but the other two showed some bleeding. Table 3 lists the measured expansion of the cement-type expansive admixtures. The volume of sample C-100 increased by 2.4%, while samples Type-1 and HI-E decreased by 7.2% and 9.5%, respectively. Table 4 lists the single-axis compressive strengths of the samples after 24 hours. Sample HI-E was the strongest (0.804 MPa); sample Type-1 showed a value of 0.554 MPa.Sample C-100, which showed the largest expansion, exhibited the lowest strength of 0.262 MPa. The results show an inverse relationship between single-axis compressive strength and expansion (Fig. 6-1 and Fig. 6-2). Table 5 lists the sizes of pores caused by air bubbles inside each specimen after crack testing. Greater expansion correlated with larger pores.

Fig. 6-1.Properties of cement-type expansive admixtures.

Fig. 6-2.Properties of cement-type expansive admixtures.

Table 3.Expansion of cement-type expansive admixtures.

Table 4.Single-axis compressive strengths of cement-type expansive admixtures after 24 hours.

Table 5.Innerpore size induced by air bubbles observed after specimen cracking.

Urethane-Type expansive admixtures

Soft, hard, and semi-hard products were used as urethane-type expansive admixtures. Three mixture ratios were tested. The urethane-to-cement ratios were 1:1.5, 1:2, and, 1:3 respectively; the water-to-cement ratio was maintained constant, while the urethane-type-expansiveadmixture-to-cement ratio was changed slightly. Water was added in the mixing sequence after the cement and urethane were first mixed together (Tables 6, 7).

Table 6.Details of the urethane-type expansive admixtures.

Table 7.Test mixing ratios.

Urethane-Type expansive admixtures: results and analysis

Volume changes in the urethane-type expansive admixtures were calculated from the changes in the mixed samples’ linear dimensions. Sample Soft 1000 and Hard 2000 showed similar results. For both of these samples, mixes #1 and #2 led to increases in volume of 4 to 5 times and 2 to 3 times, respectively, while mix #3 did not show any notable increase in volume. The Semi-Hard 3000 sample showed increases in volume of 2 to 3 times for mix #1, about 2 times for mix #2, and no increase for mix #3. Although the urethane-type expansive admixture showed great expandability, it was not included in the following main test owing to the need for a separate injection mixer and a pump. Tables 8 to 10 list the results for the urethane-type expansive admixtures. Table 11 shows pictures of the expansion test.

Table 8.Expansion properties of Soft 1000.

Table 9.Expansion properties of sample Hard 2000.

Table 10.Expansion properties of sample Semi-Hard 3000.

Table 11.Photographs of the results of expansion tests.

 

Main test

Test outline

The main test assessed the compaction effects of the expansive admixtures selected from the preparatory test. The test criteria were expansion pressure, expansion rate, single-axis compressive strength, and expansion effect verification.

Expansive admixtures from the three companies outlined above were used. Expansion was measured relative to a specimen without any added expansive admixture. Expansion pressure was measured and analyzed using a flat pressure sensor installed inside the wall of a closed acryl tube. The compaction effect was verified 12 hours after sample injection into cylindrical molds.

Eight samples, two free from expansive admixture and six containing the three admixtures at 1% and 2% each, were tested. Fig. 7-Fig. 10 show working of the expansive pressure measuring device, an expansive pressure measuring device after injection, compaction effect test using a cylindrical mold, and shape of a bulb after the compaction effect test, respectively. Table 1 lists the considered expansive admixtures, and Table 12 lists the samples’ mixing ratios.

Fig. 7.Working of expansion pressure measuring device.

Fig. 8.Expansion pressure measuring device after injection of expansive admixture.

Fig. 9.Compaction effect test using molds.

Fig. 10.Shape of a bulb after compaction effect verification test.

Table 12.Mixing ratios.

Expansion rate test: results and analysis

Admixture-free samples were set as a standard to measure the changes in height in the other samples. Sample C-100 (1%) showed the greatest expansions: with w/c = 90% it showed 18.9% expansion, and with w/ c = 70% it showed 23.4% expansion. Water-to-cement ratio of 70% was chosen equally as it showed relatively higher expansion rate among the two mixing ratios in C-100 (1%) sample test. As a result of the change, sample Type-1 (1%) with w/c = 70% showed 6.3% expansion whereas Type-1 (2%) did not change at all. Sample HI-E (1%) with w/c = 70% expanded by 6.2%, and sample HI-E (2%) expanded by 15.4%. Decreasing the w/c ratio increased the expansion of sample C-100 (1%). The Type-1 samples did not show a positive correlation between the amount of expansive admixtures and expansion, so they were not suitable for use. The HI-E samples did show a positive correlation, and their expansion was the second highest among the three samples (Fig. 11).

Fig. 11.Expansion results for expansive admixtures.

Single-axis compressive-strength test: results and analysis

Water-to-cement of 70% was chosen for the test for the aforementioned reason. The single-axis compressive strengths of the six samples (admixture-free sample, C-100 (1%), Type-1 (1%) and (2%), and HI-E (1%) and (2%)) after 1, 7, and 28 days of maturing were measured using w/c = 70% as a standard. The 2.33 MPa strength of the admixture-free sample after 1 day increased to 13.6 MPa after 28 days. Sample C-100 (1%), which showed the greatest expansion, was 2-3 times weaker than the other samples after 1day (0.726 MPa); after 28 days its strength was 8.90 MPa, and was only 1.5-2 times weaker than the other samples. Sample Type-1 (2%) exhibited the highest strength, with a maximum value of 19.1 MPa after 28 days, but it showed no expansion. HIE (1%) sample showed the strength of 17.4 MPa and HIE (2%) sample showed 14.0 MPa after 28 days. Therefore, only samples C-100 (1%), HI-E (1%) and HI-E (2%) were considered for the subsequent expansion and compaction effect test (Table 13, Fig. 12).

Fig. 12.Results of single-axis compressive strengths.

Table 13.Single-axis compressive strengths test results.

Expansion pressure test: results and analysis

Expansion pressure tests were conducted on samples C-100 and HI-E using w/c = 70%. The greatest pressure of 0.0696 MPa was achieved using C-100 (1%); the initial set was completed within approximately 30 min. HI-E (1%) achieved a value of 0.0392 MPa after 83 min, and HI-E (2%) showed 0.0490 MPa after 38 min. The initial set was presumed to have been completed when the expansion stopped. It was also estimated that the greater the expansive force, the quicker the initial set (Fig. 13). Sample C-100 showed the greatest expansion pressure, yet its single-axis compressive strength was lower than those of the other samples. Sample HI-E (2%) appears to be the most suitable considering its overall characteristics and the selection criteria.

Fig. 13.Expansion pressures.

Compaction effect test: results and analysis

To verify the compaction effect, the samples (w/c = 70%) were tested in a chamber of dried soil, and their compaction effects were assessed after 12 hours. The soil test chamber had a diameter of 3.9 cm, height of 20 cm, and volume of 238 cm3. The measured volume changes are shown in Fig. 14. The admixture samples showed volume increases, but the admixture-free sample showed a 16% decrease in volume. Sample C-100 showed an approximately 30% increase in volume, while samples HI-E (1%) and HI-E (2%) showed increases of 19% and 28%, respectively. Given all the measurements of expansion, single-axis compressive strength, expansion pressure, and compaction effect, sample HI-E (2%) was chosen as the most suitable. Its compaction effect was verified: Fig. 15 shows a bulb shape formed using HI-E (2%).

Fig. 14.Verification of compaction effects in a soil chamber.

Fig. 15.Bulbshape formed after testing HI-E (2%).

 

Conclusion

The preparatory and main tests were performed to assess the suitability of expansive admixtures. The samples were tested with regard to expansive compaction in order to develop a packer that can effectively stop water and reinforce disturbed ground in reservoir grouting. These effects would be achieved after series of compaction and expansion with an EC packer. The following conclusions were reached.