Строительство и архитектура / 3.Современные технологии строительства, реконструкции и реставрации.

D. Egn., Prof. Golovko S.I., graduate Shekhorkina N.E.

State Higher Educational Establishment «Prydniprovs’ka State Academy of Civil Engineering and Architecture», Dnipropetrovsk, Ukraine

Injectability analysis of cement grout with different water-cement ratio in fine sand

Abstract. Soil stabilization has become one of the useful solutions to treat the soft soils to achieve the required engineering properties and specification so that structures can be placed safety without undergoing large settlements. Numerous of grouting materials are available in this field now. Cement is the most popular grouting material where the strength improvement of the formation materials is the major concern. Fine sand is known to be not suitable for the application of cement based grouting. The efficiency of grouting mainly depends upon the penetration of cement grout through the pores of sand. Study of the grout injectability with different water-cement ratio in fine sand was carried out in the present research work. The results clearly indicated that water-cement ratio of grout has influence only on mechanical characteristics of sand after strengthening but practically not on the injection radius.

Key words: grouting, grouting setup, cement grout, water-cement ratio, fine sand, injection radius, void ratio.

Introduction. Grouting for ground engineering is a process of filling the voids, fissures or cavities existing in the soil to improve water-tightness or mechanical characteristics by the grouting material. The use of grouting has become more popular in the recent years due to rapid development of sub-surface infrastructure, underground facilities and underground space for commercial and civil defense uses and the need in ground control during construction.

Grouting can be used to improve the condition of site against possible construction problems, such as: to reduce permeability of soil for minimizing seepage effect, to strengthen soils for improving its load carrying capacity, excavation stability and resistance against liquefaction effect, to improve stability of existing structures and to adjust profile of distorted structures, to stabilize ground for facilitating tunneling or shaft excavation, to form a barrier or cutoff the water or contaminant flow in the ground.

Three types of grouting materials are generally recognized: suspension-type grouts, emulsion-type grouts and solution-type grouts [4, 5]. The suspension-type grouts include clay, cement and lime, while the emulsion-type grouts include bitumen and the solution-type grouts include a wide variety of chemicals. The type of grout material involved in the present study belongs to the suspension type of grout. Suspension is defined as small particles of solids which are distributed in a liquid dispersion medium, e.g. cement in water, and having a Bingham’s fluid characteristics.

In accordance with theoretical investigations [2] it was established that fine to medium sand cannot be strengthen by cement based permeation grouting in view of its small pore size and low permeability to water. But Cambefor A. found that sand ground is suitable for cement fracturing grouting [2]. This fact was confirmed by numerous practical researches made by Golovko S.I. [1]. He investigated the process of strengthening the sand by high-pressure cementation.

Although it is a well known fact that properties of grout have great influence on injection results. Even today grouting operations are based on thumb rules and existing practices rather than design principles and well defined procedures substantiated by research data.

Aim of research. In this paper an attempt is made to study the injectability of cement grout with different water-cement ratio in fine sand.

Results and discussions. Ordinary Portland Cement the properties of which are shown in Table 1 was used for the present study. The sand used for the present study was collected from the sand pit near the Dnipropetrovsk. The sand was sieved through a set of sieves and the fraction between 0.1 and 1 mm (fine sand) was used for the experiments. The grain sizes of this sand are shown in Table 2.

The grouting efficiency can be estimated by determination the injection radius and the volume of the hardened grouted samples.

In the present research grouting tests were conducted under vertical flow model where grout was injected vertically downward through sandy media in a cylindrical tank with uniform cross-sectional area under constant injection pressure for measurement of flow volume.

Table 1

Cement Properties

Sl. No.	Property	Characteristic value
1.	Standard consistency	27.5%
2.	Initial setting time	131 mts
3.	Final setting time	287 mts
4.	Specific gravity	3.14
5.	Specific surface (blane’s)	298500 mm^2/g
6.	Compressive strength 7 days	24.53MPa

Table 2

Sand Grain size distribution

Characteristic value	Sieve analysis				Results of grain size distribution
	Ground fraction, mm
	from 1 to 0,5	from 0,5 to 0,25	from 0,25 to 0,1	less then 0,1
Weight of ground sample, g	860,6				fine sand
Weight of ground fraction, g	7,32	142,14	687,48	23,66
Fraction loading, %	0,85	16,52	79,88	2,75

The grouting setup consists of a grout chamber, membrane pump with pressure-gauge, cylindrical ground tank, grouting nozzle and high-pressure hoses. General view of grouting setup is shown in fig. 1.

The cylindrical ground tank of 500 mm in high and 500 mm in diameter had a lower and an upper clamp covers. Dimensions of ground tank and grouting nozzle were determined according to the similarity theory and dimensional analysis [3]. Table 3 shows values of injection process parameters in nature and in model where the scale parameter (λ) of 0.2.

Fig. 1. General view of grouting setup: 1 – grout chamber; 2 – membrane pump; 3 – ground tank; 4, 5 – high-pressure hoses; 6, 9 – stopcock; 7 – pressure-gauge; 8 – grouting nozzle;

10 – sand bed; 11 – perfectly elastic material; 12 – upper clamp cover.

Table 3

Parameters of injection process

Parameters of cementation	Value in nature	Value in model (λ=0.2)
Diameter of grouting nozzle d, m	0.093…0.127	0.02…0.025
Pressure of injection P, MPa	0.5…1.5	0.22…0.67
Radius of injection r, m	0.78…1.5	0.11…0.24

Sand bed was prepared at the loosest unit weight of 13.4 kN/m³ and the initial void ratio (e_max) of 0.98. The layer of perfectly elastic material was situated between the sand daylight and the upper clamp covers and designed the stresses from the dead weight of sand in natural conditions. If the sand average unit weight (γ) of 15 kN/m³ the stresses from the sand dead weight (σ_zg) are 45 kPa at the injection deep of 3 m. In accordance with this fact and compressive test the level of perfectly elastic material must be higher than the wall of ground tank of 8 mm for modeling the natural conditions. Grouting nozzle was situated in the central part of ground tank. There are perforations in the middle of grouting nozzle for the flat-radial filtration of solution.

The grout was suspension-type and consisted of cement and water. Grout was prepared at water/cement ratio (W/C) of 0.5 and 1.0 and agitated well to get uniform grout solution which was poured into the grout chamber. In order to reduce the chances of the grout segregation, an agitator was provided in the grout chamber. Grout volume for injection is 7 liters. Grout was pumped under a uniform pressure of 4 atm into the prepared sand bed. During the process of cementation spill water was released from the solution because of injection pressure. There is an additional damping and therefore compaction of sand bed. The grouted samples were kept in the ground tank during 3 days for curing. General views of sand bed after cementation are presented in fig. 2. Typical photographs of grouted sample are shown in fig. 3. Characteristics of grouted samples are shown in table 4.

a)

b)

Fig. 2. General view of sand bed after cementation: a – W/C=0.5; b – W/C=1.0;

1 – damping zone; 2 – cement stone.

a)

b)

Fig. 3. Typical photographs of grouted samples: a – W/C=0.5; b – W/C=1.0;

1 – cement stone; 2 – grouting nozzle.

Table 4

Characteristics of grouted samples

Characteristic value	Grouted samples
	W/C=0.5	W/C=1.0
Diameter, mm	150	120
Length, mm	270	310
Density, g/cm^3	2.064	2.191
Mass, g	4150	3685
Volume, cm^3	2010.66	1681.9
Compressive strength, MPa 3 days	35.61	36.34

During injection there is a drilling grout loss of 3 liters in the grouting setup. Therefore only 4 liters of grout were injected in sand bed. According to the elementary mathematical analysis water absorbing is 2 liters for grout with W/C=0.5 and 2.32 liters for grout with W/C=1.0.

It can be seen from the table 4 that application of grout with W/C=0.5 is more effective. Such grout causes the bigger injection radius and therefore indicates better flow of the grout in the lateral direction.

Samples of ground from different depths were cut from the grouted mass for the determination of soil dampness and consistency. Table 5 shows the variation of sand bed properties with injection depths of 100, 200 and 400 mm from the top of the grouted bed.

Table 5

Characteristics of grouted sand bed

Depth of injection, mm	Grouted sand bed
	W/C=0.5				W/C=1.0
	ρ, g/cm^3	ρd, g/cm^3	W, %	e	ρ, g/cm^3	ρd, g/cm^3	W, %	e
100	1.548	1.458	6.2	0.82	1.681	1.594	5.5	0.66
200	1.598	1.501	6.5	0.76	1.651	1.542	7.1	0.72
400	1.597	1.531	4.3	0.73	1.59	1.513	5.1	0.75

There are better properties of sand bed for injection of grout with W/C=1.0 because it has higher water content. But lesser values of consistency and void ratio of sand bed after injection of grout with W/C=0.5 is compensated by bigger injection radius.

Conclusions. The efficiency of grouting mainly depends upon the penetration of cement grout through the pores of sand. The following conclusions are drawn from the results of injection radius determination on samples from the grouted mass, in order to assess the quantum of grout lateral flow into the sand soil. Cement grout with W/C=0.5 is more effective in fine sand compared to grout with W/C=1.0, while considering the travel distance of the grout and the properties of soil at various points in the grouted mass.

Thus, the present study undoubtedly proves the importance of water-cement content selection in grout to achieve the largest injection radius and effective strengthening of soil.

References

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2. Камбефор А. Инъекция грунтов. Принципы и методы / А. Камбефор; [пер. с фр. Р.В.Казаковой, В.Б.Хейфица]. – М.: «Энергия», 1971. – 333 с.

3. Седов Л.И. Методы подобия и размерности в механике / Л.И. Седов – М.: Наука, 1977. – 440 с.

4. Beker W.H., Huck P.J. & Walter M.I. Design and control of chemical grouting. Construction control / Beker W.H., Huck P.J. & Walter M.I. // – Washington: DC, 1982. ‑ Vol.1. – 320 p.

5. Mitchell J.K. Soil improvement/ J.K. Mitchell // State of the Art Report. ‑ Stockholm: Sweden, 1981. – P 509-565.