J. Cent. South Univ. (2019) 26: 1863−1873
DOI: doi/10.1007/s11771-019-4140-5
A new clay-cement composite grouting material for
tunnelling in underwater karst area
ZHANG Cong(张聪), YANG Jun-sheng(阳军生), FU Jin-yang(傅金阳),
OU Xue-feng(欧雪峰), XIE Yi-peng(谢亦朋), DAI Yong(戴勇), LEI Jin-shan(雷金山) School of Civil Engineering, Central South University, Changsha 410075, China © Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract:A new clay-cement composite grouting material (CCGM) for tunnelling in underwater karst a
rea was developed through the excellent synergistic interactions among cement, clay, meta-aluminate and lignin. The probable formation mechanism of the material was propod bad on a ries of experimental tests. The results show that with an optimal mass ratio (2:1:1:0.024) for water, cement, clay and additives, the obtained CCGM displayed an excellent grouting performance for karst in an underwater condition. Compared with neat cement grouts and clay-cement grouts, CCGM has faster gel time, lower bleeding rate and bulk shrinkage rate, greater initial viscosity, and a strong resistance to water dispersion. A successful engineering application indicates that CCGM not only fulfils a better grouting performance for karst in underwater conditions but also reduces the engineering cost and environmental pollution.
Key words: tunnel; karst; underwater; new grouting material; clay-cement composite
Cite this article as:ZHANG Cong, YANG Jun-sheng, FU Jin-yang, OU Xue-feng, XIE Yi-peng, DAI Yong, LEI Jin-shan. A new clay-cement composite grouting material for tunnelling in underwater karst area [J]. Journal of Central South University, 2019, 26(7): 1863−1873. DOI: doi/10.1007/s11771-019-4140-5.
1 Introduction
The rapid development of transportation infrastructures in China requires more and more tunnels to be constructed in karst regions [1−6]. Rearch shows that 50% of domestic underground engineering and over 40% of long tunnels are constructed in karst regions [7]. Karst is recognized as a complex hydrology and geology system, and is often accompanied with caves, faults and fractures, which results in unpredictable adver effects for tunnelling in this area, such as collap, ground fissures, and water inrush [8, 9]. Over the past decade, many disastrous events associated with karsts in tunnels have been reported becau of the geological complexity of karst [10−12]. Therefore, the crux of tunnel engineering construction in karst areas lies in how to avoid and address geological problems that may occur during the construction process. Grouting is one of the most effective and common ways to stabilize karst caves [13−15], in which grout is injected into cavities, voids and fractures to improve their mechanical and hydraulic properties, particularly in reducing permeability and deformability, and increasing strength and modulus of the karst ground formations [16−18].
Engineers have developed many grouting materials to deal with karst [19−21]. Among tho materials for karst grouting, cement slurry is one of the most widely ud materials becau of its high intensity, inexpensiveness and availability of the raw material source. However, since cement slurry is a particulate material, there are still some
Foundation item: Project(51608539) supported by the National Natural Science Foundation of China; Projects(2016M592451, 2017T100610) supported by the China Postdoctoral Science Foundation
Received date: 2018-05-16; Accepted date: 2018-11-07
Corresponding author:FU Jin-yang, PhD, Associate Professor; Tel: +86-188********; E-mail: ; ORCID: 0000- 0002-0632-1222
J. Cent. South Univ. (2019) 26: 1863−1873 1864
difficult problems such as long tting time, poor stability and easy shrinkage of the concretion body. Later, cement grouts were replaced by clay-cement grouts. Clay-cement grouts are widely ud in karst grouting becau of their good performance. Compared with cement grouts, clay-cement grouts have advantages such as good stability, low permeability and low cost, but the materials are easily gregated by water in underwater karst. The problems make cement grouts and clay-cement grouts unreliable to fill karst in underwater conditions. Although some engineers have developed some chemical materials to attempt to solve this problem, the materials are extremely expensive and not environmentally friendly. Thus, it is necessary to arch for a new grouting material with reliable performance to solve the karst problems in underwater conditions.
The paper prents a clay-cement composite grouting material (CCGM) for karst in underwater conditions. At first, the grouting performance and mechanical performance of CCGM for karst in underwater conditions are evaluated by a ries of tests, and the formation mechanism of CCGM is propod. A field grouting application is conducted to verify the superior performances of CCGM ud for engineering grouting in karst area in an underwater condition.
2 Materials and methods
2.1 Raw materials
In this study, the cement was Nanfang 42.5 ordinary Portland cement with a specific density of 3.17 g/cm3 and a 28-d compressive strength of 45.5 MPa. The grain size distribution of the cement is listed in Table 1.
The clay was obtained from excavations at a depth of 2−8 m in the material yard of Hunan Province, China. The basics in situ characteristics were measured at Central South University and all tests were conducted according to the Chine standard GB/T 50123-1999 [22]. The mineral components were measured using the SIMENS D500 X-ray diffractometer from Bruker, Switzerland. The particle size analysis was measured using OMEC LS-601 from Zhuhai, China. As results show that the clay i
s a kind of acidic clay of medium plasticity, and its properties make it suitable for grouting with cement. The grain size distribution is listed in Table 1 while the test results of its properties are listed in Table 2.
The modifier was made in-hou and contained meta-aluminate and lignin. Meta- aluminate is a powder of alkaline white chemical substance which can significantly accelerate the hydration reaction of cement and shorten the tting time of the grout. Lignin is a phenolic polymer that can be ud as a water-reducing agent to improve the mobility of grout.
2.2 Device of grouting experiment
楼月汤蓉
The physical testing device was designed and fabricated as shown in Figure 1, which was compod of a pressure system and a karst system. The pressure system was compod of a gas cylinder, a constant-pressure valve, and a trachea. The gas cylinder was approximately 12 MPa; after depressurization through the constant-pressure valve and trachea, an experimental design pressure of 0−2 MPa was output to the grout storage system. The schematic layout of the karst cavity system is prented in Figure 1. It compris a steel cylinder, which is 5 cm in diameter and 20 cm in height; the upper and lower sides are installed with a flange and fixed by bolts, which make
s the installation and removal more convenient. A gas hole with a diameter of 1.5 cm was sited on the surface of upper flange, and a pressure gauge was fitted to the surface to record the pressure during grouting. Some drain holes with a diameter of 0.2 cm were drilled on the bottom surface of the lower flange, and a circular groove was t on the bottom surface to install a permeable stone and filter paper. This
Table 1 Cement and clay grain size distribution
Material Parameter Value
Cement Particle size/mm 0−1.0 1.0−4.8 4.8−10.0 10.0−20.0 20.0−35.0 35.0−40.0 Content/% 1.26 10.24 24.80 11.10 16.54 18.15
缆车英文Clay Particle size/mm 0−1.1 1.1−4.1 4.1−10.3 10.3−21.6 21.6−37.7 37.7−40.0 Content/% 20.28 24.59 31.56 16.88 6.44 0.25
J. Cent. South Univ. (2019) 26: 1863−1873 1865
Table 2 In situ properties of silty clay
Parameter Value吴字五行属什么的
Specific gravity 2.68
Water content/% 25.3
Liquid limit/% 42.3
Plastic limit/% 22.5
Liquid index/% 0.34
Plasticity index/% 18.9
Void ratio 1.12
pH 5.75
w(Halloysite)/% 74.96
w(Quartz)/% 16.67
咖啡机原理w(Chlorite)/% 5.17
有关黄河的成语
Bal./% 3.20
Figure 1 Schematic layout of model test experimental tup enables one to inject grouts of different grouting parameters into a karst.
2.3 Testing program爱与教育
To prepare CCGM, the clay (smaller than the size of 75 μm) was soaked in water for 12 h and stirred by a rotating mixer at 1000 r/min for 15 min, and the specific gravity of the slurry was adjusted. Afterwards, appropriate amounts of cement and clay slurry were thoroughly mixed by a rotating mixer at 1000 r/min for 5 min to form stable clay-cement grouts. Finally, the appropriate amounts of modifier was added to the clay-cement grouts and stirred for 5 min using a rotating mixer (1000 r/min) to form the CCGM. To study the properties of the CCGM for karst in an underwater condition, we placed the fresh CCGM into the karst cavity until saturation of the karst cavity. In addition, a cons
tant-pressure injection to karst cavities was applied for 15 min. At the end, the fresh specimens were retrieved for the performance test. All the process were performed under a standard temperature ((25±2) °C).
The purpo of the experiments was to verify the performance of the CCGM for karst in an underwater condition. For comparison, the cement grouts and clay-cement grouts were also analyzed. According to previous grouting engineering experience, a relatively small pressure and a low water-cement ratio are normally ud to fill the karst cavity. Therefore, the grouting pressure of 1 MPa and water-cement ratio of 1:1 were ud in this experiment. The clay content is commonly determined bad on veral factors. In this study, the clay content of 50% was lected considering the water cement ratio and grouting pressure. Detailed information of the grouting material and grouting parameters is provided in Table 3. The gel time, bleeding water, bulk shrinkage rate and retention rate were altered by changing the amount of modifier, and the testing scheme is shown in Table 4.
Table 3 Detailed ratio information of grouting material with grouting pressure of 1 MPa
Material type
度符号
m(Water):m(Clay):
m(Cement):m(Modifier) Cement grout 1:0:1:0
Clay-cement grout 1:0.5:0.5:0
CCGM
1:0.5:0.5:0.012(meta-aluminate
0.01, lignin content 0.002) Table 4Test scheme for different modifiers with m(Water): m(Clay): m(Cement)=1:0.5:0.5
No. Meta-aluminate Lignin content
A1 0.005
A2 0.01 0.015
A3 0.015
B1 0.001
B2 0.015 0.002
B3 0.003
2.4 Testing methods
According to the testing program and mix proportion in Table 3, the fresh specimens were retrieved for the performance test. The gel time of the grouts was measured using the inverted-cup method. In this work, the ratio of the volume of bleeding water from the grouts in the grouting process (V0) to the initial volume of grouts (V) is called the bleeding rate (V0/V). The bulk shrinkage
J. Cent. South Univ. (2019) 26: 1863−1873 1866
rate is defined as the final value of (V1−V2)/V1, where V2is the volume of specimens after they have solidified in an underwater condition, and V1 is the initial volume of the specimens. All the process in this work were performed under a standard temperature ((25±2) °C, 95% humidity).
To verify the water-resistant dispersion of the material, experiments were conducted at a low flow velocity (0.2 m/s) in a transparent flume of 4 m length, 0.3 m width and 0.3 m height (Figure 2). When testing, the fresh specimens (mass, m) were removed to place in the transparent flume and th
e residual specimens (mass, m0) were weighed after scouring for 5 min. The retention rate is defined as the final value of m0/m [23].
Figure 2 Water-resistant dispersion test device
The rheological flow curves were obtained using the R/S Plus rheometer from Brookfield Ltd., USA. For the rheological model test, the shear rate was incread from 0 to 60 s−1over a period of 2 min, and the test result was analyzed using the software Rheo3000.
When we tested the mechanical properties of the grouts, the fresh specimens were kept in the karst cavity for 12 h until the grout developed a suitable strength. Then, the specimens were demolded, and a soil cutter was ud to trim the specimens into 100-mm-high samples with 50 mm diameter (Figure 3(a)). The samples were stored underwater ((25±2) °C) until the testing ages (1, 3, 7 and 28 d). The unconfined compressive strength of the specimens was tested using the STYE-3000C universal testing machine, and the compression speed during the test was controlled at 5 mm/min (Figure 3(b)).
After 28 d of curing, a layer of polyurethane with a thickness of approximately 1−2 mm was uniformly coated on the surface of the cylindrical specimens, and the specimens were presd into the karst cavity system. Then, we injected water into the karst cavity system with a constant pressure. We recorded the change in water level in the cylinder in a certain period, and the permeability coefficient was calculated using the method of constant head [24].
The microstructure of the grouting materials was examined using a HELIOS Nano Lab 600i field-emission scanning electron microscope (FEI Ltd, Hillsboro, USA) operating at 25 kV.
3 Results of CCGM performance
3.1 Gel time
The gel time is an important parameter to determine the pumping time and diffusion radius of grouting. In addition, a shorter gel time of grouts is beneficial for solidifying in underwater conditions. The gel time test results of the grouts are summarized in Table 5. Table 5 shows that the gel time of the CCGM can be controlled and it has a much shorter gel time than the cement grouts and
仙客来有毒吗
Figure 3 Photos of specimens stored (a), compression testing machine (b) and samples destruction (c)
Table 5 Gel time of grouts (min)
Cement grout Clay-cement grout CCGM A1 A2 A3 B1 B2 B3 472 551 30 39 28 19 18 20 22
J. Cent. South Univ. (2019) 26: 1863−1873 1867 clay-cement grouts, which implies that CCGM can
stably fill the karst in underwater conditions. From
A1 to A3, as the meta-aluminate content increas,
the gel time of CCGM decreas almost linearly.
From B1 to B3, as the lignin content increas, the
gel time of CCGM incread slightly.
The above result shows that the gel time of
CCGM is mainly affected by the meta-aluminate,
which is an efficient accelerator that can
significantly accelerate the hydration reaction of
cement. It is worth noting that CCGM is no longer
suitable for pumping when the meta-aluminate
content is excessive.
3.2 Bleeding rate and bulk shrinkage rate
The stability of grouts can asss by the
bleeding rate. A lower bleeding rate means the
grouts is more stable. Table 6 shows the bleeding
rate of grouts in the tests, where the addition of clay
and modifier substantially decread the bleeding
rate. For example, CCGM and clay-cement grouts
had 82.1% and 37.5% reduction in bleeding rate,
respectively, compared with the cement grouts.
From A1 to A3, as the meta-aluminate content
increas, the bleeding rate of CCGM tends to
decrea. From B1 to B3, as the lignin content
increas, the bleeding rate of CCGM increas by
28.6%. The bleeding rate of CCGM is significantly
raid by increasing the lignin content. Thus, clay
can improve the stability of clay-cement grouts, and
the stability can be further improved by adding
meta-aluminate.
Table 6 also shows the bulk shrinkage rate of
grouts in the tests. The bleeding rate is consistent
with the law of the bulk shrinkage rate. It was
remarkable that the bulk shrinkage rate of CCGM
Table 6 Bleeding rate and bulk shrinkage rate of grouts
Sample Bleeding
rate/%
Bulk shrinkage
rate/%
Cement grout 56 3 Clay-cement grout 35 1 CCGM 10 0
A1 9 0
A2 7 0
A3 4 0
B1 7 0
B2 8 0
B3 9 0 was 0, which is significantly less than that of other grouts. The bleeding rate and bulk shrinkage rate are important in grouting engineering. Lower bleeding rate and bulk shrinkage rate indicate better grouting effectiveness. In other words, CCGM is better than cement grouts and clay-cement grouts for grouting karst in underwater conditions.
3.3 Rheological properties
The rheological model of grouts can be discusd bad on the flow curves drawn by different shear rate versus shear stress. The graph of shear stress versus shear strain rate for cement grouts, clay-cement grouts and CCGM is shown in Figure 4.
Figure 4 Flow curves of grouts
The relationship between the shear stress and the shear strain rate was examined using Bingham model for all grouts. However, CCGM had a higher initial shear yield stress than cement grouts and clay-cement grouts. Therefore, CCGM can hardly be parated by water when grouting in karst under groundwater, and the diffusion range of CCGM can be controlled.
3.4 Retention rates
The water-resistant dispersion of the grouts significantly affects the grouting effect in karst under groundwater. The retention rate is an important index to asss the ability of the water-resistant dispersion of the grouts: a higher retention rate implies that the grout is more conducive to grouting in karst under groundwater. The results of the water-resistant dispersion experiments are shown in Table 7. The retention rates of cement grouts, clay-cement grouts and
