Experimental Study on Grouting Foundation ... - Science Direct

Available online at www.sciencedirect.com

ScienceDirect Procedia Engineering 166 (2016) 317 – 325

2nd International Symposium on Submerged Floating Tunnels and Underwater Tunnel Structures

Experimental study on grouting foundation treatment of immersed tunnel Ke Lia, b, c* b

a National Engineering Laboratory for Highway Tunnel Construction Technology, Chongqing 400067, China Key Laboratory of Tunnel Construction and Maintenance Technology, Ministry of Transport, PRC, Chongqing 400067ˈChina c China Merchants Chongqing Communications Research & Design Institute Co., Ltd., Chongqing 400067, China

Abstract Grouting method is one of foundation treatment methods of immersed tube tunnel, it has good effects on improvement of foundation strength and control of settlement deformation, but there is no mature method yet available for the determination of key technical parameters of foundation treatment by pressure grouting method and for the inspection and assessment of effects of treatment by pressure grouting method of immersed tube tunnel. In response to this problem, through model test, the influences of gradient, roughness, etc. of cushion layer of immersed tube tunnel on the effects of foundation treatment by pressure grouting method are researched and the method for inspection of effects of foundation treatment by pressure grouting method of immersed tube tunnel is proposed. The results show that: the changes of parameters of cushion layer regularly affect the effects of grouting by pressure grouting method and shall be considered in the design; the method combining ground penetrating radar and surface wave detection can effectively inspect the effects of foundation treatment. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-reviewunder under responsibility of organizing the organizing committee of SUFTUS-2016. Peer-review responsibility of the committee of SUFTUS-2016 Keywords: Immersed tube tunnel; foundation treatment; pressure grouting method; test research

1. Introduction Foundation treatment has always been the key technical problem of construction of immersed tube tunnel [1, 2]. The anti-floating coefficient of immersed tube tunnel is only 1. 1~ 1. 2, if the foundation treatment is proper, no

* Corresponding author. Tel.: +86-23-62653183; fax: +86-23-62653128. E-mail address: [email protected]

1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SUFTUS-2016

doi:10.1016/j.proeng.2016.11.554

318

Ke Li / Procedia Engineering 166 (2016) 317 – 325

settlement problem will occur generally. Therefore, the foundation treatment of immersed tube tunnel is generally to flatten the trench bottom in order to avoid the local damage to tube section caused by uneven force borne by the foundation or the crack arising from the uneven settlement, but not to improve the bearing capacity of foundation, which is totally different from the buildings on ground. United States had used the pre-bedding methods for laying the sand-gravel cushion layer for foundation treatment, however, as these methods have many disadvantages, they have been obsoleted gradually and replaced by post-filling methods mainly including sand blasting method, sand replacement method, pressure sand injection method, bag replacement method, pressure grouting method, pressure concrete injection method, etc., i.e. immerse the tube section on the temporary support block and lay the cushion layer of foundation between the foundation and tube section ground [3]. In Europe, sand blasting method and pressure sand injection method are widely used[4, 5], pressure sand injection method has also been used in Guangzhou Pearl River tunnel and Shanghai outer ring road tunnel in China successively; In Japan, pressure grouting method was used for foundation treatment for the first time in the underwater road tunnel of the first shipping lane of Tokyo Port (Tokyo Port Tunnel) and solved the liquefaction problem of foundation in seismic area, in 1980, pressure grouting method was used again for the construction in Tokyo Dainikoro tunnel; pressure grouting method has also been used in Ningbo Yoagjiang River tunnel and Tianjin Haihe River immersed tube tunnel in China. Pressure grouting method has been obtained from the improvement of bag replacement method, i.e. after the foundation trench is excavated, the gravel cushion layer is laid on the bottom of foundation trench, the bottom plate is embedded with pressure grouting hole tube section with check valve and immersed on the temporary support; then, the mixed mortar is injected by pressure into the bottom voids of tube section from the inside of tube section by using the grouting pump; pressure grouting method is characterized by no interference with the shipping lane, no liquefaction after grout solidification, etc. and is applicable to the conditions with potential earthquakes or other dynamic load actions, but is has relatively high requirements on the strength, workability, fluidity, bleeding, etc. of mortar and requires real-time inspection of the diffusion status of grout during the pressure grouting and the final density of filling of grout. This paper researches the diffusion process of grout during the foundation treatment by pressure grouting method under different gradient and different particle-size cushion layer material conditions through model test and inspects the foundation treatment effects by using ground penetrating radar, ultrasonic wave and surface wave method. 2. Introduction to Test 2.1. Test Devices The water tank is made by welding of steel channels and steel sheets and is 3m in length, 1.5m in width and 1m in height, as shown in Figure 1. The immersed tube section is 2.6m in length, 1m in width and 0.8m in height, the bottom plate model of immersed tube is made by bonding of organic glass board with 2cm thickness, see Figure 2 for the grouting holes and arrangement. The adjustments of flatness of gravel surface are contemplated to be made manually, the adjustments of gradients of water tank are controlled by using the jack placed at one end in order to simulate the different gradients of longitudinal slope, the water filling and discharging are controlled by using the inlet and outlet water pipes connected by welding on the openings on water tank wall. When the water tank is tilted, the water in organic glass chamber will not flow into other chamber, in order to keep the ballast even. As the scale of model is small, the sand used for the preparation of mortar is contemplated to be fine sand; for the cushion layer of base, three types of materials with different particle sizes, i.e. coarse sand with particle size of 2mm, rock flour with particle size of 5mm and gravel with particle size of 10mm are used to simulate different roughness degrees. The power grouting devices are prepared as follows: One set of grouting pump: micro cement grouting pump, with grouting pressure ˘ 2MPa adjustable, flow0.4m3/h , motor power of 0.75kW. Grouting pipe: PVC transparent steel wire pipe with diameter of 30mm. Pressure gage: with measuring range of 25kPa

319

Ke Li / Procedia Engineering 166 (2016) 317 – 325 Pressure gage

30mm PVC steel wire pipe

Stop valve

25mm UPVC pipe 30mm PVC steel wire pipe

25mm UPVC pipe

Pressure gage

Stop valve

Hopper

Water tank

Organic glass model

Reducer adjusting knob

Grouting pump

Fig. 1. Schematic diagram of test model

Single hole

Fig. 2. Arrangement diagram of grouting holes and observation lines of immersed tube model

2.2. Test Procedure (1) Smear and lay the cushion layer on the bottom of water tank (use coarse sand with particle size of 2mm, rock flour with particle size of 5mm and gravel with particle size of 10mm to simulate three types of cushion layer roughness degrees respectively according to the requirements of conditions). (2) Fill the test basin with water to a preset height, fill the organic glass box with water to 20cm, fill the iron box with water to 37.9cm. (3) Jack the box up with the jack on one side of the bottom of water tank, in order to allow the test water tank and test platform to achieve the required gradient of longitudinal slope (three types of conditions, i.e. 0°, 2° and 5° are set for the gradient of longitudinal slope). The grouting hole on the side near the bottom of slope is hole A, the grouting hole on the side near the top of slope is hole C, the middle hole is hole B. (4) Prepare the grout according to the mix ratio of cement: coal fly ash: sand: water: bentonite =189: 264.6: 1134: 302: 37.8, with consistency of 121mm, the consistency characteristics are the same with those of the mortar used for the in situ grouting test. The volume of grout for each time of grouting is about 0.1m3, two large iron buckets are used as containers, and mixer is used for mixing, in order to ensure the continuous supply of grout during the test.

320


(5) Grouting pressure control: the revolution speed of grouting pump is adjusted to minimum, the pipe valve is fully open, the flow stability of grout flow is confirmed by external pressure test, the pump is stopped and connected to the grouting pipe after the pressure has no abnormal fluctuation. (6) Start the grouting pump to begin the pressure grouting, single-hole grouting of hole C on the side near the bottom of slope is carried out first. Observe the expansion of grout disk on four measuring lines, i.e. C1, C3, C5 and C7, at the same time, observe and record the time and the pressure indicated on pressure gage. When the bottom edge on the side at the bottom of slope is fully filled with grout, stop the grouting and record the final grout expansion radii in all the measuring line directions. (7) After the grouting of hole C is completed, carry out the pressure grouting of hole A and hole B synchronously, observe the expansion of grout on the measuring lines A1, A3, A5 and A7 and the measuring lines B1, B3, B5 and B7, at the same time, observe and record the time and the pressure indicated on pressure gage. When the grout of hole B comes into contact with the grout of hole C that have been grouted, record the expansion radii, time and hole B grouting pressure; when the hole B grout and hole A grout come into contact with each other, record the expansion radii, time and the pressures of both holes. When the bottom of box is fully grouted, stop the grouting and record the final time. (8) The grouting is finished, lift the organic glass box, clean the bottom, prepare for the next test. 3. Analysis of Test Results 3.1. Influences of Gradient The test was carried out under the setting grouting pressure conditions and obtained different gradients of bottom plate (0°, 2°, 5°) and changes of grout diffusion range with time under 2mm particle-size cushion layer conditions, as shown in Figure 3, Figure 4 and Figure 5. 50

50

30 20

C1 C3 C5 C7

10 0

0

100 200 300 400 500 600 700 800 900

Distance (cm)

40 Distance(cm)

Particle size of cushion Layer: 2mm 40 o Gradient: 0

Particle size of cushion Layer: 2mm o Gradient:0

30 20 A1 A5 B1 B5

10 0

0

500 1000 1500 2000 2500 3000 3500 4000

Time(s)

Time(s)

(a)

A3 A7 B3 B7

(b)

Fig. 3. Grout diffusion distance curves at 2mm particle-size cushion layer and 0° longitudinal slopeιǣ (a) Single-hole grouting of hole c; (b) Double-hole grouting of hole A and hole B.

321

50

50

40

40 Distance (cm)

Distance(cm)


30 C1 C3 C5 C7

20 10 0

0

100

200

300

400

500

600

700

30 20

A1 A5 B1 B5

10 0

800

0

A3 A7 B3 B7

100 200 300 400 500 600 700 800 900

Time(s)

Time (s)

(a)

(b)

Fig. 4. Grout diffusion distance curves at 2mm particle-size cushion layer and 2° longitudinal slope: (a) Single-hole grouting of hole c; (b) Double-hole grouting of hole A and hole B. 50

55

A1 A3 A5 A7 B1 B3 B5 B7

50

40

45

Distance (cm)

Distance (cm)

40 35 30 25 20

C1 C3 C5 C7

15 10 5 0

0

100

200

300

400

500

600

20 10

700

0

0

400

800

1200

1600

2000

Time (s)

Time (s)

(a)

30

(b)

Fig. 5. Grout diffusion distance curves at 2mm particle-size cushion layer and 5° longitudinal slope: (a) Single-hole grouting of hole c; (b) Double-hole grouting of hole A and Hole B.

For single-hole grouting, when the gradient was 0°, the difference between diffusion speeds of grout in various directions was not large. When there was slope, the diffusion of grout obviously inclined to the side of slope bottom. In the directions of C1 and C5 measuring lines, the grout flowed along the measuring lines and expanded towards the side of slope bottom in the early period of grouting; in the middle and later periods of grouting, when the filling volume in slope bottom direction was relatively large and the expansion resistance was increased, the grout continued to expand in C1 and C5 directions. On the measuring line C7 in slope bottom direction, the diffusion speed of grout was larger than the diffusion speed of grout on C 3 in slope top direction. For double-hole grouting, when the gradient is 0°, the grout diffusion speeds of hole A and hole B were basically the same. When the gradient was 2°, the grout diffusion speed in slope bottom direction was larger than the grout diffusion speed in slope top direction. When the gradient reached 5°, the grout flow speed in downslope direction increased dramatically, by contrast, the flow speed in upslope direction was very small.

322


3.2. Influences of Roughness

50

50

40

40

30 20

Average of C,2mm Average of C,5mm Average of C,10mm Polynomial Fit of C,2mm Polynomial Fit of C,5mm Polynomial Fit of C,10mm

10 0 0

400

800

1200

1600

Distance (cm)

Distance(cm)

See Figure 6, Figure 7 for the comparison of diffusion speeds of grout disks on cushion layers with different roughness degrees under the conditions without longitudinal slopes.

30 20

Average of B,2mm Average of B,5mm Average of B,10mm Polynomial Fit of B,2mm Polynomial Fit of B,5mm Polynomial Fit of B,10mm

10 0 -500

0

Time(s)

500 1000 1500 2000 2500 3000 3500 Time (s)

(a)

(b)

Fig. 6. Comparison of grout diffusion speeds on cushion layers with different particle sizes: (a) Hole A; (b) Hole B. 50

Distance (cm)

40 30 20

Average of A,2mm Average of A,5mm Average of A,10mm Polynomial Fit of A,2mm Polynomial Fit of A,5mm Polynomial Fit of A,10mm

10 0 -500

0

500 1000 1500 2000 2500 3000 3500 4000 Time (s)

Fig. 7. Comparison of grout diffusion speeds of hole a on cushion layers with different particle sizes.

Under 0° longitudinal slope conditions, as seen from the statistical data of single-hole grouting of hole C, the grout diffusion speed on 10mm particle-size cushion layer was the fastest, the grout diffusion speed on 5mm particle-size cushion layer was the slowest. While as seen from the fitted curves of grout diffusion speeds of hole A and hole B, as the particle size of cushion layer material increased, the grout diffusion speed also increased, the grout diffusion speed was in negative correlation relationship with the particle size of cushion layer. As seen from the test situations, under the conditions with longitudinal slope, as the particle size of cushion layer material increased, the volume of grout needed to fill the bottom of test platform increased unidirectionally. Under the conditions without longitudinal slope, the influences of different particle-size cushion layers on the grouting volume had no obvious regularity. 3.3. Inspection of Grouting Effects The inspection of grouting effects was carried out on a large-scale model, the filling effects of pressure grouting were assessed comprehensively by the method combining ultrasonic wave, ground penetrating radar and surface wave detection. The inspection was divided into two steps: during the grouting and on the second day of

323


solidification after the end of grouting. The bottom plate was divided into three zones (zone A, zone B and zone C) according to the arrangement of grouting holes for the test, 8 measuring lines were arranged equidistantly in various divergence directions of grouting hole in each zone, each measuring line was subject to ground penetrating radar detection, A2, A7, B2, B7, C2 and C7 measuring lines were subject to surface wave testing and ultrasonic wave testing. See Figure 8 for the waveforms of B7 measuring line recorded by ground penetrating radar before and after the grouting. By comparing the waveform records of B7 measuring line in different stages, obvious radar responses of two types of media (concrete, underwater saturated soil) could be seen before the grouting; during the grouting, radar wave changes caused by underwater medium variations (grout flows) appeared obviously; after the grouting, another radar wave response appeared obviously between the two types of radar responses before the grouting, i.e. another medium (grouting layer) appeared.

Concre

Concrete Grout

Soil

Soil

(a)

(b)

Fig. 8. Ground penetrating radar results before and after the grouting of b7 measuring line: (a) Before the grouting; (b) After the grouting.

See Figure 9 for the surface wave inspection results before and after the grouting of B7 measuring line. The frequency spectrum changes of each measuring line can be seen from the frequency spectrum distribution diagram, it can be assumed that the low frequency component was medium water, the high frequency component was concrete or grout, the changes of high frequency zone can indicate the conversion process of grouting. Assuming that the component with the most frequency component was water medium, it can be seen that as the grouting process proceeded forward, the high frequency component of frequency began to appear, after the grouting was ended, high frequency domain, i.e. grouting layer appeared obviously.

324


(a)

(b)

(c)

Fig. 9. Surface wave results before and after the grouting of b7 measuring line: (a) B7ˉbefore the grouting; (b) B7ˉpartial grouting; (c) B7ˉ grouting finished (24 hours later).

See Figure 10 for the ultrasonic wave inspection results before and after the grouting of B7 measuring line. As seen from the diagram, the sonic time (speed) had relatively stable changes, good repeatability and uniform determination method and is a parameter that must be measured for the detection of defects. But the reactions of sonic time to defects are not sensitive enough. The reactions of amplitude to defects are sensitive, and relative comparison of the measured values of amplitude at the same measurement distance can be carried out. But the measured values of amplitude may be greatly influenced by the transducer and concrete surface coupling conditions. If the coupling conditions are good and consistent with each other, such as the coupling of water in hole, the amplitude parameter can be a quite good parameter for the judgment of defects; if the coupling conditions are poor and inconsistent, the amplitude parameter can only be a reference for the judgment of defects.

(a)

(b)

Fig. 10. Ultrasonic wave results before and after the grouting of b7 measuring line: (a) B7ˉpartial grouting; (b) B7ˉgrouting finished (24 hours later)

4. Conclusions Through the model test, the influences of gradient and roughness of cushion layer on the grouting process during the foundation treatment by pressure grouting method of immersed tube tunnel have been researched, and the grouting effects have been inspected by ground penetrating radar, ultrasonic wave and surface wave method, the results show that: (1) Under the conditions with longitudinal slope, the phenomenon of inclination of grout disk towards downslope direction was obvious, and the diffusion of grout disk was not even. It is recommended that during the


actual engineering construction, the hole in the lowest position in the construction area should be grouted first, in order to fill the bottom, then, the grouting should be carried out upwards along the slope successively, in order to avoid the loose filling defect caused by overly eccentric diffusion of grout disk. (2) Large particle-size cushion layer is helpful to accelerating the diffusion filling speed of grout disk, but at the same filling density, large particle-size cushion layer may cause the increase of the volume of the grouted mortar. When selecting the particle size of cushion layer during the design and construction, the decision shall be made in comprehensive consideration of diffusion speed, grouting volume, flattening difficulty of cushion layer and other factors. (3) Geological radar is a kind of fast and efficient technical means for real-time monitoring of grouting construction and inspection of construction effects, after the position of a defect is determined by geological radar, the inspection with higher precision can be carried out at this position by surface wave method. It is recommended that the method combining ground penetrating radar and surface wave detection should be adopted during the actual engineering construction, in order to fully control the grouting process and verify the effects after grouting. Acknowledgements This work has been supported by science and technology project of Ministry of Communications (2013318740050), National Natural Science Foundation of China (No. 41601574), Chongqing fundamental and advanced research program (cstc2014jcyjA30020, cstc2015jcyjBX0118), Chongqing application development program (cstc2013yykfB30005), Chongqing key scientific and technological project (cstc2012gg-yyjs30002). References [1] Shui YL. The Construction Technology Development of Immersed Tunnel. Applied Mechanics & Materials 2012; 204-208: 1385-1388. [2] Du CW, Wang XY. Key technology of design and construction on immersed tube tunnel. Engineering Science 2009; 11(07): 76-80. [3] Zheng A, Tan Z, Li Z. Simulation experiment of pumped sand on immersed tunnel. Engineering Sciences 2009; 11(7): 81-85. [4] Van T onger en Ir H. The foundation of immersed tunnels. Delta Tunnelling Symposium. Amsterdam: Nether lands, 1978; 48-57 [5] Rmhild C J, Rasmussen N S. Submerged structure supported on sand pumped underneath structure. Proceedings of the third Symposium on Strait Crossings. Alesund: Norway, 1994; 695-702.

325