The plate load test in the application of dynamic compaction test of subgrade bearing capacity

Civil Engineering and Technology June 2013, Volume 2, Issue 2, PP.34-39

The Plate Load Test in the Application of Dynamic Compaction Test of Subgrade Bearing Capacity Xichang Zhang#, Yuehong Su, Zhi Zhang Inner Mongolia University of Technology, College of Civil Engineering, Hohhot 010051, China #

Email: zxc312061652@126.com

Abstract This paper mainly introduces the foundation soil after dynamic compaction effect using the plate load test method to test the bearing capacity of foundation soil, based on the plate loading test of a new project in Inner Mongolia, using JYC static load test analysis system software to deal with test data. Also, this paper will discusses the test principle, test points of the plate load test, the determination of bearing capacity characteristic value, etc, and further analysis showing the applicability of the plate load test.

Keywords: Plate Load Test; Dynamic Compaction Method; P-S Curve; Characteristic Value of Bearing Capacity

1 INTRODUCTION Plate load test is an important method for the determination of in situ geotechnical foundation parameters. The method is closer to the foundation actual working condition and can more truly reflect the compressibility of soil under loading. Plate load test will evaluate, step by step, the foundation soil load on the bearing plate by measuring pressure and deformation characteristics of foundation soil in situ testing methods, thus determining bearing capacity of foundation soil. The quality of the dynamic compaction method in the construction will be evaluated with the method of plate load test.

This paper mainly describes dynamic compaction ground plate loading test[1], used in the process of detection method, to determine the allowable bearing capacity of dynamic consolidation foundation and their corresponding deformation parameters (settlement, modulus of deformation), as well as the dynamic compaction of foundation bearing capacity factors and data processing method, the principle of the plate load test, etc. The bearing capacity of foundation is evaluated by the plate load test.

2 PROJECT EXAMPLE 2.1 Test profile A new project in Inner Mongolia of dynamic consolidation foundation detection with the method of plate load test bearing capacity of foundation soil after dynamic compaction for the evaluation, first, determine the settlement under different load levels, according to the relationship of load and settlement and, then, assess the bearing capacity of foundation soil. One section of the new project measured data, using JYC static load test analysis system software to deal with test data, finally, gets a load - settlement curve (P -S curve).

2.2 Test device, principle and key points for operation 1) Test device This test method of equipment is made of the bearing plate, loading system, the reaction system and the settlement # CITATION: Xichang Zhang, Yuehong Su, Zhi Zhang. The Plate Load Test in the Application of Dynamic Compaction Test of Subgrade Bearing Capacity [J]. Ivy Publisher: Civil Engineering and Technology, June 2013, Volume 2, Issue 2, PP.34-39

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observation system (test scene rendering shown in figure 1). The role of each part can be summarized as: loading system control and stable load size; through the reaction system the reaction will load the bearing plate, bearing plate transfer uniform load to the foundation soil; the determination of foundation soil deformation by the observation system.

FIG. 1 TEST THE SCENE RENDERING

â‘ Bearing plate a) Bearing plate should be rigid, having enough rigidity, no damage, no bending, linking the piece at the bottom of the flat. Light, size and power transmission must be focused accurately. Also, the carrying is convenient. It can generally be processed into a square or round shape. The material is steel, reinforced concrete and plain concrete. b) The area of the bearing plate for the natural foundation should include the following rules: it should be 0.25 ~ 0.50m2; larger size should be adopted for soft soil pressure plates, otherwise easy to tilt; for gravel soils, attention should be paid to the maximum particle size of gravel; for harder fractured clay and rock strata, to pay attention to the influence of a crack. Furthermore, for composite foundation, the single pile composite foundation load test must pick up a stake to undertake the processing area. Pile composite foundation load test, according to the actual number of processing area, is determined. â‘Ą Loading system Loading system refers to the device by being weighed on the slabs the foundation load, divided into loading device and the load measuring device. Common loading devices in general can be divided into four categories: a) A single manual hydraulic jack loading device; b) Two or more than two jacks in parallel loading, high pressure oil pump; c) Jack automatic load control device; d) Pressure loading device (direct weighing stacks).

Common load measuring devices in general can be divided into three categories: a) Oil pressure gauge measuring load, hydraulic table shows hydraulic jack wall installation, according to the calibration curve, will jack hydraulic conversion into load or oil pressure gauge installed in the pump display oil pressure, and then converted to load. b) Standard dynamometer measuring load, placed at the top of the jack standard dynamometer (pressure ring), by direct measurement of the dial indicator on the dynamometer load. Commonly used specifications for: 300KN, 600KN, 1000KN, 2000KN, 3000KN. c) Load sensor measuring load through the load sensors placed on the jack. The load signal is converted into - 35 http://www.ivypub.org/cet

electrical signals through specialized display. Display load size, the better for the hub and spokes load sensor is the level of resistance to lateral ability. ③ Reaction system By adjusting the reaction system and loading system, the system of force balance between the loads keep vertical force state. The common reaction system can be divided into four categories: a) Pile heavy platform counterforce device: using steel ingot, concrete block, sandbag the weight bearing platform of pile in the building, such loading should be before the start of the test of a plus, uniform and stable platform. b) Anchor-pile beam counterforce device: (two piles, four piles, six piles, eight piles) maximum counterforce of up to 40000 KN. c) Umbrella framed anchor counterforce device: d) Supporting wall counterforce device: apply natural soil, soil hole wall stability, hole depth of 1.5m above. e) Engineering machinery: according to the test requirements, make full use of the construction site of engineering machinery and provide the reaction force of balancing. ④ Settlement observation system Determination of foundation soil subsidence measurement system happens by the observation datum of stents and measuring instruments. a) Observation of the benchmark bracket device for the fixed measuring instrument occurs when the benchmark bracket and the supporting jig on the structure of measurement instruments are ensured to be unaffected by temperature, vibration and other external environmental factors and the vertical displacement, in order to ensure stability of this system. b) Measuring instrument mainly include precision level, mechanical dial indicator, commonly used digital displacement meter and dial indicator.

2) The basic principle of test Plate load test of foundation soil can be applied to determine the front pressure plates under the stress of foundation soil bearing capacity and deformation parameters of main influence scope [2]. The test of choice is circular bearing plate. Loading classification should not be less than a magnitude 8. The most numerous loadings should be not less than 2 times of the design requirements (in this engineering example the foundation design bearing capacity is 200KPa). Loaded per level, according to the interval of 10min, 10min, 10min, 15min, 15min sensing a settlement, the interval of half an hour after sensing a settlement, when 2 hours continuously, settlement amount per hour is less than 0.1 mm, see that it has stabilized and can added to the next level load. The load can be obtained (P) - settlement curve (S) (namely, P -S curve). Uninstall series for half of the load series, equal to, each discharge level of interval for half an hour. Read the springback amount. After discharging a full load, three hours to read, write total amount of springback. Plate load test P -S curve can be divided into three phases (as shown in figure 2) :

FIG. 2 THE TYPICAL P -S CURVE

3) The main steps of test: - 36 http://www.ivypub.org/cet

① Site test surface should be smooth. When on a slope, load board bearing surface shall be level. ② Placed flat load meter: a) When the load plate is placed in the test on the ground, we should make good contact with the ground load board by laying a thin layer of dry sand when necessary (2 ~ 3mm). Turn right or left load board and gently hit the top of the surface. Make its contact with the ground complete. At the same time, adjust level by level. b) Put counterforce device carrying part in load above board, and apply the brake. c) Place the jack to the counterforce device below ball hinge seat close to the reaction force of load on board, available extension rod and by adjusting screw, make jack at the top of the bearing part. When assembling, keep the jacks vertical, not appearing tilted. d) Beckman beam: The Beckman beam placement must be symmetrical to each other and should maintain equidistance with loading plate center. ③ Load testing: a) For solid load board, plus 0.01MPa load in advance, about 30seconds, after being stable loading, unloading dispatch the dial indicator reading to zero or read the sink of the dial indicator reading as the initial reading. b) With increment of 50KPa, step by step load, subsidence stability load increase level should be in after the readings load intensity and subsidence. c) When the total subsidence in excess of the prescribed benchmark or load intensity is more than the estimated actual maximum contact pressure, or reach the yield point foundation, the test can be terminated. d) When abnormal during the test (such as load test board has a serious tilt or the load board sinks excessively), there should be dig sites under the equivalent load. The depth of the plate diameter should be tested again. Also, any abnormality should be indicated in the test record[3].

2.3 The test data analysis Now, taking a section of the measured date of a new project in Inner Mongolia, using JYC static load test analysis system software to deal with test data, obtains load - settlement curve (P–S curve), settlement - time logarithmic curve(S-lgt curve), settlement - load logarithmic curve(s-lgp curve) test data and conclusions (as shown in table 1, figure 3, figure 4, figure 5). Measure the section zh-2, zh-3 chart analysis data in the same way.

TABLE 1 THE RESULTS LIST OF ENGINEERING EXAMPLES

Project name: A new project in Inner Mongolia

Trial period: zh-1

Test date:2011-05-25

Platen area:0.50m2

Deformation modulus: Eo=23.11MPa

Allowable bearing capacity: [σ]≥200KPa

load (KPa)

0

50

100

150

200

250

300

350

400

Settlement of the current (mm)

0.00

1.20

1.40

1.12

1.16

1.23

1.19

1.40

1.46

0.00

1.20

2.60

3.72

4.88

6.11

7.30

8.70

Cumulative settlement (mm)

10.16

When determining the bearing capacity[4], as a result of soil structure without damage in the process of loading and the proportion of P -S curve no obvious boundaries, the characteristic value of subgrade bearing capacity values according to the S/d = 0.01. Bearing plate is made of round steel plate in this engineering example, the diameter of d = 0.8m, and S should be equal to 0.008m. During the load test by 3points to 400KPa when the largest settlement is 10.16mm, P -S curve basic for slowly settling curve, measured three point value is less than 30%. According to the - 37 http://www.ivypub.org/cet

analysis we can calculate the section number three piles characteristic value of subgrade bearing capacity as S= 8mm corresponds to load value in order to, namely, fak1=325.00KPa, fak2=351.50KPa, fak3=332.89KPa. Measured 3 points of fak (average = 336.46KPa) and this test for identification of type test, and the method to determine the characteristic value of subgrade bearing capacity should not be more than half of the most numerous loadings, which determine the section of allowable bearing capacity of foundation: [σ]≥200KPa. From the analysis of the above test results, the dynamic compaction ground compaction effect is very good. The bearing capacity of the foundation is in line with the requirements of design and use[5].

p-s 0

s-lgt

curve

50 100 150 200 250 300 350 400

0.00

p (kPa)

10

s-lgp

curve

20 30 45 60 90 120

300

0.00

t (min)

50 100 200 400 0.00

1.20

1.20

50 kPa

1.20

2.40

2.40

100 kPa

2.40

3.60

3.60

150 kPa

3.60

4.80

4.80

200 kPa

4.80

6.00

6.00

250 kPa

6.00

7.20

7.20

300 kPa

7.20

8.40

8.40

9.60

9.60

350 kPa

curve p (kPa)

8.40 9.60

400 kPa 10.80

10.80

10.80

12.00

12.00

12.00

s (mm)

s (mm)

FIG. 3 P-S CURVE

FIG. 4 S-LGT CURVE

s (mm)

FIG. 5 S-LGP CURVE

3 CONCLUSIONS The dynamic compaction method to reinforce foundation is a good way to improve the foundation bearing capacity.

According to field test conditions combined with many experiments, are the following conclusions: (1) Plate load test, in this engineering example of load test has three points. Specification requirement is not less than 3. If test points less there would be increased at random or to chance. For the plate load test to determine the bearing capacity of foundation and the method of E0 it must select a representative sample of the dot when selecting sites and has very important meaning for the engineering quality. Therefore, calculating the foundation bearing capacity, and so on, the technical parameters are more practical.

(2) As described in this paper, reaction device has many types of experiments on site with the bearing platform. S must consider the effect of test load range (note: general provisions S is equal to 2.5-3.0d, d is the diameter of the steel plate or side) so in the erection of the weight of the location, the S must pay attention to safety. In the use of another counterforce device at the same time, S also needs to pay attention to this to ensure the trial is scientific.

(3) The plate loading test is closer to the foundation actual working condition. Adopt the method of plate load test to detect the foundation to insure it has very good visual and reliability. Plate load test measurement indicators can be directly linked to deformation characteristics. Loading capacity’s big, wide influence can reflect a certain range of compacted fill in the overall situation producing disturbance to soil, without destroying the soil structure, and providing intuitive test data. Therefore this method has great value in engineering practice and popularization.

REFERENCES [1] Zhu Yingyan, Cheng Xianxie. Dynamic compaction foundation static load test analysis [J]. Journal of geotechnical foundation, 2010(6), 24 (3): 91 [2] The ministry of communications highway research institute. Highway engineering quality inspection evaluation standard [M].

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Beijing: people's traffic press, 2005 [3] Zhu Xia. Highway engineering test technology [M]. Beijing: higher education press, 2004 [4] Gao Yang, Duan Yan. Plate load test to determine the bearing capacity of foundation [J]. Journal of Shanxi architecture, 2010 (5), 36(15): 77 [5] China construction science research institute building foundation treatment technology specification (JGJ79-2002) [S]. Beijing: China building industry press, 2002

AUTHORS 1#

Xichang Zhang (1986-), male, hanzu,

Master.Areas

of

Research

Geotechnical

engineering

Interests:

construction

technology.

2

Yuehong Su (1961-), male, hanzu, Master tutor, Professor.

Areas of Research Interests: Foundation treatment and reinforcement, Roadbed stability study.

Director of the institute of highway in Inner Mongolia, A

Education background: 2007.09~2011.07:

member of the institution of civil engineering test board, Journal

Inner Mongolia Agricultural University,

editor of foreign building materials

Forestry, Forest Engineering (Direction of Roads

and

Bridges),

Double

major

bachelor

degree.

2011.09~2013.06: Inner Mongolia University of Technology, College

of

Civil

Engineering,

Architecture

and

Civil

Engineering, Master's degree. Email: zxc312061652@126.com

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