Ground coefficient K30 detection and method (Hangzhou Sansi Instrument)

1, the ground coefficient K30 detection

The purpose of subgrade compaction quality control is to control the bearing capacity and settlement deformation of the subgrade, to maintain the stability and smoothness of the line, to ensure that the train can be safe, comfortable and high-speed operation, while the standards, methods and equipment for controlling and detecting the quality of compaction are It is the way and measure to ensure the quality of compaction.

The flat load test is widely used in ground testing of railways, highways, airports and other industrial and civil construction projects. As an indicator of strength and deformation, the foundation coefficient can visually characterize the stiffness and load carrying capacity of the subgrade.

Since the construction of the Dazhong Heavy-duty Railway in China, the K value of the foundation coefficient has been introduced as the detection and control index for the compaction quality of the roadbed filling, which has been promoted and applied in the construction of railway subgrade. The K30 plate load test is an effective construction site test method for detecting the compaction quality of roadbed. At present, the foundation coefficient K has become one of the main indicators for the compaction quality of the newly-built railway control bed and embankment.

The contents of this chapter mainly include the concept and development of K30, the applicable conditions and requirements of the test, test instruments and test methods, calculation of test results and verification methods of test instruments.

1.1 Concept and development

1.1.1 Concept of foundation coefficient K30

The foundation coefficient K" is the size of the compressibility of the soil surface under the action of plane pressure. It is a static load plate load test using a rigid load plate with a diameter of 300 mm, taking the measured stress for the first load - The load Qs corresponding to s on the displacement (q--s) curve at 1.25 mm is calculated by K30=Qs/1.25, and the unit is MPa/m.

The area of the load-bearing plates used in the test is not the same, and a circular load plate with a diameter of 750 mm or 762 mi'il is usually used. The diameter of the load plate used is different, and the measured foundation coefficient is also different. Generally, the diameter of the load plate is added. For example, the load plate diameters are 30111 HI, 600 mm, and the foundation coefficients of 750 mm are represented by K30, K60, and K75, respectively. Therefore, Ka30 is one of the foundation coefficients. In order to save the labor and the convenience of operation, Japan uses a 300mm diameter load plate and takes K30 as the standard value. The foundation coefficient measured by other diameter load plates can be converted into the standard K30 value according to the relevant formula.

1.1.2 Development of K30 Plate Load Test

Since the 1930s, the United States has proposed a compaction index, that is, a compaction coefficient K, a relative density D, or a porosity n, which is still used as a compaction quality standard for soil design and construction control in countries around the world. Although the subgrade compaction quality standard with compactness is the parameter has the advantages of compaction test to guide on-site construction and on-site inspection, but for high-speed railway or other conditions that require strict strength indicators, only the compaction parameter is used to reflect the filling. The compaction quality of soil has its limitations.

In order to ensure the strength index of roadbed filling, in the 1970s and 1980s, many countries began to use the strength and deformation index as the quality control parameters for roadbed filling, the so-called resistance test method. These include the US CBR (California Carrying Ratio) standard, the static deformation modulus EV2 standard in Germany, France, Austria, and Switzerland, and the Japanese ground coefficient K30 standard. It can be seen that the use of strength and deformation parameters as control indicators is a major advancement in roadbed quality standards.

The Chinese railway system introduced Ks from the construction of the Daqin line in 1985. Since the flat load test, it has been gradually applied in railway construction. From the perspective of the application of the K30 in China's railway system, both the equipment, the test methods, and the design standards have matured. The foundation coefficient K30 has become one of the main indicators for the compaction quality of the new railway control bed and embankment, and has been officially listed in the “Quality Inspection and Evaluation Standard for Railway Subgrade Engineering” (TB10414-2003) and the “Code for Design of Railway Subgrade” ( TB10001—2005). As a kind of strength and deformation index, K30 plate load test can visually characterize roadbed stiffness and bearing capacity. China refers to Japan's "Plate Load Test Method for Highways" (JISA1215--1995 revised edition) and Germany's "Plate Load Test" (DIN 18134-1993 revised edition), and absorbs recent scientific research results and construction experience, while Aiming at the problems in practical application, the K30 plate load test method was developed. This method was officially included in the "Technical Rules for Railway Engineering Geotechnical Engineering" (TB10102-2004) for the first time.

1.2 Applicable conditions and requirements for K30 flat load test

There are many factors affecting the size of the test value of the board load test. Including the nature of the filler, grading, compaction coefficient, water content, rolling process, maximum dry density, optimum water content, test operation method and test surface uniformity. In order to standardize the test process, the applicable conditions and requirements for the plate load test are proposed.

1.2.1 Particle grading of test objects

The K30 plate load test is applicable to all kinds of soil and earth and rock mixed fillers with a particle size not larger than 1/4 of the diameter of the load plate.

Because the load plate of the K30 is only 300mm in diameter. Therefore, there is a certain limit on the particle size and gradation of the filled soil. Otherwise, the particle size is too large and the gradation is not uniform. The test result of K30 will bring a large error, which is difficult to truly reflect the pressure of the subgrade. Real situation. According to the experience of Qinshen Passenger Dedicated Line, it is suitable for the foundation coefficient K30 of uniform foundation soil (such as coarse and fine grained soil). It is also in compliance with the test requirements for the uniform mixing of gravel, but for the uneven particles of the gravel. Soil, its K30 test is difficult to obtain accurate and reliable test results.

1.2.2 Effective test depth

The K30 plate load test has an effective depth range of 400 to 500 nm.

Because the K30 plate load test results reflect the ground soil properties within the depth range of about 1.5 times the platen diameter under the pressure plate, in order to truly and comprehensively reflect the situation of deeper soil layers, it is necessary to conduct comprehensive evaluation in combination with other detection methods.

1.2.3 Impact of changes in water content

For homogenous sand with fast water volatilization, the surface is hard shelled, softened, or soil disturbed by other factors, the plate load test shall be placed below the disturbance zone.

There are many factors affecting the K30 test results, but the change in water content is the main factor causing the accidental error of the K30 test results, which means that the K30 test results are time-sensitive. In general, the control is applied near the optimum water content, the roadbed compaction coefficient is high, the subgrade quality is good, the surface stiffness of the bed is large, and the K30 test result is high. However, due to the influence of seasonal and weather temperature changes, the degree of evaporation of water is different, and the water content is different, so the water content is a variable. Practice has proved that after the completion of rolling, when the water content of the subgrade is high, the K30 test result is small; when the water content is low, the K30 test result is large. Since the compacted soil is in an unsaturated state, the water content has a great influence on its mechanical properties. This causes the K30 test results to be highly discrete and poorly reproducible due to changes in water content. For this reason, field tests should eliminate soil water content changes. Impact.





Hangzhou Sansi Instrument Co., Ltd. Main Products

Anchor dynamometer, geotechnical instrument, building test instrument, highway instrument, cement test instrument, asphalt instrument, analytical laboratory instrument, sputum test instrument, various analytical standard sieve, product warranty for one year, lifetime maintenance

Sales hotline: 0571-86688649

QQ: 2318806276