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TB/T 2487-2016 English PDF (TBT2487-2016)

TB/T 2487-2016 English PDF (TBT2487-2016)

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TB/T 2487-2016: Test method for dynamic stress of subgrade

This Standard specifies the subgrade dynamic stress test objectives, test principle and test points burying, test equipment requirements, sensor calibration and burying, arrangement of test results.
TB/T 2487-2016
TB
NATIONAL RAILWAY INDUSTRY
STANDARD OF THE PEOPLE REPUBLIC OF CHINA
ICS 45.020
S 04
Replacing TB/T 2487-1994
Test Method for Dynamic Stress of Subgrade
ISSUED ON. AUGUST 16, 2016
IMPLEMENTED ON. FEBRUARY 16, 2017
Issued by. National Railway Administration of PRC
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Test Objectives ... 4
3 Test Principle and Test Points Arrangement ... 4
4 Test Equipment Requirements ... 5
5 Sensor Calibration and Burying ... 6
6 Arrangement of Test Results ... 7
Foreword
This Standard was drafted as per the rules specified in GB/T 1.1-2009.
This Standard replaced TB/T 2487-1994 Test Method for Dynamic Stress of Subgrade Bed; compared with TB/T 2487-1994, this Standard has the major technical changes as follows.
--- Add the arranging principle of measurement points of non-ballasted-track subgrade bed (see 3.2);
--- Add the basic requirements for collecting device (see 4.3).
This Standard was proposed by and under the jurisdiction of China Academy of Railway Science ?€? Standard and Metrology Research Institution.
Drafting organization of this Standard. Railway Engineering Research Institute of China Academy of Railway Sciences.
Chief drafting staffs of this Standard. Wang Lijun, Zhang Qianli, Cai Degou, Ye Yangsheng.
The historical edition replaced by this Standard is as follows.
--- TB/T 2487-1994.
Test Method for Dynamic Stress of Subgrade
1 Scope
This Standard specifies the subgrade dynamic stress test objectives, test principle and test points burying, test equipment requirements, sensor calibration and burying, arrangement of test results.
This Standard is applicable to the dynamic stress test of subgrade for newly-built and existing railways.
2 Test Objectives
2.1 Learn the dynamic load level of subgrade, so that provide basic data for the analysis and evaluation of the subgrade structure.
2.2 Analyze the change regularity of train load on different track types, states, and subgrade bed stress filed with new subgrade bed structure.
2.3 Analyze the dynamic stress change regularity between subgrade and bridge, tunnel, culvert, and the like transitional section with different structures. 2.4 Analyze the influence degree of subgrade bed disease on the subgrade bed stress.
2.5 Verify that the subgrade bed structure is reasonable, so that provide basic data for the optimized design parameters.
3 Test Principle and Test Points Arrangement
3.1 Convert the pressure into electrical signals through the pressure sensor (hereinafter referred to as sensor); use data acquisition system to record and convert the electrical signals into the pressure values.
3.2 According to the structures of track, subgrade and transitional section, select the representative positions to arrange the test points.
a) For ballasted track, the cross-section shall select the following positions to arrange test points as per requirements like under track, track center, sleeper end, ballast curb, and the representative positions of subgrade bed; it is shown in Figure 1; while the longitudinal-section shall be arranged the test points under sleeper, between sleeper, and the representative positions of subgrade bed. b) For non-ballasted track, the cross-section shall select the following positions to arrange test points as per requirements like under track, track center, edge of track plate (track bed), edge of base seat (supporting layer), and the
representative positions of the subgrade bed; it is shown in Figure 2; while the longitudinal-section shall be arranged test points on the rail support, end of track plate, middle of track plate, and the representative positions of subgrade bed. c) Test points shall be arranged along the depth direction on the structural layer or the middle of structural layer with different natures and different state of filler. d) Select the representative positions of transitional section between subgrade and bridge, tunnel, culvert.
e) When studying the stress state under the new track, the test points can be confirmed briefly.
3.3 Bury the qualified sensor into the to-be-tested position; connect the sensor with the acquisition system; use the acquisition system to directly record and display the stress changes on such point when the train is passing by.
3.4 The record method of stress test shall be performed as per the relevant regulations and instructions.
4 Test Equipment Requirements
4.1 The sensor and acquisition equipment for test shall meet the relevant national measurement requirements.
4.2 The sensor shall be selected as per the following requirements.
a) Range selection. the upper limit shall be 1.5~2.0 times of the estimated or theoretically calculated maximum stress value; while the lower limit shall satisfy that the sensor has sufficient sensitivity;
b) The sensor shall be selected the round-cake shape; its diameter shall be no less than 10cm; the diameter of bearing surface shall be 10 times greater than the largest particle size of the soil medium;
c) The ratio between sensor thickness of H and Diameter of D shall be no greater than 0.2;
d) The ratio between sensor?€?s equivalent deformation modulus Eg and soil medium deformation modulus Es shall satisfy Eg/Es???60H/D;
Figure 1 -- Ballasted Track Subgrade Cross-Section Pressure Sensor Layout Figure 2 -- Non-Ballasted Track Subgrade Cross-Section Pressure Sensor
Layout
e) The operating frequency of sensor shall be higher than the highest resonant frequency of the tested signal. The sensor mass shall be equal to the mass of sodium medium replaced;
f) The insulation resistance of sensor shall be greater than 200M???.
4.3 The acquisition equipment shall be selected as per the following requirements. a) The accuracy of acquisition equipment shall be no less than 0.5%FS (full scale); b) The sampling frequency of acquisition equipment shall be 10 times higher than the frequency of tested signal.
5 Sensor Calibration and Burying
5.1 For the sensor calibration, the calibration boundary shall be, in principle, consistent with the practical conditions; the sensor can be calibrated through loading the soil specimen that buried the sensor indoors; if permitting, the calibration can be performed on site.
Bed Surface
Bed Lower layer
Embankment under bed
Line spacing
Bed Surface
Bed Lower layer
Embankment under bed
5.2 The pressure-bearing surface of the sensor shall be oriented towards the to-be- tested stress direction, and is vertical to it; place stably, so that the pressure-bearing surface shall not rotated during the test period.
5.3 Burying method of sensor.
a) Pre-burying method. firstly, flatten the soil surface of the to-be-tested point; dig the approximate pit as per the sensor size on the test point; the pit bottom shall be paved with medium and fine sand; place the sensor into the pit; use hand to press gently; the sensor shall be 1cm~2cm higher than the soil surface; level it with leveling instrument; fix the lead wire; ram and backfill the surrounding fillers; then pave medium and fine sand on the surface of the sensor; then cover the subgrade bed filling and ramming;
b) Post-burying method. dig pit or trench in the predetermined position; then bury and backfill according to the method in 5.3a). The pit diameter or trench width shall be no less than 2 times of the overfill layer height; the excavated filler shall be stacked in a special location; after the sensor is buried, backfill and ram all the fillers.
5.4 When burying on site, the density of soil around the sensor shall be consistent with the soil density before burying.
5.5 For the buried sensor, the wires shall perform anti-moisture and safety protection. When measuring, the insulation resistance of sensor shall be no less than 50M???. 6 Arrangement of Test Results
6.1 According to the stable test results (except the abnormal test values caused by the external factors), calculate the stress value on each test point as per the calibration coefficient before measurement.
6.2 Perform statistics against the characteristic values of stress data under the same test conditions, such as mean, variance, maximum value, medium value, etc. 6.3 Analyze the distribution regularity of stress value along the longitudinal and cross section and depth; and the relationship with various influential factors; then arrange them into the corresponding chart.

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