1 CHAPTER 1: RAILWAY ENGINEERING DAMAGE TO RAILWAY ENGINEERING Liao Shuqiao and Gu Zuoqin* I. Introduction There were four trunk lines: Beijing to Shanhaiguan, Tianjin to Pukou, Tongxian to Tuozitou and Tianjin to Jixian and more than 100 branch lines including Tangshan to Zunhua, Hangu to Nanbao, etc. and there were special lines for mines and factories in the Tangshan region. The distribution of railways and seismic intensity is shown in Fig. 1. The Beijing to Shanhaiguan Line, a Class I trunk line, was constructed by Britain and Japan in 1887, had a total length of 414.5 kilometers, all double lines. It was an important trunk line between the Northeast and the North, and the Northeast and central part of China. After the liberation rebuilding or reinforcing of some railway facilities of this line was done, consequently, the design standard, structural type and material, design data, and geology and foundation of this line were not known. Crossing the Jidong Plain the Beijing to Shanhaiguan Line was mainly laid on a smooth terrain of alluvium and diluvium with loose saturated fine sand stratum locally. The Tongxian to Tuozitou Line, a Class I trunk line with a total length of 189.8 kilometers, was constructed from 1973 to 1976. To the west of Fengrun Station was smooth terrain and to the east was hilly land with better geological conditions and deep ground water. The design standards, type of structure and material of the trunk line and branch line constructed after the liberation were uniform. All railway engineering in the Tangshan region was done with no consideration for earthquake resistant design. After the Haicheng earthquake in 1975 the Beijing Railway Bureau adopted some earthquake resistance measures for large and medium bridges which survived the Tangshan earthquake with only slight damage. In the earthquake region rails, embankments and bridges were damaged to different degrees and collapsed buildings broke communications, electricity, water supply, and locomotive equipment, consequently, traffic was stopped as shown in Table 1. A large amount of railway damage showed that the damage was closely related to the site condition, i.e. geology and hydrogeology mainly. The Beijing to Shanhaiguan Line, Tongtou Link Line and the Nanbao Special Branch Line were constructed on a saturated loose sand layer (Class III soil) with a high water table so embankments, bridges and rails of these lines were seriously damaged even if they were in an intensity VII region. On the contrary, in Tangshan * The First Survey and Design Institute, Ministry of Railway 2 City, intensity XI, the railway located on dense soil (Class II) with deep ground water had embankments, bridges and rails that were slightly damaged. The experience of rapid repairing of the railway in the seismic region indicated that bridges, which were difficult to repair, controlled opening of traffic. For example, the repair of the Ji Canal Bridge and the Luanhe Bridge controlled the Beijing to Shanhaiguan Line and the Douhe River Bridge controlled the Tangshan to Zunhua Line. After repairs to the Beijing to Shanhaiguan Line were made it was opened to traffic again on August 10, 1976. By September 16, 1976 the train velocity over a 287 kilometer section reached 60-80 kilometers per hour and over a 175 kilometer section reached 110 kilometers per hour, which was the level before the earthquake. But there were still 27 bridges that restricted travelling velocity to 15-60 kilometers per hour, which controlled transportation over this line. During the repair of railway lines most of the manpower was spent on bridges. But the repair of communication, signal, water supply, electricity and machinery, which were mostly broken by collapsed buildings, were easy to restore by taking temporary measures within a short time. Some data from the Beijing to Shanhaiguan Line and the Tongxian to Tuozitou Line are shown in Table 2. This experience shows that the earthquake resistant design of railway bridges and buildings with important equipment (including communication, electricity, water supply and locomotive, etc.) is very important. During the repair and restoration of the Beijing to Shanhaiguan Line and the Tongxian to Tuozitou Line stone ballast of 102,760 m3 and 20,000 m3 were used respectively. II. Trains When the earthquake occurred there were 28 freight trains and 7 passenger trains travelling on the railway; 7 freight trains and 2 passenger trains were turned over or derailed. A derailed train is shown in Fig. 1. No passengers were injured. On the damaged trains only part of the cars were turned over or derailed. The damaged trains are shown in Photos 1-4. The No. 40 express train partly derailed and the locomotive caught on fire (Photo 3). Two locomotive drivers talked about what they experienced during the earthquake. (1) Train No. 117, No. 0017 locomotive driver Ma Decai, deputy driver Wu Jian and trainee Liubaozhu said that the train was travelling at a velocity of 100 kilometers per hour on the section from Beitang to Chadian on the Beijing to Shanhaiguan Line (intensity VII). They saw the signal mast shaking and the locomotive shook from right to left then the emergency brake was put on at once. The derailed locomotive is shown in Photo 1. (2) Train No. 129, No. 4278 locomotive driver Zhang Yaowu and deputy driver Han Zhonghua said that the train was travelling at a velocity of about 90 kilometers per hour to Guye Station (intensity X) at 3:40 a.m. in the morning. They saw flashes of lightning, the locomotive shook up and down and then right to left, the emergency brake was put on and the train stopped at 3:43 a.m. III. Rails Damage to rails on loose foundation soil can be divided into two types: 3 (1) Embankments which had a height of more than 2 meters were generally damaged causing the rail to become deformed both in profile and in plan. A typical section was located on the up- link line (plan as shown in Fig. 7, profile as shown in Fig. 8) from Tongxian to Tuozitou (intensity IX area). It was founded on loose saturated fine sand and the height of the embankment fill was about 2-14 meters. The embankment was damaged and the rail was seriously deformed during the earthquake (Photos 5 and 6) but at section K0+920-K1+350 of this line the railroad was located on a sandstone cut and the rail was undamaged (see Photo 7). (2) Some of the embankments that had a height lower than 2 meters were damaged. The ground surface deformed during the earthquake causing the rail to bend seriously in plan and slightly in profile. Near the Beitang Station on the Beijing to Shanhaiguan Line (intensity VII area) the bent continuous rail is shown in Photo 8. The Nabao Branch Line (intensity VIII) was used for salt transport from Hanggu to Lutai. It was a total of 33.7 m in length built on a saturated silt layer with a shallow ground water table (<1.0 m). The embankment height was only 1 to 2 m, water and sand spouts occurred at the foot of the embankment (Photo 9) and the rail bent (Photo 10). There were 32 bent rails with a maximum rise of 1.56 m on this 33.7 m branch line as shown in Table 4. Figure 2 shows the rail bending on the Nanbao Branch Line from K1+650 to K1+703.1. At the Lutai Station yard (intensity IX) on the Beijing to Shanhaiguan Line water and sand spouting occurred (Photo 11) causing some rails to bend (Photo 12 and Fig. 3) At Xugezhuang Station (intensity X) and at Tangshan Station (intensity XI) the foundation soil was dense and stable; the ground water was deep (Tangshan Station, 4.7-6.3 m) and the rail was basically intact even in the epicentral zone (Photos 13 and 14). IV. Road Subgrades and Retaining Walls Most of the railway subgrade in the Tangshan earthquake region were embankments with a few cuts and retaining walls. During the strong ground motion the railway subgrades were seriously damaged which interrupted traffic on the Jing-Shan, Tong-Tuo, Tong-Tuo Up-link and Nanbao lines, etc. (Table 1). The distribution of embankment damage to all main lines and branch lines is shown in Fig. 4. In the restoration of these embankments over 100,000 m3 of stone ballast and rubble was used and approximately 1.5 kilometers of steel rail was replaced. The following describes earthquake damage to railway subgrades. 4 1. Embankments In the Tangshan earthquake region the embankment height is about 1-3 m, 4-11 m in some special sections and the tallest is 14 m on bridge approaches. Cohesive soil is mostly used as filling material and silty, fine and medium sand is also used in some places. The degree of damage to embankments was clearly related to the intensity of ground shaking, site condition (mainly geology and hydrogeology), embankment height and filling material, etc. (Table 5). The embankment damage phenomena mainly included sinking, cracking, slope sliding and cave-in, etc. Some took place individually but many occurred simultaneously. Embankment subsidence is a general damage case. Generally, the embankment subsidence took place in soft clayey soil and liquefied sandy subsoil. Especially in liquefied sandy subsoil a great deal of sinking and cave-ins occurred within a short section so as to severely damage the embankment. There were many cases of rail suspending, lateral displacement, bending and distorting, etc. as a result of the embankment subsidence. But at rock or dense soil sites damage to the embankment was reduced.