Zhou Shengen, 1 Zhang Sumin 2

Transcription

1 439 CHAPTER 5: SOILS AND FOUNDATIONS EXPLORATION INFORMATION ON THE LIQUEFIED FOUNDATION SOIL IN TANGSHAN AND ITS VICINITY Zhou Shengen, 1 Zhang Sumin 2 Sand boils and waterspouts occurred in an extensive area in the Tangshan earthquake. The survey on the liquefaction-induced damage and the foundation soil exploration were performed by the Exploration Corporation of Ministry of Machine Building Industry, Academy of Railway Sciences of Ministry of Railway, No. 3 Institute of Exploration and Design of Ministry of Railway, etc., in the liquefied sites of the suburbs of Tangshan, Fengnan County, Luannan County, Laoting County and Baigezhuang village, etc., from 1977 to 1978, respectively. 1. Distribution of Test Sites A total of 36 sites were investigated; all sites, excluding Baigezhuang Village, were situated in the alluvial fan of the Luanhe River (see Fig. 1). Table 1 and Table 2 show the distribution of test sites and the intensity in different areas, respectively. Most of the test sites were situated at the morphological units, such as the newly deposited alluvial fan of the Luanhe River, the offshore alluvium of marine-continent substitution facies, the marine plain, the valley flat of the Douhe River and the first level terrace. In these areas there were relatively loose silty fine sand layers or a few moderate sand layers in the upper stratum. The water table was rather high, generally only 1-3 m below the ground surface. 2. Test Items and Method Three tasks were carried out at each test site: (1) Borehole sampling for determining the physical properties of soils; (2) standard penetration tests and (3) static cone penetration tests. Generally one borehole was used to secure samples for determination of properties. Two to three holes were used for standard penetration tests. One to three holes were used for static cone penetration tests. Spacings between two neighboring boreholes were about 2 m. 1 Academy of Railway Sciences. 2 Exploration Corp., H.Q., Ministry of Machine-Building Industry

2 440 In the standard penetration test, slurry was used for protecting boreholes. Impact and cyclic slurry techniques were adopted for drilling. The dropping hammers used were all falling automatically from the hook. In the test, it is required that settlement of the hole bottom be controlled within 5 cm. The standard penetration can fall generally to the desired depth. Double-cylinder type static cone penetration apparatuses with an aperture of 60 were used in the static cone penetration test. A resistance-strain type probe with a wall of 70 mm in length was used. Measurement was recorded automatically, or by a YJD-1 model static strain meter, while penetration resistance was recorded at every 10 cm in depth. 3. Exploration and Test Data Exploration and test results at each test site are given in Table 3-38 in tabular form. Sampling data are presented only for items related to sandy soils. Standard penetration blow counts shown in the table are average values. Blow counts over 50 blows are taken as 50 blows. In all tables, the following units are used: length (or depth) in m; water content, %; volume weight, g/cm 3 ; particle size, mm; specific penetration resistance kg-force/cm 2. (Translator: Lu Rongjian) Area Table 1. Distribution of Test Sites in Different Areas. Number of test sites With sand boils With no sand boils Total Tangshan City Fengnan County Luannan County Laoting County Baigezhuang Luan County Intensity Table 2. Distribution of Test Sites in Different Intensity Areas. Number of test sites With sand boils With no sand boils Total VII VIII IX X 5 4 9

3 441 Table 3. Exploration data of Borehole 1. (Tangshan Douhe Bridge; area of intensity X; water table: 3.7 m; soil liquefied; date: Aug ) Type of soil Static cone penetration Standard penetration Sampling data test Particle analysis Filled land Depth Light Loam # of blow Sampling depth Water content Vol. wt <0.1 Fine sand Medium sand Clayey soil Clay

4 442 Table 4. Exploration data of Borehole 2. (Wali, Tangshan city; area of intensity X; water table: 1.25 m; soil liquefied; date: Aug. 1977) Type of soil Clayey soil Static cone penetration Standard penetration Sampling data test Particle analysis Depth # of blow Sampling depth Water content Vol. wt <0.1 Fine sand Medium sand Silty clayey sand Silty sand Clayey soil Clay

5 443 Table 5. Exploration data of Borehole 3. (Xugezhuang, Fengnan County; area of intensity X; water table: 1.5 m; soil unliquefied; date: Oct. 1978) Type of soil Surface soil Clayey soil Static cone penetration Standard penetration Sampling data test Particle analysis Depth # of blow Sampling depth Water content Vol. wt <0.05 Silty sand Fine sand Light loam Silt Light loam Silty sand

6 444 Table 6. Exploration data of Borehole 4. (Gaozhuangzi, Fengan County; area of intensity X; water table: 1.1 m; soil unliquefied; date: Sept. 1978) Type of soil Filled land Clayey soil Light Loam Static cone penetration Standard penetration Sampling data test Particle analysis Depth # of blow Sampling depth Water content Vol. wt Fine sand <0.05 Medium sand Fine sand Silty sand Medium sand Fine sand Clayey soil Light loam Silty sand

7 445 Table 7. Exploration data of Borehole 5. (Plant Seed Ranch, Tangshan City; area of intensity X; water table: 3.6 m; soil unliquefied; date: Aug. 1978) Type of soil Light Loam Static cone penetration Standard penetration Sampling data test Particle analysis Depth # of blow Sampling depth Water content Vol. wt < Silt sand Fine sand Medium sand Silty sand Medium sand Light loam Fine sand Clayey soil

8 446 Table 8. Exploration data of Borehole 6. (Daifutuo, west of Tangshan; area of intensity X; water table: 1.5 m; soil liquefied; date: Aug. 1977) Type of soil Clayey soil Static cone penetration Standard penetration Sampling data test Particle analysis Depth # of blow Sampling depth Water content Vol. wt < Clay Fine sand Medium sand ` Fine sand Silty sand Medium sand Fine sand Medium sand Clayey soil Clayey soil Medium sand Fine sand

9 447 Table 9. Exploration data of Borehole 7. (Daifutuo, west of Tangshan; area of intensity X; water table: 3.0 m; soil liquefied; date: Aug. 1977) Type of soil Clayey soil Static cone penetration Standard penetration Sampling data test Particle analysis Depth # of blow Sampling depth Water content Vol. wt < Clayey soil Fine sand Medium sand Fine sand Clayey soil Fine sand Medium sand Silty sand Clayey soil

10 448 Table 10. Exploration data of Borehole 8. (Laobianzhuang, Tangshan; area of intensity X; water table: 3.2 m; soil liquefied; date: Aug. 1977) Type of soil Cultiv. Soil Clayey soil Static cone penetration Standard penetration Sampling data test Particle analysis Depth # of blow Sampling depth Water content Vol. wt < Clay Medium sand Silty sand Fine sand Silty sand Clayey soil Fine sand

11 449 Table 11. Exploration data of Borehole 9. (Daodi, Fengnan County; area of intensity X; water table: 1.1 m; soil unliquefied; date: Sept. 1978) Type of soil Static cone penetration Standard penetration Sampling data test Particle analysis Filled land Depth # of blow Sampling depth Water content Vol. wt Clayey soil < Silty sand Light loam Fine sand Silty sand Fine sand Silty sand

12 450 Table 12. Exploration data of Borehole 10. (Jingzhuang, Fengnan County; area of intensity IX; water table: 1.45 m; soil liquefied; date: Sept. 1978) Type of soil Static cone penetration Standard penetration Sampling data test Particle analysis Filled land Depth Light Loam # of blow Sampling depth Water content Vol. wt < Silty sand Fine sand Medium sand Silty sand

13 451 Table 13. Exploration data of Borehole 11. (Fanzhuang, Fengnan County; area of intensity IX; water table: 0.85 m; soil liquefied; date: Sept Type of soil Static cone penetration Standard penetration Sampling data test Particle analysis Filled land Depth # of blow Sampling depth Water content Vol. wt <0.05 Fine sand / Clayey soil Silty sand

14 452 Table 14. Exploration data of Borehole 12. (Xuanzhuang, Fengnan County; area of intensity IX; water table: 1.55 m; soil liquefied; date: Sept. 1978) Type of soil Filled land Clayey soil Static cone penetration Standard penetration Sampling data test Particle analysis Depth # of blow Sampling depth Water content Vol. wt <0.05 Silty sand Fine sand Light loam Silty sand Clayey soil Silty sand Clayey soil Silty sand

15 453 Table 15. Exploration data of Borehole 13. (Caogezhuang, Fengnan County; area of intensity IX; water table: 1.05 m; soil liquefied; date: Sept. 1978) Standard Type of Static cone penetration Sampling data soil penetration test Particle analysis Filled land Depth # of blow Sampling depth Water content Vol. wt Clayey soil <0.05 Silty sand Fine sand Silty sand Light loam Fine sand

16 454 Table 16. Exploration data of Borehole 14. (Yanjiazhuang, Fengnan County; area of intensity IX; water table: 1.25 m; soil liquefied; date: Sept. 1978) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Silty fine sand Depth # of blow Sampling depth Water content Vol. wt < Medium sand Fine sand Silty sand Silty light loam Silty sand Clayey soil Fine sand

17 455 Table 17. Exploration data of Borehole 15. (Xiezhuang, Luan Fengnan County; area of intensity IX; water table: 1.0 m; soil liquefied; date: Apr Standard Type of Static cone penetration Sampling data soil penetration test Particle analysis Fine sand Depth # of blow Sampling depth Water content Vol. wt Medium sand < Silty sand Fine sand Medium sand Fine sand Medium sand Fine sand Silty sand Clayey soil Fine sand Clayey soil

18 456 Table 18. Exploration data of Borehole 16. (East Tuozitou, Luan County; area of intensity IX; water table: 3.5 m; soil unliquefied; date: Apr. 1977) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Fine sand Depth # of blow Sampling depth Water content Vol. wt < Light Loam Medium sand Silty sand Clayey soil Fine sand Clayey soil Medium soil Clayey soil Fine sand

19 457 Table 19. Exploration data of Borehole 17. (Zhuanglizhuang, Luan County; area of intensity VIII ; water table: 2.8 m; soil unliquefied; date: Aug. 1977) Standard Type of Static cone penetration Sampling data soil penetration test Particle analysis Cultiv. soil Depth Clayey soil # of blow Sampling depth Water content Vol. wt < Fine sand Silty sand Fine sand Medium sand Silty sand Clayey soil Silty sand Clayey soil

20 458 Table 20. Exploration data of Borehole 18. (Wangguanzhai, Luannan County; area of intensity VIII; water table: 3.6 m; soil liquefied; date: Aug. 1977) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Light loam Silty sand Depth # of blow Sampling depth Water content Vol. wt < Medium sand Clayey soil Fine sand Light loam Fine sand Medium sand Silty sand

21 459 Table 21. Exploration data of Borehole 19. (Jianpao, Luannan County; area of intensity VIII; water table: 1.1 m; soil liquefied; date: ug. 1977) Standard Type of Static cone penetration Sampling data soil penetration test Particle analysis Cultiv. soil Depth # of blow Sampling depth Water content Vol. wt Fine sand < Medium sand Fine sand Medium sand with a small amount of gravel Clayey soil

22 460 Table 22. Exploration data of Borehole 20. (Gaocaozhuang, Luannan County; area of intensity VIII; water table: 1.1 m; soil unliquefied; date: Aug. 1977) Standard Type of Static cone penetration Sampling data soil penetration test Particle analysis Cultiv. soil Depth # of blow Sampling depth Water content Vol. wt < Fine sand Clayey soil with silty sand interca lation Fine sand Silty sand Clayey soil Silty and fine sand intercal Clayey soil

23 461 Table 23. Exploration data of Borehole 21. (Crematorivum, Luannan County; area of intensity VIII; water table: 3.1 m; soil unliquefied; date: Aug. 1977) Standard Type of Static cone penetration Sampling data soil penetration test Particle analysis Filled land Depth Silty sand # of blow Sampling depth Water content Vol. wt < Medium sand Silty sand Clayey soil and silty sand intercalation Clayey soil Fine sand Clayey soil

24 462 Table 24. Exploration data of Borehole 22. (Xinzhuangzhi, Luannan County; area of intensity VIII; water table: 0.8 m; soil liquefied; date: Aug. 1977) Standard Type of Static cone penetration Sampling data soil penetration test Particle analysis Sandy clay Depth Fine sand # of blow Sampling depth Water content Vol. wt. > <0.1 Clayey sand Fine sand Coarse and Medium sand Light loam

25 463 Table 25. Exploration data of Borehole 23. (Weigezhuang, Luannan County; area of intensity VIII; water table: 1.35 m; soil liquefied; date: Aug. 1977) Standard Type of Static cone penetration Sampling data soil penetration test Particle analysis Clayey soil Depth # of blow Sampling depth Water content Vol. wt < Fine sand Clayey soil Fine sand Medium sand Clayey soil

26 464 Table 26. Exploration data of Borehole 24. (Baigezhuang Ranch, Branch No. 6; area of intensity VIII; water table: 1.0 m; soil liquefied; date: Oct. 1978) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Depth # of blow Sampling depth Water content Vol. wt Silty sand Silty clayey soil Silty sand Silty clayey soil Silty sand Silty clayey soil Silty sand Silty clayey soil <0.05

27 465 Table 27. Exploration data of Borehole 25. (Baigezhuang Ranch, Branch No. 11; area of intensity VIII; water table: 0.65 m; soil liquefied; date: Oct. 1978) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Clayey soil Depth # of blow Sampling depth Water content Vol. wt < Silt Silty sand Silty sand Clayey soil

28 466 Table 28. Exploration data of Borehole 26. (Baigezhuang Ranch, Branch No. 4; area of intensity VII; water table: 0.75 m; soil liquefied; date: Oct. 1978) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Clayey soil Depth # of blow Sampling depth Water content Vol. wt Silty light loam Silty sand Silty sand Silty sand Fine sand Silty sand Light loam Silty sand Clayey soil Silty sand <0.05

29 467 Table 29. Exploration data of Borehole 27. (Chemical Fertilizer Plant, Baigezhuang Ranch, area of intensity VIII; water table: 0.65 m; soil liquefied; date: Oct. 1978) Standard Type of Static cone penetration Sampling data soil penetration test Particle analysis Filled land Depth # of blow Sampling depth Water content Vol. wt <0.05 Silty clayey soil Silty fine sand Clayey soil Silty sand

30 468 Table 30. Exploration data of Borehole 28. (Baigezhuang Ranch, Branch No. 3; area of intensity VII; water table: 0.65 m; soil unliquefied; date: Oct. 1978) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Clayey soil Depth # of blow Sampling depth Water content Vol. wt < Silt Light loam Silty sand Silty clayey soil Light loam Silty sand Silty sand

31 469 Table 31. Exploration data of Borehole 29. (Baigezhuang Ranch, Branch No. 1; area of intensity VII; water table: 1.0 m; soil unliquefied; date: Oct. 1978) Standard Type of Static cone penetration Sampling data soil penetration test Particle analysis Filled land Depth Silty clayey soil # of blow Sampling depth Water content Vol. wt <0.05 Silty sand Silty clayey soil Silty fine ` sand Silty sand

32 470 Table 32. Exploration data of Borehole 30. (Magezhuang, Laoting County; area of intensity VII; water table: 2.5 m; soil unliquefied; date: Aug ) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Clayey soil Depth # of blow Sampling depth Water content Vol. wt < Fine sand with inter calation Medium sand Medium sand Light loam with inter calation of silty sand Fine sand

33 471 Table 33. Exploration data of Borehole 31. (Longwangmiao, Laoting County; area of intensity VIII; water table: 2.25 m; soil liquefied; date: Aug. 1977) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Sandy clay Depth # of blow Sampling depth Water content Vol. wt < Silty sand Silty clayey soil Silty sand Fine sand Gravel sand Clayey soil

34 472 Table 34. Exploration data of Borehole 32. (Caigezhuang, Laoting County; area of intensity VIII; water table: 2.3 m; soil liquefied; date: Aug. 1977) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Clayey soil Depth # of blow Sampling depth Water content Vol. wt < Medium sand Clayey soil Fine sand Medium sand

35 473 Table 35. Exploration data of Borehole 33. (Liubianzhuang, Laoting County; area of intensity VIII; water table: 2.3 m; soil liquefied; date: Aug. 1977) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Clayey soil Depth # of blow Sampling depth Water content Vol. wt <0.1 Fine sand Clayey soil with an intercalation of fine sand Medium sand Clayey soil

36 474 Table 36 Exploration data of Borehole 34. ( Cotton oil plant, Laoting County; area of intensity VIII; water table: 2.5 m; soil liquefied; date: Aug. 1977) Clay Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Depth # of blow Sampling depth Water content Vol. wt < Silty sand Silty clayey soil Medium sand Gravel sand Light loam Silty sand Fine sand Medium sand

37 475 Table 37. Exploration data of Borehole 35. (Upper Yuzhuang, Laoting County; area of intensity VIII; water table: 2.9 m; soil liquefied; date: Aug. 1977) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Depth # of blow Sampling depth Water content Vol. wt < Clayey soil Fine sand Fine sand Coarse sand Clayey soil

38 476 Table 38. Exploration data of Borehole 36. (Maozhuang Commune, Laoting County; area of intensity VIII; water table: 2.3 m; soil unliquefied; date: Aug. 1977) Standard Sampling data Type of Static cone penetration soil penetration test Particle analysis Depth # of blow Sampling depth Water content Vol. wt < Clayey soil Fine sand Medium sand Clayey soil with a thin intercalation of silty sand Fine sand

39 477 Figure 1. Distribution of test locations.

40 478 SAND LIQUEFACTION AT LUJIATUO MINE Wang Buyun* Lujiatuo Mine is situated about 20 km northeast of Tangshan at the first level terrace on the west bank of the Shahe River. Its geographic position is shown in Figure 1. The surface elevation was 28-29m (before the 1976 quake). The site is about 500 m wide in the northsouth direction and 1100 m in the east-west direction as shown in Figure 2. The site is located in the area of intensity IX in the Tangshan earthquake. The foundation soil at the Lujiatuo Mine was mainly composed of saturated fine sand layers which were liquefied to some extent in the Tangshan earthquake. To investigate the seismic effect on saturated foundation sandy soil, standard penetration tests, static cone penetration tests and other geotechnical tests were performed along with earthquake damage surveys after the earthquake. Results are compared with the exploration data prior to the quake. 1. Macro-Investigation of Sand Liquefaction (1) Water spouts and sand boils. Water spouts and sand boils in the eastern and western parts of the working site were more extensive than in the central part. Sand boils in the western part were distributed in a leaf-shaped pattern, and the diameter of sand boils was generally 2-4 m with a spouting water column as high as 400 mm during the quake. In the eastern area, the sand boils were generally distributed in a pattern of circular dots like a series of pearls with diameters about 1-2 m; slightly smaller than those in the western part. Most sands brought to the ground surface in the sand spouting were light yellow in color, fine grained and uniformly distributed. The gradation of the sand taken from the sand boils is summarized in Table 1. The particle composition of the undisturbed sand in the vicinity of E-1 and E-2 pump houses is listed in Table 2. By comparison, the gradation of the spouted sand is similar to that of the undisturbed sand above the depth of 5.40 m and is different from that below 7.71 m in depth (Figure 11). Water spouts and sand boils not only occurred outdoors but indoors as well. In the boiler house east of the site, the ground heaved and cracked, and its surface was submerged in water from the liquefied sand. Water spouts also occurred in the basement of a winch workshop of the main shaft in the west, and a total of about 1 m 3 of sand was brought to surface. Differential settlement of the workshop resulting from the sand boils reached 90 mm high and 60 mm wide. This caused the reinforced concrete foundation of the winch workshop to fracture (Figure 3). * Shanxi Design Institute of Coal Mine

41 479 (2) Uneven heaving in buildings. The peat precipitation tanks were located on the east side of the site (Figure 2). There were four main tanks, Nos. 1 to 4 from west to east. Tanks are 4 m in width and height. The length of No. 1 and No. 4 tanks was m and that of No. 2 and No. 3, 146 m. Adjacent to the main tank to the south were secondary tanks. The total storage capacity of the tanks was 108,000 m 3 (Figure 4). During the quake, all tanks were full of peat water. A 40 m wide, 10-ton crane was parked on top of the reinforced concrete rail wall about 30 m from the west end of the No. 3 tank (Figure 5). The ground, rail wall and tanks cracked in the quake, causing serious leakage of peat water from the tanks. In fact, the peat water was completely drained in just 5 hours after the quake. The wall near the No. 3 and No. 4 tanks experienced large horizontal displacements and differential settlements. The damage survey conducted in October, 1976 indicated a large relative horizontal displacement of the north wall of 268 mm, the south wall 150 mm, a vertical settlement of 93 mm for the north rail wall, and 139 mm for the south rail wall (Figure 6). Moreover, a longitudinal crack went through the No. 3 and No. 4 tanks near the tank bottom along the edge of the tank foundation. The crack was 5-40 mm wide, about 200 m long, and offset of the fissure was mm with sand from sand boils found in the crack. Transverse cracks, 5-10 m in length also occurred parallel to the longitudinal crack. Serious depression occurred locally on the bottom of the tank, and two large pits due to the depression were found. The largest pit was located across the south-east corner of the No. 4 tank and the north-east corner of the secondary tank. The area of depression was about 150m 2 (Figure 7). Liquefaction-induced fracture and offset were also found in both pipelines buried at 3 m depth and observation wells at the south side of the No. 3 and No. 4 tanks (buried depth of which was over 3 m). A boiler house is located in the south-central area of precipitation tanks. The building covered an area of only 5.7 m 7.0 m. The west wall of the building was placed directly on an existing curtain wall; the foundation was rather shallow. Due to liquefaction of the foundation soil, the entire building tilted to the west nearly 20. The foundation of a pump house, west of the boiler house, was 9 m deep. Although sand boils occurred in the vicinity of the building, no building damage or tilting was found. The drying plant of the floatation processing plant was 7 stories high with a total height of 32.5 m. Below the height of m was a four-story cast-in-place reinforced concrete framed structure with a reinforced concrete raft foundation. Above the height of m were steel beams and columns, R.C. cast-in-place slab and steel roof trusses with precast corrugated roof slabs. The foundation sandy soils liquefied during the earthquake and a few sand boils were observed in the neighborhood of the plant. After the quake, the cinder block wall above the height of m experienced cracks, and the roof top displaced 50 mm. (3) Ground deformation. The whole ground surface at the site settled. Because all bench marks in the mining district were destroyed, settlements were difficult to measure. Based on the measured relative settlement of the building, the average settlement of the ground at the site was estimated at up to 30 cm. In addition, there were some depressions, m in diameter, in the southeast and central parts of the site. The greatest depression exceeded 1 m in depth. This could be caused by the collapse of some small coal mine shafts.

42 480 (4) Cracking of the shaft. Circular cracks of different severity occurred on the walls of all vertical shafts located in the area with soil liquefaction. The inner diameter of the secondary shaft was 5.6 m and the thickness of the upper shaft wall was 500 mm. A circular crack occurred at 13.6 m from shaft entrance. The shaft wall fractured and dislocated up to 130 mm in the southeast direction. Cracks developed along a height of 1 m from the entrance (Figure 8). Sand was observed to continue to flow out of the cracks with the total amount estimated at 1 m 3 on November 15, Moreover, the mine shaft of the Xujialou Mine and the Qianjiaying Mine cracked similarly. The vertical shaft of the Xujialou Mine dislocated laterally mm at a depth of m; sand-water mixture was found to blow out of the cracks. The shaft tower of the vertical shaft, m high, inclined to the west and south by 335 mm and 145 mm, respectively. Elevating center line at the entrance of the shaft displaced mm to the west and mm to the south. The average settlement of the shaft was 200 mm. Many cracks occurred on the walls of the R.C. box foundation (Figure 9). Some cracks were observed to concentrate at the girder support of the wall at the east and west sides from the bottom slab to the top; some cracks occurred on the foundation beam from the top of the beam to the bottom slab. The sleeve of the bore hole in the Dongfeng shaft of the Qianjiaying Mine tilted northwestward from 10 m above, and displaced 400 mm on the surface. 2. Exploration of the Liquefied Sandy Soils The subsurface exploration did not indicate significant lateral variation of the foundation soils at the Lujiatuo Mine (Figure 10). The boring log in Figure 11 shows shallow layers of the Quaternary system. (1) Standard Penetration Test (SPT). Winch, automatic off-hook and free falling techniques were used in the standard penetration test. Due to significant difference in blow counts obtained in the standard penetration tests by use of rotating boring and impact boring techniques, with the impact boring giving smaller blow counts (Figure 12), the rotating boring was used and the borehole was filled with slurry. Blow counts are quite scattered. Blow counts of soils at the same depth but from the borehole only a few meters apart can be quite different. To obtain accurate test results, 10 SPT tests were conducted at the depth interval of 1 meter in an area. For statistical analysis, the maximum or minimum values were deleted (not exceeding 10%). Then, the average value was calculated. Figure 13 and Table 3 show the comparison of SPT results before and after the quake. The data indicate that the blow counts of saturated fine and medium sands located at 5.4 meters below the ground surface are 1 to 5 blows less after the quake than before. The blow counts of the sand layer at the depth of 4.0 to 5.4 meters decrease greatly after the quake. It must be pointed out that these tests were carried out 9 months after the quake. (2) Static cone penetration test (SCPT). Static cone penetration tests were carried out to identify the liquefaction of saturated sandy soils in the Lujiatuo Mine. A hydraulic double

43 481 cylinder cone was used. The transducer element was a single bridge probe with a wall of 7 mm and the cross sectional area of the cone was 15 cm 2, having a penetration velocity of 1.5 m/min. The results were recorded automatically. Comparison of the data obtained before and after the quake is shown in Figure 14. Comparison of the data on the saturated sand layers above the depth of 5.4 m is listed in Table 4. The specific cone penetration resistance of saturated fine and moderate sand layers above the depth of 5.4 m was found to decrease after the quake. This implies that sand layers to a depth of 5.4 meters were loosened by the earthquake. The sand below the depth of 8 meters was found to have densified somewhat. (3) Correlation between SPT and SCPT results. For the saturated uniform, fine and medium sands at the Lujiatuo Mine, the functional relation between corrected SPT blow counts, N 63.5, and specific SCPT resistance, P s, is determined by statistical analysis (Curve 1 in Figure 15): Ps = N 635. The correlation coefficient of g = 0.9 indicates a strong correlation between the two. In addition, similar correlation curves from Japan, India, Greece and the U.S.S.R. are also plotted in Figure 15 for comparison. Because the cone top resistance was plotted against the standard penetration resistance (or blow count N) for all foreign data, it is reasonable that Curves 2-4 from the foreign data are situated below Curve 1. (4) Soil properties 1) Physical properties of clayey soils in the surface layer are listed in Table 5. It can be seen that density of the soil decreased slightly after the quake. 2) Physical properties of the saturated fine and moderate sands and the relative density derived from N 63.5 value are listed in Table 6. Data in Table 6 show that the saturated sands at the Lujiatuo Mine are fine and uniform with relatively low densities. This implies low resistance of this sand to earthquake-induced liquefaction. 3) The clayey soil at m below the ground surface had low plasticity and changed into light loam at the depth of m. Their liquidity index ranged from This indicated that they could be in a flow and plastic state and liable to vibro-liquefaction. The static cone penetration test results obtained before and after the quake showed that the soil had densified somewhat after the quake (Table 7). At the depth of m, the plasticity index of the soil was 11 and that of the light loam usually about 9. The gradation analysis indicated that 30 to 33% of the soil had grain size greater than 0.05 mm and 17-21% of the soil had grain size smaller than mm and was classified as clayey soil. The soil was not susceptible to liquefaction, particularly for the soil with high clay content and with sand content less than 40%. Although this soil had not liquefied, the SPT drill rod under a static load of 63.5 kg weight fell 10 to 15 cm when it reached the top of the layer and the penetration of the first

44 482 blow was quite large, up to cm. This happened frequently in the area where liquefaction was serious. 4) The saturated silty sand layer below the depth of 7.7 m was slightly densified after the quake. Such densification of the soil after the quake can be estimated using the specific penetration resistance from the static cone penetration tests (Figure 14). P s values of the soil ranged from 135 to 150 kg-force/cm 2 and the soil was still a stable dense sand after the quake. (5) Effects of effective overburden pressure on liquefaction. The ground surface at the Lujiatuo Mine is quite flat and the groundwater hydraulic gradient is very small. The Tangshan earthquake occurred during the rainy season and the water table was about 1.2 m below the ground surface. The groundwater table during the exploration (April 1977) was 1.7 m and the head difference was only 0.5 m. Thus, the ground topography and the groundwater table either had not changed or had not changed much from the time of the quake to the time of the exploration. The foundation soil was quite uniform in the horizontal direction. When neither density nor sand content varied much, the overburden pressure became an important influencing factor for liquefaction. The liquefaction at the site, in fact, was serious in the eastern and the western section where the overburden pressure was small, but mild in the central area where the effective overburden pressure was comparatively greater. The curve in Figure 16 shows the variation of the effective overburden pressure in the west-east direction. The boundary value of effective overburden pressure between the lightly liquefied area and the seriously liquefied area is 0.4 kg force/cm 2. This shows that the initial overburden pressure does affect the liquefaction resistance of soil to a certain extent. There is another similar example. The working area of the Fangezhuang Mine and the proposed site for the Coal Processing plant, close to the west of the working area, were sites both located in the area of intensity IX. Both the particle size distribution and the relative density of sand at these two sites were similar. At the Coal Processing Plant, the sand layer was exposed without an overlying layer and the water table was close to the surface. Severe sand boils at the site indicated serious liquefaction. To the west of the mine shaft located next to the plant, there was an overlying layer m thick over the sand layer with an effective overlying pressure of about 0.3 kg-force/cm 2. The water table was about 2 m deep. Liquefaction was also rather serious at the site. At the site east of the main and secondary shaft entrances, where the sand had an overburden layer of m thick with an effective overburden pressure of about 0.5 kg. force/cm 2, liquefaction was quite mild and almost no sand boils occurred. (Translator: Lu Rongjian)

45 483 Table 1. Grading of sand particles from sand boils. Sampling location >1 (mm) E-1 Pump house E-2 Pump house W-1 Workshop (mm) Sieve Analysis (%) (mm) (mm) <0.1 (mm) Natural slope inclination (under water) Average particle size (mm) Effective particle Inhomogeneity size (mm) coefficient Classification Fine sand Fine sand Fine sand

46 484 Sampling depth (m) >1 (mm) (mm) Sieve Analysis (%) (mm) Table 2. Particle composition of the undisturbed sand (mm) <0.1 (mm) Natural slope inclination (under water) Average particle size (mm) Effective particle Inhomogeneity size (mm) coefficient Classification Fine sand (Light yellow) Fine sand (Light yellow) Moderate sand (Light yellow) Fine sand (Greyish green)

47 485 Table 3. Comparison of standard penetration blows, N 63. 5, before and after the quake. Depth (m) N 63.5 (Individual value /Ave. Value) Difference of Decrease rate blows* (%) Before the quake After the quake N DN/ N before the quake / / / / / / / / *"-" indicates that the average blow count after the quake is Less than the blows before the quake Table 4. Specific penetration resistance, P s, before and after the quake. P s (kg force /cm 2 ) Decrease Depth (m) Before the quake After the quake Ps rate (%) / / / / / / / / Table 5. Physical properties of clayey soil in the surface layer. Index Testing time Water content Vol. Weight (g /cm 3 ) Dry vol. wt. (g /cm 3 ) Porosity Degree of saturation Before the quake After the quake

48 486 Table 6. Physical properties of saturated sand layers. Effective Relative density Index particle Ave. particle Inhomogeneity Before After the Depth (m) size (mm) size (mm) coefficient the quake quake Variation Table 7. P s value for the clayey soil and the light loam. ps kg force cm2 Difference of Depth (m) Name of soil Before the quake After the quake P s Values (kg-force /cm 2 )* Clayey soil Light loam *Plus sign indicates that p s value after the quake is greater than that before the quake. Figure 1. Geographic Position of Lujiatuo Mine.

49 Main shaft; 2. Bye-shaft; 3. Main workshop of the coal processing plant; 4. Boiler; 5. Peat precipitation tank. Figure 2. Schematic diagram for the working site of Lujiatuo Mine. Figure 3. Fracture of the raft foundation of the winch workshop in the main shaft of Lujiatuo Mine

50 488 Figure 4. Arrangement of peat precipitation tanks (Elevation: m; size: mm). Figure 5. Construction of the rail wall(elevation: m; size: mm).

51 489 Figure 6. Horizontal relative drift of the rail wall and differential settlement of the rail.

52 490 Figure 7. Crack and local depression occurred in the bottom slab of No. 4 main tank. H depth(m); N63.5 standard penetration blow count; e penetration; γ volume weight (g/cm 3 ) Figure 8(a). Log diagram for the secondary shaft well of Lujiatuo Mine Figure 8(b). Cracks on the secondary shaft well of Lujiatuo Mine.