* B-2. distance (cm) (cm) B-3-3 B-1 B-1 B-3. Figure 5 Obtained compacted earth from the Tumulus mound and the profile o

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1 Geotechnical properties of Takamatsuzuka tumulus and its stability Mamoru Mimura and Mitsugu Yoshimura Introduction Takamatsuzuka tumulus was discovered at Asuka village in Nara prefecture in Mural paintings were found on the lime wall-plaster of the chamber stones, which are made of tuff-breccia quarried from Nijo mountain. The paintings and tumulus have been designated national treasures and special historical relics respectively, and they have been preserved by maintaining the same conditions inside the chamber as in the surrounding natural underground environment (Fine Arts Division, Department of Cultural Properties, Agency for Cultural Affairs, Government of Japan 2007). Takamatsuzuka tumulus is constructed on a gentle south facing slope. The lower mound has a diameter of 23 m, the upper 17.7 m (Agency for Cultural Affairs, Government of Japan 2006, Watanabe and Ishibashi 2008). The chamber is constructed of 16 tuff-breccia stones: four floor stones, four ceiling stones, three east side stones, three west side stones, one north side stone, and one south side stone. The chamber is 2.65 m deep, 1.03 m wide, and 1.13 m tall. The mound of the Takamatsuzuka tumulus is constructed of compacted earth, Hanchiku in Japanese, one layer of which is only several centimeters thick. The material of the compacted earth is mainly a decomposed granite called masado, that can be widely seen around Asuka Village. The mural paintings of the Takamatsuzuka tumulus have been seriously damaged by various fungi on the lime wall-plaster of the chamber stones (Kigawa et al. 2006). On the basis of scientific discussion among professionals, a decision was made to dismantle the painted stone chamber, and the stones were transferred to a preservation facility for restoration as it was found impossible to preserve the mural paintings in situ (Agency for Cultural Affairs, Government of Japan 2005). A geotechnical investigation was carried out to evaluate the reasons for the damage as well as to derive the mechanical soil parameters. A series of laboratory tests were conducted on undisturbed samples obtained from the Tumulus mound. In-situ tests were also carried out to determine the physical and mechanical properties of the tumulus mound for stability analysis during excavation of the mound and dismantling of the chamber stones. Structure of the Tumulus mound Before the stone chamber was dismantled, archaeological investigation was carried out beginning October 2, Geotechnical investigation was conducted during the excavation of the Tumulus mound. A cross-sectional view of the Tumulus mound is shown in Fig.1. However, it should be noted that this cross-sectional view is schematic; the exact coordinates and dimensions of the Tumulus mound will Outer compacted earth Fig.1 Fig.2 Inner compacter earth (White Hanchiku) 石室 chamber 石室 Lower compacted earth (Alternating with decomposed granite and planed tuff breccia) Schematic structure of Takamatsuzuka tumulus Appearance of the inner compacted earth surrounding the stone chamber Kyoto University 83

2 wet (g/cm density 3 ) 10 m * stone chamber Figure 4 Location of sampling at the mound of Takamatsuzuka Tumulus be given in the forthcoming official report. It is clear from Fig.1 that different types of compacted earth were used in the mound. The outer part of the mound is made of ordinary decomposed granite, brown to red in color, while the stone chamber is covered by a stiffer inner compacted white earth (Fig.2), underlain by alternating compacted earth with the ground powders from the chamber stones and decomposed granite (Fig.3). distance (cm) (cm) wet (g/cm density 3 ) B-3-3 Fig.3 Lower compacted earth with alternating layers of decomposed granite and planed tuff breccia from the chamber stones Figure 5 Obtained compacted earth from the Tumulus mound and the profile o Sampling from the Tumulus measured mound was by RI core densimeter (sample from B-3 borehole) performed in 2005 at the designated points shown in Fig.4 (Mimura and Ishizaki 2006). A sophisticated procedure, the Air-boring Method (Okuda et al. 2006), was adopted to avoid: the effect of vibration on the mural paintings; water intrusion to the stone chamber; and damage to the mound surface. Eighteen soil samples in 1m transparent acrylic samplers were Fig.5 Compacted earth obtained from the Tumulus mound and the profile of wet density measured by an RI core densimeter (sample from B-3 borehole) B-1 B-1 Fig.6 Earthquake induced cracks and fissures in the Tumulus mound Fig.4 10 m * B-2 B-3 B-3 * stone chamber Location of sampling at the mound of Takamatsuzuka Tumulus successfully taken from the mound. A radio isotope (RI) density measurement was carried out on all the samples to determine the profile of the RI density of the compacted earths. Fig.5 shows an example of the soil samples together with the distribution of the density. The definite horizontal structures of thin layers caused by compaction during construction of the mound can be seen. The result of the RI density measurement shows that the density at the compacted surface tends to be higher, whereas the measurement 84

3 at the bottom plane of each strewed soil becomes lower due to the dispersion of compaction energy. It is surprising that the effect of compaction energy on the density structure of the tumulus mound is still occurring 1300 years after construction. Innumerable cracks and fissures caused by huge earthquakes were found inside the Tumulus mound. Those cracks and fissures were originally found on the excavated walls (Nara National Research Institute for Cultural Properties 2006, Mimura and Ishizaki 2006). The large-scale excavation prior to the dismantling of the stone chamber in 2006 gave us additional information about the three-dimensional distribution of those cracks and fissures. One example of the observed cracks and fissures is shown in Fig.6. Serious ground motion due to huge subduction earthquakes hitting Japan every 100 to 140 years is the most probable cause of the damage to the Tumulus mound. The instability of the Tumulus mound is one reason why it was judged to be impossible to preserve the mural paintings in situ. Physical and mechanical properties of compacted earth based on laboratory experiments The physical properties of the compacted earth materials (Hanchiku) in terms of the density of Table 1 Density of soil particles and natural water content Percentage Finer% 100 ρ s (g/cm 3 ) w n (w min - w max ) % B ( ) B ( ) B ( ) Fig.7 Lower Green 0 Diameter of Particlesmm B-1 B-2 B-3 Inner White Grain size distribution curves for each compacted earth soil Shear stress (kn/m 2 ) Shear stress (kn/m 2 ) Shear stress (kn/m 2 ) Fig.8 B-1 specimen Vertical stress (kn/m 2 ) B-2 B-2 specimen Vertical stress (kn/m 2 ) B-3 B-3 specimen Vertical stress (kn/m 2 ) Stress paths of direct shear tests on outer compacted earth soils and derived parameters c and φ particles and natural water content are shown in Table 1. Grain size distribution relationships are shown in Fig.7 for each compacted earth. The water content of the materials lies between 16 and 20%, except the lower compacted earth, which has very low values 85

4 because it contains crushed breccia. Each material was found to be well-graded, with about 40% finer content. These well-graded soils were very suitable for making compacted earth (Hanchiku) because they are easily compacted and densified. As shown in Fig.7, the mound is composed of well compacted sandy soil with sufficient fine contents for compaction. In the present research, a series of direct shear tests were conducted on specimens with a diameter of 60 mm and a height of 20 mm. It was almost impossible to make triaxial specimens (50 mm in diameter and 100 mm in height) due to the difficulty of trimming. The testing results in terms of the stress paths are shown in Fig.8 for the outer compacted earth. Here, B-1, B-2, and B-3 denote the boreholes Shear stress (kn/m 2 ) Fig.9 Shear stress (kn/m 2 ) Vertical stress (kn/m 2 ) 33 Stress paths of direct shear tests on inner compacted earth soils and derived parameters c and φ 48 Vertical stress (kn/m 2 ) Fig.10 Stress paths of direct shear tests on lower compacted earth soils and derived parameters c and φ shown in Fig.4. As shown in Table 1, the B-2 soils have a relatively higher water content compared with the other soils, such as B-1 and B-3. The test results for B-2 reflect the different behavior from that of decomposed granite. The results for B-1 and B-3 are more realistic. On the basis of the experimental results shown in Fig.8, the mechanical parameters were evaluated as the cohesion c equal to 100 to 120kN/m 2 and as the friction angle φ equal to 35 to 36 degrees. These values were adopted for the stability analyses for excavation of the mound as well as for the evaluation of the bearing capacity of the foundation for the crane that was required to lift the chamber stones. The experimental results for the inner compacted earth and lower compacted earth are shown in Figs. 9 and 10. The performance of the inner compacted earth is similar to that of the outer one shown in Fig.8. The mechanical parameters are evaluated as the cohesion c equal to 120kN/m 2 and the friction angle φ equal to 33 degrees. On the other hand, the compacted earth beneath the stone chamber exhibits much stiffer behavior than the outer and inner compacted earths. Based on the experimental results, the cohesion c and friction angle φ are derived as 250 kn/m 2 and 48 degrees, respectively. Evaluation of in situ strength of the Tumulus mound In situ tests are very useful for detecting the mechanical parameters in terms of the strength index without the effect of disturbance. Penetration tests such as the standard penetration test (SPT) and cone penetration test (CPT) are normally adopted for construction projects. Those tests are associated with the destruction of the ground due to penetration because the strength is generally defined as the stress at failure. In the case of historic remains which cannot be damaged or destroyed, in situ tests which might damage them and cannot be used. In the present study, therefore, the needle penetration test was adopted as the one with the least impact on compacted earth needle spindle spring Fig.11 Figure Schematic 11 Schematic View of Needle View of Penetration Needle Testing Penetration Testing Apparatus 86 (a) (b) (c)

5 (Mimura and Yoshimura, 2008). A schematic structure of the needle penetration testing apparatus is shown in Fig.11. When the frontal needle is manually driven into the target soil, the penetration force, P, can be calculated from the deformation at the spindle caused by the compression of the spring. Once P is derived, the ratio Δ=P/L is calculated. Here, L is defined either as the penetration depth at peak penetration force or the maximum penetration depth (10mm). On the basis of the calibration between Δ and the unconfined compression strength, q u (kn/m 2 ), the in situ measurement with the needle penetration test can give the unconfined compression strength, qu for the target soil. Penetration tests on the plane were carried out on: (1) the circumferential ridge of width 93 cm where the base of the crane frames will be set (2) the inner white compacted earth 10 cm above the ceiling stones (3) the lower accumulated compacted earth just beneath the floor stones Using a transparent nylon sheet with a grid mesh (10 cm x 10 cm), penetration tests were conducted on the intersection of the grids allowing the necessary parameters for stability analysis to be determined, based on reliable information from the overall distribution of strength of the target plane, thereby avoiding the influence of irregular values. The distributions of the calculated unconfined compression strength, q u are shown in Fig.12. First, let us consider the strength of the plane on the circumferential ridge of the crane foundations shown as a contour in Fig.12(a). The soil on this plane is outer compacted earth, a sample of which is shown in Fig.5. Superior strength distributes in the range of 200 to 400 kn/m 2 while q u tends to become slightly larger as the penetration point approaches the center. Because cohesion c is defined as c=q u /2, the derived cohesion c from the needle penetration test distributes 100 to 200 kn/m 2, which almost matches the results from laboratory tests on the same compacted earth materials (Fig.8), although the in situ values were slightly overestimated. It should be noted that the derived values of c are large for compacted earth with decomposed granite. Considering that the Tumulus mound was constructed using manual compaction, the construction technique and procedure at the time have to be highly regarded. The graph of the unconfined compression strength on the inner white compacted earth at 10 cm above the ceiling stones is shown in Fig.12(b). Compared to Fig.12(a), superior (a) (b) (c) Setup Surface for Crane Setup Surface for Crane N-S Ridge N-S Ridge N-S Ridge E-W Ridge Inner White Hanchiku E-W Ridge E-W Ridge Antechamber Antechamber Antechamber ( 10 2 kn/m 2 ) q u Fig.12 Distribution of the transformed strength, qu from the measured results by needle penetration tests, (a) surface of the circumferential ridge where the foundation of the crane frame will be set, (b) 10 cm above the ceiling of the chamber, (c) beneath the floor stones 87

6 strength distributes in the larger range of q u =400 to 600 kn/m 2 (c=200 to 300 kn/m 2 ). This is because the inner compacted earth is thought to be constructed of greater strength to protect the stone chamber. It was also confirmed by archaeological evidence that the thickness of each layer of the inner compacted earth is smaller (3 cm each), and traces of re-compaction of particles 3 to 4 cm diameter to gain more strength are found (Matsumura 2008). The higher strength inside the circumferential ridge shown in Fig.12(a) was caused by the existence of the inner compacted earth just beneath this area. The graph of the unconfined compression strength on the lower accumulated compacted earth beneath the floor stones is shown in Fig.12(c). As was stated before, this compacted earth alternated between decomposed granite and ground powder from the chamber stones. The superior strength distributes in the range of q u =600 to 1200kN/m 2 (c=300 to 600kN/m 2 ). The derived strength is definitely much larger than that for the outer and inner compacted earth soils. It was inferred that the lower compacted earth was constructed firmly enough to support the stone chamber and maintain its stability for a long time. Stability assessment of the Tumulus mound during excavation and during dismantling of the stone chamber A large scale excavation, more than 5 m in depth, was required in order to dismantle the stone chamber and take the chamber stones out of the Tumulus. The stability of the excavated wall plaster was one issue as was the bearing capacity of the Tumulus mound where the foundations of the crane were to be placed No-rail Crane Steel Plates Stone Camber Mound of Compacted earth Soilbag (mound) oss-section Fig.13 Schematic of dismantling cross-section site of with dismantling crane foundations site with crane foundations Stability analysis of the excavated wall and the evaluation of the bearing capacity of the crane foundation were assessed using the strength parameters derived from the in-situ and laboratory test results stated in the previous chapters. A schematic cross-section of the dismantling site is shown in Fig.13. The lower excavated zone where the stone chamber exists was excavated leaving about 1m between the edge of the excavation and the side wall of the stone chamber. This was to avoid destroying too much of the Tumulus mound. At the top of the lower excavated zone, the circumferential ridge (93 cm in width) was made to function as the foundation for the crane frames. The necessary support system needed to be put in place to ensure the stability of the excavated walls of the Tumulus during excavation as well as the lifting of the dismantled chamber stones. However, schemes ordinarily used for construction projects could not be used in this site because piling and anchorages would damage the precious historical remains. Initially, the stability of the crane frame foundation (in terms of the bearing capacity of the circumferential ridge in the Tumulus mound) was evaluated. The soil parameters were derived from the in situ needle penetration test as well as the laboratory direct shear test. The wet unit weight, γ is determined as kn/m 3 based on the results from the in situ RI density measurement. The maximum applied force to the crane foundation, q max is assumed to be 44 kn/m 2 assuming that 4.5 t, the full weight of both the steel crane and the lifted stone, is applied to one base of the crane foundation set up on the steel plate on the ridge with a width of 93 cm. The calculation and the results of the assessment are listed in Table 2. Compacted earth is assumed to consist of c materials with designated values of c that are determined from the in situ needle penetration test and the simplified bearing capacity test. To be on the Table 2 Parameters and estimated results of the stability analysis for the crane foundation Cohesion, c (kn/m 2 ) Friction Angle, Allowable Baring Capacity Judgement (Factor of Safety) Case kn/m 2 (9.3) Case kn/m 2 (5.4) Case kn/m 2 (6.0) Case kn/m 2 (4.9) Case kn/m 2 (0.9) Case kn/m 2 (0.5) Notes Needle Penetration Test Simplified Bearing Capacity Test (CASPOL) Stones 88 Ceiling 4 Status of Earth Retaining Wall No Earth Retaining Wall Load of Lifting Lift up

7 safe side, the friction angle φ is assumed to be zero although its value is 35 to 36 degrees, as shown in Fig.8. Additional cases such as Cases 3 and 4 are introduced where the cohesion c is declined with 1σ considering the scattering of the testing data and the effect of anisotropy of the compacted earth soils. The values of c derived from the laboratory direct shear test are also included in this range. The assumption that the compacted earth is complete frictional materials without cohesion (Cases 5, 6) is introduced as extreme cases to understand the calculated sensitivity. The baring capacity formula by Terzaghi is introduced to derive the allowable bearing capacity for these particular problems as follows: 1 q a = α c N c 3 (1) Here, q a is an allowable bearing capacity, α is set to be 1.3 for rectangular foundation, and N c is the coefficient of the bearing capacity which is set at 5.1 for cohesive soil. In the case that the material is fully frictional, the following equation for q a should be used (for Cases 5 and 6). 1 q a = β γ 1 B η N γ 3 (2) Here, β is set as 1.3 for the rectangular foundation, γ 1 is the wet density of the soil (16.43 kn/m 2 is adopted), B is the minimum width of the base of the foundation, and η is defined as (B/B 0 ) 1/3 where B 0 is assumed to be 1.0. The coefficient of the bearing capacity N γ can be derived from the internal friction angle φ of the soil. The calculations of the allowable bearing capacity for all cases are also listed in Table 2 together with the safety factors in terms of q a /q max. Except Cases 5 and 6, which are the cases for sensitivity analyses as reference with unrealistic assumptions for the compacted earth, the stability for the bearing capacity of the crane foundation is completely guaranteed. It is true the stability of the Tumulus mound in terms of the equilibrium of forces is confirmed during lifting the dismantled chamber stones out of the lower excavated area, but additional concerns about deformation which would induce instability of the Tumulus mound has to be evaluated. Mainly due to the existence of innumerable cracks and fissures in the Tumulus mound, the following unfavorable situations could occur. (1) Differential settlement at each foot of the crane frame possibly takes place because of the compression of cracks and fissures due to the applied force of the dead weight of the steel crane frame and the chamber stones. (2) Unexpected deformation toward the inside of the lower excavated area could occur as there are no structures to resist soil movement. (3) If there are dip slope cracks and fissures in the mound, serious sliding failure is expected. If any one of those situations listed above occurs, the crane frame would become unbalanced, which may cause the crane not to function. Unexpected deformation of the excavated mound would also endanger the investigators and technicians in the excavated area. In order to avoid this, an earth retaining system was introduced. The adopted retaining wall structures for the excavated area of the Tumulus mound are shown in Fig.14. Here, the earth retaining system was updated as the dismantling process progressed. First, steel plates were set up on the circumferential ridge in order to support the dead Stones Ceiling 4 North Wall Ceiling 3 West Wall 3 East Wall 3 Ceiling 2 East Wall 2 Ceiling 1 West Wall 2 West Wall 1 East Wall 1 South Wall Status of Earth Retaining Wall No Earth Retaining Wall Load of Lifting Lift up Footpath Lift up Lift up Footpath Earth Retaining WallsWooden Sheet Pile 1.6m, L type Reinforced H-steel 1.4 Load of Lifting 190cm Wooden 160cm Earth Retaining Walls Aluminum Sheet Pile 2.5m, L type Reinforced H-steel m Load of Lifting Aluminum Sheet Pile 250cm ed Fig.14 earth retaining Adopted wall earth structures retaining for excavation wall structures of Tumulus for mound and d excavation of Tumulus mound and dismantling of the stone chamber 89

8 A C A: Stone chamber (covered for protection) B: Steel plate on the circumferential ridge C: Aluminum sheet pile D: Wooden sheet pile E: H-steel wale F: L type reinforce H-steel Fig.15 Layout of earth retaining wall system introduced for stability of the excavated Tumulus mound against lifting the chamber stones weight of the steel crane frame and chamber stones. The steel plates make the foundations safer by dispersing the concentrated load at the crane base. Wooden and aluminum sheet piles were introduced to cover the excavated walls supported by H-steel wales. Instead of struts, L-type reinforced H-steels were adopted to restrain the movement of sheet piles F B E D toward the inside of the excavated area. The actual view of the layout of the earth retaining system is shown in Fig.15. The sequence of dismantling and lifting the chamber stones is shown in Fig.14, together with the corresponding earth retaining wall structures adopted. Stress analyses were conducted for the earth retaining system. The weight of the crane, crane frame, and chamber stones were applied to the foundation of the crane base. Active earth pressure induced by the applied forces was assumed to apply to the sheet piles, and the resultant force from active earth pressure on the sheet piles was assumed to act on the H-steel wales and L-type reinforced H-steel. The calculated results are summarized in Table 3. It was confirmed that the adopted earth retaining system is safe because the mobilized bending stresses on the sheet piles, wales and L-type reinforced H-steel do not exceed the allowable stresses in all cases. Based on this assessment, the earth retaining system was found to function without any difficulties. Table 3 Estimated stability of earth retaining wall structure for dismantling of the stone chamber of Takamatsuzuka tumulus Stones Status of Earth Retaining Wall Bending Stress of Sheet Piles Allowable (kn/m 2 ) Wooden: Aluminum: Bending Stress of Wales Bending Stress of L type Reinforced H- steel Allowable (kn/m 2 ) Allowable (kn/m 2 ) Ceiling 4 None None None None North Wall Wooden Sheet Ceiling 3 Pile 1.6m & L West Wall 3 type Reinforced East Wall 3 H-steel 1.4m Ceiling West Wall 2 Aluminum Sheet East Wall 2 Pile 2.5m & L Ceiling 1 type Reinforced West Wall 1 H-steel 1.4m and East Wall 1 2.0m South Wall

9 Conclusions The stone chamber of Takamatsuzuka tumulus was dismantled and all the chamber stones stored in a preservation center at a temperature of 21 degrees and a humidity of 55%. In association with the archaeological investigation, a series of geotechnical investigations were carried out to discover the physical and mechanical properties of the compacted earth (Hanchiku) of the Tumulus mound. Different types of compacted earths were found. The outer compacted earth was ordinary decomposed granite, while the stiffer inner white compacted earth was constructed to protect the stone chamber, and was underlain by the lower alternating compacted earth with decomposed granite and the ground breccia from the chamber stones. In-situ needle penetration tests were conducted at each different compacted earth, as stated above. The lower alternating layers of compacted earth exhibit very high strength to support this stone chamber that should be free from inclination and deformation. The inner compacted earth was also found to be strong enough to protect the stone chamber from destruction and intrusion of harmful materials from the outside, such as water and insects. Although the outer compacted earth is the weakest in strength, the compacted earth with decomposed granite is still very firm and has sufficient strength to maintain the structure of the Tumulus for over 1300 years. The strength calculated from the in-situ needle penetration tests was well supported by the results derived from laboratory direct shear tests on undisturbed samples from the Tumulus mound. Based on these results, the necessary input parameters were determined for stability analyses of the excavated Tumulus mound as well as evaluation of the bearing capacity of the foundation of the steel crane frame during the lifting of the chamber stones. Geotechnical assessment of the bearing capacity of the foundation of the steel crane foundation and stability of the excavated walls of the Tumulus mound have shown that the Tumulus mound was kept completely stable during both the dismantling of the chamber and the lifting of the stones. While the compacted earth of the Tumulus mound had sufficient strength, to be absolutely sure, the sophisticated earth retaining system with sheet piles supported by wales and L type reinforced H-steel was adopted for chamber dismantling and lifting the chamber stones. Finally, the mural paintings were removed from the Tumulus mound and kept in a room under controlled conditions. Acknowledgements The present research was conducted in association with the preservation project for the mural paintings of the Takamatsuzuka tumulus by the Agency for Cultural Affairs, Government of Japan. The staff of the Agency for Cultural Affairs, Government of Japan as well as those of the National Research Institute for Cultural Properties, Tokyo and Nara gave innumerable help and suggestions. Their courteous cooperation is greatly appreciated. References Agency for Cultural Affairs, Government of Japan duka_kentoukai5. html (in Japanese) (2005) Fine Arts Division, Department of Cultural Properties, Agency for Cultural Affairs, Government of Japan Current situation of the mural paintings of Takamatsuzuka Tumulus, Gekkan Bunkazai, No. 506, pp (in Japanese) (2007) Kigawa, R., C. Sano, T. Ishizaki and S. Miura Concept and measures of the conservation of Takamatsuzuka Tumulus for thirty years and the present situation of biodeterioration, Science for Conservation, No. 45, pp (in Japanese) (2006) Matsumura, K. Excavation for dismantlement of Takamatsuzuka stone chamber, Gekkan Bunkazai, No. 532, pp (in Japanese) (2008) Mimura, M. and T. Ishizaki Current status of Takamatsuzuka Tumulus and its geotechnical properties, Geotechnical Journal, 1 (4), (in Japanese) (2006) Mimura, M. and M. Yoshimura Structure and mechanical properties of compacted earth from Takamatsuzuka Tumulus and Its Stability, Proceedings of the Symposium on Construction and Preservation Technology for Historical Geotechnical Relics, JGS, pp (in Japanese) (2008) Nara National Cultural Properties Research Institute Excavation Report of the Takamatsuzuka Tumulus 2004, pp. 61 (in Japanese) (2006) Okuda, S., M. Mimura and T. Ishizaki Geotechnical investigation and sampling at Takamatsuzuka Tumulus by Air-boring System, TSUCHI-TO-KISO, 54 (4), 91

10 10-12 (in Japanese) (2006) Watanabe, T. and S. Ishibashi General description of Takamatsuzuka Tumulus, Gekkan Bunkazai, No.532, pp.8-11 (in Japanese) (2008) 92