Lacustrine sedimentary responses to earthquakes—soft-sediment deformation structures since late Pleistocene:A review of current understanding

The traces left by earthquakes in lacustrine sediments are studied to determine the occurrence of ancient earthquakes by identifying seismically induced soft-sediment deformation structures(SSDS).Dating can help reconstruct the relative frequency of earthquakes.Identifying seismically induced seismites,which carry abundant seismic information from numerous SSDS,is both critical and challenging.Studying the deformation mechanism of SSDS and learning about the common criteria of seismically induced SSDS improve the identification of earthquake triggers.With better research into SSDS,seismic events can be effectively captured,and temporal constraints can be carried out by 14C dating and optically stimulated luminescence(OSL)dating to identify and date the occurrence of ancient earthquakes.The present contribution primarily addresses the meaning and mechanism of SSDS and their relationship with earthquake magnitude as well as the common criteria of the SSDS induced by earthquakes.

A Preliminary Study on the Soft–Sediment Deformation Structures in the Late Quaternary Lacustrine Sediments at Tashkorgan, Northeastern Pamir, China

This study identified soft-sediment deformation structures （SSDS） of seismic origin from lacustrine sediments in the late Quaternary paleo-dammed lake at Tashkorgan, northeastern Pamir. The observed deformation structures include sand dykes, liquefied diapir and convolute structures, gravity induced SSDS, and thixotropic pillar and tabular structures. We conducted a preliminary study on the morphology, formation and trigger mechanisms of pillar and tabular structures formed by liquefaction of underlying coarse sand and thixotropy of the upper silty clay. The regional tectonic setting and distribution of lacustrine strata indicate that the most probable trigger for the SSDS in lacustrine sediments was seismic activity, with an approximate earthquake magnitude of M〉6.0; the potential seismogenic fault is the southern part of the Kongur normal fault extensional system. AMS ^4C dating results indicate that the SSDS were formed by seismic events occurring between 26050±100 yrBP and 22710±80 yrBP, implying intense fault activity in this region during the late Pleistocene. This study provides new evidence for understanding tectonic activity and regional geodynamics in western China.

Typical Soft–Sediment Deformation Structures Induced by Freeze/Thaw Cycles: A Case Study of Quaternary Alluvial Deposits in the Northern Qiangtang Basin, Tibetan Plateau

With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at Dogai Coring, northern Qiangtang Basin, Tibetan Plateau. Deformation is present in the form of plastic structures(diapirs, folds and clastic dykes), brittle structures(micro–faults) and cryogenic wedges. These soft–sediment deformation features(except the micro–faults) are mainly characterized by meter–scale, non–interlayered, low–speed and low–pressure displacements within soft sediments, most commonly in the form of plastic deformation. Taking into account the geographic setting, lithology and deformation features, we interpret these soft–sediment deformation features as the products of freeze/thaw cycles, rather than of earthquake–induced shock waves, thus reflecting regional temperature changes and fluctuations of hydrothermal conditions in the uppermost sediments. The micro–faults(close to linear hot springs) are ascribed to regional fault activity;however, we were unable to identify the nature of the micro–faults, perhaps due to disturbance by subsequent freeze/thaw cycles. This study may serve as a guide to recognizing the differences between deformation structures attributed to freeze/thaw cycles and seismic processes.

Soft-sediment Deformation Structures Related to Earthquake from the Devonian of the Eastern North Qilian Mts.and Its Tectonic Significance

Devonian in the North Qilian orogenic belt and Hexi Corridor developed terrestrial molasse of later stage of foreland basin caused by collision between the North China plate and Qaidam microplate. The foreland basin triggered a intense earthquake, and formed seismites and earthquake-related soft-sediment deformation. The soft-sediment deformation structures of Devonian in the eastern North Qilian Mts. consist of seismo-cracks, sandstone dykes, syn-depositional faults, microfoids （micro-corrugated lamination）, fluidized veins, load casts, flame structures, pillow structures and brecciation. The seismo-cracks, syn-depositional faults and microfolds are cracks, faults and folds formed directly by oscillation of earthquake. The seismic dykes formed by sediment instilling into seismic cracks. Fluidized veins were made by instilling into the seismo-fissures of the fluidized sands. The load casts, flame structures and pillow structures were formed by sinking and instilling caused from oscillation of earthquake along the face between sandy and muddy beds. The brecciation resulted from the oscillation of earthquake and cracking of sedimentary layers. The seismites and soft-sediment deformations in Devonian triggered the earthquake related to tectonic activities during the orogeny and uplift of North Qilian Mts.

The Seismic Induced Soft Sediment Deformation Structures in the Middle Jurassic of Western Qaidamu Basin

Intervals of soft-sediment deformation structures are well-exposed in Jurassic lacustrine deposits in the western Qaidamu basin. Through field observation, many soft-sediment deformation structures can be identified, such as convoluted bedding, liquefied sand veins, load and flame structures, slump structures and sliding-overlapping structures. Based on their genesis, soft-sediment deformation structures can be classified as three types： seismic induced structures, vertical loading structures, and horizontal shear structures. Based on their geometry and genesis analysis, they are seismic-induced structures. According to the characteristics of convoluted bedding structures and liquefied sand veins, it can be inferred that there were earthquakes greater than magnitude 6 in the study area during the middle Jurassic. Furthermore, the study of the slump structures and sliding- overlapping structures indicates that there was a southeastern slope during the middle Jurassic. Since the distance from the study area to the Altyn Mountain and the Altyn fault is no more than 10km, it can be also inferred that the Altyn Mountain existed then and that the AItyn strike-slip fault was active during the middle Jurassic.

Earthquake-induced Soft-sediment Deformation Structures in the Dengfeng Area,Henan Province,China:Constraints on Qinling Tectonic Evolution during the Early Cambrian

Soft-sediment deformation structures are abundant in the Cambrian Zhushadong and Mantou formations of the Dengfeng area, Henan Province, China. Soft-sediment deformation structures of the Zhushadong Formation consist of fluidized deformation, synsedimentary faults, seismo-folds and plastic deformation; the Mantou Formation is dominated by small-scale horst faults, intruded dikes, fluidized veins, and seismo-cracks. These structures are demonstrated to be earthquake-related by analysis of trigger mechanisms, and may indicate the activity of the Qinling tectonic belt during the early Cambrian. Furthermore, the assemblages of soft-sediment deformation structures altered with time： large-scale, intense deformation in the Zhushadong Formation alters to small-scale, weak deformation in the Mantou Formation. This striking feature may have been caused by changes in hypocentral depth from deep-focus to shallow-focus earthquakes, indicating that the Qinling tectonic belt developed from the subduction of the Shangdan Ocean to the extension of the Erlangping back-arc basin. This study suggests that soft-sediment deformation structures can be used to reveal the activity of a tectonic belt, and, more importantly, changes in deformation assemblages can track the evolution of a tectonic belt.

Soft Sediment Deformation Structures in the Maastrichtian Patti Formation, Southern Bida Basin Nigeria: Implications for the Assessment of Endogenic Triggers in the Maastrichtian Sedimentary Record

Detailed fieldwork carried out in the southern part of Bida Basin, Nigeria, allowed the documentation of soft sediment deformation structures (SSDS) in the Maastrichtian Patti Formation. The aim of this study is to examine the sedimentary successions, describe and analyse these deformation features, discuss their deformation mechanisms and potential triggers. The Maastrichtian Patti Formation is composed of lithofacies interpreted to have been deposited in tidal and fluvial sedimentary environments. Soft sediment deformation structures recognised in the tidal sediments were clastic dykes, load cast, isolated sand balls, dish-and-pillar structures, convolute lamination, diapiric structures and recumbent folds. Severely deformed cross beds, ring structures, associated sand balls, normal folds and recumbent folds were identified in the fluvial sediments. SSDS recognised were interpreted to have been caused by effects of liquefaction and fluidization. Field observations, facies analysis and morphology of the SSDS indicate that there are relationship between the depositional environments and SSDS. Endogenic processes are considered as the trigger agents and they are represented by rapid sedimentation and overloading, impact of breaking waves, pressure fluctuations caused by turbulent water flow, cyclic stress and current generated by storm waves and changes in water table. The present study did not identify exogenic processes as trigger agent. The occurrence of SSDS in southern Bida Basin strongly favoured a non-tectonic origin but a clear relationship high energy processes in tidal and fluvial depositional environments.

Earthquake-related Tectonic Deformation of Soft-sediments and Its Constraints on Basin Tectonic Evolution

The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolution. One representative of the syn-sedimentary extension structure is syn-sedimentary boudinage structure, while the typical example of the syn-sedimentary compression structure is compression sand pillows or compression wrinkles. The former shows NW-SE-trendlng contemporaneous extension events related to earthquakes in the rift basin near a famous Fe-Nb-REE deposit in northern China during the Early Paleozoic （or Mesoproterozoic as proposed by some researches）, while the latter indicates NE-SW-trending contemporaneous compression activities related to earthquakes in the Middle Triassic in the Nanpanjiang remnant basin covering south Guizhou, northwestern Guangxi and eastern Yunnan in southwestern China. The syn-sedimentary boudinage structure was found in an earthquake slump block in the lower part of the Early Paleozoic Sailinhudong Group, 20 km to the southeast of Bayan Obo, Inner Mongolia, north of China. The slump block is composed of two kinds of very thin layers-pale-gray micrite （microcrystalline limestone） of 1-2 cm thick interbedded with gray muddy micrite layers with the similar thickness. Almost every thin muddy micrite layer was cut into imbricate blocks or boudins by abundant tiny contemporaneous faults, while the interbedded micrite remain in continuity. Boudins form as a response to layer-parallel extension （and/or layer-perpendicular flattening） of stiff layers enveloped top and bottom by mechanically soft layers. In this case, the imbricate blocks cut by the tiny contemporaneous faults are the result of abrupt horizontal extension of the crust in the SE-NW direction accompanied with earthquakes. Thus, the rock block is, in fact, a kind of seismites. The syn-sedimentary boudins indicate that there was at least a strong earthquake belt on the southeast side of the basin during the early stage of the Sailinhudong Group. This may be a good constraint on the tectonic evolution of the Bayan Obo area during the Early Paleozoic time. The syn-sedimentary compression structure was found in the Middle Triassic flysch in the Nanpanjiang Basin. The typical structures are compression sand pillows and compression wrinkles. Both of them were found on the bottoms of sand units and the top surface of the underlying mud units. In other words, the structures were found only in the interfaces between the graded sand layer and the underlying mud layer of the flysch. A deformation experiment with dough was conducted, showing that the tectonic deformation must have been instantaneous one accompanied by earthquakes. The compression sand pillows or wrinkles showed uniform directions along the bottoms of the sand layer in the flysch, revealing contemporaneous horizontal compression during the time between deposition and diagenesis of the related beds. The Nanpanjiang Basin was affected, in general, with SSW-NNE compression during the Middle Triassic, according to the syn-sedimentary compression structure. The two kinds of syn-sedimentary tectonic deformation also indicate that the related basins belong to a rift basin and a remnant basin, respectively, in the model of Wilson Cycle.

Deformation mechanism and hydrocarbon significance of Eocene organic-rich fine-grained soft sediments in the Leijia Region,Liaohe Depression

The deformation structure of soft sediments has always been a research hotspot,which is of great significance for analyzing the tectonic and sedimentary evolution background of a basin,as well as the physical properties of reservoirs.Previous studies have reported that a large number of soft sediment deformation structures are developed in the western part of Liaohe depression.In this study,through core observation and thin section identification,various types of deformation structures are identified in the core samples which are collected from the upper Es4 in the Leijia region,western sag of Liaohe depression,such as liquefied dikes,liquefied breccia,convoluted laminae,annular bedding,synsedimentary faults,vein structures,etc.Based on the characteristics of core structure,single well profile and continuous well profile,combined with the regional background,this study clarifies that the deformation structure of soft sediments in the study area is mainly caused by seismic action.It is found that the permeability and porosity of deformation layers in the study area are higher than those of the undeformation layers,which proves that the deformation structure of soft sediments has a good effect on improving the physical properties of reservoirs.

Researches of soft-sediment deformation structures and seismites in China—A brief review

During the past 30 years （1987-2016）, a great progress has been made in researches of soft-sediment deformation structures （SSDS）, seismites and pataeoearthquakes in China. However, the research thought of this academic fietd is not open enough. It is atmost with one viewpoint or one voice, i.e., atmost art the papers pubtished in journals of China considered the layers with SSDS as seismites. On the other hand, the authors are very glad to learn that the professors and students of China University of Petroleum （East China） have proposed different academic viewpoints on the origin of SSDS in Lingshan Istand, Qingdao, Shandong Province, China. It is a very active academic atmosphere. The authors＇ ideas are as follows： （1） The SSDS are sedimentary structures with multi-origin. The term ＂SSDS＂ is a good sedimentary and geological term and shoutd be utilized continuat[y. （2） The term ＂seismites＂ is a term which is definitety assigned to the layers with SSDS induced by earthquakes. It is one type of the tayers with SSDS. It is not equal to SSDS. （3） Some geotogists suggested obsoleting the term ＂seismites＂. These suggestions are rational However, since the term ＂seismites＂ has been utilized for a long time in China and worldwide, to obsolete this term should be discussed and agreement should be acquired from numerous geologists in China and worldwide. It may be suitable that let the geological practice decide whether to obsolete it or not. （4） Hopefully, further progress will be made in the researches of SSDS.

Typical earthquake-induced soft-sediment deformation structures in the Mesoproterozoic Wumishan Formation, Yongding River Valley, Beijing, China and interpreted earthquake frequency

The Mesoproterozoic Wumishan Formation, composed of dolomite is a widely distributed stratigraphic unit in the Beijing area. It was formed over a long period of time in the Yan-Liao aulacogen, a stable peritidal environment that was ideal for recording earthquakes in the form of soft-sediment deformation structures (SSDS). Numerous examples occur in the upper part of the Wumishan Formation, along the Yongding River Valley. In addition, brittle structures include intrastratal fault and seismically cracked breccias. The soft-sediment deformation structures include liquefied features (diapirs, clastic dykes, convolute bedding), compressional deformation features (accordion folds, plate-spine breccias, mound-and-sag structures), and extensional plastic features (loop-bedding). Based on the regional geological setting and previous research, movements along the main axial fault of the Yan-Liao aulacogen are considered as the triggers for earthquakes since the Early Mesoproterozoic. The number and distribution of the SSDS suggest the major earthquake frequency in the Wumishan Formation of 20 to 32 thousand years.

Earthquake-induced soft-sediment deformation structures in the Mesoproterozoic Wumishan Formation,North China,and their geologic implications

Soft-sediment structures are key to defining seismites. Two soft-sediment deformation horizons, bounded by undeformed carbonate strata, have been found in the Wumishan Formation in the Jumahe region, 175 km southwest of Beijing. One is in the lowest part of Wumishan Formation; and the other is in the uppermost part of Litho-member I. The soft-sediment structures in these two horizons fall into three categories: mould-and-sag structures, hydraulic shatterings and liquefaction dikes. The mould-and-sag structures are divided into two types: one developed in tidal-flat sediments, accompa-nied by many liquefaction-related structures and characterized by autochthonous post-earthquake sediments in sags, and the other type developed in deep-water environments, is not associated with liquefaction structures, and is overlain immediately by seismogenic tsunamites. The hydraulic shat-terings are composed of pockets of fluidization conglomerate, sand intrusions, and syndepositional faults. The liquefaction dikes fall into two categories: hydraulic-fracturing dikes and lateral-spreading dikes. The former are steep, planar, and pinch out upwards. The latter are snake-like and characterized by no diapir-related drag structures in surrounding rocks. Examination of the attitudes and strati-graphic positions of these structures suggests that these soft-sediment structures are seismogenic, and consequently, are seismites. Most seismites in the Wumishan Formation are developed near the former western, margin fault of Yanliao rift. This occurrence suggests that they could be related to movements on this fault. Other geological implications are discussed.

Global case studies of soft-sediment deformation structures(SSDS): Definitions,classifications, advances, origins, and problems

Soft-sediment deformation structures（SSDS）have been the focus of attention for over 150 years.Existing unconstrained definitions allow one to classify a wide range of features under the umbrella phrase＂SSDS＂.As a consequence,a plethora of at least 120 different types of SSDS（e.g.,convolute bedding,slump folds,load casts,dish-and-pillar structures,pockmarks,raindrop imprints,explosive sandegravel craters,clastic injections,crushed and deformed stromatolites,etc.）have been recognized in strata ranging in age from Paleoproterozoic to the present time.The two factors that control the origin of SSDS are prelithification deformation and liquidization.A sedimentological compendium of 140 case studies of SSDS worldwide,which include 30 case studies of scientific drilling at sea（DSDP/ODP/IODP）,published during a period between 1863and 2017,has yielded at least 31 different origins.Earthquakes have remained the single most dominant cause of SSDS because of the prevailing＂seismite＂mindset.Selected advances on SSDS research are：（1）an experimental study that revealed a quantitative similarity between raindrop-impact cratering and asteroid-impact cratering;（2）IODP Expedition 308 in the Gulf of Mexico that documented extensive lateral extent（〉12 km）of mass-transport deposits（MTD）with SSDS that are unrelated to earthquakes;（3）contributions on documentation of pockmarks,on recognition of new structures,and on large-scale sediment deformation on Mars.Problems that hinder our understanding of SSDS still remain.They are：（1）vague definitions of the phrase＂soft-sediment deformation＂;（2）complex factors that govern the origin of SSDS;（3）omission of vital empirical data in documenting vertical changes in facies using measured sedimentological logs;（4）difficulties in distinguishing depositional processes from tectonic events;（5）a model-driven interpretation of SSDS（i.e.,earthquake being the singular cause）;（6）routine application of the genetic term＂seismites＂to the＂SSDS＂,thus undermining the basic tenet of process sedimentology（i.e.,separation of interpretation from observation）;（7）the absence of objective criteria to differentiate 21 triggering mechanisms of liquefaction and related SSDS;（8）application of the process concept＂high-density turbidity currents＂,a process that has never been documented in modern oceans;（9）application of the process concept＂sediment creep＂with a velocity connotation that cannot be inferred from the ancient record;（10）classification of pockmarks,which are hollow spaces（i.e.,without sediments）as SSDS,with their problematic origins by fluid expulsion,sediment degassing,fish activity,etc.;（11）application of the Earth＇s climate-change model;and most importantly,（12）an arbitrary distinction between depositional process and sediment deformation.Despite a profusion of literature on SSDS,our understanding of their origin remains muddled.A solution to the chronic SSDS problem is to utilize the robust core dataset from scientific drilling at sea（DSDP/ODP/IODP）with a constrained definition of SSDS.

Soft-sediment deformation structures related to volcanic earthquakes of the Lower Cretaceous Qingshan Group in Lingshan Island, Shandong Province, East China

The study on soft-sediment deformation structures(SSDS) of Lingshan Island has been one of the hot topics of sedimentology researches in China in recent years,and SSDS developed in turbidite system in the Laiyang Group are widely known by domestic researchers.However,few studies were conducted on the SSDS in fan delta system in the Qingshan Group,Lingshan Island.This study analyzes the classification and characteristics of SSDS especially their lithofacies association and tithologic characteristics through field outcrops investigation and thin section analysis as well.A conclusion was acquired that the paleoenvironment was a fan delta system with occurrence of several volcanic eruptions,where the water became gradually shallower.The SSDS types in the Qingshan Group includes load and flame structure,ball and pillow structure,waterescape structure,hydroplastic deformation structure,plastic sandstone breccia structure,volcanic drop stone and V-shaped ground fissure mainly caused by volcanic earthquakes of three types:(1)seismic waves,(2)gravity and inertia effect of pyroclastic flows,(3)instant differential air pressure;which is different from slumping and tectonic earthquakes occurred in the Laiyang Group.In addition,with the lithofacies association analysis between pyroclastic flow and SSDS beds,a distribution model of SSDS related to volcanic earthquakes can be established:SSDS types changed gradually with their distance further away from the volcanic activity core.Brittle deformation which was common in the proximal zone disappeared gradually;liquefied and plastic SSDS continued to dominate in the medial zone;and slightly liquefied SSDS were developed in the distal zone.Meanwhile,the scale and size of SSDS is negatively correlated with the distance of SSDS depositional locations from the volcanic vent.

滇中芹河隧洞软岩破碎段围岩大变形与支护结构相互作用研究

软岩大变形是滇中引水工程建设中较为突出的工程地质问题之一,以大楚段芹河隧洞4#支洞为研究对象开展软岩大变形特征及承载结构受力研究。4#支洞在施工过程中发生影响洞室稳定的问题,洞周围岩大变形不同程度侵限,导致钢拱架扭曲断裂、喷混凝土掉落现象时有发生。为了充分认识隧洞变形特征、破坏模式及成因机制,结合工程地质勘察、现场监控量测、数值反演及施工模拟分析等手段和方法对其进行综合研究。研究成果表明:破碎软岩洞段施工期围岩监测变形量大、变形速率较快,变形具有明显的时效性;围岩完整性差,洞周变形差异大;围岩以剪切破坏为主;围岩时效变形对支护结构受力影响大,部分承载结构受力超限,导致局部结构破坏。可见,针对破碎的软岩隧洞施工,需要采取超前注浆、减少减小施工扰动、及时跟进初期支护、尽快封闭成环,加强施工期围岩变形监测,选取合理的衬砌支护时机,实时指导和优化隧洞支护结构施工设计。

软土地层45m级超深基坑工程实测变形性状分析

以上海软土地区某挖深45m级超深基坑工程为背景,分析了其实测变形特性。结果表明:地下连续墙的侧向位移随开挖深度的增大而逐渐变大,且变形空间效应显著;由于开挖深度大,地下连续墙的绝对侧向变形量也较大,但最大侧向位移平均值与开挖深度的比值仅为0.43%,与上海软土地区挖深小于30m的基坑变形统计平均值接近;地下连续墙及立柱受开挖卸荷影响,竖向位移表现为隆起,且在底板浇筑工况下隆起值趋于稳定,立柱的最大回弹达65mm;各道支撑轴力增量基本发生在紧邻下方土体开挖工况,且最大轴力值基本发生在第六、七、八道支撑中;基坑外地表沉降均呈“凹槽形”,随施工阶段的推移地表沉降逐步增加,且发生最大沉降的位置随之逐步向坑外发展,而无量纲化地表沉降仍处于上海软土地区统计的沉降包络线范围之内;此外,基坑周边管线、磁悬浮的变形均较小,表明基坑工程的安全可控。

软土深基坑变形及环境影响分析方法与控制技术

随着基坑规模日益增大以及邻近环境设施愈加复杂,合理评估并控制基坑变形及对周边环境影响成为软土基坑工程面临的重要挑战。基于理论分析与工程应用,对软土深基坑变形与环境影响分析方法及控制技术进行了系统研究。首先,在统筹考虑安全与经济的前提下,提出了软土深基坑环境保护等级和变形控制指标,为基坑周边不同类型环境设施的保护提供了依据。其次,系统建立了便于工程应用的基坑变形影响简化分析方法,并提出了基于土体小应变特性的基坑开挖对环境影响的计算分析方法以及确定全套小应变本构模型参数的实用方法,为复杂环境下深基坑环境影响分析提供了重要手段。同时,针对承压水降水影响难以准确量化评估的难题,提出了根据群井抽水试验反演确定关键水文地质参数并评估深层承压水降水对地层和环境变形影响的计算方法,满足了复杂地层承压水降水影响分析的工程需求。此外,还提出了包括支护结构与主体地下结构相结合、数字化微扰动搅拌桩加固、混凝土支撑主动变形控制、承压水控制超深隔渗帷幕等绿色、低碳、环境低影响的基坑变形控制新技术。成果在全国大量工程中成功应用,促进了软土深基坑工程全过程变形影响精细化分析和系统化控制技术的发展,为大规模地下空间的开发利用提供了技术支撑。

水牛蹄型深海集矿机履齿设计及牵引性能研究

作为深海采矿系统的重要组成部分,深海集矿机的技术研究和开发一直是许多国家的难题。为了提高深海集矿机在稀软沉积物上的牵引性能,基于水牛蹄的曲面结构特征和特殊几何结构,设计了一款仿水牛蹄蹄型履齿。以该款履齿的结构参数为研究对象,通过对朗肯被动土压力理论的优化,得到了仿水牛蹄蹄型履齿的牵引力解析解,建立了对应的履齿仿生参数对履齿牵引力的影响公式。结合正交试验方法进行了不同形式履齿在沉积物上运动的单、多履齿剪切试验,将仿水牛蹄蹄型履齿与直型履齿、仿水牛蹄轮廓履齿(另一种仿生履齿)进行对比试验,并通过模型车试验验证了该款履齿的可行性。结果表明:3种履齿中,仿水牛蹄蹄型履齿提供的最大牵引力最高。研究可为进一步优化仿水牛蹄蹄型履齿结构参数和提高深海稀软底质机械的牵引性能提供参考依据。

典型软土地层管廊基坑垫层换撑可行性研究

针对基坑传统换撑方法换撑工序复杂,对管廊结构施工延续性及施工效率影响较大的问题,基于典型软土地层,以广东中山某管廊深基坑工程为背景,提出了利用垫层换撑的新方法.首先,对基坑进行三维Abaqus数值模拟并与实测数据进行对比分析;然后,提出垫层换撑方法并进行数值模拟正交试验,探究采用垫层换撑方法在拆撑后不同因素对基坑围护结构变形影响情况;最后,通过现场试验验证管廊深基坑垫层换撑新方法的合理性和可行性,并将垫层换撑方法与传统换撑方法对于围护结构水平位移影响进行对比.研究结果表明:影响围护结构变形的3个主要因素为垫层改良区域(垫层梁)厚度、混凝土强度等级和纵向钢筋直径,其中垫层改良区域(垫层梁)的厚度极差最大,为影响围护结构变形最显著的因素;垫层换撑现场实验在拆除底部横撑后,围护结构最大水平位移平均实测值仅为21.79 mm,有效解决了软土区围护结构易变形过大的问题,验证了垫层换撑方法的适用性;在基坑地层及开挖条件相同情况下,采用垫层换撑方法围护结构最大水平位移约为传统方法的84%,相较于传统换撑方法能够更好地控制基坑变形.

高应力软岩隧洞稳定性及支护模拟研究

为分析高应力软岩隧洞的变形特征和支护效应,采用FLAC3D软件模拟滇中引水工程深埋输水隧洞软弱围岩稳定性与支护措施,对毛洞和支护条件下围岩的位移场、应力场和损伤破坏区的分布规律以及衬砌受力状态进行分析和围岩稳定性评价。结果表明:对深部软岩施加锚喷支护可以提高岩体的围压和承载能力,显著减小软弱围岩的变形和损伤破坏程度,但仅依靠锚喷支护时,围岩变形仍然较大。施加永久衬砌时的围岩位移释放率越大,衬砌的内力越小,但围岩的变形量越大。建议对高应力软岩洞室采用全断面锚喷支护,提高初期支护的刚度和强度。可根据不同围岩位移释放率条件下永久衬砌的内力和隧洞的变形特征,结合永久衬砌的承载能力和隧洞的净空要求,确定合适的永久衬砌支护时机。