WO2022134224A1 - 一种混凝土扩大头预应力抗拔锚杆的施工方法 - Google Patents

一种混凝土扩大头预应力抗拔锚杆的施工方法 Download PDF

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Publication number
WO2022134224A1
WO2022134224A1 PCT/CN2021/070590 CN2021070590W WO2022134224A1 WO 2022134224 A1 WO2022134224 A1 WO 2022134224A1 CN 2021070590 W CN2021070590 W CN 2021070590W WO 2022134224 A1 WO2022134224 A1 WO 2022134224A1
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steel
casing
concrete
steel casing
peripheral surface
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PCT/CN2021/070590
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English (en)
French (fr)
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李仁民
耿小波
葛立瑞
王涛
刘小波
刘飞
王建兰
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江苏东合南岩土科技股份有限公司
南京深地智能建造技术研究院有限公司
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Publication of WO2022134224A1 publication Critical patent/WO2022134224A1/zh

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    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
    • E02D5/74—Means for anchoring structural elements or bulkheads

Definitions

  • the invention relates to a construction method of a concrete enlarged head prestressed pull-resistant anchor rod.
  • the enlarged end bolt is also called an enlarged head bolt. Because the enlarged head is formed at the bottom end of the bolt through special construction treatment, this kind of bolt can greatly improve the pullout resistance of the bolt.
  • the pullout resistance of the enlarged head bolt is determined by the frictional resistance between the anchor body and the rock and soil mass and the bearing capacity of the end enlarged head. Therefore, under the same conditions, this type of bolt can be used in weaker clay layers and It is used in soil layers where the length of the bolt is limited, which overcomes the weakness that the cylindrical bolt has only the frictional resistance between the anchor body and the rock and soil mass.
  • the commonly used reaming methods for soil expansion head bolts include high-pressure jet cutting and mechanical cutting reaming.
  • the high-pressure jet cutting method uses a rotating high-pressure jet (liquid or gas-liquid mixture) to cut the soil in the anchoring section of the enlarged head to form the required aperture, because it needs to be equipped with a high-pressure grouting pump, and it is necessary to increase the process of replacing the cut slag. , resulting in a large initial investment, and the quality of the cement-soil expansion head is unstable.
  • the mechanical cutting and reaming is a reaming drill using a mechanical linkage mechanism, and the reaming tool has disadvantages such as difficulty in controlling the quality of the reaming, cumbersome operation and unsmooth retraction.
  • the present invention proposes a construction method of a concrete enlarged head prestressed anti-pull anchor, which comprises the following steps:
  • the steel casing is movably pressed against the pile end anchor, and then the steel casing and the pile end anchor are sunk to a set depth together.
  • the pile end anchor includes an anchoring plate; A steel strand is fixedly connected to the tool, and a protective tube is sleeved on the steel strand, and the protective tube is fixed on the anchoring plate;
  • the slump of the fine stone concrete is preferably 180-300mm;
  • the steel strand in this application is preferably an unbonded steel strand, and the unbonded steel strand is made of anti-corrosion grease and an outer casing for double anti-corrosion, which has good durability.
  • the height of the fine stone concrete poured upward exceeds the set height of the pile body by 1-3 meters to make up for the drop caused by the fine stone concrete in the process of settlement and compaction.
  • a static pile driver can be used to directly sink the steel casing and the pile end anchor to the set depth, and when the soil quality is a hard layer such as hard plastic loess, a long Screw or rotary excavation equipment leads the hole, and then vibrates into the steel casing and pile end anchorage.
  • the steel casing is used for pile driving, and the static pile driver with higher pressure can be used for pile driving, so that the pile end anchorage can pass through the dense sand layer, residual soil and strongly weathered rock layer, so as to achieve the design durability. force layer.
  • the expansion head is formed of fine stone concrete.
  • the fine stone concrete spreads into the surrounding soil under the extrusion of the steel casing, and the surrounding soil also synchronously moves outward.
  • the inside of the formed enlarged head is a complete fine stone concrete, and the outer layer is cement soil formed by fine stone concrete and plain soil, so that the enlarged head and the surrounding soil form a whole, with higher pull-out bearing capacity.
  • the enlarged head is directly extruded from the fine stone concrete, there is no hole bottom sediment problem in the prior art.
  • the pile hole is first drilled, and then concrete is injected into the pile hole, and then the concrete is vibrated with a tamping rod, so that the concrete diffuses outward to form the expansion head.
  • the drill bit is hoisted out of the pile hole, the concrete can be injected.
  • the drill bit is hoisted out of the pile hole, it is easy to touch the soil around the pile hole, causing part of the earth to fall to the bottom of the hole. Since these earthworks are difficult to calculate accurately, it is easy to make the enlarged head deviate from the original design height.
  • the pile end anchor also includes a pile shoe arranged on the lower side of the anchor plate, and the outer peripheral surface of the pile end anchor extends beyond the outer peripheral surface of the steel casing.
  • the shoe is provided with a shotcrete hole, and a first grout pipe is inserted between the steel casing and the protective pipe, and the lower end of the first grout pipe extends into the shotcrete cavity after passing through the anchor plate;
  • the pure cement slurry is injected into the shotcrete cavity through the first grouting pipe, and then the pure cement slurry is sprayed out from the shotcrete hole.
  • a grout retaining wall is formed on the inner wall.
  • cement slurry retaining wall In the process of sinking the steel casing and the pile end anchor, the pure cement slurry is sprayed at the same time.
  • the pure cement slurry spreads around and adheres to the inner wall of the pile hole under the extrusion of the pile end anchor to form a cement slurry.
  • the retaining wall, the cement slurry retaining wall can strengthen the inner wall of the pile hole, and avoid the soil collapse of the pile hole due to the steel casing touching the inner wall of the pile hole during the reciprocating process of upward lifting and downward insertion of the steel casing fall, affecting the normal progress of construction.
  • Cement slurry retaining wall also has great advantages in areas with relatively soft soil, which can avoid the collapse of holes due to loose soil, and cannot form available pile holes. Using this application, even in areas with relatively loose soil, it can also be formed smoothly. Available pile holes to allow construction to proceed normally.
  • step (3) after completing the construction of the concrete enlargement head and the pile body, a first grouting is performed through the first grouting pipe, and during the first grouting process, the first grouting is carried out.
  • the grouting pipe is lifted upward, and pure cement slurry is injected at the same time until the bottom end of the first grouting pipe is lifted to the set height.
  • a second grouting pipe is arranged in the protective pipe.
  • the second grouting pipe is used for secondary grouting, During the secondary grouting process, the second grouting pipe is lifted upward, and pure cement slurry is injected into the protective pipe at the same time; Make anti-seepage anchors.
  • the secondary grouting of the protective pipe makes the steel strand wrapped by the cement body as a whole to avoid the corrosion of water body and other substances.
  • the strength of the protective pipe can be guaranteed, and the protective pipe can be prevented from being damaged by external pressure over time. Inward concave deformation, thus affecting the service life of the entire pullout bolt, due to the cement body formed by the secondary grouting, the deformation of the protective pipe can be avoided.
  • the tension of the steel strand is divided into two steps.
  • the first step is to pre-tension 1-4 times with the design value of the pull-out bearing capacity of the pull-resistant bolt to make the steel strand completely straight;
  • the second step stretch for 10-20 minutes at 1.05-1.10 times the design value of the pullout bearing capacity of the pullout anchor, and then unload to the design value of the locking load for locking.
  • the steel strand can have sufficient deformation time, so as to avoid that the tensioning speed of the steel strand is too large, and the steel strand is plastically deformed, and the required internal stress cannot be generated.
  • an inner sleeve is fixedly installed on the upper surface of the pile end anchorage, and the top of the inner sleeve exceeds the set top elevation of the concrete enlarged head.
  • the steel sleeve can be sleeved on the inner sleeve; the fine stone concrete flows out from the gap between the steel sleeve and the inner sleeve.
  • the limiting effect of the inner casing is used to prevent the first grouting pipe from being greatly bent outwards driven by the fine stone concrete.
  • the lower end of the inner casing can be sealed on the upper surface of the pile end anchor, or it can have a small gap, which should not allow a large amount of fine stone concrete to leak out. outflow.
  • the steel casing After the inner casing is set, when the steel casing moves up and down within the height range of the inner casing, the amount of fine stone concrete flowing out is small, and the steel casing can vibrate the fine stone concrete that has flown out for multiple times. tamping, so that the fine stone concrete can spread out in a wider range and push the soil to move outward to form a concrete expansion head.
  • a guide frame is provided on the top of the inner casing, the guide frame has a slurry channel, and the slurry channel is used for the outflow of the fine stone concrete; the steel casing can go upwards beyond the top of the inner casing during the upward lifting process. and does not exceed the top of the guide frame.
  • the steel sleeve goes upwards over the inner sleeve, it can avoid the deviation of the steel sleeve due to no restriction, and during the downward movement, it is pressed against the top of the inner sleeve and cannot make the steel sleeve.
  • the tube moves down smoothly.
  • the steel casing can smoothly complete the reciprocating motion of upward lifting and downward insertion, and vibrating and extruding the fine stone mixed soil.
  • the outer edge of the guide frame is flush with the outer edge of the inner sleeve.
  • a plug ring is installed at the bottom of the steel sleeve, and the outer peripheral surface of the plug ring does not exceed the outer peripheral surface of the pile end anchorage outward; and the inner peripheral surface of the plug ring exceeds the inner peripheral surface of the steel sleeve inward. , or the outer peripheral surface of the plug ring exceeds the outer peripheral surface of the steel sleeve; under the driving of the steel sleeve, the plug ring can move up to the height range of the guide frame.
  • This design can effectively expand the lower end face of the steel casing, so that when the steel casing vibrates and squeezes the fine stone concrete, it has a larger area to act on the fine stone concrete, so that each downward movement of the steel casing can be achieved. Insertion can make more fine stone concrete diffuse outwards and improve construction efficiency.
  • a plug ring is installed at the bottom of the steel sleeve, the inner peripheral surface of the plug ring exceeds the inner wall of the steel sleeve inward, and the outer peripheral surface of the plug ring does not exceed the outer peripheral surface of the pile end anchor, the The plug ring is slidably sleeved on the outer peripheral surface of the inner sleeve; when the plug ring is sleeved on the inner sleeve, an annular gap is formed between the steel sleeve and the inner sleeve.
  • This design can effectively reduce the contact area between the steel casing and the inner casing, reduce the friction between the steel casing and the inner casing, especially the friction on the steel casing, because the steel casing is not in the construction after the completion of the construction. , to be pulled out and reused to reduce the friction on the steel casing, so as to improve the service life of the steel casing.
  • the fine stone concrete will inevitably enter the gap between the steel casing and the inner casing, and these fine stone concrete will cause greater damage to the steel casing and the inner casing.
  • This application adopts steel pipe pile driving, no mud and slag, and it is green and environmentally friendly.
  • the present application can effectively reduce the crack of the bolt by applying prestress to the steel strand.
  • This application has good economics.
  • the anchor rod formed in the present application has high bearing capacity, smaller diameter than anti-floating piles, and requires less concrete.
  • the strength of the steel strand is high, and under the condition of providing the same bearing capacity, the amount of steel bars is less than that of ordinary steel bars.
  • Ordinary reinforced concrete bolts need to be equipped with a large number of steel bars to reduce the crack width, and the crack width can be effectively controlled after prestressing, so when the requirements for bolt cracks are strict, the invention can save 20%-30% of the cost.
  • FIG. 1 is a schematic flow chart of the present invention.
  • Figure 2 is a schematic diagram of the locking structure of the steel strand.
  • the pile end anchoring device 14 includes an anchoring plate 141 extending in the horizontal direction, and a spud shoe 142 fixedly connected to the lower surface of the anchoring plate 141.
  • a shotcrete cavity 145 is formed between the anchoring plate 141 and the spud shoe 142.
  • the shoe 142 is provided with a spray hole 144 .
  • An inner sleeve 11 is fixedly installed on the upper surface of the anchoring plate 141 , the inner sleeve is made of steel pipe, and the lower end of the inner sleeve is sealed and welded on the upper surface of the anchoring plate.
  • the top of the inner casing 11 rises above the set top elevation of the concrete enlargement head.
  • the inner sleeve can also be fixed on the anchoring plate with bolts, and there can be a gap of less than 5mm between the inner sleeve and the anchoring plate, and the gap will only cause a small amount of fine stone concrete to move toward the anchoring plate. External seepage will not affect the overflow of fine stone concrete from the top of the inner casing.
  • a through hole 143 through which the first grouting pipe 31 described below is passed is formed in the anchor plate.
  • the top of the inner sleeve 11 is provided with a guide frame 12.
  • the guide frame 12 includes ten round bars 121 welded on the top of the inner sleeve.
  • the ten round bars extend in the vertical direction and are arranged at intervals.
  • Steel bars 122 are welded on the inner side of the round steel 121 to increase the stability of the round steel.
  • the outer edge of the round steel is flush with the outer edge of the inner sleeve, that is, the outer edge of the guide frame is flush with the outer edge of the inner sleeve.
  • the hole between the round steel 121 and the steel bar 122 is formed as a slurry channel. During the upward lifting process of the steel sleeve 13 described below, it can upwardly exceed the top of the inner sleeve and not exceed the top of the guide frame.
  • the steel sleeve 13 is movably arranged on the upper side of the pile end anchor 14, and a plug ring 15 is installed at the bottom of the steel sleeve 13, and the plug ring 15 inwardly exceeds the inner wall of the steel sleeve.
  • the steel sleeve 13 can carry out the reciprocating movement of upward lifting and downward insertion.
  • the plug ring 15 can be slidably sleeved on the inner sleeve, when the plug ring 15 is sleeved
  • an annular gap 22 is formed between the steel sleeve 13 and the inner sleeve 11 .
  • the plug ring 15 is installed on the inner side of the bottom of the steel sleeve, that is, the inner peripheral surface of the plug ring exceeds the inner peripheral surface of the steel sleeve inward, and the outer peripheral surface of the plug ring does not exceed the pile The outer peripheral surface of the end anchor.
  • the plug ring can also be installed on the lower end surface of the steel sleeve, and the inner peripheral surface of the plug ring exceeds the inner peripheral surface of the steel sleeve It faces outward beyond the outer peripheral surface of the steel casing, but does not exceed the outer peripheral surface of the pile end anchor, so that the plug ring can be slidably sleeved on the inner casing.
  • the outer peripheral surface of the anchoring plate 141 extends outwardly beyond the outer peripheral surface of the spud shoe 142 and outwardly beyond the outer peripheral surface of the steel sleeve. It can be understood that, in another embodiment, the outer peripheral surface of the anchoring plate may also be coplanar with the outer peripheral surface of the spud shoe, and the outer peripheral surface of the anchoring pressing plate extends beyond the outer peripheral surface of the steel sleeve. Alternatively, the outer peripheral surface of the spud shoe extends outwardly beyond the outer peripheral surface of the anchor plate, and the outer peripheral surface of the spud shoe faces outwardly toward the outer peripheral surface of the tapped sleeve.
  • the outer peripheral surface of the pile end anchoring tool extends beyond the outer peripheral surface of the steel casing. Since the outer peripheral surface of the pile end anchorage exceeds the outer peripheral surface of the steel casing, there is a distance between the outer peripheral surface of the steel casing and the pile hole formed by the pile end anchorage, so that the steel casing can move up and down during the up and down movement. , to avoid touching the inner wall of the pile hole, causing the earth to slump and affecting the construction.
  • step a in 1 movably press the steel sleeve 13 against the pile end anchorage, and then sink the steel sleeve 13 and the pile end anchorage 14 together to the set depth.
  • the steel strand 16 is fixed on the anchor plate 141, and a protective tube 17 is sleeved on the steel strand 16, and the protective tube 17 is made of steel pipe and welded on the anchor plate.
  • the first grouting pipe 31 is inserted into the inner casing 11, and penetrates downward through the anchoring plate 141 and then extends into the grouting cavity 145.
  • the pure cement slurry is injected into the shotcrete cavity 145 through the first grouting pipe 31 , and then the pure cement slurry is sprayed out from the shotcrete hole 144 to form a cement slurry protective wall 40 on the inner wall of the formed pile hole.
  • step b in 1 pour fine stone concrete 20 between the steel casing 13 and the protective pipe 17.
  • the inner casing is sealed with the anchoring plate, the fine stone concrete entering the inner casing is kept in the inner casing, and the fine stone concrete that enters the inner casing will be removed from the slurry when the plug ring upwards exceeds the inner casing.
  • the channel flows out and out through the gap between the steel sleeve and the inner sleeve.
  • the slump of the fine stone concrete is 220 mm. It can be understood that in other embodiments, fine stone concrete with a slump of 180 mm, 200 mm, 250 mm or 300 mm can also be selected.
  • the height of the poured fine stone concrete is 2 meters higher than the set height of the pile body to make up for the drop produced by the fine stone concrete in the process of settlement and compaction. It can be understood that, in other embodiments, the height of the pile body may be 1 meter, 1.5 meters, 2.5 meters or 3 meters higher than the designed height of the pile top.
  • first grouting pipe 31 After completing the construction of the concrete enlargement head and the pile body, grouting is carried out through the first grouting pipe 31. During the first grouting process, the first grouting pipe is lifted upward, and pure cement slurry is injected simultaneously until the The bottom end of the first grouting pipe is lifted to a set height.
  • step e in 1 to pull out the steel sleeve.
  • steps e and f in excavate the earthwork to the set depth, complete the construction of the cushion layer 41, and after the concrete expansion head reaches the curing period, stretch the steel strand and lock it with the anchor 74 , to complete the construction of the concrete expansion head prestressed uplift anchor.
  • a second grouting pipe 32 is arranged in the protective pipe. After the tension of the steel strand 16 is completed, the second grouting pipe 32 is used for secondary grouting. The slurry pipe is lifted upward, and pure cement slurry is injected into the protective pipe 17 at the same time; the top of the anti-pulling anchor is compacted through the second grouting pipe, and then the C35 micro-expanded concrete is used to seal the anchor.
  • the tensioning of the steel strand 16 is divided into two steps.
  • the pretensioning is performed twice with the design value of the pull-out bearing capacity of the pull-out anchor, so that the steel strand is completely straight;
  • the second step is to stretch for 15 minutes at 1.10 times the design value of the pullout bearing capacity of the pullout anchor, and then unload to the design value of the locking load for locking.
  • the stretching may be performed only once, or the stretching may be performed three or four times.
  • tensioning can also be performed at 1.05 times, 1.07 times or 1.09 times the design value of the pullout bearing capacity of the pullout bolt, and keep it for 10 or 20 minutes.
  • the specific tensioning process can be selected according to the needs and the specific conditions of the steel strand.
  • the bottom plate of the underground structure includes a foundation leveling layer 61 , a foundation waterproof cushion layer 62 and a raft layer 63 sequentially from bottom to top.
  • the basic leveling layer 61 and the basic waterproof cushion layer 62 are collectively formed as the cushion layer 41 .
  • the end steel pipe 51 with the protective layer positioning steel bar 52 welded at the bottom is sleeved on the top of the steel strand 16, and inserted into the upper end of the protection pipe 17 through the end steel pipe 51.
  • the outer side of the top steel pipe 51 is surrounded by a spiral rib 53 , and the end steel pipe 51 extends upward from the protective pipe and into the raft layer 63 .
  • the top of the protective pipe is located in the foundation leveling layer 61, and the top of the end steel pipe is filled with waterproof mortar to form a first waterproof part 75 to seal the top of the end steel pipe. Then pour waterproof mortar on the top of the protective pipe 17 to form a second waterproof part 71 to seal the gap between the end steel pipe and the protective pipe.
  • the second waterproof part 71 is wrapped on the outer wall of the end steel pipe 51.
  • the second waterproof part The top of 71 is the same height as the top of the foundation leveling layer, and then paint waterproof paint and lay waterproof membrane 711 at the angle between the second waterproof part 71 and the end steel pipe 51, and then install the waterproof expansion strip 73.
  • a waterproof steel plate 72 is welded on the upper part of the end steel pipe 51, the waterproof steel plate 72 is located in the raft layer 63, and the three-hole YM anchor 74 locks the steel strand 16 on the top of the end steel pipe 51, and connects the steel strand
  • the top end 161 of 16 is left 400mm long, then the top end 161 is degreased and the ball head is anchored into the raft layer.

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Abstract

一种混凝土扩大头预应力抗拔锚杆的施工方法，步骤为：(1)将钢套管(13)活动地抵压在桩端锚具(14)上并一起下沉到设定深度，该桩端锚具(14)上固定连接有钢绞线(16)，并在钢绞线(16)上套设有固定在锚固板(141)上的防护管(17)；(2)在钢套管(13)与防护管(17)之间灌入细石混凝土(20)；(3)反复将钢套管(13)向上提升和向下插入，使细石混凝土(20)流出钢套管(13)，逐渐形成混凝土扩大头(21)；继续灌入细石混凝土(20)，在钢套管(13)内形成设定高度的桩体；(4)拔出钢套管(13)；(5)开挖土方到设定深度，在混凝土扩大头(21)达到养护期后，对钢绞线(16)进行张拉并锁定。混凝土扩大头(21)由细石混凝土(20)形成，且与周围的土体形成为一个整体，具有更高的抗拔承载力，在施工过程中，没有孔底沉渣问题。

Description

一种混凝土扩大头预应力抗拔锚杆的施工方法 技术领域
本发明涉及一种混凝土扩大头预应力抗拔锚杆的施工方法。
背景技术
端部扩大型锚杆也称为扩大头锚杆，由于在锚杆的底端经过特殊的施工处理形成扩大头，这种锚杆能够大大地提高锚杆的抗拔力。扩大头锚杆的抗拔力由锚固体与岩土体间的摩阻力和端头扩大头的承载力所共同决定，因此在相同的条件下，这类锚杆能在较软弱的粘土层及对锚杆长度有限制的土层中使用，克服了圆柱形锚杆仅有锚固体与岩土体间的摩阻力的这一弱点。
目前土层扩大头锚杆常用的扩孔方法有高压射流切割和机械切削扩孔2种。高压射流切割法是采用旋转的高压喷射束流(液体或气液混合)切割扩大头锚固段土体，形成需要的孔径，因其需要配置高压注浆泵，及需要增加置换切削下来的废渣工序，带来初期投入大，水泥土扩大头质量不稳定。而机械切削扩孔是采用机械连杆机构的扩孔钻具，扩孔机具存在着不易控制扩孔质量，操作繁琐及收放不顺等缺点。
目前抗浮桩和抗浮锚大部分均采用普通钢筋混凝土结构，由于钢筋强度低，因此其钢筋用量较大，造价高。在高水位或地下水有腐蚀性的环境下，由于混凝土受拉时其裂缝难以控制，因此抗浮桩或抗浮锚杆的防锈、防腐蚀难度大，施工质量不易控制，即耐久性难以满足规范要求。
发明内容
为解决上述问题，本发明提出了一种混凝土扩大头预应力抗拔锚杆的施工方法，其包括如下步骤：
(1)将钢套管活动地抵压在桩端锚具上，然后将钢套管和桩端锚具一起下沉到设定深度，该桩端锚具包括一锚固板；在桩端锚具上固定连接有钢绞线，并在钢绞线上套设有防护管，该防护管固定在锚固板上；
继续灌入细石混凝土，在钢套管内形成设定高度的桩体；
(2)在钢套管与防护管之间灌入细石混凝土；细石混凝土的塌落度优选180-300mm；
(3)反复将钢套管向上提升和向下插入，使细石混凝土由钢套管与桩端锚具之间的缝隙向外流出钢套管，并在钢套管的挤压下、逐渐向外扩散形成混凝土扩大头，直到混凝土扩大头的体积达到设定的体积；
(4)拔出钢套管；
(5)开挖土方到设定深度，在混凝土扩大头达到养护期后，对钢绞线进行张拉并锁定，完成混凝土扩大头预应力抗拔锚杆的施工。
本申请中的钢绞线优选采用无粘结钢绞线，无粘结钢绞线采用防腐油脂和外侧套管双重防腐，耐久性好。
在形成桩体的过程中，灌入细石混凝土的高度向上超过桩体设定高度1-3米，以弥补细石混凝土在沉降密实过程中所产生的落差。
本申请中，当土质较差时，可以采用静力压桩机直接将钢套管和桩端锚具下沉到设定深度，当土质为硬塑状黄土等硬质地层时，可以采用长螺旋或旋挖设备引孔，然后采用振动方式沉入钢套管和桩端锚具。
本申请中，采用钢套管进行沉桩，能够采用较高的压力的静力压桩机进行沉桩，能够使桩端锚具通过密实的砂层、残积土和强风化岩层，达到设计持力层。
本申请中，扩大头由细石混凝土形成，在形成扩大头的过程中，细石混凝土在钢套管的挤压下，向周围的土体中扩散，并使周围的土体也同步向外挤压，使所形成的扩大头内部为完全的细石混凝体，外层为细石混凝土与素土所形成的水泥土，使扩大头与周围的土体形成为一个整体，具有更高的抗拔承载力。
由于直接由细石混凝体向外挤压来形成扩大头，因此没有现有技术中的孔底沉渣问题。在目前，形成混凝土扩大头时，是首先钻设桩孔，然后在桩孔内注入混凝土，再用捣杆对混凝土进行振捣，使混凝体向外扩散从而形成扩大头，由于在钻孔时，需要将钻头吊出桩孔后，才能进行混凝土的注入，但在将钻头吊出桩孔的过程中，易于对桩孔周围的土体进行触碰，使部分土方掉落到孔底，由于这些土方难于精确计算，因此易于使扩大头偏离原设计高度。
在完成扩大头的形成后，继续超罐一定量的细石混凝土，以在扩大头的顶部形成一段桩体，以保证管内压力，使扩大头的顶部也能达到设定的密实度。
进一步，
该桩端锚具还包括设置在锚固板下侧的桩靴，该桩端锚具的外周面向外超出钢套管的外周面，该桩靴与锚固板之间形成一喷浆腔，在桩靴上设置有喷浆孔，在钢套管与防护管之间插设有第一注浆管，该第一注浆管的下端穿过锚固板后伸入到喷浆腔内；在将钢套管和桩端锚具一起下沉过程中，将纯水泥浆经第一注浆管注入到喷浆腔内，然后纯水泥浆由喷浆孔向外喷出，在所形成的桩孔的内壁上形成水泥浆护壁。
在下沉钢套管和桩端锚具的过程中，同时进行喷射纯水泥浆，这些纯水泥浆在桩端锚具的挤压下向四周扩散并附着在桩孔的内壁上，形成一个水泥浆护壁，该水泥浆护壁能够对桩孔的内壁进行加强，避免钢套管在向上提升和向下插入的往复过程中，由于钢套管触碰到桩孔的内壁，而造成桩孔的土方塌落，影响施工的正常进行。水泥浆护壁在土质较软的区域也 有较大的优势，可以避免由于土质疏松而造成塌孔，无法形成可以利用的桩孔，利用本申请，即使在土质较为疏松的区域，也可以顺利的形成可以利用的桩孔，以使施工能够正常进行。
在形成水泥浆护壁后，由于能够对桩孔外部的土体形成有力的支撑，在拔出钢套管过程中，不会带动桩孔周围的土体，从而避免塌方，当造成塌方时，由于此时的细石混凝土尚处于流动状态，塌方的土方会对桩体造成缩颈、断桩等不良质量。
进一步，为了提高混凝土扩大头的强度，步骤(3)中，在完成混凝土扩大头和桩体的施工后，经第一注浆管进行一次注浆，在进行一次注浆过程中，将第一注浆管向上提升，并同时注入纯水泥浆，直到将第一注浆管的底端提升到设定高度。
进一步，为了对钢绞线形成保护，在防护管内设置有第二注浆管，步骤(5)中，在完成对钢绞线的张拉后，经第二注浆管进行二次注浆，在进行二次注浆过程中，将第二注浆管向上提升，并同时将纯水泥浆注入到防护管内；通过第二注浆管对抗拔锚杆的顶部进行密实，然后用C35微膨胀混凝土进行防渗封锚。
对防护管的二次注浆，使钢绞线整体被水泥体包裹，避免水体以及其他物质的腐蚀，另外也可以保证防护管的强度，避免随着时间的推移，在外部压力下，防护管向内产生凹陷变形，从而影响整个抗拔锚杆的使用寿命，由于二次注浆所形成的水泥体，可以避免防护管产生变形。
进一步，对钢绞线的张拉分为两步，第一步，以抗拔锚杆的抗拔承载力设计值进行预张拉1-4次，使钢绞线完全平直；第二步，以抗拔锚杆的抗拔承载力设计值的1.05-1.10倍张拉10-20分钟，然后卸荷至锁定荷载设计值进行锁定。
采用上述张拉方式，能够使钢绞线具有充分的形变时间，避免对钢绞线的张拉速度过大，而使钢绞线产生塑性形变，无法产生所需要的内应力。
进一步，在桩端锚具的上表面固定安装有一内套管，该内套管的顶部向上超过混凝土扩大头的设定顶部标高，在该钢套管向上提升和向下插入的往复过程中，该钢套管能够套设在该内套管上；细石混凝土由钢套管与内套管之间的缝隙向外流出。为避免细石混凝体在向外流出时，带动第一注浆管产生向外的弯曲，造成钢套管与第一注浆管产生触碰，最好使第一注浆管插设在内套管中，利用内套管的限制作用，从而避免第一注浆管在细石混凝土的带动下向外产生较大的弯曲。
内套管的下端可以密封地安装在桩端锚具的上表面，也可以具有一个小的缝隙，该缝隙不应当使大量的细石混凝土漏出，细石混凝土主要还是由内套管的顶部向外流出。
设置内套管后，当钢套管在该内套管管的高度范围内上下移动时，细石混凝土向外流出的量较少，钢套管能够对已经流出的细石混凝土进行多次振捣，使细石混凝土能够更大范围内向外扩散，并推动土体向外移动，以形成一个混凝土扩大头。
进一步，在内套管的顶部设置有导向架，该导向架具有浆液通道，该浆液通道用于细石混凝土向外流出；该钢套管在向上提升过程中，能够向上超过内套管的顶部且不超过导向架的顶部。设置导向架后，当钢套管向上超过内套管时，可以避免钢套管由于没有限制而产生偏移，以及在向下移动过程中，抵压在内套管的顶部，无法使钢套管顺利地向下移动。利用导向架，能够使钢套管顺利地完成向上提升和向下插入的往复运动，对细石混合土进行振捣和挤压。
进一步，为避免钢套管在向下移动过程中，触碰到内套管的顶部，造成移动卡顿，导向架的外侧边缘与内套管的外侧边缘平齐。
进一步，在钢套管的底部安装有一堵头环，该堵头环的外周面向外不超出桩端锚具的外周面；且该堵头环的内周面向内超过钢套管的内周面，或者该堵头环的外周面向外超过钢套管的外周面；在钢套管的带动下，该堵头环能够向上移动到导向架的高度范围内。
该设计可以有效地扩大钢套管的下端面，使钢套管在对细石混凝土进行振捣和挤压时，具有更大面积作用在细石混凝土上，使钢套管的每次向下插入，均能够使更多的细石混凝土向外进行扩散，提高施工效率。
或者，在钢套管的底部安装有一堵头环，该堵头环的内周面向内超过钢套管的内壁，且该堵头环的外周面向外不超出桩端锚具的外周面，该堵头环能够滑动地套设在内套管的外周面上；当堵头环套设在该内套管上时，钢套管与内套管之间形成一环隙。
该设计能够有效地减少钢套管与内套管之间的接触面积，减少对钢套管和内套管的摩擦，尤其是可以减少对钢套管的摩擦，由于钢套管在完成施工后，要进行拔出并重复利用，减少对钢套管的摩擦后，以提高钢套管的使用寿命。在钢套管的上下移动过程中，细石混凝土不可避免地会进入到钢套管与内套管之间的缝隙中，这些细石混凝体会对钢套管和内套管造成较大的磨损，使堵头环向内超过钢套管的内壁、且设置环隙后，堵头环、内套管以及钢套管三者之间会形成一个环形槽，细石混凝土会保持在该环形槽内，当钢套管上下移动时，在堵头环的带动下，保持在环形槽的细石混凝土会同步上下移动，不会对钢套管产生摩擦，或仅在下降过程中，产生少量的摩擦，由此减少对钢套管的磨损。
本申请采用钢管沉桩，无泥浆和渣土，绿色环保。本申请通过对钢绞线施加预应力，可以有效减小锚杆的裂缝。本申请具有良好的经济性。本申请所形成的锚杆承载力高，直径较抗浮桩小，需混凝土量少。钢绞线强度高，对提供同等承载力情形下，较普通钢筋用量少。普通钢筋混凝土锚杆需配置大量的钢筋才能较小裂缝宽度，而施加预应力后可有效的控制裂缝宽度，因此对锚杆裂缝要求严格情况下，采用本发明可节约20％-30％成本。
附图说明
图1是本发明的流程示意图。
图2为钢绞线的锁定结构示意图。
具体实施方式
以下首先对桩端锚具及相应的结构进行说明，请参阅图1中的a步骤，
桩端锚具14包括一沿水平方向延伸的锚固板141、固定连接在锚固板141的下表面上的桩靴142，在锚固板141与桩靴142之间形成一个喷浆腔145，在桩靴142上开设有喷浆孔144。在锚固板141的上表面固定安装有一内套管11，该内套管采用钢管制作，且内套管的下端密封地焊接在锚固板的上表面上。内套管11的顶部向上超过混凝土扩大头的设定顶部标高。可以理解，在另一实施例中，内套管还可以采用螺栓固定在锚固板上，且内套管与锚固板之间可以具有小于5mm的缝隙，该缝隙仅仅会使少量的细石混凝土向外渗出，不会对细石混凝土由内套管的顶部向外溢出造成影响。
在锚固板上开设有供下述的第一注浆管31穿过的贯穿孔143。
在内套管11的顶部设置有导向架12，该导向架12包括焊接在内套管的顶部、的十根圆钢121，十根圆钢沿竖直方向延伸、并间隔设置，在十根圆钢121的内侧焊接有钢筋122，以增加圆钢的稳定性，圆钢的外侧边缘与内套管的外侧边缘平齐，即导向架的外侧边缘与内套管的外侧边缘平齐。圆钢121与钢筋122之间的孔道形成为浆液通道，下述的钢套管13在向上提升过程中，能够向上超过内套管的顶部且不超过导向架的顶部。
钢套管13活动地布置在桩端锚具14的上侧，在钢套管13的底部安装有一堵头环15，堵头环15向内超过钢套管的内壁，在外力作用下，该钢套管13能够进行向上提升和向下插入的往复移动，在钢套管13进行往复移动过程中，该堵头环15能够滑动地套设在该内套管上，当堵头环15套设在该内套管11上时，钢套管13与内套管11之间形成一环隙22。
具体在本实施例中，堵头环15安装在钢套管的底部的内侧，即堵头环的内周面向内超过钢套管的内周面，且堵头环的外周面向外不超出桩端锚具的外周面。
可以理解，在另一实施例中，该堵头环还可以安装在钢套管的下端面上，且使堵头环的内周面向内超过钢套管的内周面，堵头环的外周面向外超过钢套管的外周面、但向外不超出桩端锚具的外周面，以使堵头环能够滑动地套设在内套管上。
本实施例中，锚固板141的外周面向外超出桩靴142的外周面、且向外超出钢套管的外周面。可以理解，在另一实施例中，锚固板的外周面还可以和桩靴的外周面共面，且锚固按板的外周面向外超出钢套管的外周面。或者，桩靴的外周面向外超出锚固板的外周面、且桩靴的外周面向外朝出钢套管的外周面。即该桩端锚具的外周面向外超出钢套管的外周面。由于桩端锚具的外周面向外超出钢套管的外周面，使钢套管的外周面与由桩端锚具所形成的桩孔之间具有距离，能够使钢套管在上下移动过程中，避免触碰到桩孔的内壁，造成土方塌落，对施工造成影响。
以下对混凝土扩大头预应力抗拔锚杆的施工方法进行具体的说明，具体步骤为：
(1)请参阅1中的a步骤，将钢套管13活动地抵压在桩端锚具上，然后将钢套管13和桩端锚具14一起下沉到设定深度。钢绞线16固定在锚固板141上，并在钢绞线16上套设有防护管17，该防护管17采用钢管制作，并焊接在锚固板上。
第一注浆管31插设在内套管11中，并向下贯穿锚固板141后伸入到喷浆腔145内，在钢套管13与桩端锚具14一起下沉过程中，将纯水泥浆经第一注浆管31注入到喷浆腔145内，然后纯水泥浆由喷浆孔144向外喷出，在所形成的桩孔的内壁上形成水泥浆护壁40。
(2)请参阅1中的b步骤，在钢套管13与防护管17之间灌入细石混凝土20。
由于本实施例中，内套管与锚固板密封连接，进入到内套管内的细石混凝土保持在内套管内，后续进入到细石混凝土会在堵头环向上超过内套管时，从浆液通道向外流出，并经由钢套管与内套管之间的缝隙向外流。
本实施例中，细石混凝土的塌落度为220mm，可以理解，在其他实施例中，还可以选择塌落度为180mm、200mm、250mm或300mm的细石混凝土。
(3)请参阅1中的c、d两步骤，反复将钢套管向上提升和向下插入，从钢套管与内套管之间的缝隙中流出的细石混凝土由钢套管与桩端锚具之间的缝隙向外流出钢套管，并在钢套管的振捣和挤压下、逐渐向外扩散形成混凝土扩大头21，直到混凝土扩大头21的体积达到设定的体积，完成混凝土扩大头的施工。
继续灌入细石混凝体，灌入细石混凝体的高度向上超过桩体设定高度2米，以弥补细石混凝土在沉降密实过程中所产生的落差。可以理解，在其他实施例中，桩体的高度还可以较设计桩顶的高度高1米、1.5米、2.5米或3米。
在完成混凝土扩大头和桩体的施工后，经第一注浆管31进行一次注浆，在进行一次注浆过程中，将第一注浆管向上提升，并同时注入纯水泥浆，直到将第一注浆管的底端提升到设定高度。
(4)请参阅1中的e步骤，拔出钢套管。
(5)请参阅1中的e、f两步骤，开挖土方到设定深度，完成垫层41的施工，在混凝土扩大头达到养护期后，对钢绞线进行张拉并用锚具74锁定，完成混凝土扩大头预应力抗拔锚杆的施工。
在防护管内设置有第二注浆管32，在完成对钢绞线16的张拉后，经第二注浆管32进行二次注浆，在进行二次注浆过程中，将第二注浆管向上提升，并同时将纯水泥浆注入到防护管17内；通过第二注浆管对抗拔锚杆的顶部进行密实，然后用C35微膨胀混凝土进行防渗封锚。
在本实施例中，对钢绞线16的张拉分为两步，第一步，以抗拔锚杆的抗拔承载力设计值进行预张拉2次，使钢绞线完全平直；第二步，以抗拔锚杆的抗拔承载力设计值的1.10倍张拉15分钟，然后卸荷至锁定荷载设计值进行锁定。
可以理解，在其他实施例中，在进行张拉的第一步过程中，还可以仅仅张拉一次，或进行三次或四次张拉。在进行张拉的第二步过程中，还可以以抗拔锚杆的抗拔承载力设计值的1.05倍、1.07倍或1.09倍进行张拉，并保持10或20分钟。具体的张拉过程，可根据需要和钢绞线的具体情况进行选取。
以下对钢绞线的锁定结构进行说明，请参阅图2，本实施例中，地下结构的底板由下至上依次包括基础找平层61、基础防水垫层62和筏板层63。其中的基础找平层61、基础防水垫层62共同形成为垫层41。
在进行钢绞线的锁定时，首先将底部焊接有保护层定位钢筋52的端部钢管51套在钢绞线16的顶部，并经端部钢管51插入到防护管17的上端部内，在端部钢管51的外侧环绕有螺旋筋53，端部钢管51向上伸出防护管、并伸入到筏板层63内。防护管的顶部位于基础找平层61内，将防水砂浆填充到端部钢管的顶部，形成第一防水部75，以密封端部钢管的顶部。然后在防护管17的顶部浇注防水砂浆，形成第二防水部71，以密封端部钢管与防护管之间的空隙，第二防水部71包裹在端部钢管51的外壁上，第二防水部71的顶部与基础找平层的顶部等高，然后在第二防水部71与端部钢管51的夹角处涂刷防水涂料并铺设防水卷材711，然后安装防水膨胀条73。在端部钢管51的上部焊接有防水钢板72，该防水钢板72位于筏板层63内，三孔YM锚具74将钢绞线16锁合在端部钢管51的顶部，并将钢绞线16的顶端部161留长400mm，然后将顶端部161除油并轧花球头锚入筏板层内。

Claims (10)

  1. 一种混凝土扩大头预应力抗拔锚杆的施工方法，其特征在于，包括如下步骤：
    (1)将钢套管活动地抵压在桩端锚具上，然后将钢套管和桩端锚具一起下沉到设定深度，该桩端锚具包括一锚固板；在桩端锚具上固定连接有钢绞线，并在钢绞线上套设有防护管，该防护管固定在锚固板上；
    (2)在钢套管与防护管之间灌入细石混凝土；
    (3)反复将钢套管向上提升和向下插入，使细石混凝土由钢套管与桩端锚具之间的缝隙向外流出钢套管，并在钢套管的挤压下、逐渐向外扩散形成混凝土扩大头，直到混凝土扩大头的体积达到设定的体积；
    继续灌入细石混凝土，在钢套管内形成设定高度的桩体；
    (4)拔出钢套管；
    (5)开挖土方到设定深度，在混凝土扩大头达到养护期后，对钢绞线进行张拉并锁定，完成混凝土扩大头预应力抗拔锚杆的施工。
  2. 根据权利要求1所述的施工方法，其特征在于，
    该桩端锚具还包括设置在锚固板下侧的桩靴，该桩端锚具的外周面向外超出钢套管的外周面，该桩靴与锚固板之间形成一喷浆腔，在桩靴上设置有喷浆孔，在钢套管与防护管之间插设有第一注浆管，该第一注浆管的下端穿过锚固板后伸入到喷浆腔内；在将钢套管和桩端锚具一起下沉过程中，将纯水泥浆经第一注浆管注入到喷浆腔内，然后纯水泥浆由喷浆孔向外喷出，在所形成的桩孔的内壁上形成水泥浆护壁。
  3. 根据权利要求2所述的施工方法，其特征在于，步骤(3)中，在完成混凝土扩大头和桩体的施工后，经第一注浆管进行一次注浆，在进行一次注浆过程中，将第一注浆管向上提升，并同时注入纯水泥浆，直到将第一注浆管的底端提升到设定高度。
  4. 根据权利要求1所述的施工方法，其特征在于，在防护管内设置有第二注浆管，步骤(5)中，在完成对钢绞线的张拉后，经第二注浆管进行二次注浆，在进行二次注浆过程中，将第二注浆管向上提升，并同时将纯水泥浆注入到防护管内；通过第二注浆管对抗拔锚杆的顶部进行密实，然后用C35微膨胀混凝土进行防渗封锚。
  5. 根据权利要求1所述的施工方法，其特征在于，对钢绞线的张拉分为两步，第一步，以抗拔锚杆的抗拔承载力设计值进行预张拉1-4次，使钢绞线完全平直；第二步，以抗拔锚杆的抗拔承载力设计值的1.05-1.10倍张拉10-20分钟，然后卸荷至锁定荷载设计值进行锁定。
  6. 根据权利要求1所述的施工方法，其特征在于，
    在桩端锚具的上表面固定安装有一内套管，该内套管的顶部向上超过混凝土扩大头的设定顶部标高，在该钢套管向上提升和向下插入的往复过程中，该钢套管能够套设在该内套管上；细石混凝土由钢套管与内套管之间的缝隙向外流出。
  7. 根据权利要求6所述的施工方法，其特征在于，
    在内套管的顶部设置有导向架，该导向架具有浆液通道，该浆液通道用于细石混凝土向外流出；该钢套管在向上提升过程中，能够向上超过内套管的顶部且不超过导向架的顶部。
  8. 根据权利要求7所述的施工方法，其特征在于，
    导向架的外侧边缘与内套管的外侧边缘平齐。
  9. 根据权利要求6-8任一项所述的施工方法，其特征在于，
    在钢套管的底部安装有一堵头环，该堵头环的外周面向外不超出桩端锚具的外周面；
    且该堵头环的内周面向内超过钢套管的内周面，或者该堵头环的外周面向外超过钢套管的外周面；在钢套管的带动下，该堵头环能够向上移动到导向架的高度范围内。
  10. 根据权利要求6-8任一项所述的施工方法，其特征在于，
    在钢套管的底部安装有一堵头环，该堵头环的内周面向内超过钢套管的内壁，且该堵头环的外周面向外不超出桩端锚具的外周面，该堵头环能够滑动地套设在内套管的外周面上；当堵头环套设在该内套管上时，钢套管与内套管之间形成一环隙。
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