SI21320A - Prestressed geotechnical anchor of variable stiffness - Google Patents

Abstract

The invention of a prestressed geotechnical anchor of variable stiffness from the field of geotechnics is solving the technical problem of anchoring structures in worse geotechnical conditions where the application of anchors of higher bearing capacity with steel strands (14) of the same free length (7) and the same binding length (8) is not possible because of high concentration of shear stresses and tensile cracks within the anchor's cylinder, which would produce the excess creep and yielding of anchors. The technical problem of yielding is solved by using anchors manufactured of several high-alloyed steel wire cords or strands (14) of various free (7) and various binding lengths (8) but the same total length (7+8). Such anchors enable uniform application of tensile force to the whole binding part of the anchor (3), assure a more uniform activation of adhesion strength between the anchor's cylinder and soil (12) on the whole binding length (3) foreseen and offer, consequently, a higher bearing capacity, improved durability, increased reliability, less creep and smaller loss of tensile force within the anchor. During the application of the invention, separate prestressing of individual steel strand groups with the same free (7) and the same binding length (8) is required.

Description

VARIABLE GEOTECHNICAL ANCHOR OF VARIABLE RIGID

1. TECHNICAL FIELD

The present invention is in the field of geotechnics and relates primarily to prestressed geotechnical anchors, which are used in construction in almost all geotechnically advanced facilities. It also refers to passive anchoring in hills and partly in the field of construction when anchoring into massive structures in the rehabilitation of existing structures.

2. DISPLAY OF THE PROBLEM

The concept of anchoring includes the following working stages: design of anchor systems, implementation of anchor holes, formation and installation of geotechnical anchors, primary injection, prestressing of anchors, validation of design requirements for acceptable load and durability, locking of steel anchor strands, secondary injection and multiple injection the anchoring system in question allows. Anchors are special structural elements mainly because they interact with the hinterland and are therefore more difficult to control and control.

As a rule, problems with proper load-bearing capacity occur due to the excess creep and looseness in the contact surface between the injected part of the anchor and the ground, respectively. anchorage hill, which in the event of excessive deformation also affects the durability of the anchorage system. The load-bearing capacity of steel anchors and the adhesive clamping of steel braids or strands in the anchor cylinder are, as a rule, not problematic and are not the subject of the present claim. An important parameter is the transverse contraction of the anchor cylinder, which also reduces the load capacity.

The origin of these problems with standard anchors is in the excess concentrations of normal stresses in the anchor cylinder and the concentration of shear stresses in the contact surface between the cylinder sheath and the ground in the area of transition from free to binding length of the anchor.

Problems with the load carrying capacity of prestressed anchors occur especially when anchoring under poor geotechnical conditions in soils and brittle hills such as meles, alumina, poorly bonded sandstones, where the shear stress reduces the adhesive strength and thus the adhesion strength between the injected sheath and the anchor coat. Due to the insufficient axial stiffness of the anchor roller, it is therefore not possible to utilize the increased adhesion strength of such anchors due to the roughness of the anchor bore.

3. BACKGROUND OF THE INVENTION

Geotechnical anchors belong to the E04 B International Patent Classification. They represent special elements of geotechnical structures and are intended primarily for the safe transfer of tensile loads to the ground. Their use is widespread throughout the globe. They are used for anchoring supporting structures, foundations of bridging structures, protection of tunnel excavations, mines, protection of construction pits, etc.

Depending on the type of construction, anchors with anchor blocks and injected anchors are distinguished. Depending on how the anchor forces are applied, the anchors may be passive or active, or. prestressed and, depending on the function in the structural system, permanent and temporary anchors. In practice, standard, test and control anchors are also known.

Several types of anchoring systems are currently used in Slovenia, GNSS-Gradis anchors are Slovenian, and all other anchors are imported from abroad. The use of different systems is subject to the requirement to comply with the requirements laid down in SIA Recommendations 191/95 or. SODOC-16. In Slovenia there is a solution of permanent prestressed geotechnical anchor type GNSS according to the patent no. P-9700320.

The tensile forces are transmitted at anchorage by adhesion strength between the steel strands or. braids on the injected anchor cylinder and then with adhesive and friction part of the shear strength along the anchor cylinder sheath into the foundation soil. Dual corrosion protection of the anchor is ensured by a PP ribbed protective tube and adequate electrical resistance. The anchors are two-phase injected. DE 3400741 A1, Deichert, Ernst, Dipl. Ing., 8011 Poring DE.

The use of increased adhesion resistance due to the roughness of the anchor hole at the greater length of the injected roller for the transfer of tensile forces into the ground is the subject of a claim, since it has not been possible to achieve it under poorly used geotechnical conditions. As a rule, excessive stress concentrations, tensile cracks in the injected cylinder and excess adhesion along the anchor roller mantle appear in the transition area from free to connecting anchor length, which therefore begins to loosen and an unacceptable creep of the anchor and / or anchorage occurs. reducing the prestressing force and thus reducing the load capacity and reliability of the anchor.

Therefore, in the case of injected geotechnical anchors, only the anchor cylinder sheath at limited lengths, which are for individual hills and / or climbs, can be used for transferring tensile forces into the ground. the lands to which we anchor are experimentally determined and are roughly as follows: for limestones, dolomites and other compact hills - 6.0m, for marls and sandstones - 7.0m, for slate marls and sandstones - 8.0m, for clays and mills 11.Om, for well compact gravels - 9.0m, medium-sized gravels - 10.Om and sand gravels - 9.0m.

There is also an anchor system called Single Bore Multiple Anchor System. abbreviated SBMA, where several anchors are installed in a single hole in a row, but not interconnected. Such an anchorage system allows the use of the borehole to carry the tensile forces over a longer length, but due to the anchor roller having the same axial stiffness, excessive stress concentrations are still generated, and the associated loss of adhesion and creep or creep. loss of geotechnical anchor bias. The system also becomes more complex and economically less variable in the case of installation of a large number of different anchors. At the same time, the safety of the anchor system is also reduced because the failure of the first anchor in the set is possible. Separate primary injection of individual anchors as well as separate provision and control of corrosion protection is also required.

4. DESCRIPTION OF THE NEW SOLUTION

The subject matter of the invention is a prestressed variable-stiff geotechnical anchor whose basic properties such as load-bearing capacity, durability and economy are significantly better than those currently used in geotechnical practice.

The essence of the invention is the controlled insertion of a tensile force over the entire anchorage length of the anchor into the injected cylinder, resulting in lower concentrations of tension in the anchor whose rigidity is variable and therefore the entire contact surface between the anchor roller and the ground, including increased adhesion resistance, can be used to transfer the tensile force. the roughness of the anchor hole sheath.

All the necessary materials and equipment for the implementation of the proposed product are available on the Slovenian market and therefore the solution will be immediately applicable in geotechnical practice.

The invention solves the problem of uniform activation of adhesion strength along the contact surface between the anchor cylinder sheath and the anchor hole, as also shown in the accompanying figures.

FIG. 1 Example of anchoring a pilot wall with normal or with variable-rigidity geotechnical anchors

FIG. 2 Schematic of a classic prestressed geotechnical anchor

Si. 3 Injected anchor cylinder and diagrams of design and actual activated adhesion along the anchor cylinder sheath

FIG. 4 Anchor cylinder and diagrams of design and actual actuated adhesion for a geotechnical anchor of variable axial stiffness in poor geotechnical conditions

FIG. 5 Load carrying capacity limits for classic anchors and for variable-strength anchors

Figure 1 shows an example of the use of pre-stressed geotechnical anchors in providing stability of a supporting structure-anchored pilot wall, where the clay slope (4) is secured by a pilot wall which is clamped and anchored to a marl half-hill (5). The free length of the anchors (1) and the connecting lengths of the anchors for the case of prestressed classical anchors (2) and anchors with variable stiffness (3) are also shown.

Typical components of pre-stressed geotechnical anchors are shown in Figure 2 and are as follows: locking head (6), high-grade steel beams (14) lined with grease or PVC at their free length (7). on its binding (adhesive) part (8) without lining and grease and bonded adhesively to the expansion mineral grout (11) by an anchor roller which is adhesively bonded to the ground (12) into which the object is anchored. Important components are the injection pipes (15) and the protective smooth PVC pipe (9) in the open air and the ribbed PP pipe (10) over the entire connecting length of the anchor, which provide the anchor with anti-corrosion protection.

Figure 3 shows a diagram of the design adhesion strength (16) and a diagram of the activated part of the adhesion strength (17), which shows that only by increasing the bond length of the anchor (2), its load capacity cannot be increased. When prestressing due to the concentration of the shear stresses along the anchor roller, the adhesion strength is released, which causes creep and loss of prestress in the anchor.

Figure 4 shows the design of the variable-stiff geotechnical anchor and the associated design diagram (16) and activated shear strength (17). It is apparent from the diagrams that the construction of the variable stiff anchor allows a more uniform transfer of the tensile force into the ground. Therefore, it is possible to achieve a higher efficiency of adhesion strength, because by correct sizing of the anchors, plasticization or abrasion can be avoided. shear bursting of the hill in the contact surface between the injected roller and the ground.

Figure 5 shows graphically the influence of different free (7) and bond lengths (8) of variable stiffness anchors on the total bearing capacity of geotechnical anchors in characteristic gravel sands of medium density D _r = 0.5, at a depth greater than

5.0m and for anchor hole diameters greater than 12cm. Figure 5 shows the values of limit load capacities (18) and (19), respectively. (20) are characteristic of anchors to the extent that they would be made classically by all strands with equal free and binding lengths and with two or more strands. three different combinations of free (7) and binding lengths (8) for individual groups of steel beams.

Individual strands of high grade steel belonging to a single group with equal free (7) or. pre-tension the connection lengths (8) simultaneously with two, three or more tensioners according to special instructions or. anchoring protocol.

The number of prestressing steel beams with individual tensioners may vary, but in order to achieve the optimum effects of the anchoring system provided, it is advisable to prestress them less in the first stage than in the following. Suitable combinations are as follows: two, three and three strands for anchoring in low-quality layered carbon marls, two and four strands for anchoring in higher-quality sandstone and sandstone marls, and one, two, two and three strands for anchoring in tectonically damaged sandstone and alumina. When determining the number of strands that are prestressed in individual groups, it is necessary to take into account the deformability and shear strength of the soil, the axial stiffness of the injected roller and the adhesion strength between the injected anchor roller and the ground.

By introducing a tensile force into the injected anchor connecting part over the entire length and by increasing the axial stiffness of the injected anchor cylinder, the present invention reduces the concentrations of normal stresses in the anchor, the tensile deformations in the anchor cylinder and the shear stresses between the anchor roller and the ground, thereby reducing the anchorage after prestressing and improves the durability of the anchorage system. I believe that the proposed new system has the following advantages in particular:

The invention of prestressing geotechnical anchors of variable stiffness enables the implementation of high-quality high-strength anchors in virtually all geotechnical conditions, where anchoring with existing types of geotechnical anchors is possible.

Compared to existing new systems, e.g. The Single Bore Multiple Anchor System, SBMA has the advantage of anchoring under poor geotechnical conditions, where increasing the rigidity of the anchor roll is essential to activate as much adhesion strength as possible without creep. loosening due to local excess adhesion. It is also distinguished by the fact that we are dealing with only one anchor.

Compared to conventional anchors, we can significantly improve the load-bearing capacity and reliability of prestressed anchors in all geotechnical conditions, where they are classical or anchored. the anchoring technologies so far allowed only the anchoring of small load carrying capacity of 300-450kN.

The invention enables the construction of anchors with lower loss of prestress due to reduced creep and increase the durability of the anchors by reducing the tensile deformations in the connecting part of the anchor cylinder at almost the same cost.

Since the submitted system is essentially a system of sequential and interconnected geotechnical anchors, while the anchors are unrelated to the other new systems, such a system is more secure because the failure of an individual anchor is prevented.

Anchors with anchors arranged at different depths in the ground are safer and more reliable than in the case of parallel anchors at short distances, where there is a risk of failure of all anchors at the same time.

The invention theoretically makes it possible to achieve arbitrary load-bearing capacity of geotechnical anchors by increasing their rigidity and bonding part. The equipment at the disposal of geotechnical contractors in Slovenia already, without any significant changes, enables the implementation of the proposed type of geotechnical anchors with a maximum carrying capacity of up to 1,941.11 kN in virtually all geotechnical conditions.

The type of anchor provided has significant economic advantages in anchoring with very large free-length anchors, where the greatest cost is the total length of the anchors, the number of anchors used and the construction of the anchor holes.

Because by increasing the bonding part and the rigidity of the individual anchor parts, using strands of different free lengths, it is possible to achieve similar anchorages in all geotechnical conditions, the invention will allow the anchors to be typed (all may be structurally identical), which will also allow for easier industrial production.

Compared to all other anchoring systems, the submitted system is very economical also because it requires only one primary and one single secondary injection, one single PP and PVC protective tube and only one measurement of electrical resistance (according to SIA V 191/95) for the control of corrosion adequacy protection.

From the point of view of safety, economy and reliability, the presented system also has advantages in anchoring in inhomogeneous soil and tectonically damaged, soaked, layered and weathered hill structures.

5. THE MOST APPROPRIATE WAY TO USE THE INVENTION

The proposal for a new type of anchors is suitable for use in anchoring in carbon materials, residual marls, sandstones and sandstones, lavender and in all types of soil in Slovenia.

Because the anchor is formed, installed and injected similar to the existing classical geotechnical anchors, except that the steel beams have different free and connecting lengths, the invention is of interest to companies that already have equipment for the implementation of classical geotechnical anchors. Only slightly more complex pre-stressing procedures are required, which are carried out separately for each group of steel beams of equal free lengths.

It is therefore possible to use already available anchoring equipment and the components of existing anchors already used by geotechnical contractors in Slovenia for the manufacture, installation, prestressing and testing of anchors.

The process is described in the description of the invention and shown in five figures.

Should potential contractors need further guidance and information, this is available from the applicant listed on the first page of the patent documentation.

Claims (1)

PATENT APPLICATION Prestressed geotechnical anchor of variable rigidity is in comparison with the current state of the art, where the anchors are made of several identical steel braids or strands of high-grade steel (14) embedded in a smooth PVC pipe (9) in the free (1) area and in a ribbed PP pipe (10) in the area of the entire anchor length (2) and carefully fitted into the anchor hole of the selected diameter with spacers, then injected with an expansive mineral grout (11) inside and outside the protective tubes (9 and 10) and prestressed and tested simultaneously and lock with anchor cones into the anchor head (6) electrically isolated from the anchor building structure (13) or. newer systems incorporate several different anchors into one anchor hole, Characterized by the fact that in each anchor there are high-grade steel strands of different free (7) and different bonding-adhesive lengths (8) and of the same total lengths (7 + 8), which, after installation and injection, are simultaneously prestressed in groups of one , two or more strands of equal free lengths (7), thereby enabling uniform application of tensile force over the entire anchorage part of the anchor, and at the same time, due to the increased rigidity of the anchorage portion of the anchorage, also ensures the activation of the shear adhesion strength between the anchor roller and the ground (12) on any or all. significantly longer length (3) than normal or other anchors (2), and therefore the present invention reduces the concentrations of normal stresses in the anchor cylinder and the concentrations of shear stresses in the contact surface between the anchor cylinder and the ground, which significantly improves the load-bearing capacity, reliability and durability and economy of prestressed geotechnical anchors.